Your opinion wanted....

[Fiftydriver]

To all,

What is your opinion on the effects on accuracy concerning variation in case wall thickness.

What I mean is say one side of the case body wall is 0.030" thick and the opposite side is 0.045" thick.

I am talking extreme range consistancy. External dimensions would be true BR quality, Just wondering what your thoughts or experiences are with case wall thicknedd variation. Necks would be trued by turning so they would be consistant.

Thank you for your thoughts.

Kirby Allen(50)

 

[abinok]

Fifty,
Are you familiar with the series of articles that were published some time back in PS that dealt with the shooting going on at the "houston warehouse"? Some folks had the opportunity to do a good bit of shooting in a warehouse in houston... and found, among other things, that reducing variations in case wall thickness (by sorting) reduced group sizes... to a point, but that at the very extreme end of sorting, cases with some variation shot better than those with no variation at all. Groups were shot with some regularity that measured between .06 and .04.

 

[3sixbits]

This issue has had recent airing in these forums. Having said that, you have qualified the question by writing for extreme range. This makes it next to impossible to give a considered response because of the many variables in shooting conditions at long range. Now that I've gotten that off my chest, I wish to relate a conversation I had with Allen Hall at a BR match. The topic was long various short cases and accuracy. I took the side of the short case and he related an experience he had in a BR match shooting against R.L. WILSON. R.L. won the match using a 30-06 against all the .222's and it's variations. The reason was because with the tools available to him (that he made of course)He was able to get straight cases to work with. If the case neck shows a lot of variation then so will the case body. The real truth of all this is a great barrel, properly fit in the hands of a shooters that can dance with the wind will cover a lot of sins. Yes it all plays, there are many parts each with many pieces of the puzzle. The trick with all this is , is to eliminate the alibis. And to give the loose nut behind the trigger the confidence to win.

 

[brian b]

Fiftydriver,
You pose an interesting question and I can not give you an exact answer but let me explain. I bought a lot of 300WM brass and ran it over my neck thickness variance guage , 7 cases were way out from the norm so I culled them but still use them for load developement and fouling shots . the other 93 I neck turned and use for all my target and game shooting ,never really giving the other 7 a fair chance to see how they compare. Goodgrouper and 7mmrhb dont cull out cases doing load developement they neckturn them all and square the case heads and they seem to perform quite well. this makes thing's clear as mud . I think case weight ,bullet weight,powder weight and bearing surface length uniformity are all more important.
B

 

[BountyHunter]

I have a Juenke machine and use it to sort fired cases. I have seen cases that are out of norm with the others continuously throw a shot out of the main group.

I do the same thing with most bullets ie run them across the Juenke to catch the odd one.

BH

 

[Guest]

I read the warehouse article and they tried to really get you to think that it made a difference.. but I really think it doesn't make a consistient everytime all the time difference...

I don't do much brass prep compared to most... I just sort out the real bad ones...

extreme range consistency I think would be as much barrel related as case related... pretty much you're talking velocity consistiency right? if every bullet weighed exactly the same...
so if you measure case wall thickness I think you'd have to measure and weigh each bullet as well...

then you hope you have a good barrel too!

 

[Fiftydriver]

Thanks for the thoughts guys, interesting reading.

Let me give a bit more detail on my projects.

First off, we all know barrel bore quality, rifle machining quality, bedding quality, stock stiffness, rest sturdiness, shooters consistancy, load quality and external conditions variables effect accuracy tremendously at extreme range.

For this debate, lets assume we are shooting in a eutopia vacume with all these variables out of the eqation.

My reason for the post is I am testing a certain brand of brass as a canidate for an upcoming member of the Allen Mag family of wildcats.

Because of the size of this project and the nature and expense of the round I am a bit concerned with what I have found in case wall consistancy in the sample brass I have on hand.

I have 50 cases which I agree is not a large enough sampling to make a solid judgement on case quality but while many are very good some are very inconsistant and I was looking to see if anyone had any solid evedince that case wall thickness variation would result in inconsistant performance down range.

