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What is the least amount of taper possible in a cartridge case?
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I am curious to know the least amount of cartridge case taper that is practical for 308 (short action) and 30-06 (standard action) based rounds. Both have 0.470” base diameters. The least amount of taper I can find in a SAAMI 308 based round is the 30 TC with a 0.464” shoulder. The 280 ackley has a .454” shoulder. I’ve read of wildcats with steeper shoulders in the 30-06 length, but what is max? Thanks.


Matt
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Posts: 3123 | Location: Northern Colorado | Registered: 22 November 2005Reply With Quote
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The 30 TC works out to about 6 thousandths per inch taper, which I believe is right at max.
 
Posts: 377 | Registered: 07 January 2012Reply With Quote
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Originally posted by whelenite:
The 30 TC works out to about 6 thousandths per inch taper, which I believe is right at max.


Thanks for your opinion. The Griffin and Howe 400 Whelen has a 0.458” shoulder, which is about as radical as I’ve seen the ‘06 case get taken. That seems to follow along with your 0.006” taper per inch theory. However, it’s hard to find a 308/‘06 case base diameter these days that isn’t a few thousandths of an inch under spec. Weird.


Matt
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Posts: 3123 | Location: Northern Colorado | Registered: 22 November 2005Reply With Quote
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For the record, the absolute least body taper for a commercial cartridge is zero body taper. The 5.7x28 has no body taper at all due to the dead straight 50-round box magazine for the P90 sub machine gun it was designed to fit. There is one caveat. The gun is of blowback design and the cases are coated in a lacquer that actually causes the cases to stick to the inside surfaces of the chamber to help delay blowback. I was a very early adopter of the cartridge and had a set of dies before the semi-auto carbine version of the subgun was available. Once I finally got my carbine, I found that the coating on the cases would wear off and chip after one reload and sometimes after even the first firing. Once the coating was gone, the bolt would accelerate so quickly that the necks of the cases would be blown out almost straight. That was all happening a couple of inches away from my eyeballs because of the bull pup design. The only recourse was to reduce loads below the level of 22 magnum rimfire to make the gun work correctly and safely. Since factory ammo was expensive and I couldn’t handload effective ammunition for it, I divested myself of the rifle and loading equipment.

My vote for the least body taper is the 470 Capstick case. It is 2.85” in length and has a total of 0.014” of body taper from base to mouth. That works out to only about 0.005” per inch of body taper. I would personally stick with PO Ackley’s standard of about 0.008” per inch of case. He had it pretty well figured out with years of testing alternatives.

RC


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Posts: 567 | Location: Central Texas, U.S. | Registered: 20 December 2001Reply With Quote
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I believe the Gibbs used a .458. As stated the 400 Whelen is a .458. When I started designing my PDK dimensions I probably spent to much time worrying about shoulder dia. I chose .458 the reamer left me with .460. I've been using that .46 shoulder for 40 yrs with no issue.


As usual just my $.02
Paul K
 
Posts: 12808 | Location: Mexico, MO | Registered: 02 April 2001Reply With Quote
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case? well, that's not really a question -
what CHAMBER taper, is the functional question - one could have zero taper in the case, but .001 in the chamber, or a bit more in slop, and the case would come right out


opinions vary band of bubbas and STC hunting Club

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