# Case design

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Matt27, Jul 11, 2004.

1. ### Matt27Well-Known Member

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313
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Sep 3, 2002
I have a project in mind and was wondering when doin a wildcat and by technical terms overbore if their is some mathematics that when designing the case by increasing or decreasing the shoulder angle if it would help any with throat erosion. I want to take the 9.3x62 case lapua makes and neck it down to 6.5cal.The case has a 17 degree shoulder and i was thinking of making it to 30 or 35 degrees.
Any thoughts or reccomendations?
I am going to call Dave Kiff And Manson reamers this week and discuss it with them also. Thanks for any help

Matt

[ 07-11-2004: Message edited by: Matt27 ]

2. ### GuestGuest

Matt,

I presume that you mean 9.3 x 62.

Producing a wildcat can be one of the most satisfying things that a hunter/shooter can do. We don't need any reason other than 'I want to...' to send us off in pursuit of a design, all the while thowing tidy sums of cash into the mix simply because there isn't anything standard or off-the-shelf that we can make work correctly. I'm with you on this, BTDT.

But...(and if you've already done this, ignore me) take a look at:

6.5 X 68S
6.5-06 Ackley Improved
6.5 Gibbs
6.5 x 64 Brenneke
6.5 x 65 RWS
.264 Hawk
6.5 Rem. Mag.

With exception of the 6.5 Rem. Mag., these are all basically what you are trying to get to without a lot of necking down, neck turning (or reaming) and all of the custom stuff that goes along with a project like this. They all have gently sloping shoulders that beg to be improved and in fact the 6.5-06 AI and the 6.5 Gibbs obviously have already been through the process. The 264 Hawk is close to that. They all have case capacities of 68 gr. to 86 gr. of water. So why beat yourself up making cases the hard way?

The angle of the shoulder should work in conjunction with the length of the neck to curtail throat erosion. It's when the plasma gets directed right at the sides of the throat that a great deal of erosion takes place. The idea is to channel the plasma straight down the bore or get it to impinge on the inside of the neck before it hits the throat.

Unburned, long grain powder has a definite negative effect on the throat of a chamber. It acts like sandblasting by scrubbing the surface of both the throat and the bore. The heat of the plasma does enough damage without adding the scrubbing on top of that. The effect of steep shoulders is that the powder gets delayed slightly in the case, allowing more of it to burn in the case as opposed to on the way down the barrel.

Regards.

3. ### Matt27Well-Known Member

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313
Joined:
Sep 3, 2002
Crispin

Thanks, went back and edited my mistake. I am not dead set on this idea but what intrigued me was that Lapua makes 9.3x62 brass and it should be consistant. I haven't bought any of the brass yet to see but my 308 and 338 Lapua brass is very consistant. Before i do anything I will buy 100 pieces and take a look at the brass to see what it is like. I have Load from a disk and created this round and it is very intrigueing. What my intention is, i want to hit the accuracy node for the 139scenar and 140 class bullets over the 3000fps mark. All i remember about the beginning of the 6.5x.284 was that it was suppose to reach that and be accurate but the accuracy is around 2900fps.

I like to tinker and would like to do somethin nobody has tried yet(at least to my knowledge).
Thanks for the response and what you said is basically what i had heard before.

Matt

4. ### a.JRWell-Known Member

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98
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May 28, 2003
Matt,What u will end up with is basically is a 280 thou longer 6.5x 55..In it's imp form this is a formidable cartridge for L/R bench at the required 2910 to 2950 fps in an 8 twist but there is no need for the larger boiler room unless you change up to a 9 twist and approx 3050 to 3080fps..H1000 is a good starting powder with a 30in tube with 140 CLOs..Dave Kiff i'm sure will recomend a 6.5 Rogue front on your 9.3 case and should give approx 6.5.06AI performance..You are right about checking the brass first as not all Lapua brass is created equal(from a design point) also..JR..Jeff Rogers