"Gotchas" of building an AR pistol?

[Hawkeye]

Hey all-

(First, I put this in the Rifle section even though it's technically about pistols since it's AR related and most AR stuff is in here. If that was incorrect I apologize.)

Ok, so here's the deal:
I've got several pre-Oct'13 lowers sitting in my safe. Eventually they may end up as rifles. They may end up as SBRs. They may end up as hockey pucks. Who knows. The first thing that they're both going to be, however, is pistols, for all of the obvious reasons.

I am fairly well aware of the legal issues surrounding the building of pistols, what they can and can't have feature wise, and what you can and can't do with them in a legal sense. I've built (from stripped lower and stripped upper) my own AR rifle already (which I've put +/- 1000 rounds through with no issues), so I've got at least a minimum of knowledge there. Some other stuff I have a hazy understanding of but I don't want to go into this with a "hazy" understanding. What I would like this thread to be about is the technical, mechanical aspects of building 5.56mm AR pistols. (Later I'll likely do another one on 9mm, since I'd like a 9mm PDW type gun at some point.) Things like:

What are the "gotchas" in building a pistol compared to a rifle?
What gas tube length is good or bad (pistol vs. carbine mostly)?
What buffer to be used with what gas tube?
What buffer spring?
What kind of buffer tube?
What kind of muzzle device (specifically the flaming pig type things that you see on a lot of pistols - what are they specifically supposed to do, do they actually have any effect, and when should you or should you not use them)?
Any lower-specific stuff that needs to be looked at or changed from a standard AR lower build?

My plan is this:
I would like to end up with at least one of these lowers becoming a 5.56 pistol that I could also eventually suppress. The other may go 9mm, or .300BLK if I end up buying a 9mm specific lower (Engage or QC10). My understanding is that this generally requires at least a 10.5" barrel for most suppressors (not to mention the MD 29" requirement should I ever want to SBR it). I don't particularly care about super accurate barrels or whatever - these aren't going to be sniper rifles. I do generally care about decent componentry that isn't going to crap out on me after 1000 rounds or fall apart or ruin my lower or whatever.

Both of my lowers are PSA Forged.
Stuff I am looking at so far:

Likely a PSA Premium BCG. (have one now, like it)
BCM Gunfighter charging handle. (have one now, like it)
BCM Gunfighter grip. (have one now, like it)
PSA lower build kit, preferably with a QMS or ACT trigger. (guess what... have one now, like it)
Likely a Phase5 buffer tube, maybe a CAA cover.

If I go pre-built upper, something like this:
Palmetto 10.5" upper.

If not then who knows. If I build my own upper again, I may be tempted to take the VLTOR CASV handguard off of my rifle and replace it with a slick keymod one or something.

So what are the general thoughts on what goes together and what doesn't to end up with a suppressable AR pistol?

 

[friendlyhippo]

What do you mean by "gotchas"? Legal ramifications? technical issues you may or may not run into? Please elaborate.

Either gas tube will work. Just don't use one of those "pigtail" gas tubes. They're ridiculous, ineffective snake oil meant for the sole purpose of separating you from your dollars.

Buffers aren't a function of gas tube length. You can run a rifle buffer on a pistol-length gas system. Buffer is related to receiver extension, and the majority of "pistol tubes" out there will utilize a carbine-length buffer. You don't have to spend extra for a pistol-specific tube, though; just wrapping a standard carbine extension with 550 cord is enough to render it unable to readily accept a stock and perfectly legal. Length aside, buffer *WEIGHT* could be a factor, and your best bet is to buy a carbine and an H3. The H3 will have 3 heavy weights inside, the carbine will have 3 standard weights. Between the two of them you'll be able to configure 4 different buffer weights to tweak your cycle timing.

Just a standard spring intended for whatever receiver extension you need. Rifle for rifle, carbine for carbine.

Covered this above; use whatever tube is the correct length for the type of buffer you're going to run. For the vast majority of pistols, a carbine-length extension is the common choice, and a standard 6-position mil-spec diameter extension is perfectly acceptable (and frequently less expensive than pistol-specific setups) provided you do something simple like wrap it with 550 cord. Makes it a little more comfortable for cheek weld anyway.

muzzle device is up to you. there's no 'should' or 'should not' really....totally subjective and user-defined. an effective brake will be loud as hell and concuss the crap out of anyone next to you, but will definitely tame muzzle flip. a flash hider will not be nearly as concussive, may not tame muzzle flip, and if you decide to SBR later, could be counted as a so-called "naughty feature".


any of your choices above will suppress well. 9mm is blowback, so it doesn't fall in the same category as 300blk or 5.56; those two will be great to suppress. the blackout was actually designed for suppressed short-barreled applications. and it's a lot of fun.

