I tried this thread on another site and started a bun fight. Now I know that the members of this site are intellectually mature and will discuss this topic with honor and respect for the opinions, experiences and views expressed by other members. We can disagree without becoming disagreeable.

As reloading data in published reloading manuals is conservative (because of potential liability) the full potential of your firearms may not be fully utilised by staying within the limits suggested in these publications. Although, the author strongly encourages the beginning reloader NOT to exceed recommended maximums, many experienced reloaders find that they can safely go slightly above the recommended maximums with careful attention to signs of high pressure.

Also reloading is all about exploring the limits of performance of your pet round(s) and firearm(s). Accordingly, we need measures to tell us when we are reaching those limits and preferably a bit before we reach them. Additionally, those of us who load wildcat and obsolete cartridges sometimes there is no recommended load published for current powders.

Share with us what measures you use to suggest that you are reaching maximum loads for your firearms. I'm certain that the beginning as well as the experienced reloader would benefit from the wisdom and expereince of others.

Magnum

stubblejumper is correct, My hunting partner has a Browning A-Bolt in 7mm Rem Mag that shows severe signs of pressure well below the published max in all of the powders we tried.

Interesting question, which those without seriously expen$$ive equipment, need to devote some careful thought to.

My serious (big game) hunting calibres are irrelevant to the question, as I load them well within their (book)limits. I do 'squeeze the envelope' a little with my .220 Swift, though. Anybody who has ever hunted Baboons in the mountains will understand the need to REALLY reach out in order to tap 'old Kees' on the shoulder. And more often than not, a 'tap' just won't cut it ......

The first sign of pressure my rifle gives me, is flattening of the primer. I watch this carefully (every shot, with a magnifying glass) as I load up, and I will stop before the primer flattens completely, but I'm not concerned about tooling marks on the primer. A very 'loose-and-fast' criterion this, so maybe I should explain that I still want to see some sort of rounding on the cup of the primer, although it can be flat up to a fraction off the edge. When that last fraction fills up with primer, I go back to my last accurate load and call that max for my rifle.

I also chronograph all my load development, and calculate a V/C for every load (Velocity / charge weight). All this gives, is a measure of velocity gain per unit of charge increase. By and large, the increase is pretty much linear, but when it peaks, or I see a point of significantly diminishing return, I apply the brakes. In my rifle (lo-o-ong leade), this is normally over the book's max.

It's been a very long time since I've had a bolt which was sticky to open. When that happens, I pack up and go dig out my bullet puller for the balance of the batch.

Once I've settled on a load, I load up several (20+) and shoot them over the chronograph (very slowly, to keep the barrel 'cool'). This gives me a better idea of accuracy than simply going on a 3-shot group, and gives me a much better test sample of extreme spread, V/C factor and primer flattening.

Somchem, our powder manufacturer, don't print batch numbers on the cans anymore, and I don't trust their statement that "there is no significant change in burning rates from batch to batch". So with every new can of powder, I load up a couple, and confirm primer condition / V/C factor. If there is significant change in any of the above, I'll back off and work up.

Other than the above, I keep everything as consistent as I possibly can. All my flash holes are uniformed on new brass, my primer pockets are reamed after every shot, and I trim the necks after every shot (those that are 0.1mm or more over my nominal length).

It's a very primitive, low-tech, system, but it has worked for me and my rifle for a very long time (probably 15 years or more).

It would be interesting to hear from the pundits whether they think I'm on track

In the 98 Mauser, I look for brass life.

If the primer is falling out on the first firing, back off on the powder charge.



If brass life is the reason for wanting to know pressure, then measuring with a strain gauge and tranlating to brass life will just introduce error.



But if you want to write a load book, want to talk on the internet, want to sell commercial ammo, or want to load for a gun weaker than the brass [and I do and I do], then a strain gauge or load book is where to get the pressure signs.

Hi Magnum, actually, you didn't start the bunfight, a certain other person did, unfortunately. There is a wealth of good info there, but some people just seem to want to argue for the sake of arguing... hope you have better luck here...

the difference in what a reloading manual says is max and what you think your gun's max is meaningless in hunting. you won't see the difference in the distance in the shot you can take(especially from a hunting position).

steelrain is ALWAYS a bad sign.

or
a deer don't know 100 feet per second.

