Pistol caliber AR question(s)

[Sigsour7]

Im planning on building a .40 cal ar15 using one of the lowers that utilizes glock mags by new frontier armory.

I know .40 cal is usually on pistols,

so, when shopping for barrels and barrel length.

What should i consider for length?

Im using Accurate No.5 powder which is a quick burning powder for barrels around 5 inches smaller. (use it for 9mm on p938,does awesome)

But what happens if i get a 10.5 in barrel?

Any advantages or disadvantages in getting the 10.5?

does that do anything to the gases, i mean, if i get a 10.5 in barrel, my ballistics should be much better than the shorter 7.5 in barrel.

What do you think?

(I own a 7.5 and a 10.5 ar uppers, so i know what the difference in feel is when shooting these)

So I'm wondering about the pistol caliber with a longer barrel.

Repeating myself, but ya, you guys get it i think

[heidad01]

That is nice. Good luck.

[Quiet]

Im planning on building a .40 cal ar15 using one of the lowers that utilizes glock mags by new frontier armory.

I know .40 cal is usually on pistols,

so, when shopping for barrels and barrel length.

What should i consider for length?

Im using Accurate No.5 powder which is a quick burning powder for barrels around 5 inches smaller. (use it for 9mm on p938,does awesome)

But what happens if i get a 10.5 in barrel?

Any advantages or disadvantages in getting the 10.5?

does that do anything to the gases, i mean, if i get a 10.5 in barrel, my ballistics should be much better than the shorter 7.5 in barrel.

What do you think?

(I own a 7.5 and a 10.5 ar uppers, so i know what the difference in feel is when shooting these)

So I'm wondering about the pistol caliber with a longer barrel.

Repeating myself, but ya, you guys get it i think

If you are building an AR style pistol, then read the 2017 AR pistol master thread.

If you are building an AR style rifle, then it needs to comply with Federal NFA laws, CA SBR laws, and CA assault weapons laws.

If the barrel length is less than 16", then you will be making a SBR.
^Unless you have BATFE approval and CA DOJ approval, making a SBR is a felony (both Federal and CA).

If you use a barrel length of less than 16", then you must permanently attach a muzzle device to bring the length to 16" or greater, in order to be legal under Federal and CA laws.

9x19mm and .40S&W AR style firearms are typically blow-back operated.
^Which means they do not utilize a gas-system.

In addition to the required barrel length of 16" or greater, the overall length of the semi-auto centerfire rifle will need to be 30" or greater.

If the semi-auto centerfire rifle has any restricted features (pistol grip, folding/collapsing stock, VFG, flash suppressor, etc), then it must also operate using a fixed 10 round magazine that can not be removed without disassembling the firearm's action or is welded/epoxied/riveted into the magazine well.

[Sigsour7]

right i know all that stuff about lengths and whatnot.

anyone have any feedback that owns a .40 cal AR?

[hermosabeach]

I went with the 9mm as it is just a fun rifle... oh I did the rifle in 9mm.

Unless you want to do .45 so you can also try the .460 Rowland, I don't see the point in 40 cal for a range toy as the ammo costs more...

[Spyder]

My AR in 40 is really really fun!

[sdsu]

if you can, stay around 5.5" on a pistol build. you aren't losing a significant amount of feet / second relative to a longer barrel.

[Robert1234]

I've read you get max velocity at 10" of barrel. After that you have burned all of your powder.

Most pistol caliber rifles I see are at USPSA matches where ammo is tuned for power factor and that means just over 1000 FPS from 125g bullets.

They're blow-back guns so the bolt and buffer are heavy. This will mean higher velocity will come with higher bolt speed and you'll feel that as well as see it in your sights.

That said, they're a lot of fun to shoot..

[CGZ]

What bolt and barrel do you plan to use?
I built a 9mm AR with a New Frontier glock lower and PSA upper and other parts, and it works well, just dosent have a last round hold open.

Was looking into buidling one in .40 but the barrels and bolts I found were not in the price range I liked, I could get those just right carbines for the same price to build my own.

[Sigsour7]

Id be getting the quarter circle 10 barrel. probably use their bolt, or NFA



i know its going to be a LITTLE more pricey, but it'll be my one of a kind.....

[meanrock]

The first response from Quiet caught a few of your questions...

so, when shopping for barrels and barrel length.

What should i consider for length?

Weight, legal requirements, and intended use. You will gain (very marginally) velocity out of a 10.5" barrel over the 7.5"- but I'd go with the 7.5 as it is much easier to maneuver/manipulate and keep on target.

But what happens if i get a 10.5 in barrel?

Any advantages or disadvantages in getting the 10.5?

You end up with a longer pistol. It's heavier, you get maybe... 50? fps more velocity depending on the cartridge. Are you going to shoot +P out of it?

does that do anything to the gases, i mean, if i get a 10.5 in barrel, my ballistics should be much better than the shorter 7.5 in barrel.

No- pretty much all AR's in pistol caliber are blow back- not gas impingement.

[leadstorm]

right i know all that stuff about lengths and whatnot.

anyone have any feedback that owns a .40 cal AR?

I have a Ruger PC40...it's not an AR, though, so I guess I'm out (?).

Seriously, though...my PC40 (16" barrel) has muzzle velocities about 200fps faster than the pistol it shares mags with (Ruger P94 with a 4" barrel). The difference between a 7.5" and a 10.5" pistol is splitting hairs as far as ballistic performance goes. Since you're likely to use an optic on an AR, sight radius doesn't matter.

.40S&W is a high-pressure round, and is riding the edge of what you can cram into it volumetrically. In other words, playing around with powders won't gain you anything because you won't be able to fit enough slower powder in to make a difference.

There is no such thing as +P .40S&W ammo other than: stuff marked +P for marketing purposes, and stuff loaded beyond SAAMI pressure spec (35ksi).

[Spyder]

Sour, aren't you up around me somewhere? If you want to meet up at UGC sometime, I'll bring mine for you to blast as much ammo as you want through it. It's a 16" carbine, takes glock mags, and has a red dot on it. Good fun.

I'm thinking about taking one of my 9mm SMG mags and seeing if I can make it work with 40. RRA has SMG style mags and a mag block for 40, but they're out of stock everywhere and last time I emailed them a couple weeks ago they said they were moving production to another facility and didn't have an expected timeline to start making them again.

I still can't decide if I prefer Glock or SMG style...

[Robert1234]

Got a Glock mag and Colt mag 9mm. Both seem to work well. The Glock mag version does look better, the Colt mag gun looks like an afterthought.

Glock mags are easier to come by and cheaper so there's that as well. And extensions are also cheaper for the Glock mag gun, though after July that won't matter for those who stay in this state.

They are fun to shoot.

[Spyder]

Got a Glock mag and Colt mag 9mm. Both seem to work well. The Glock mag version does look better, the Colt mag gun looks like an afterthought.

Glock mags are easier to come by and cheaper so there's that as well. And extensions are also cheaper for the Glock mag gun, though after July that won't matter for those who stay in this state.

They are fun to shoot.

Yer nuts! The Glock mag looks like it's trying to catch up, and the Colt SMG style is classic original Colt goodness. The old DOE SMG's are rad and I love them.

And SMG mags are like twelve bucks.