 

[Hawkeye]

What do you mean by "gotchas"? Legal ramifications? technical issues you may or may not run into? Please elaborate.

That's what the whole second paragraph of that post was about.

Thanks for the rest of your post. When I built my rifle, I didn't have to make some of these choices, because, for example, the VLTOR stock assembly I bought came complete with stock, tube, buffer, and spring so that was some potential complexity removed.

My first thought in this case is the Phase 5 assembly but if there are better out there I'm open to it.

 

[friendlyhippo]

that's a really expensive receiver extension that, frankly, doesn't do anything a standard 20-dollar carbine buffer tube won't do. I have a couple spools of 550 cord if you don't have any, you're welcome to many numbers of feet so you can wrap.

There really aren't any technical "gotchas" that i'm aware of, to be honest. The only thing that makes a pistol different from an SBR is the fact there's a thing on the back that lets you shoulder it easily. barrels, bcgs, buffers, and gas tubes have no cognizant pattern of thought to acknowledge it's time to malfunction due to what's on the receiver extension. (although I'm with a lot of other people reading this thinking "sure seems that way sometimes!" )

Use quality parts (faxon firearms and ballistic advantage make some great budget-oriented barrels that shoot quite well) and you'll be fine.

 

[SoMD_Gen4]

I will tell you this, I just finished my pistol build and I spent the extra money for the Noveske Kx5 Flaming Pig! It is SO worth the money. It directs all that energy forward and it really doesn't sound all that different than rifles, from the shooters perspective. I have shot a few without the flaming pigs, and they were hand cannons. Definite headaches after about 50 rounds. Buy once, cry once.....get the Kx5 or Kx3!

 

[BradMacc82]

The flaming pig also has a tendency to enhance the already over-gassed nature of most pistol builds. Which I suppose isn't an issue if you run adjustable gas, but not everyone does.

 

[erwos]

The biggest gotcha is that AR pistols suck, and you'd be way better off building an SBR from the start, even if it takes longer and costs a couple bucks more. That goes double when you're talking about spending non-trivial dollars on a Phase5 tube and a CAA cover.

 

[friendlyhippo]

That goes double when you're talking about spending non-trivial dollars on a Phase5 tube and a CAA cover.

Agreed. Mostly because that can add up to very nearly the cost of the stamp in the first place.

 

[Hawkeye]

that's a really expensive receiver extension that, frankly, doesn't do anything a standard 20-dollar carbine buffer tube won't do. I have a couple spools of 550 cord if you don't have any, you're welcome to many numbers of feet so you can wrap.

Fair enough. I figured the pricing wasn't as bad as it seemed because that included the spring, buffer, end plate, and castle nut as well, but I suppose that a standard tube with a paracord wrap would work just about as well. In the end, I don't mind spending an extra dollar or 20 here or there as long as it's not absurd. When I built my rifle I went "blingy" on a lot of the parts (YHM diamond fluted barrel, VLTOR stuff, etc) because I wanted to.

Thanks for the offer on the paracord, but I've got a ton also.

Use quality parts (faxon firearms and ballistic advantage make some great budget-oriented barrels that shoot quite well) and you'll be fine.

That's kind of what I figured, but as I said, just checking. I know that sometimes people run in to problems with gassing on short barrels, and I want to arm myself with as much knowledge as I can before I do this. I suppose that with carbine length gas and a standard buffer setup I'd be fine.

I will tell you this, I just finished my pistol build and I spent the extra money for the Noveske Kx5 Flaming Pig! It is SO worth the money. It directs all that energy forward and it really doesn't sound all that different than rifles, from the shooters perspective. I have shot a few without the flaming pigs, and they were hand cannons. Definite headaches after about 50 rounds. Buy once, cry once.....get the Kx5 or Kx3!

The flaming pig also has a tendency to enhance the already over-gassed nature of most pistol builds. Which I suppose isn't an issue if you run adjustable gas, but not everyone does.

This is why I was asking about the flaming pig. I understand that they're great for lessening the amount of concussion experienced by the shooter, but I don't want to run into gassing problems.

As to adjustable gas...

I've seen people discuss it around suppressed SBRs. Would it be worth it to build with adjustable gas out of the gate if I might end up suppressed later on?

 

[erwos]

Adjustable gas is pretty much always a good thing, provided you have a good gas block.

 

[BradMacc82]

If you plan on doing a pistol/sbr or plan on going suppressed at a later date, adjustable gas is definitely a good idea.

Instead of being locked in with a standard gas block and having to tune the system via buffers, buffer spring and so on - it's so much easier to just add/take a few clicks on the gas and be done with it.