Load to where you rifle is accurate, and you get acceptable velocity within the cartridge selected, and enjoy hunting..

that last 50-100 FPS "left" in a round is at the expense of a STRONGLY increasing pressure curve.

to put it another way, a 308 will NEVER be a 300 winmag, factory pressure to factory pressure....

i've seen IDJITS trying to get to 300 winmag and try to tell me it's "Safe".... I tell them I disagree and move far away from them

jeffe

Magnum:

I believe most of us are the same in one aspect: we don't want to blow our heads off. We just have different ways of preventing this from happening.
Quote: " many experienced reloaders find that they can safely go slightly above the recommended maximums with careful attention to signs of high pressure."

I've found this may not always be the case. For every rifle that I've seen where one can safely exceed published data there is another where one cannot. I'm 58 and I've been reloading since I was 14. I've had a lot of wildcat and other non-standard chambers. Here is what my experience has shown me that works.

First of all I have bolt actioned rifles of modern manufacture. I treat even standard chambers as wildcats and start with a fairly low load. I always fireform new brass to the chamber of the rifle in question. I size the cases so that I can feel the bolt bolt close on the shoulder of the case so I know there are no excessive headspace issues. I watch the case heads closely. I look for any marks on the head. I watch closely for primer flattening and cratering. I will mike both the case heads and the expansion rings. I always pay attention to the bolt lift after firing a round. I do all my testing with a chronograph. I'm watching for changes in velocity increases as I add powder. If for any reason I need it I do have access to an Oehler pressure testing set-up. But, I also watch the pattern of the groups that I'm shooting. If in all of this feedback from the rifle I see any sign that something isn't right or doesn't make sense I sit back, think, and apply some common sense. I have a loading set-up that enables me to load at the range. That makes testing much easier.
After all these years, I find that I'm still intact and so are my rifles. Remember, every rifle is an individual; don't get bull-headed and try to make the rifle into what you want it to be. Just let that gun tell you what it wants.

knobmtn

Magnum is right, for hunting an extra 100fps is not going to make a difference. And accuracy does deteriorate when you push past maximum for that rifle.

Then again, I am into experimenting so�

Primers falling out is usually a bad sign, but I had some soft 223 Chinese brass that wouldn�t/didn�t hold the primers very tightly.

Primers flat or cratered is a good sign of a problem, but I have seen a rifle do this with factory ammo. I �think� the firing pin hole was too large on that rifle.

Expansion of the brass in the web area is a sign. (especially if you get a bulge!).

Stuck bolt is bad. I get this when I shoot Calvim ammo in a Steyr with a match chamber. The same ammo is not an issue with an M1A. When I examined the brass, it appears to be long.

Since I have seen all the above, I should probably back down some loads and stop pushing my luck.

�There are old reloaders. There are bold reloaders. But there are no old bold reloaders.�

stubblejumper

Quote:

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I have tried several loads that showed pressure signs before reaching the maximum powder charge listed in the manual.Just because a load is listed in the manual does not mean that it is safe in your gun.

---

Man.....if that ain't the truth!!! I certainly agree and it can't be overstated.

That said, the reason I like the Hodgdon's and Hornady handbooks so much is because I've not yet found it with their data.......and of the two I'd take the Hodgdons because it also publishes loads for lots of mfr's bullets and also their COMPETITORS powder.

BTW....no one has pasted the link to Steve's pages.....and it's some of the best info on pressure signs I've ever seen. It should be required reading before posting on any reloading forum.

Sometimes adding more powder does not add more speed but does add more pressure. This is when a chrono gets real handy. A rifle's most accurate load is often below max listed in a load manual, so that's the place to be. Sometimes not. I have a 7 mag that shoots a particular most accurate load that is over max in any manual, but it's just that one in particular. Again, the chrono is a real help. sundog

Another valid point for this thread is that high pressure signs can be evident before reaching the maximum loads in some manuals. Though this ought to be less frequent today as manufactures are aware of this and reduce the recommended "published" loads accordingly. But it is still a consideration. Some posters have already mentioned this.

High pressure in any firearm can be potentially dangerous so being able to recognise signs of this early is vital for the handloader. Whilst loading manuals can be used as a guide for when we ought to expect these signs this is not always the case, e.g. wilcats and cartridges for which there are no published loads in manuals. I have a couple of these plus I have found in one or two of my other hunting rifles (I'm not a target shooter) that the higher loads tend to shoot good (tight groups).

