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Discussion Starter · #1 ·
I have a complete lower reciever and its from palmetto state armory. I want to build it into a pistol. Want to get an upper which is 7.5 and i want to know what twist should i get?
 

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1/7, 1/8 or 1/9 you can shoot out to 200, 300 yards with a 10.5in bbl but a 7.5in won't give you the V to reach out that far unless your aiming at a 747.

If your going to use it for HD go with 70gr or more slugs.

I'll add more later
 

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1:7. Your bullet isn't going very fast and needs all the spin it can get before it leaves the barrel. I'll let you decide what to use for ammo, but keep in mind the .223 Rem was not designed for low speeds, and thus the bullet technology will not perform as advertised. That's why I asked what the caliber was because 300BLK performs best in short barrels. 10.5" to be exact.
 

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May want to recommend a bullet weight as well to match the barrel. With that short of a barrel I'm not sure which weight to go with?
 

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I would not build anything shorter than 10.5 in barrel. the longer gas system makes it more reliable.
 

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I would not build anything shorter than 10.5 in barrel. the longer gas system makes it more reliable.
don't try to dissuade him man... he wants a 7" pistol, let him build it. give him the best advice you can to help him get what he wants.
 

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May want to recommend a bullet weight as well to match the barrel. With that short of a barrel I'm not sure which weight to go with?
light. VEEEERY LIGHT. long and/or heavy bullets will just tumble as soon as they leave the barrel.
 

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will a light round at low speeds really be so effective in a home defense situation?
that sounds more like a low cost plinking formula to me.
but then. what do i know
 

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will a light round at low speeds really be so effective in a home defense situation?
that sounds more like a low cost plinking formula to me.
but then. what do i know
well there is a brief discussion on short barrel ballistics on barfcom and the happy medium, as far as the TAC bullets go, is around the 60 gr mark. But that is from a barrel that is an inch and a half longer than the OP intends to use, so his results are gong to be different. Whatever he uses the bullets have to be designed to fragment or expand at low speeds or they'll cruise right through. Many say not to use a FMJ in pistol length rifles as it does not carry the speed to fragment at all and cruise right through, like the steel core does in m855.

I'd look for blunted softpoints.
 

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For Home Defense distances (what I consider to be less than 30 yards), it really doesn't matter what twist because any of them will launch any of the bullets all the same.


But since you said it was an option, my vote is a 1:7 or 1:8 twist for the reason listed above. To impart the most twist you can in such a short barrel while still giving slightly better longer range accuracy.


Just FWIW, and I'm not going to try to tell you what to build or do, only throw this out there in case you don't know, but a 10.5 or 11.0" use a standard CAR length gas setup and finding parts (gas tube, standard car length forend, etc) are much easier to buy and service than the shorter "pistol length gas" setup that you WILL have to use for the 8.5" or less barrel.


And another thought is that many serious SBR HD weapons will eventually wear a suppressor. I don't know of any suppressor manufacturer that warrants their (556/223) cans on less than 10.5 inch barrel due to the excessive heat and unburned powder that acts as a sandblaster on the suppressor baffles.
 

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I'd recommend a 9mm in a 7.5" PDW-type AR, particularly for the HD role.

If you've never fired a 7.5" AR, the flash and blast is massive--and in an indoor range, it's almost debilitating. I've read that the concussion of the blast is comparable to a flash-bang...

In 9mm, however, you're going to get great performance out of standard velocity loads, without the fireball and blast.

If you are dead set on a 7.5" 5.56, though...I'd run a 50-55gr ballistic-tip type bullet. Twist won't matter much at the ranges you're considering; but I'd go 1:7.
 

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Discussion Starter · #14 ·
Thx guys for the help im a beginner at this. 10.5 300 blk out is my next build but ammo are hard to find i live in CA. Other than that, i heard u can shoot an alternative bullet is that true? Well, i just want to know more about ar pistol because mobility is a plus for my height and iim not that tall lol. Still debating on what upper should i get. How about an upper that shoots 7.62? Plus i dont know what bcg i should get. Any info will help me decide.
 

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I'm not a lawyer, but you may want to read this if you haven't already.


It pertains to California NFA ownership and the extra state requirements.


California Legal NFA Firearms
 

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Discussion Starter · #16 ·
Yes i hear you. Thats SBR. but i heard you can use a pistol buffer tube instead of using an adjustable stock and it will be legit without tax stamps. So is that possible?
 

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I'd go with 1:7 twist (and a 10.5" barrel honestly). 1:9 is [best?] for 55gr, but almost no one, especially for 5.56, uses the 45gr. I'd go 1:7 so that the heavier stuff shoots better. Being unable to properly stabilize the bullet will open groups up a bit.
 

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Yes i hear you. Thats SBR. but i heard you can use a pistol buffer tube instead of using an adjustable stock and it will be legit without tax stamps. So is that possible?
I think it was more about the suppressor talk than SBR, since you stated early on that your intention was a pistol build.

All i'm going to say is follow all laws.

As for BCG, just buy something quality. BCM has good products.
 

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I'd go with 1:7 twist (and a 10.5" barrel honestly). 1:9 is [best?] for 55gr, but almost no one, especially for 5.56, uses the 45gr. I'd go 1:7 so that the heavier stuff shoots better. Being unable to properly stabilize the bullet will open groups up a bit.
but remember, you need reliability in expansion or fragmentation. a slower bullet is not going to do it's job if it's not going fast enough.
 

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whoops. I missed the OP saying he was building a pistol.


Pistols are not nfa regulated, and it makes more sense to do a 7 inch build with pistol gas to cut front end weight.


Sorry, I just saw all the chatter about a short barrel and assumed it was going on a rifle instead of a pistol.
 
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