Gentlemen:
This is a compilation of questions to the "Ph.D.'s" of load devlment.I read the recent gammut of reloading entries on this forum and it thankfully invites clarification.
My setting:I am in the process of building this precision bullet launcher in 300 RUM
26" SS barrel,throated to the bullet length I will have to provide.1:12 twist to center around 165 gr bullets or lighter in monolithic.The necks will also be tight.

So to summarize this setting :this is a non factory barrel with a "tight chamber" in magnum caliber.

I read the helpful loads from Saaed in 300RUM,he states that he "blindly" loads all bullets regardless of caliber etc to a COL of 3.60" (I think)There are notes that Rem factory barrels vary somewhere around that chamber length,I presume mine will be shorter.

There are notes that in tight chambers primer flattening is not a reliable pressure gauge.Head diameter expansion is noted to be the only reliable warning,I presume this will also be of limited use in a tight chamber using neckturned cartridges.

SO by now you probably get the flavor of my concern:ho do I dvlp loads in this setting?
Given the (?) fact that I will have minimal to no external evidence of too high a pressure.
Do I need to measure pressure directly with a strain gauge? or do I limit myself to published muzzle speeds?

Comparing soft jacketed bullets c harder monolithics even the speed/pressure relationship is probably poor.
The software program often quoted here as QuickLoad probably also does not know about my tight chamber
So ho do I find the max safe load prior to blowing up the chamber and my face?

The 2nd question:I thought I would start seating the bullets the customary 0.03 to 0.05" from the rifling and then optimize this distance.I read about the problems doing this in the Weatherby Mag c large freebore,do you think this is a generic problem c Mag loads?

thanks

sheephunter

the reason saeed used 3.600 is that is how long the magazine is on the 700.just work up like any other rifle.the heavy bolt lift and loose primers are my first signs.

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SPEED KILLS

Sheephunter,

Your 12" twist barrel has less twist than the factory standard 10". I am guessing that you are going to shoot your sheep with the 165 grain bullet, and forget about using bullets over 180 grains.

For monolithic bullets like the Barnes X folks who use them that I know like to seat the bullet off the lands quite a bit --- like 150 thousandths. I don't know if you re using them or a conventional design.

Your 3.6" cartridge overall length is again the factory number set by the Rem M700 magazine as noted above.

I like to collect chronograph data and watch the delta V as charge weight increases, and also mike the case heads for each shot. I also graph the final head size versus charge weight -- this should be linear.

You should observe case expansion going up as your charge weight increases. It is not going to start so low you can't measure it, and suddenly jump to o my God too high pressure.

The chrono data will initially climb roughly the same amount with each grain of charge increase, but will start to fall as you get to "too hot".

I have not tried one of these big cases with a too tight neck. What is that supposed to do for you? I have shot BR rifles with tight necks though.

jim dodd

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"if you are to busy to
hunt, you are too busy."

Thanks Eric,yes I fathomed that Saeed used stock=factory chamber length,but even that has been reported here to vary in unshoot new rifles.In my situation the chamber will be reamed to accomodate the longest bullet I am shipping to the smith,and yes,I am focusing mainly on weights around 165 gr and probably monolithic for hunting.Gerard sells and recommends a 150gr bullet which I will try,Barnes has the 168gr XLC.
Why and how did I get into the turned neck business:it was recommended by my gunsmith
I read all the trouble that these chambers may cause in the bush.I only use handloads so the factory brass problem is not evident.
the only other problem might be "gunk",which I hope to be able to control.
At the basis of my thinking is that I can always widen the throat diameter.The brass is supposed to last indefinitely with a tight throat and with accurate parameters I had hoped to ring out a little better accuracy by having a defined neck tension too.Admittedly maybe not valid in hunting situations but hell,I dont give up anything at this early stage and haven't been burned yet.My hunting style usually consists of firing 1 bullet,maybe c a "make sure" follow up per season.So I like to make it count rather then hope for the "next time".

I will try to graph head expansion c successive larger loads,but in a tight chamber I dont know how that would come out.
I am planning to neck size rather than full body size- if it works.

The other point you were making Jim is that the muzzle speed will fall off after max pressure is reached? or at least optimum speed has been reached?Sounds weird to me,sorry.The barrel doesn't know what is safe for it,at least in my laymans thinking,please dont think I have deeper knowledge here.
All I am saying is that with the described nonstandard chamber and monolithic bullets the published load data might be off by some,and I dont want to get close to it.

sheephunter

Sheephunter, I think what Jim is alluding to is something I've noticed with some of my rifles as well. As you increase the powder charge, the velocity goes up in fairly regular increases. Then you'll reach a point where the velocity increase gets smaller for the same size increase in powder. I'm not sure why this happens, I'm still experimenting with it, but I've noticed it in more than a few calibers. I don't have a way of measuring chamber pressure yet, so whether it's a plateau in the pressure curve or what I can't say. - Dan

Dan & Sheephunter,

I was indeed talking about the "Delta V" or amount of change of velocity per grain of charge increase. You do indeed hit some kind of knee in the curve, and you get less of an increase in this region. Velocity will still go up, but not as much.

If I ever knew why this happens, I am not remembering. But you can observe it and use the data.

jim dodd

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"if you are to busy to
hunt, you are too busy."