In a recent testing session in my .308 Win (pre 64 M70 fwt) with ADI AR2206 powder (roughly equivalent to BLC(2), I think) and designed for the 7.62 NATO military round, I found that 47.5 and 48 grs (Winchester cases and primers) both shot extremely well off the bench (in some cases putting shots virtually through the same hole) and gave velocities up to 2,966 fps (out of a 22" barrel) with 150 gr Nosler solid base and Winchester silvertips. Although there is no load for this powder with 150 gr bullets in the ADI manual my estimation is that these are "hot"loads (I built them up over a period of 6 month or more from 40 grs). On the 48gr load the primers were just starting to creater, but were not flattening neither was there evidence of case stretching (measured before and after with a digital caliper) and there was no noticable difficulty in extraction.

That was one of the reasons for this thread. To hear from others what signs or measures they use for detecting when high pressures are being approached. I have been loading for more than 30 years but do not profess to have any monopoly on wisdom in these areas. Though I have learnt a lesson or two over this period, I am always looking for ways to learn and have learnt that the experience of others is one such way.

Regards,
Magnum

Magnum,

I think this thread is similar to the Australian one in that most responders are referring to "using loads" as distinct from their methods of arriving at maximum "using loads"

I see you have altered the post you made on the Australian form.

Is rugeruser referring to me in his post. If so, he should read the thread and start at the third post.

Mike

If I see a extractor grove imprint on my brass head . Pressure is too high.



I have noticed that unfired brass will show a more flatened primer compared to once fired neck sized brass with the same load. I have been useing winchester primers, so i dont get to conserned about flatened primers. I get flat primers in first fired brass with light powder loads.



If my primers come out easy then new ones seat real easy with a worked up load ,I will back off with the powder charge as loose primer pockets indicate possible high pressure.

[quoteBTW....no one has pasted the link to Steve's pages.....and it's some of the best info on pressure signs I've ever seen. It should be required reading before posting on any reloading forum.

---

You can't say that anymore...

http://stevespages.com/diagnosingproblems.html

Thanks RICCIARDELLI.....

One of my most trusted methods of estimating pressure is to measure the case immediately ahead of the extractor groove using a good blade micrometer. Mine is a mitutoyo and is about a $80 tool

Measure the case diameter before and again after firing and if you measure as little as .0005" growth you might want to reassess your load. It don't tell you everything you want to know.......but in my load workup it's avery important tool.

A digital or dial caliper is not good enough tool for this purpose.

Too bad it is unreliable.



http://www.shootingsoftware.com/ftp/dbramwell%20july%2019%2004.pdf

You can't say that anymore...

http://stevespages.com/diagnosingproblems.html

---

I've got to say that is the best description of high pressure signs I've yet to read. Thanks Steve!

I think that the best pressure checking device that the average handloader has access to is a Chronograph. I don't believe that there is such a thing as "Fast Barrels", if you are running velocities 200fps faster than anyone else it's because you are running at higher pressures not because of your "fast barrel" and brilliant reloading skills.
When I start reloading a cartridge I like to survey all the Data I can find. I'll make a powder and load chart that shows the loads for a given powder and bullet weight from 7 to 10 different manual, magazines, internet, etc.. Of one source is high or low I discount it. I'll work up loads with several different powders to see which will give me the best combination of accuracy and velocity that approaches what the 7 to 10 sources tell me I should be able to get.
If I'm getting higher than max velocities at lower powder charges I'll back off a little. If my velocity is still lower than normal I may bump up a little powder for that particular gun.
The traditional "pressure signs" are something that I look for on the way to the target velocity. I don't keep adding powder till I get the "Pressure Signs". I have 2 different Micrometers that measure in tenths, I have a Web thickness measuring tool. I check for stiffness in bolt lift, I look at primer condition, I check primer pocket tightness and how many reloads I'm getting from the cases. But again the "pressure signs" aren't what should be telling you what limits to go to, Velocity < !--color--> is . ......................DJ

Okay people...time to put away your calipers and micrometers (be the rounded, flat, blade, digital or dial).



It's also time to pack up your chronies, regardless if they be 2-screen or 3-screen and regardless of what name is painted on the case.



Here is the simplest way to determine if your loads are either under-pressure or over-pressure. And it doesn't require a math degree or $20,000 worth of test equipment!



Use your eyeballs, and maybe a cheap $2 magnifying glass (glass is opetional).



LOOK AT THE CASE...

If after firing it looks any different than it did before firing (other than the enlargement of the case neck) you have either an under-pressure or an over-pressure problem.



Scratches, bright spots, indentations, deformations, missing parts or pieces, more than one piece...



If you have any of them, you have a problem...



And if you have a problem, then you have to find out what that problem is.



