450 Corvette

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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Re: 450 Corvette

Postby Earnhardt » Thu Jan 04, 2018 7:30 am

So the best bet would be make sure the barrel has a little bigger gas port, and I can use an adjustable block to set the pressure I need to operate the action?
Not only to ensure that the barrel gas port doesn't have to get re-drilled, but to allow for various bullet/powder combos to be worked up and tuned.

I know the powder capacity isn't the biggest on a 450 BM, bullet the range of bullet weights is pretty significant.

With my Christensen 6.5 CM barrel I adjust the block from ~ 60-80% open, depending on the bullet weight, for smooth operation. That's with 120 grain to 147 grain bullets, all in factory Hornady rounds.
That's a range of 20-25% in bullet weight.
With the 450 BM loads you guys are using, with a range of 200-300 grain bullets, that's a 50% difference. Crazy....
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Re: 450 Corvette

Postby Hoot » Thu Jan 04, 2018 12:47 pm

Earnhardt wrote:So the best bet would be make sure the barrel has a little bigger gas port, and I can use an adjustable block to set the pressure I need to operate the action?
Not only to ensure that the barrel gas port doesn't have to get re-drilled, but to allow for various bullet/powder combos to be worked up and tuned.

I know the powder capacity isn't the biggest on a 450 BM, bullet the range of bullet weights is pretty significant.

With my Christensen 6.5 CM barrel I adjust the block from ~ 60-80% open, depending on the bullet weight, for smooth operation. That's with 120 grain to 147 grain bullets, all in factory Hornady rounds.
That's a range of 20-25% in bullet weight.
With the 450 BM loads you guys are using, with a range of 200-300 grain bullets, that's a 50% difference. Crazy....


You're not stuck using a fixed amount of powder across different bullet weights, such that the pressure is less with the lighter ones. If you use different charge weights to keep that range of bullets at 38k psi, they will cycle the DI action just fine. The time that the different bullet weights take traveling down say a 20" barrel will vary but the action is fairly tolerant. I've shot 185 to 325 grain bullets from both a carbine and mid length barrels and they all ejected when everything else was right with the gun. I may have gotten some head swiping on occasion when the bullets were slower but it was rare and mostly with the carbine length gas system, starting to unlock too soon. I've never needed an adjustable gas block. It will allow more gas through when the gas is sampled at a lower pressure point further down the barrel. That satisfies the amount of gas but it doesn't satisfy when it occurs. If I could offer one really useful piece of advice, it would be to get a Mid length gas sampled barrel if you're not getting a short barrel and yes, I consider a 16" barrel to be short. Aka a Carbine Length Barrel. IE Best served by a Carbine Length gas system. One advantage I saw with the Carbine length gas system on my first (20") barrel, was that it would still cycle with light loads and I'm talking 200gr bullets at 1600fps. Talk about tame loads! It also cycled with the same bullets traveling 2500fps. The further down the barrel that you sample the gas, the more you are forced to load them up in velocity in order to get trouble free cycling. I had a lot of successful recipes from that carbine length barrel, fail to cycle for the short time I was playing with my rifle length gas system barrel. So, it would seem that a good compromise would be the mid length gas system. My mid length Bartz worked fantastic with resized (.458) Hornady 325gr FTX bullets at velocities up to 2100fps, which was all the faster I ran the 5-shot tests up to before I ran out of bullets. It was a lot of work sizing them down to .452, so I won't be continuing that experiment. I don't hunt Bison where I live. ;)

I have a Rifle Length gas system, 20", 1:24 barrel sitting on the shelf ever since I got my Mid Length 20", 1:24 barrel for a reason.

WRT barrel length. If I could get a 24", 1:24 barrel for a non-custom price, that's what I would use. In that case, I would be inclined to go with a Rifle Length gas system as it could take advantage of slower powders without throwing some out the muzzle unburned. Keep the chamber pressure down while keeping the bore pressure up.

Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.
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