This is a very large case so this must be taken into consideration. Lets just say case capacity will be more then 130 gr so variations in this size of a case will not effect results as much as say a RUM case with a 100 gr capacity or such.

Still this wildcat will have one main use, extreme range shooting.

Thanks for your time and thoughts as always!!

Kirby Allen(50)

 

[LB]

[ QUOTE ]
The real truth of all this is a great barrel, properly fit in the hands of a shooters that can dance with the wind will cover a lot of sins

[/ QUOTE ]

And, that little pearl of wisdom is why it is so difficult to reach valid conclusions, especially under long range conditions, with it's unique variables. By the time you are on to something, your barrel is toast....and your next barrel shows a lot more sensitivity to the tested component. Harmonics may be set up all different, etc. Just seems real hard to nail down, and how to weight the results? Reading the tea leaves is more art than science.

Good hunting. LB

 

[Ballistic64]

Just my thinking,but wouldnt the best way to see the effects of the case variation on accuracy at extreme range be to load some known extremely uniform cases against the more ununiform cases and run them through the crono to see the ES between them?

 

[Fiftydriver]

Ballistic64,

Yes that is the best and only true way to do this.

The problem is that with this wildcat design, it will take a personal investment of roughly $6000 /ubbthreads/images/graemlins/shocked.gif to get from where I am now to being able to do what you recommended which I agree is the only GOOD way to see what the result is.

Just wanting to get some opinions before I commit to this level of spending!!!

I am sure you can understand that /ubbthreads/images/graemlins/grin.gif!!

Doing research on paper can prevent alot of issues and save alot of money with these wildcats, as can sever different sets of experienced eyes looking at the system. I appreciate all the input!

Good Shooting!!

Kirby Allen(50)

 

[Mysticplayer]

Kirby, my thoughts are that case volume is more critical then a slight misalignment with the neck.

You said that the exterior is match quality ie, the case w/ bullet will line up with the chamber and bore with runout approaching zero. That to me is the most important factor. Any misalignments here WILL throw off your bullet.

Next is case volume. This is a combustion chamber after all. The closer you get to identical volumes the better. If the volumes are within 2%, I would say good to go because...

The biggest variable in internal ballistics is actually the powder. Will it burn consistently enough. I am sure if you put a pressure guage on one case and fired it several times with the same amount of powder, you would get differences in pressure peak and duration. That leads to velocity variations and stringing at longer ranges.

When you get into cases that big, your powder options are limited. Will H50BMG or WCC 872 work???? Will your primers ignite this stuff consistently enough???

I have never worried much about the case as I feel it plays a small part of the accuracy equation. Of course, the case must be within the specs discussed above. Consistency in neck annealing is way more important.

All that powder goes boom in a few milliseconds and expands to many times it volume. That gas rushes out of the neck at 65000PSI and 5500fps. I just don't see it giving a rip if it is a few thou one side or the other. The neck and bore is the real funnel that matters. Since the case volume is the same and the neck/shoulder/boreline is good, the gas will travel the 'same' path.

Then there is that whole bullet barrel thing.

I bet the shape of the stock and how it recoils will play a larger role then anything associated with the case for long range accuracy.

Jerry

 

[jb1000br]

Kirby -- the cases will probably turn themselves into bananas with firing and sizing because the thick and thin parts will react different to the firing/sizing pressure and movement.

If you can keep cases straight with dies that size JUST enough and keep velocities tight, that is all that should matter IMO

JB

 

[Coyboy]

Boring boring boring, you guys keep talking case thickness this and case stretching that.

Lets talk about somthing exciting like this 338 Allen Mag. Kirby is working on. (lucky guess)???

130 grains of powder should really move a 300 smk.

The cats out of the bag, I want details.

 

[Ballistic64]

The problem is that with this wildcat design, it will take a personal investment of roughly $6000 /ubbthreads/images/graemlins/shocked.gif

Just wanting to get some opinions before I commit to this level of spending!!!



Good Shooting!!

Kirby Allen(50)

[/ QUOTE ]


Aww,come on Kirby,break out some of that moldy money. /ubbthreads/images/graemlins/grin.gif