450 Corvette???

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450 Corvette???

Postby TacoTaco » Wed Feb 20, 2019 9:13 am

Hey guys. It’s been a long time since I’ve posted here. Having kids tends to take away your free time. Who knew?

Anyway, last time I was active around here there was talk of a 450 Corvette round. From what I recall it was a rifle length gas system 450B that could handle hotter loads. Did this round ever materialize? My Google-Fu is weak...I can only see, to find posts from ~2014 relating to that setup.

I’m looking to rebarrel a Mk12Mod0 clone to 450B, and this idea popped into my head.
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Re: 450 Corvette???

Postby Hoot » Wed Feb 20, 2019 9:58 am

Active promoting of the 450 Corvette dwindled as Wildcatter's participation ebbed. He was visiting the site every once in a while after 2014 but he didn't participate in many discussions after 2016. He hasn't been by since last July. I don't know of any members who have taken up the mantle since he drifted away. Great ideas move forward even after the originator lets go of them. The lack of forward progress speaks to the fact that the barrel mod didn't buy as much as it may have been promoted to do, given the marketing savvy, sexy name assigned to it. Right now, more participation is evident in the bolt action variants of the 450b, where "true muscle" can be flexed for no other reason than the additional action strength. Non-Corvette models are eclipsing the performance that the Corvette offered. The other reasons bolt actions are more active appear to be less expensive for a complete firearm, less magazine compatibility challenges and a lot more folks don't like the AR platform than I ever realized in this caliber, or they live in states that don't like them.

Right or wrong, that's my read on it and I've had two 20 inch "Corvette Style" barrels that I toiled with for a while. Too fussy getting the gas port to function across a wide variety of bullet weights and powder speeds. Both went to a new homes.

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Re: 450 Corvette???

Postby TacoTaco » Wed Feb 20, 2019 3:23 pm

Roger that Hoot, thanks for the reply. Sounds like I’ll need to go a different route then. Shame Wildcatter has dropped off the board. Years ago he was a wealth of knowledge on this cartridge, for obvious reasons.
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Re: 450 Corvette???

Postby Bmt85 » Wed Feb 20, 2019 8:47 pm

I was looking Into the 450 Corvette a while back, and I also found old posts and no one doing the conversions. I stumbled across BHW offering 450B barrels and they offered a rifle length gas system. They were having a sale, so I ordered a 20” rifle gas 450B. Took something like 2 months to get the barrel, another few weeks to put it together. I have it set up with a non adjustable gas block and Slash’s XH buffer. It has just enough to cycle factory ammo. With handloads, it will cycle 225 FTX’s with, I believe 39gr of Lilgun, might be 40. I also have a 12.5” 450B with carbine gas from BHW, and it too takes 39 or 40gr of Lilgun to cycle a 225 FTX. So not too bad for a rifle length gas. Unfortunately, the bolt I had in the 20” cracked before I really tried leaning on it. The bolt manufacturer has had quite a few issues with Grendel bolts, so it doesn’t surprise me mine didn’t last 100rds.

I haven’t really played with the 450B’s for a while, too many build’s going on, and not having much time to shoot or reload in general. With the little I have played with it, it has worked well, and shows a lot of promise. I will probably get to around to playing with it more when I put my 10.5” 450B (Spec’d for subsonics) together, which will be after a 270 AR build.
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Re: 450 Corvette???

Postby Rockglock86 » Sun Feb 24, 2019 10:37 am

I have been talking with people across ar15.com, the MSRevo forum, and other places about a "high pressure" 450 Bushmaster build, using a Oly .22-250 bolt and extension and the overall consensus is as long as it's held at 55k psi then it should run fine and strong. So if I spin up a 20" rifle gas barrel, use a Oly bolt and extension, and even running at 50k psi. I should see decent numbers and actual "Corvette" performance. If anyone has some Corvette or high pressure load data they would share that would be much appreciated or if they have any insights into a build such as this throw it in the pot.

Justin
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Re: 450 Corvette???

