Please excuse a stupid question. I just recently picked up a chronograph to play with. Okay, so I now know the actual velocity of my loads. That's cool but how do I best use the information? For example, I fired a string with my 30-06 loaded with 165 gr. Partitions ahead of 57.0 gr of IMR-4350. My average velocity was about 2660 fps. This load is a book max from the Nosler manual which shows a velocity of a bit over 2800 fps. Does this mean I can continue to increase the charge for my rifle to get to a pressure level that should put me in that ballpark? Or does it mean stay where I'm at and be happy with a load that shoots well and has been very effective on game for me?

Jeff

Thats a real good question - I sort of look at it this way -especially with loads I have seen in and have had experience with in the Nosler manual in particular.
I suspect Nosler uses test barrels/chamber and I believe they are pretty tight. They need to make sure that none of their loads are unsafe in just about any rifle our there. What I have seen in a 270, 7mm Mag and 338 is that I can increase the charge to the point where the velocities sort of match up to their upper end loads - but - I also look for all the other high pressure signs - primer pocket expansion being a good one - short case life (4-5) reloads is sign that you are walking on the high end of the safety net - also, use other manuals for cross reference - I find the Lyman manual to be pretty accurate for the loads I use in my rifles. One thing about having a chrono is it sure takes the guess work out of reloading - and it is common for shooters to test a load they have been using for years and to find out when they first chrono the thing it is a fair amount slower than they thought. Good luck - and be safe.

Use all the information that you have available. This starts with the manuals that you mention and what happens in your particular gun. The chronograph is just another piece of information and it's readings must mesh with other observations.



There is no proof right now that your chronograph is even right! In fact it must be off by some amount. So go by everything that you see as Hagel was right and every gun is different.

It seems to be generally accepted that you shouldn't exceed the book max powder charge or the book velocity for the powder you are using, whichever comes first. For the most part, if you are exceeding the book velocities, you are exceeding the pressures the manufacturer loaded to. If you are at the max powder charge with less velocity than quoted, you may be at lower pressures, but then again, you may be at max pressures and still getting less velocity. Better safe than sorry. FWIW, my son's .243 gives about 250fps less than the books say it should with any given load.

John

skibum,

There seems to be a universal error in all reloading manuals. The average error seems to be ~ 150 fps greater velocity than one achieves in reality. The error varies from one reloading manual to another, and in magnatude from 50 fps to 200 fps. I have yet to see a reloading manual, or factory load specification, which errored low. They always quote a higher velocity than is achieved.

With regard to loading up. It has been my experience that the book pressure values are close to reality, even though their velocities aren't. For example, a given load is said to have a velocity of 2740 fps and a pressure of 62000 psi (this is a 308 Win). What I discovered with strain gage and chrono was, muzzle velocity of this load was 2650 fps with a chamber pressure of 62500 psi (pressure is +/- 5% error in electonics and gage itself).

So long story short. I would not exceed the published load maximums! Just realize that one must take the velocity claims with a grain of salt.


Scott

Both the chronograph and the manuals are nothing more than a tool. You must use them properly as with any other tool. They are not a substitute for common sense.

Read the manuals and particularly the components and the barrel used for the tests of the published load. All they are telling you is that the load published was determined in that particular barrel with the components listed, and it was safe. If the manual publishes pressures, so much the better. It's just another source of information to give you a guideline from which you can apply your common sense on your own loads. If their barrel is 26" and yours is 24", their velocity will be higher than yours if you use all the components listed. In other words, it's just a ball park figure and you are safest not exceeding either the velocity or powder charge listed.

SkiBum:

That is not a stupid question. Secondly you had the intelligence to go out and buy a chronograph, which definitely does not indicate anything stupid about you.

You will always get good advise and experience from Bob 338, Savage 99 and Eldegeullo ( hope I did not screw up the spelling that bad).

You can always try another powder, such as 4831, if you think you need more velocity to accomplish what you are looking for. I have found from personal experience that in any 06 I have owned with Hodgdon 4831, I can't get into trouble with filling the case and using a 200 grain Speer. Therefore, with a 165 you will be running less pressure than the 200 grainers. Play with that if you think you need more velocity.
Work up etc, use the old noggin:

Another route to look at is the following. YOU are getting 140 less fps velocity than the factory claims. So look at Nosler's trajectory chart and actually see how 2660 fps and 2800 fps compare in velocity and trajectory.
According to the manual in front of me, if you had a hundred yard zero, the difference in trajectory between 2600 fps and 2800 fps are as follows:

at 200 yds: 4/10ths of an inch.

at 300 yds: 9/10th of an inch

at 400 yds: 1.4 inches

Unless you are varmint shooting for flies, I would not worry about it. click you scope adjustments up two clicks and you just compensated for the 200 fps of velocity difference.

If you are at 2660, the difference is even slightly less.

You can mess with it, or just load it up, and go out and shoot instead of messing with something that really is sort of inconsequental in the real world.