Thanks for your experience,
my thoughts about this would be that Delat V exists because of a fixed barrel length.Increasing powder charge would need a longer barrel,therefore one would expect a plateau of pressure/muzzle speed c that combination.If one desired a faster speed/pressure one would have to go to a faster powder maybe,one that would burn within the fixed barrel length?what do you think about this theory?
If that a correct explanation Delta V would have little to do c max allowable chamber/barrel pressure,it would only be coincidental?

2 o you think a tight chamber has variable
head expansion?I thought part of ones ability to get away c necksizing rather than full sizing is the fact that the brass expands and to the max allowable room and then no more.Really dont know how much a curve of head expansion one gets

thanks for sharing
sheephunter

Ok, just a swag, but the barrels' length affects the volume available for burning powder. So I think that part is correct. The expansion of the brass, as a variable, would be a function of time over pressure. This would depend on the hardness of the brass. The maximum chamber dimensions shouldn't change, at least not until you've gotten some truly horrendous pressures. Basically, as I think you've stated, the differance in brass would effect when the pressure curve reaches maximum more then the maximum pressure itself, again assuming the pressures are kept at reasonable levels.

Hunterjim and Dan,

When you see a drop in velocity per grain of powder as you mentioned you have reached maximum pressure. Sierra X-ring news letter had a great write up just this topic, but do you think I could find it in my mess!?

From what I can remember, the drop in velocity despite the increase in powder charge is because you have reached the point of maximum efficiency for that cartridge and component combination. Sorry I can't really explain more about it right now, but I'll dig around a little and see if I can find the news letter and post it here.

Turok

It figures, just after I post a message, I find the article... Anywho, here is the Sierra X-Ring article I was talking about

"Putting a Chronograph to Work" by Paul Box

With the availability of more affordable chronographs comming on the shooting scene over the past tweney years, many shooters are adding this valuable tool to their equipment list. Most of us use one to tell us the velocity of our loads, but we're going to look at another aspect of load development using a chronograph.

Our shooter (Bob), just bought a new 25-06 and wants to work up some varmint loads with the 87 gr. bullet. Bob starts working with IMR-4350 and loads three shells at the starting load and fires them checking both for accuracy and velocity. Pressures look fine so he bumps his load up a grain and checks again. Bob notices that each grain of increase is giving an average of 80 fps.

Bob continues increasing his load and notices the primers are starting to flatten, but no other pressure signs are showing. Now the velocity increase has dropped to 30 fps. Bob becomes a little more cautious and increases the load by .5 of a grain and checks again. To his surprise the load drops in velocity by 15 fps. Even though no other pressure signs have occured, the top has been reached.

Every cartridge will have an efficiency range with a given combination of components. Once that range is passed, pressures will increase sharply and velocity will increase minimally. Changing to a different burning rate of powder will change this pressure curve and might give better velocity along with better accuracy. Bob now has the tool to find out."

Well, there it is! Take from it what you will and have a Merry Christmas!

Turok

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Make it idiot proof, and some one will make a better idiot

Thanks Turok. Useful info, and well explained. Turok from the comic book or the video game? Or just because, like me, you're waiting for the dino's to come back, and that's why we need all these big bores. Hey, it could happen, right? Take care and Meery Christmas - Dan

Thanks Turok,
I reviewed the cited article in the Sierra Website and am not impressed.It does cite the Delta V principle naming it "efficiency" but provides no explanation.That kind of blind faith in an article and unknown author can send you to hell and back.
I believe we all agree that the chronograph measurement of the Delta V principle will work to stay away from increasing the powder charge beyond what works in a certain barrel/powder/bullet combination but I think this has absolutely nothing to do with staying clear of dangerous pressures.
2: the measurement of brass expansion,while a qualitative illustration of preesure" is definitely not quantitative even in a relative or cursory way.As outlined in another thread about Micrometer/pressure.
I agree that brass hardness varies probably greatly dependant on # and type of prev usage etc.Use of a micrometer for fine measurements is a skill that needs to be learned if accurate measurements are desired.
It is of course easy to obtain "a" measurement,that takes minimal skill as we know.The amount of pressure applied is by "feel" and also a fct of the surface area and type.
Given all these misgivings from my Doubting Thomas mind we still dont have a means of staying away from unsafe pressures.
I wonder how the powder manufactures devlp their load,whether they just "assume" the barrel will hold and really only report on the ballistics.

sheephunter

Sheephunter,

There is no blind faith in reloading. Well... There is blind faith for some (see the mic post you refered to), but there isn't for me. To tell you the truth, I honestly don't know enough about math and physics to give you the detailed answer you are looking for.

My understanding of the article is that it was written by a ballistic tech. (i.e. the sub-title "Technical Newsletter From Your Ballistic Technicians"), not to mention that Sierra isn't in the business to doll out bad advise with the intention of harming their customers.

I do agree with you in that there is no way to entirely stay out of dangerous pressures. Anything can happen regardless of how careful you are. To date, we have no means of directly measuring pressure. And until someone invests the time in inventing such a devise, your best bet is to rely on all of the methods.

For further info on the article and the uses of a chrono etc., I suggest that you contact Sierra themselves or any one of the other bullet companies. Perhaps they could provide you with a more adequate answer than I have.

Sierra tech line - 1-800-223-8799

Turok

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Make it idiot proof, and some one will make a better idiot