.243 Ackley

[David Henry]

No bashing intended of the Ackley Improved chambers what so ever, as a matter of fact your 257 Roberts is one of the ones that really shines head and shoulders above some of the others. I guess it would be true to say that when Ackley started blowing out chamber wall and shoulder dimensions he was dealing with cartridges that were at the time military surplus cartridges of mediocre pressures like the 7X57, 30-40 Krag and the 6.5 Swede to name a few and the gains achieved after his conversions were remarkable for their time. In the more modern case designs as mentioned by a previous post the 308 Winchester family shows much less of a leap in comparison when the numbers are crunched. D.H.

[260 Rem]

What DH said X2. Apparently there are a number of AI versions for the 257 Roberts which has a moderately tapered case. The versions which blow much of the taper out from base to shoulder, blow the shoulder forward, and steepen the shoulder angle to at least 40 degrees .... are quite capable of the gains documented by gunner. More space for powder yields increased velocity. I don't know, but I would also suspect the AI version is operating higher internal pressures. I hope my stay at the Holiday Inn was not in vain

[6.5x47 lapua]

If you improve the 243 you will have a greater chance of improvement than all the others built off the 308 case.If you use palma brass you can safely step up the pressures a bit.My whole idea of improving is buying more case capacity so you can go to a slower powder and not run out of case capacity with heavier bullets.

[260 Rem]

Originally Posted by 6.5x47 lapua

If you improve the 243 you will have a greater chance of improvement than all the others built off the 308 case.If you use palma brass you can safely step up the pressures a bit.My whole idea of improving is buying more case capacity so you can go to a slower powder and not run out of case capacity with heavier bullets.

Definitely sounds like a good strategy for stretching the distance with a long 6mm bullet. The Lapua Palma brass has small primer I think.

[6.5x47 lapua]

Originally Posted by 260 Rem

Definitely sounds like a good strategy for stretching the distance with a long 6mm bullet. The Lapua Palma brass has small primer I think.

its my next build for 1000 bench for the non windy days.the 7 gunworx gets the nod when the wind starts to blow.