Skibum:

The only dumb question is the one you don't ask,,,,,, What I've always looked for in my chrono. testing is not the average nor the highest velocity. Rather, I'm looking for the load the gives me the least deviation from the average. Its the standard deviation figure. Almost, but not quite always, a load with a standard deviation number in the single digits gives the most accuracy. In other words a five shot string that varied only 5 fps each way from the average of the 5 would give me better accuracy than a load the had 100 fps difference. I think it is another sign of consistency and that is what I always thought that accuracy comes from.

knobmtn

When I see something like this, the chronograph data is just another data point for me to make a decision to keep going forword or not increasing my loads. For instance, if I see 150fps less than expected, and see no case expansion and no flattening primers or hard bolt lift, I would go forward increasing my loads if I wasn't happy with my groups I got. Where it gets hazy for me is when I see 50fps greater velocity than expected, but no pressure signs on the brass. At that point usually I call it a day if my groups are acceptable. If not, I might venture out past max to see the effects on my groups.

Great information guys. I'm not necessarily looking to wring every ounce of velocity out of a rifle. Just trying to understand how it all fits together. This site is like a graduate course for dummies like me. Seafire, you have a good point about trajectory. Last fall I killed a mule deer in Idaho with that load with one shot from 422 yards (Customstox was sitting next to me with a rangefinder). That lumbering slug still managed to give complete penetration and the buck staggered about 10 feet and fell over. I don't think 150 fps would have impressed him any. One final thought. I was shooting this past weekend in about 20 degree weather. I'm guessing on a hot day I would be pushing a little more steam.

Jeff

Good advise from all. Your chrono can help in finding a good load for YOUR particular rifle. Manuals are a starting point / guide line (been said). If you are running low on vel. switch powders. I had this same problem in my .280, just couldn't get close to the book vel. w/ IMR4350/RL19. A switch to IMR7828 did the trick. Std. dev. is good info. but I have had some of my most accurate loads exceed 30fps dev. (single digits is what you strive for).

As you increase powder charge the vel. should go up in a fairly linear fashion (say 50fps/grain, hypothetical). You may find that you get a big jump, could be indicating too much pressure. You can also see a flattening of the vel. at that point you may be exceeding the optimal load for your rifle, increasing pressure w/o any gain in performance. Alwyas look for pressure signs & use your chrono as a guide. You can also check your chrono by shooting known high quality ammo over it as a baseline. I like match .22LR of .45acp.

Oh, yea, during a summer day you might expect another 40-100fps with some powders. I encountered something this weekend like that. I made up this 308 load with 45gr 4064 and 150 triple X barnes. It worked fine at 5 degree F weather, but had real hard bold lift at 40 degree weather and flattened primers. Also my groups went from 1.1" groups on average to 1.8" average. Dropped the load to 44gr and all is better now. I didn't get my chrono going to measure velocity differences due to weather conditions.

Best use the chrono to extrapolate trajectory. Since you know actual velocity, you can better estimate drop at ranges other than sight in.

As a pressure gauge, I personally consider them worthless. Too many variables affect max pressure. Look at various load data that lists pressure. Among a single bullet, rank them according to velocity, then according to max pressure. Are they the same? I thought not! How can a .308 win and any 300 mag have similar pressures and very different velocities with the same bullet?

Chronos give bullet velocity. Extrapolating velocity to max chamber pressure is a HUGE stretch.

Two quick points.



1. I believe most load manuals use data developed in a pressure barrel, which is usually 26" long. So if you are using a typical rifle with 22" or 24" barrel, that could account for your velocity difference right there. Speer's manual is real clear that you should expect lower velocities than they publish, when using a sporter-length barrel.



2. Temperature counts! For some powders more than others, I understand. I shot a .308 load with 46gr. of H335 last August and zeroed my scope for it at 200 yards. Shot a group last weekend, and first group was about an inch low. After about 45 mins shooting some other loads, I tried that one again and the group had dropped 4". The only thing I can think is that the powder went from about room temp on the first group, to about freezing on the 2nd group. That's about a 40% drop.



Again, that affects some powders more than others, from what I hear.



Oh yeah, if it were me, I would not change the load you've been using so successfully, just because the velocity differs from published data.

Don't even worry about velocity whe working up a load!



Leave the chrony at home.



AFTER you have developed the load that shoots the smallest 5-shot group at the range of your maximum capability, then get the chrony out and measure a few rounds.

Generally the boys with strain gagws will tell velocity and pressure are closely related,however there are some barrels that develop higher pressures than velocities.I just rebarreled because of one.

422 yds SkiBum;
I strikes me that you have your fecees wrapped tight as we said in the Army.

Sounds like we don't have to be concerned about your ability to shoot.

Nice Job!

SkiBum-
As others have already said this isn't a stupid question.
Some real good information by all the above posters,I like that given by eldguello.
A couple of things I haven't seen that could change your velocity readings.
Are your "Loads the Exact Same as the Manual"?
Different cases, primers and O.A.L can affect not only velocity but pressure as well.
Distance from the muzzle to the Chrongraph will affect readings also.