Keep in mind that every firearm, every bullet, every grain of powder, every case, every primer is an individual item in a very complex formula...and varying any one piece will result in a totally different outcome.

jackfish

Quote:

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Too bad it is unreliable.

---

And what AI calibers do you reload for?

Magnum,

I also have to second Stubblejumper's first post and Denton's also. I would like to expand the discussion by adding some of my thoughts on the subject.

In the 1970' and 1980's it was common to claim that reloading manuals were published with conservative data. I beleive that fewer people feel this way today because of the increased use of chronographs.

First of all, we must aknowledge the existance of slow rifle barrels. I am referring to those with a somewhat oversize bore or chamber which produce lower than expected velocities with a given powder charge.

I have had several of said slow rifles. After reloading a listed max load of X powder behind Y bullet fifteen times in the same case, and the primer is still tight, one might be tempted to increase the powder charge beyond the listed max.

I have done this with several rifles. Many of us have developed our own max loads in our rifles which are quite a bit beyond manual loads.

I too was convinced that the reloading manual was publishing conservative data.

Then I bought a chronograph, and I discovered that I had not acheived any magic load. My loads were developing velocities right in line with the maximum velocities listed in the manual. My rifle for one reason or another just needed a little more powder to get there.

I have examined primers, gauged pressure rings, and carefully looked for extractor marks. I am convinced that the most reliable indicator of Max Pressure is when you reach the Maximum Velocity listed in the manual for the cartridge, bullet, and powder you are working with, (with the exceptions previously mentioned by Denton). Some of the manuals will even tell you what the pressure is at that point.(Hogdgons) Increased velocity is only due to increased pressure. The Hogdgons manual shows that it requires a 6,000 CUP increase in pressure to realize a 130 fps velocity increase, using bl-c2 in the 308 with the 150 gr bullet. The relationship will often become far from linear at the top end.

I also use case life as a secondary indication of pressure. I want to see at least ten loads from my brass. Granted it takes a little less force on the Lee Auto Prime to seat that tenth primer, but it is still secure in the pocket.

A real cause for concern though, is what some might be tempted to call a "fast rifle". We have all heard of the rifle which developes velocities above those shown in the manual with the same charge weight. Such as you mentioned with your 308.

The "fast rifle" is one which has an extremely tight chamber or bore or some other feature which causes it to develope a little higher initial pressure. This accelerates the entire combustion process, and causes an increased chamber pressure which leads to higher velocities.

While interior balistics is a very complicated science, which I have far from a thorough understanding of, I do see how some rifles can create unsafe pressures with a commonly published load which is safe in most other rifles.

As for your question, about being able to predict or recognize these signs early. I still maintain that the chronograph is the easiest and cheapest method available to today's handloader. "These unexpected pressures will not occur without the attendant velocity increases." EDIT to read "These unexpected velocities will seldom occur without the attendant rise in pressure".

Specifically to discuss your 308 I checked with the Hogdgons manual:

it shows 45.5 gr bl-c2 w/ 150 gr @2706 fps & 44,400 CUP

.........49.5 gr bl-c2 w/ 150 gr @2835 fps & 50,400 CUP

We might extrapolate that your load is reaching the nieghborhood of 57,000 CUP (If your powder is very comparable to bl-c2). While I do not claim that this type of extrapolation is accurate, it will give a very rough aproximation of pressure.

This pressure level is probably not immediately dangerous. But I do not think I would want to feed my prized pre 64 model 70 a steady diet of such stiff loads.

In this respeect we are much more fortunate than those reloaders who went before us. Without a chronograph available, they would have shot such hot loads for years with no idea of the increased velocity or associated high pressure.

Stubble, I'm not at all surprised by a 100fps or so difference in Velocity. Maybe Denton or one of our other statistics experts can give us an idea of how much variation from identical rifle to identical rifle is to be expected.
On another thread one poster was claiming velocities 580fps faster than the max listed in 2 different sources I had. It's this kind of nut that needs to come down to earth before he hurts himself, not someone who gets 3150 rather than 3100fps...........DJ

My method is to build a pressure gun and work up loads ever so slowly:

Quote:

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Meet my new finder of fact:

I had a Sendero in 270 Win (don't ask me why, I don't know) that was pretty straight and had even bearing between the two lugs. My gunsmith (George Vais) squared the receiver and took off two turns and faced the barrel.



He trimmed the bolt face flat and flush.



For the initial calibration of the strain gauge he turned the barrel butt to 1.200" and recut a min spec chamber.



How tight do I torque it? Until the little line and the little circle make a little lollipop, of course .

