450 Corvette

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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Re: 450 Corvette

Postby Bmt85 » Tue Jan 02, 2018 2:16 pm

Earnhardt wrote:Are these 450 Corvette conversions still being made?
Thanks


I honestly don't know. The only person I knew, doing the conversions, was Wildcatter. Haven't seen him post in quite a while. As far as I know, he was taking the Bushmaster factory 20" uppers (they have 2 gas blocks, only one functional), pulled the gas blocks, welded the factory gas port, put a new port at the other block (rifle length I believe), and reinstalled that gas block. You could do your own version by purchasing a Franklin Armory 20" barrel, or like I did, custom order a 20" from Black Hole Weaponry.
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Re: 450 Corvette

Postby Earnhardt » Tue Jan 02, 2018 7:03 pm

Thanks Bmt85!

How about the longer 450 BM barrels, such as 22-24" long?
Use the rifle length gas with an adjustable block?
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Re: 450 Corvette

Postby Bmt85 » Tue Jan 02, 2018 8:16 pm

I don’t personally know of anyone offering a 22” or 24” 450B barrel for the AR. I know Bartz built a 24” with a rifle length gas system and had no issues, but as far as I know, he doesn’t offer them. I only shot my 20” BHW w/rifle length gas about a total of 12 shots before my scope (from one of my other 450B’s) died. Apparently, it was on its way out. Lol. I ended up only shooting 225 FTX and Lilgun at 36, 37, and 38gr. All were a little under gassed. 38gr was almost there, so 39gr or 40gr should get it to completely cycle. Still within book, so a rifle length gas system on 22” and 24” should work just fine, without an adjustable gas block.

Edit - Forgot to mention, I’m not running an adjustable gas block, but I am running a Slash’s XH buffer w/ a stock carbine spring. So that does change things a bit.
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Re: 450 Corvette

Postby Hoot » Wed Jan 03, 2018 6:03 am

Any competent gunsmith can properly drill you a rifle length gas port. You dont have to weld the carbine length port shut, just cover it with a low profile gas block rotated to obscure the hole. IMHO if you're going to get your barrel re-drilled, go with a Mid-length on a 20" barrel. I have a melonited, 20" Franklin barrel with the Rifle length port and about 50 shots through it. Its a well made barrel but I'd trade it even up for a melonited, Mid-length 20" with similar wear any day. Any Day! I haven't put a round through it since I got my 20" Bartz upper with the Mid-length gas port. IMHO, the Corvette mod is not a game changer. Just an alternate universe. I suspect as already mentioned, that a Rifle length gas port might be more interesting in a 22-24 inch barrel. A lot of AR platform owners seem hung up on short barrel lengths. I have many bolt action hunting rifles in other calibers. They all have 24-26 inch barrels and are balanced, well handling rigs. :roll:

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Re: 450 Corvette

Postby Al in Mi » Wed Jan 03, 2018 8:43 am

wonder if you'd gain anything with a 800 series bolt and extension?
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Re: 450 Corvette

Postby Bmt85 » Wed Jan 03, 2018 8:57 am

800 or 750 extensions would be great! I don’t think factory brass will stand up to 55k psi (assuming), though. Might have to convert 284 brass. Although I just got an idea....
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Re: 450 Corvette

Postby Hoot » Wed Jan 03, 2018 9:09 am

Bmt85 wrote:800 or 750 extensions would be great! I don’t think factory brass will stand up to 55k psi (assuming), though. Might have to convert 284 brass. Although I just got an idea....


That would indeed be a game changer! The Hornady brass appears to be a little tougher line compared to the Star. Many moons ago, I did a graph of the difference between the .284 wall thickness ad the Hornady 450b. They are different but i'm at work and don't feel like Googling the thread. If I ever get tired of my 30 RAR, I have considered having it rebarreled with a 450b barrel. The bolt handles Hornady 450b brass just as well as the 30 RAR brass.

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Re: 450 Corvette

Postby Al in Mi » Wed Jan 03, 2018 12:06 pm

Bmt85 wrote:800 or 750 extensions would be great! I don’t think factory brass will stand up to 55k psi (assuming), though. Might have to convert 284 brass. Although I just got an idea....


I have no doubts about the brass taking it, I've ran some pretty steep loads thru my bolt gun and still holding up.
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Re: 450 Corvette

Postby Earnhardt » Wed Jan 03, 2018 10:35 pm

So with a rifle length gas system, are guys drilling a certain size gas port?
A one size fits all of sorts when it comes to load variability?
Or are some guys installing adjustable blocks if they start mixing up load/bullet combos?

With my Creedmoor it's pretty easy to tame and tune any load with the turn of the gas valve on the adjustable block.
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Re: 450 Corvette

Postby Hoot » Thu Jan 04, 2018 5:57 am

Earnhardt wrote:So with a rifle length gas system, are guys drilling a certain size gas port?
A one size fits all of sorts when it comes to load variability?
Or are some guys installing adjustable blocks if they start mixing up load/bullet combos?

With my Creedmoor it's pretty easy to tame and tune any load with the turn of the gas valve on the adjustable block.


I spent a day running back and forth between home and the range trying to get my gas port size to where it would cycle on fast, lighter bullets. The emphasis was Go Slow opening the port up. Basically one numerical drill bit increment at a time. IIRC, my barrel came from the factory drilled like it had 5.56 gas pressure (much higher than 450b) something like .078. Wildcatter was still in circulation and we corresponded during the process. Again, IIRC, I wound up needing to go up to .113 or .116 before it would cycle flatter shooting, 200gr FTX bullets, across the range of velocities I ran them at (2200-2500fps). Wildcatter said that he had to open up some Corvette jobs he did, greater than .120 before they cycled. I recall him saying that tighter chambers required more gas than looser ones. Reamers only last for x amount of cuts before wear makes them out of tolerance. New ones cut looser chambers and as they wear down, the chambers get tighter, then they get tossed. So, now its not just whether your rifle was made on a Friday, but whether it was chambered with a new reamer or old. The barrel I spoke of in not so glowing terms was made on the last day of the work week, going into a long holiday weekend, while the boss (small shop) was off for surgery. Lucky me :roll:

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