I'm not sure who was more surprised, the buck or me? Normally I wouldn't consider taking that shot. The buck had suffered a previous injury, in a fight it looked like, there was no wind, we had a range finder, we got busted trying to sneak across an open slope trying to get closer. We cobbled together a rest consisting on a packframe, jacket, and Chic's shoulder. He had his bino's in one hand and a finger from the other in his ear. It's handy to hunt with an engineer when you want to figure trajectory I held a body width over his back and dropped the bullet square through his chest. It was pretty cool although packing him down the mountain for 3 hours in the dark had me questioning the wisdom of shooting. I think the point I'm trying to make is that velocity is far from the be all and end all from my experience. Thanks for all the advice here.

Jeff

The idea that, if you are achieving the same velocities as the manual shows using the same powder that your pressures are the same as the publishers, is quite erroneous! There are a number of factors that affect the muzzle velocities produced by each individual rifle, and peak breech pressures are only one of them!! Even two rifles that come off the assembly line one after the other can evidence significant velocity and pressure differences firing identical ammunition!!

---

What I said in previous post:

"For the most part, if you are exceeding the book velocities, you are exceeding the pressures the manufacturer loaded to."

Please don't think I was implying that if you get the same velocities, you are getting the same pressure. What I am attempting to relay is that if you exceed the velocity listed using same components and same barrel length, you are exceeding the listed pressure. On the other hand, you might reach the listed pressure before you reach the corresponding velocity, and you would have no good way of knowing as traditional pressure signs don't show up until you are well past SAAMI pressures. Here is a good read on the subject. Of particular interest are those post by OKShooter. He is an engineering consultant for the US Army's Field Artillery Branch:

Discussion on chronographs and pressures from 24 Hour Campfire

John

"Please don't think I was implying that if you get the same velocities, you are getting the same pressure. What I am attempting to relay is that if you exceed the velocity listed using same components and same barrel length, you are exceeding the listed pressure."

The two sentences above directly contradict each other.You start by saying that you should not assume that just because your velocity is the same as listed, the pressure will also be the same.In other words you are saying that velocity does not correspond directly to pressure when different guns are used.The very next sentence goes on to state that if your velocity exceeds the listed velocity your pressure is higher which implies that the same components, barrel length and pressure should produce the same velocity.
The bottom line is that chronographs are intended to measure velocity which is not directly convertible to pressure.If it was oehler would not bother to sell both chronographs and pressure measuring equipment.

SJ, you were heavily involved in the thread I mentioned in my previous post, so you must have read what OKShooter had to say about it. But for those who haven't read the whole thread, here's some of the highlights:

"Hondo64d -- As you have noted, a chronograph is one of the most useful tools that a handloader can have. I have done a lot of test firings in different rifles outfitted a with strain gage and plugged into my M43 and am convinced that a chronograph is a useful instrument for estimating pressure ranges if one is using reliable data."

"A chronograph is a reasonably reliable way to qualify pressure range if one has other independent, reasonably reliable data. (Note that I specifically said here and in my previous post 'qualify' and not 'quantify.') Obviously I haven't tested every load combination in any of the manuals, but I have tested more than a few from each major manual spread across several different cartriges. As I said in my previous post, I consider Hodgdon and Speer data from their current manuals sufficiently reliable for most purposes."

"While on this subject, let me add one more observation. I am convinced that there is no such thing as "fast barrels" and "slow" barrels but only barrels that produce more or less pressure. For example, many of the loads I tested in the '06 in both the M700 and M70 produced virtually the same velocity even though the M700's barrel was 2" shorter than the M70. It did it, of course, because it produced higher pressures."

Now, I don't own any pressure measuring equipment, so I have to defer to those that do. And, given his background, I believe OKShooter to be a credible source. As far as my statement as quoted by you, I stand by it. Unless one has pressure measuring equipment, he is taking a risk if he either exceeds published velocities with given components, or exceeds the maximum load listed. I believe john Barsness pointed this out in an article he wrote based on the results of some research with someone who has pressure testing equipment. I would have to do some digging to find the article, but I consider Barsness to be a credible source, too.

John

While on this subject, let me add one more observation. I am convinced that there is no such thing as "fast barrels" and "slow" barrels but only barrels that produce more or less pressure.



O.K shooter has done some work with the oehler 43 and has gathered some data.However,from what he has shared with us it was basically comparing a very small sample of the pressures and velocities in some loading manuals to those with a few guns that he has access to.I believe that the samples that he used (both loads and guns)were too small to be of much significance as scientific data and as such really did not prove a great deal.How much can you really learn about a manual containing thousands of loads by comparing a few loads in a few chamberings?How much can you really learn about pressures and velocities in various guns of which millions exist by testing a few sample in a few chamberings.None of that data that he has shared with us of it could be used to scientifically prove the "fast barrel" "slow barrel" theory one way or the other.



To do so a person would have to equip several rifles(the more the better statistically) chambered with the same cartridge and the same length barrel with strain guages and hook them up to the oehler preesure measuring equipment.You would then have to develop loads using the same components for each rifle and adjust them until each rifle was producing the same pressure with it's specific load.Then you simply shoot the guns over the chronograph and compare the velocities.Unfortunately to my knowledge this has never been done and few people have the resources to conduct such a test so it is unlikely that it will be done soon if at all.Until then you can speculate all you want but we will never know for sure.