How do I get the spent cases out? An old seized up Dewey cleaning rod and a small dead blow hammer, I hope .

Many thanks to Mike Brady for passing on this concept to me.

After I pay Big Sam the money I owe him next week I will order Lilja Barrels in .375 and .416.

I will also fill the stock with Devcon and lead shot before I mount a Limbsaver (with the Remington logo on it, of course).

Isn't science fun?

---

JCN

Stubble, I think that there are more likely Slow Barrels than fast ones. Oversized chambers, loose bores, rough bores etc. can cause barrels to shoot slower because of energy lost working the brass to fit the chamber etc. etc. I think think that even when you get up to pressure some of these issues can cause a loss of speed.
I tend to think that a "fast" bore is one that is tight and builds to pressure more quickly than normal. I've had at least 2 guns that would shoot at top velocities with less than normal powder charges. 1 was a 300 Win mag with a 24" barrel that would shoot at the same velocity I got in 3 other 300 Win mags with 26" barrels with 2 grains less of the same powder with the same bullets. Another I had was a 7 Dakota that got to the std. velocity with as much as 5 grains less powder than was listed in the Hornady manual. With both of these the normal powder charges did result in higher velocities but with "pressure signs" such as stiff extraction, ejector marks etc. So I didn't think they were "fast" barrels, I thought that they were tighter than normal and to get above nominal velocities I had to run what was for me uncomfortable pressures.
Again I could be wrong but I would think that if normal velocities was say 3100fps, guns that ran 3050 and 3150 would be normal statistical variation. Again I hope the Stat experts chime in to correct me if I'm wrong here........


The stat question reminds me of a story about a French Mathmatician named Diderot. A famous Bon Vivant had started an arguement with Diderot about whether or not God exits. Diderot responded with something to the effect of "32xyz squared to the inverse power integrated sequentially = 1, Therefore God Exists!". The Bon Vivant had no chance of agueing Mathmatics with Diderot and left befuddled not being able to counter Diderot's ficticious arguement. With Statistics I sometimes feel like the Bon Vivant. I think I know what they should be but can't explain why anymore than I can explain if God exists or not........DJ

Stubble, I think the effect that you are seeing is real, in one sense: The numbers in different manuals are different. As nearly as I can tell, the reason for this is random error in the measurement systems the reloading labs use, and failure to control a very key variable in the pressure mix.



SAAMI uses a 10-shot average to test pressure. The error in the measurement systems is so great, that if you take 20 cartridges, and split the lot, and test 10 today and 10 tomorrow, in the same equipment, you'll be lucky to get two results within 1,000 PSI of each other. Toss in variation from lab to lab, tech to tech, measuring system to measuring system, and I would guess the number is twice that bad. Hence, my frequent statements that I don't think reloading labs can reliably detect a change of .25-.5 grains in an '06 case.



Part of the reason the numbers are so bad is that SAAMI does not control barrel temperature. They do control ammo temperature, far more than they need to. And they specify a 70F room for doing the testing. But they do not control the temperature of the barrel itself, and the barrel temperature is about 3X as influential as ammo temperature.



The current instructions say to shoot a couple of warming shots, and to not let the barrel get "too hot".



I do my pressure measurements at constant temperature. I slap a thermocouple on the barrel, just ahead of the receiver, and that makes all the difference.



So, the short version: The manuals do not agree because the measurement system is decent, but not perfect.



And, anyway, unless you are running on the ragged edge, 2 KPSI is not really a big deal anyway.



Averaging several books, and tossing the outliers is a VERY prudent practice. Random error "averages down".



Most important: The muzzle velocity does not get to choose what it wants to be. It has to be what the pressure, friction, bullet weight, etc., all tell it to be. If you have identical cartridges, in identical rifles, you will get identical MV's. But subtle differences in bore diameter, chamber length, etc., do make a difference. If identical cartridges give different results, one of those factors is at work.



A chronograph is an extremely useful load development tool. As you are working up, if you get the book MV that is equal to the book, you're at max. Stop. Basic physics forbids that you can get a faster bullet with a lower integral of the pressure curve. If you're working up, and MV is flattening severely as you increase powder, you are over the top. Back down.



If you are getting "conventional pressure signs" you are WAY over the top. Back down 3-5 grains. 1-2 is not enough. The fact that you have been doing this for 80 years, and still have all your fingers is not proof that what you are shooting is "safe". Safe is in quotes, because SAAMI specs are not hovering on the brink of catastrophic failure. They are an economical operating point. Above this point, wear and tear on your equipment accelerates dramatically. Your chances of a catastrophic failure are perhaps 10X what they would be at spec, but still quite slim. If you like those odds, and are willing to pay for the extra wear, go for it. You cannot get a quart out of a pint, and you cannot get higher speed at lower pressure, all other things equal.



