Deciding to build a big bore upper. Bolt question. Anybody have experience with the 6BR bolt .

[IceAxe]

In narrowing it down between the 458 SOCOM and the 450 Bushmaster I am favoring the 450b for the following reasons;

SOCOM uses low pressure pistol brass and the 450 b uses high pressure rifle brass
More energy in the 450b loads with greater potential in hand loading,
458 bullets can be swaged to 452 and used in the 450b negating any advantage there,
The strait wall case would make it legal to hunt with in my home state of Michigan on visits.

It appears to me that the weak spot in both the SOCOM and the 450b is in the hogged out 556 bolt. I have found a modified ar10 bolt and extension that can be used in the ar15 platform. At least that's what it looks like to me. They call it a 6 BR offered by AR Performance.

Does anyone have any experience with these bolts. Feel free to tell me where and if this will not work. Thanks


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[MarkCO]

I have both a 450BM and a 450BM-C (Corvette). I have three .450BM bolts, one from the factory and 2 made from .223 bolts with 7.62 extractors. They have been fine (but I have a spare) and I have not heard of anyone breaking one. The stresses are not in the right direction to cause any problems with the thinner skirt of the bolts modified for the .450BM.

Good choice BTW. Same reasons I went with the .450BM over the .458SOCOM.

[IceAxe]

Good to hear. I also heard very good reports on accuracy. Much better than I expected, are you satisfied with the accuracy? I am planning to run open sights on mine if you have any recommendations.


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[MarkCO]

Very pleased with the accuracy. I have a modified stab crimp die, which is one of the little tweaks that helps some. But even without, both of my rifles are capable of putting 5 rounds into 1" at 100 yards with an optic. I run an MTAC 1.5-6 on them. There is something very satisfying about tossing 5 250 grain slugs downrange and ending up with a silver dollar sized hole in the target. :)

[IceAxe]

That's very good.....what is a 450 b corvette?


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[MarkCO]

Tim LeGendre, the developer of the .450 Professional and the .450BM makes a conversion for the 450BM called the 450Corvette. As a fellow firearms engineer, Tim did the conversion for me, but swore me to secrecy on how it actually works. Long story short, it runs the .450BM factory ammo as well as handloads past the "wall". The wall is about 44Kpsi, at which point you have extraction, and the appearance of pressure issues with the stock configurations. Some guys run M16 carriers with heavy buffers and get a little better case life with a little better performance. Basically, at the 44kpsi, the pressure in the case does not drop fast enough and you are trying to unlock the action with the pressures still too high. Being able to run up closer to 55Kpsi without tearing up brass lets us push either heavier bullets, or lighter bullets faster, than the factory fodder. Tim uses a proprietary gas system that allows the higher pressure as well as the lower pressure rounds to be shot through the same rifle reliably.

[AKA-Spook]

It appears to me that the weak spot in both the SOCOM and the 450b is in the hogged out 556 bolt. I have found a modified ar10 bolt and extension that can be used in the ar15 platform. At least that's what it looks like to me. They call it a 6 BR offered by AR Performance.


I've had to remove the bottom two lugs on the ARPerf .478 dia bolts on a bunch 45 acp builds Ive done. They have a tendency to drag on cases without a shoulder.
Its no biggie the bolt is plenty strong even minus two lugs....and requires its own extension.
Ive also used MGI socom bolts on several socom builds pretty much without issue. They are considerably less costly than H's bolt/extension combo but are obviously weaker units.

[IceAxe]

MarkCO. What length barrel(s) are you running? And could the same thing be accomplished with an adjustable gas block? I was considering an 18 barrel with a 1/18 twist.


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[IceAxe]

Spook are these the radiused lug bolt/extension(s)? Could you post a picture as I may end up in the same boat?


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[MarkCO]

My 450BM is a 16" and my 450BM-C is an 18". It would be very difficult to accomplish the same thing with an adjustable gasblock. Most of them will fail if you actually adjust them, they are more of a set it and lock it in type of thing.

[IceAxe]

MarkCO, have you developed a preference between the two?


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