Postby Hoot » Sun Feb 24, 2019 8:50 pm

Rockglock86 wrote:I have been talking with people across ar15.com, the MSRevo forum, and other places about a "high pressure" 450 Bushmaster build, using a Oly .22-250 bolt and extension and the overall consensus is as long as it's held at 55k psi then it should run fine and strong. So if I spin up a 20" rifle gas barrel, use a Oly bolt and extension, and even running at 50k psi. I should see decent numbers and actual "Corvette" performance. If anyone has some Corvette or high pressure load data they would share that would be much appreciated or if they have any insights into a build such as this throw it in the pot.

Justin


A setup like that would leave the Corvette in its dust. The Corvette concept was to run heavy bullets using powders that are generally too slow for this caliber, hence the rifle length gas system. Yes in theory (see sig) that would best the performance available from a 450b with its original carbine length gas system pushing heavy bullets but that was the only scenario. Now, with more and more 450b barrel manufacturers offering mid-length gas systems, we are seeing a small performance boost across all bullet weights, including the heavy bullets.

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Re: 450 Corvette???

Postby Bmt85 » Sun Feb 24, 2019 9:23 pm

Al in Mi and I were talking a bit about this some time ago. The Oly bolt and extension should work, seeing as MDWS now use them on their 308 based wildcats.

They only thing I would be concerned about is the brass holding up. I know it was brought before and others disagree with me. From my experience, we can push the 450B to 45 Raptor/Vrap territory, and still be relatively safe. However, I have worked up to loads that take brass out of spec (shouldn’t reload again), in one or two firings. Both Starline and Hornady. That’s also on standard bolts.

So in my opinion, running a bigger bolt and extension will add a nice safety factor, but I don’t think there will be a whole lot to gain performance wise from that alone. With a rifle length gas you may get a little. I still think about doing this project, but have too much going on at the moment. One suggestion I have, use Chrome Moly Steel, not Stainless for the barrel. CM is stronger, even the fat cats done by MDWS and those guys are only done with CM barrels.
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Re: 450 Corvette???

Postby Rockglock86 » Mon Feb 25, 2019 4:24 am

Noted on the CM barrels versus stainless. In speaking with Moleman, the weakest point in the whole setup would be the .736 thread relief cut for the barrel extension. Things get pretty thin there.
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Re: 450 Corvette???

Postby Hoot » Mon Feb 25, 2019 5:22 am

Worth noting is the fact that the 450b case parent cartridge is the 284 Winchester, which is spec'd at 63k psi.

I have a 30 Remington AR upper that I picked up when they were being dumped a couple years ago. It utilizes the oversize bolt and BE like my Oly 300 OSSM upper had. While the 30 RAR is quite a respectable caliber, the platform is ripe for re-barreling in a fatter caliber some day as a project. Money in the bank, or should that be money to be spent, in the bank. ;) Like many of the members here, I'm short on disposable time to play with for another year, 8 months and 6 days. Assuming everything goes OK up until then, my new mailing address will be the gun club 8 minutes down the road. :D

Wifey may have some say in that however. "If Mama ain't happy, ain't nobody happy"...

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Re: 450 Corvette???

Postby Bmt85 » Mon Feb 25, 2019 2:53 pm

Hoot wrote:Worth noting is the fact that the 450b case parent cartridge is the 284 Winchester, which is spec'd at 63k psi.

I have a 30 Remington AR upper that I picked up when they were being dumped a couple years ago. It utilizes the oversize bolt and BE like my Oly 300 OSSM upper had. While the 30 RAR is quite a respectable caliber, the platform is ripe for re-barreling in a fatter caliber some day as a project. Money in the bank, or should that be money to be spent, in the bank. ;) Like many of the members here, I'm short on disposable time to play with for another year, 8 months and 6 days. Assuming everything goes OK up until then, my new mailing address will be the gun club 8 minutes down the road. :D

Wifey may have some say in that however. "If Mama ain't happy, ain't nobody happy"...

Hoot


Yeah, with something like this, .284 brass might need to be used.

I look every once in a while for a 30 RAR upper someone wants to unload for a decent price. No luck so far. That would be a better route in my opinion, except if the bolt goes, then your SOL.
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