If you are trusting either the PRE or CHE method, please spend some time with http://www.shootingsoftware.com/ftp/dbramwell%20july%2019%2004.pdf, and mend your ways. They are not reliable methods. They have far too much random noise in them, about 10X as much as the piezo system.



If you really want to know what's going on, spend the $200 to instrument your rifle with a strain gage. That's by far the best instrument for pressure measurement available for a home experimenter.

Quote:

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On another thread one poster was claiming velocities 580fps faster than the max listed in 2 different sources I had. It's this kind of nut that needs to come down to earth before he hurts himself, not someone who gets 3150 rather than 3100fps

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Exactly so.



..::magazine empty::..

Stubblejumper,

In my previous post I was only referring to your first, very short response. I had not seen your second response when I posted mine, as your response was posted while I was typing.

I had to log off of the computer for a few minutes, and when I came back I saw that I needed to rephrase my post in light of your second response.

Perhaps you have access to much more detailed data than I, but I as an amatuer handloader have seen no evidence to suggest that the different loading manuals are achieving such disparate velocity numbers for the same cartridge, bullet, and powder with identical pressure measurements.

And no I am not saying that identical peak pressure leads to identicle muzzle velocity. If such were the case we could load the 7mm STW with Unique to generate 3400 fps with a 140 gr bullet.

But work is dependant on force, which means that it requires more area under the pressure curve to accelerate a bullet to higher velocities. This means either a higher peak in the curve or a wider curve, or both.

You make a very valid point with your question about pressure signs before you reach expected velocities. The 264 win mag for example, is prone to this phenomenon when using 140 gr bullets, particularly the partition or other bullets with a long bearing surface. This can be explained in the case of the 264 by the extreme amount of friction and resistance to initial movement at ignition. This contains the combustion of a slow powder and causes it to behave much more like a fast powder, thus giving an early pressure spike without the expected muzzle velocity increase. You gain height in the curve but lose width. With this consideration, I must modify my original statement "These unexpected pressures will not occur without the attendant velocity increases" I should have stated that these unexpected pressures will seldom occur without the attendent velocity increases.

One might also get into trouble if you run into a fast lot of powder or switch to a hotter primer.

It is never wise to ignore any signs of high pressure including muzzle velocity. And basically that is the point I was hoping to make. I would have made it better I suppose if I had written "These unexpected velocities will seldom occur without the attendant rise in pressure".

Denton,
You obviously are far more literate, in regards to this subject than I. I appreciate you sharing the benefit of this knowledge. Your post was very informative.
Thanks

Idaho Shooter...

I was going to say the same about you.... If there is anything wrong with what you've posted, I sure can't find it.

[Quote]
A chronograph is an extremely useful load development tool. As you are working up, if you get the book MV that is equal to the book, you're at max. Stop. Basic physics forbids that you can get a faster bullet with a lower integral of the pressure curve. If you're working up, and MV is flattening severely as you increase powder, you are over the top. Back down.

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Sir, I've yet to understand the value in using a chrono
for pressure guidence.
Eg. All say that there may be a fair difference in Vel
with different rifles,same ammo. And the "books" ususally
use a long barrel. My .223 Rem is nearly 20" , so that makes
for another large difference to "their" max velosity figure.
The flatting out of vel. I can understand but you admit
that you are then over pressure, and this is just what we
are trying to avoid.
John L.

Good question. Let me give it a twirl.

First, even if the lab uses a different length barrel, you're not totally at sea. You know that if your barrel is 22", and the lab's is 24", you have to knock about 50 fps off the lab barrel for a fair comparison. So the book says 3000 fps, and you know that you're going to get 2950, assuming all other factors are equal.

The stored chemical energy in the powder is converted to kinetic energy of molecules of gas. The actual pressure and temperature of the gas depend linearly on the amount of space the gas is allowed to occupy. Bullet speed is directly proportional to the area under the pressure curve, minus engraving force and friction.

If your powder is reasonably close to the test lot used by the lab, and you are using the same bullet as the lab, and your MV, corrected for barrel length is the same as the lab's, and your barrel and ammunition temperatures are the same as the lab's, then you are very close to the same peak pressure as the lab measured. The basic gas laws require it.

So, if you hit the book MV before you hit the book max charge, you're done. Stop.