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Old October 11, 2021, 09:07 PM   #1
nhyrum
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New AR-15 build caliber debate

I figured I'd add my "what should I build next" to the heap. I just acquired another ar15 lower, so off we go

For some reason, I've got this thing against super poplar calibers, so I really don't want 5.56/223. I've got a SBR blackout, so I'm thinking I'll use that lower for anything with a short barrel.

My only other non-22lr rifle is a 300 ultra mag, so I've got quite the gap to fill.

I'd REALLY like a 458 socom, but I'd want it with about a 10.5 inch barrel, so that would go on the SBR.

So since this will be a full, carbine length rifle, I'm wanting something... Basically "better" than 223/5.56. I do reload, and I'm a bit fond of wildcats, and case forming and having little to no load data does not bother me.

I'm thinking of something that's 3 gun/prs ish for the build, although I know an ar15 really doesn't have the space to have anything really big enough to get easily spotable hits past like 6-800 yards, so I know that's unrealistic.

Cartridges I'm contemplating are, 224 valk, 6.5 grendel, 224 grendel and 22 nosler. Something 6mm I think would really fit the bill, but I don't know much about those 6mm ar wildcats like the 6mm ar turbo improved, 6mm arc, etc. My real only concern is case and component availability. If it's a wildcat, I'd like it to be something that the parent case is plentiful, but not the only consideration.

I'm kind of torn between a 6mm ar turbo 40 improved, although I HATE the name, or a 224 grendel.



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Old October 11, 2021, 09:29 PM   #2
Shadow9mm
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From what I have seen I would not touch 224 valk. Issues with twist rate and getting bullets to be stable.

What pops into mind that kinda has me interested is the 25 GPC (general Purpose Cartridge). You can form brass from 6.8SPC. Interesting looking little cartridge.

heres a chanel I follow explaining his build and the caliber
https://www.youtube.com/watch?v=N4dA...LBsgyp&index=9


and a playlist of his, has some load development, as well as hunting with it.
https://www.youtube.com/playlist?lis...JYSWBp6_LBsgyp
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Old October 11, 2021, 09:41 PM   #3
nhyrum
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Yeah I wasn't really considering a Valkyrie. That 25 gpc looks interesting.

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Old October 11, 2021, 09:57 PM   #4
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What is a "full carbine length"--do you mean you contemplate a barrel length of around 14.5" to 16"? I have a 458 socom build that uses a 18" barrel--the length you are contemplating for that is going to be "handful" because it has a heck of a report and gas charge and you are contemplating that close to your face. The reason I mention that is the cartridge choice is only part of the equation--you'll need to consider things like report and gas system balance.
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Old October 11, 2021, 10:01 PM   #5
Shadow9mm
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I have never done a wildcat, for some reason though the 25gpc really keeps nagging at at me.
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Old October 11, 2021, 10:08 PM   #6
stagpanther
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Quote:
I have never done a wildcat, for some reason though the 25gpc really keeps nagging at at me.
You got me interested in it too, my experience doing wildcats based on the 6.8 case is that its a great choice for a parent case. Only reservation I would have about a 25 using the 6.8 is my gut feeling is you'll be limited in bullet choice and might not be able to power efficiently the "new generation" of 25's like Blackjack's and Berger's very high BC bullets--which is why I eventually chose the PRC as the base for my new 25 build. SAUM would be a good choice too.
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Old October 11, 2021, 10:08 PM   #7
nhyrum
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Quote:
Originally Posted by stagpanther View Post
What is a "full carbine length"--do you mean you contemplate a barrel length of around 14.5" to 16"? I have a 458 socom build that uses a 18" barrel--the length you are contemplating for that is going to be "handful" because it has a heck of a report and gas charge and you are contemplating that close to your face. The reason I mention that is the cartridge choice is only part of the equation--you'll need to consider things like report and gas system balance.
Yeah sorry, I mean a barrel of 16+"

The 458 socom I would build would be suppressed sitting heavy subs, so report is a non issue, and gas balance would be dealt with in building the upper. Probably with a forward venting gas block.

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Old October 11, 2021, 10:18 PM   #8
stagpanther
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Quote:
Yeah sorry, I mean a barrel of 16+"

The 458 socom I would build would be suppressed sitting heavy subs, so report is a non issue, and gas balance would be dealt with in building the upper. Probably with a forward venting gas block.
A big sub bullet stabilizing in a short slow twist barrel? Good luck with that.

Back to your carbine build, a myriad of choices out there depending upon what you want it for--though these days I do builds for no other reason than to simply try a new cartridge out.
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Old October 11, 2021, 10:21 PM   #9
nhyrum
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Originally Posted by stagpanther View Post
A big sub bullet stabilizing in a short slow twist barrel? Good luck with that.
Well, it wouldn't be a slow twist then. But of course I'd make sure the bullet I want to shoot would stabilize. There are people shooting 500 grain bullets out of a 10.5" with 1-14 twist fine.

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Last edited by nhyrum; October 11, 2021 at 10:38 PM.
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