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need help designing a new case

 
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Old 11-14-2009, 02:51 PM
TH TH is offline
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need help designing a new case

Guys,
I want to be able to shoot the 30 cal 240grn smk 3300 to 3400 fps can you help me? I want to use no longer than a 34inch barrel. Can anyone help me?
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Old 11-14-2009, 05:27 PM
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Re: need help designing a new case

You're asking an awful lot out of a 30 cal.

A strong contender would be the 300 Allen Express. Based on the Lapua case.

Indicated potential out of a 27"-30" bbl is 3450-3550 MV w/180 gr bullets and 3000-3100 MV w/265 gr bullets.
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Old 11-14-2009, 05:40 PM
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Re: need help designing a new case

I have a 338 Allen Mag I know its possible to achieve 3300 to 3400 fps accurately with a 300grn smk. I have always loved the 240smk there has ben several world records shot with them. I was just trying to figure out how to shoot the 240 at high speeds. I also have a 300 yogi which is a 30 - 338 Laupa improved. I was only able to achieve 3100fps the extra velocity would make a huge difference. The only combination that I could come up with would be take the 408 chey tac case shorten it and neck it down to 30 cal and im still not sure that velocity is achieveable.
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Old 11-14-2009, 06:00 PM
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Re: need help designing a new case

None of the 338 Norma/Lapua cases are going to get you there.
You will have to work with something in the 408 Chey-Tac case. But why would you want to ?
It would burn a barrel out in short order.
My 300 JAZZ(30-338 Norma Improved) shoots the 240gr SMK @ 2850fps w/ a 28" barrel, and so far has shot 1.5" groups out to 650yards. I dont see the need to push the 240gr to 3400 fps. With a 34" barrel out of a 300 JAZZ you would get to 2950-3000fps.
If you already have a 338 AM, you already have a hammer of a rifle.
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Old 11-14-2009, 06:39 PM
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Re: need help designing a new case

Maybe you don't need to design a new cartridge. Use 308/510 sabots in a 34" 50 BMG. With a 240 grain SMK bullet and a 60 grain sabot (300 grain total) about 250 grains of VV-N560 should give about 3800 fps+ muzzle velocity at under 47000 psi (a moderate load for a 50 BMG. Thats calculate with 0.5" sabot seating depth. You will need a barrel with a 10" to 11" twist to stabilize it at sea level. The standard 50 BMG is 15". Pac-Nor can supply a 10" twist 50 BMG barrel.

A 30-378 Wby can't quite drive a 240 SMK to 3200 fps with a 34" barrel. 103 grains of VV-N570 shows 3190 fps at SAAMI max. Anything in a 30 cal bore which will give 3300+ fps is going to have poor barrel life, but maybe thats ok.

I haven't tried i either of the above loads, they're just Quickload simulations but they should be close.

You could save a lot of bother by getting some surplus 50 BMG M903 SLAP ammo. It's got a 30 cal ~355 grain tungsten penetrator and is rated 4000 FPS from a 45" M2HB barrel. It's stable in a 15" twist barrel because tungsten is much denser than jacketed lead. I've seen it for sale at gun shows a couple of time for $25/round.
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Old 11-14-2009, 07:35 PM
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Re: need help designing a new case

I can push the 240 SMK close to 3200 fps out of my .30-.416 Rigby Improved. After that, accuracy falls of dramatically, not to mention case life.

My accuracy load is running around 3100 fps, and has gone under 12 inches at a mile.

I can't see the need to want to drive that bullet any faster. The .416 Rigby case is about the largest case that I would consider using, and it's an ordeal to prep 100 pieces of brass.
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