 

[outrider58]

If you plan on doing a pistol/sbr or plan on going suppressed at a later date, adjustable gas is definitely a good idea.

Instead of being locked in with a standard gas block and having to tune the system via buffers, buffer spring and so on - it's so much easier to just add/take a few clicks on the gas and be done with it.

Second^^^$120 or so will buy you a SLR adjustable bass black. Don't mess with the clamp-on. Get the other model and get it pinned.

 

[Biggfoot44]

My AR Pistol wears a Phase 5 . I bought just the tube with foam, not the assy. Don't recall the $ , but in the initial post Newtown crunch it was comparable to everything else, and it happened to be in stock.

A Flaming Pig is an orthopedic muzzle device. Yes it directs blast forwards, AND increases gas pressure. Lots of other muzzle devices can direct blast forewards. I know there is an ethos to wargame out all your ultimate selections , and buyeverything first before starting, but with short bbl AR's ( pistol or SBR ) there is inherently trial and error at work.

Start out with std carbine buffer , and either A2 or no device. Testfire. If functions reliably, give yourself a high five ! Then go with presumably the "gas nuetral" blast deflecting device of your preference. If it is under- , or over- gassed , then you go to different buffer , or gas increasing muzzle device as needed. But you don't need them, unless you need them.

 

[friendlyhippo]

For what it's worth, righttobear.com has a mil-spec 6-position buffer tube kit (tube, standard carbine buffer, spring, end plate, castle nut) on sale for 28 bucks.

labor day weekend sale, looks like it goes back to 50-ish after the weekend.

 

[BradMacc82]

For what it's worth, righttobear.com has a mil-spec 6-position buffer tube kit (tube, standard carbine buffer, spring, end plate, castle nut) on sale for 28 bucks.

labor day weekend sale, looks like it goes back to 50-ish after the weekend.

And one of the owners is an active duty member here. Good people, what they have on-site ships really quickly.

 

[outrider58]

AR pistol with the option of someday turning it into an SBR, if you're in 'Merlin', 10.5'' barrel with carbine length gas.

300 Blk with the same intention, 10.5'' with a pistol length gas system.

If you live outside of merlin, you can go shorter but here, 10.5 seems to be the magic number for bbl. length. You could go a little shorter on the bbl. but, in order to make the Md. minimum SBR length requirements 29''+ You kinda limit your selection on stock choices.

 

[Merlin593]

I built a pistol last year and didn't run into any gotchas.
I really enjoy shooting it and its as reliable as my 16" carbine.
I started with an Andersons stripped lower, basic CMMG lower parts kit and Phase 5 complete buffer kit http://phase5wsi.com/ar-15-complete-pistol-buffer-tube-assembly.html with a sig brace on the end. Many are really impressed with the quality of these buffer tube assemblies.
Put a Radical firearms 10.5" complete upper on it http://www.radicalfirearms.com/product-p/rfupper10.5-5.56m4-10fqr.htm. Note - They use a micro block...
I had an upgraded OSS Bannar muzzle brake put on instead of a typical birdcage or flaming pig: http://www.capitolarmory.com/oss-bannar-alpha-bravo-flash-hiding-muzzle-brake.html
The OSS is great for reducing muzzle rise, flash and recoil.
topped the whole thing off with a red dot http://www.primaryarms.com/Holosun_Paralow_HS503C_Circle_Dot_Sight_p/hs503c.htm

This gun eats everything you feed it - 55 grain .223, 5.56, m855, Mk318, etc.
I have never had a feeding, ejection or extraction issue.
Good luck in whatever you end up building. They are a lot of fun!
Best,
Jim

 

[AJRB]

If you plan on doing a pistol/sbr or plan on going suppressed at a later date, adjustable gas is definitely a good idea.

Instead of being locked in with a standard gas block and having to tune the system via buffers, buffer spring and so on - it's so much easier to just add/take a few clicks on the gas and be done with it.

I made a choice to not bother trying to suppress a 7.5 inch AR pistol barrel, and stayed with a normal gas block.

To compensate for the over gassing problems being mentioned with a short 7.5 inch barrel with flaming pig, I use a "red" Sprynco heavy spring, with a Spike's ST-T2 Heavy Buffer. I have not had any malfunctions with this set up.

http://www.sprinco.com/tactical.html the link has a list of the different springs and colors associated with them. I got mine for Engage Armament in Rockville quite a while ago

The weight of pull on the charging handle is noticeably heavier than on my full length carbine with standard spring and buffer.

 

[AJRB]

The biggest gotcha is that AR pistols suck, and you'd be way better off building an SBR from the start, even if it takes longer and costs a couple bucks more. That goes double when you're talking about spending non-trivial dollars on a Phase5 tube and a CAA cover.

I absolutely love my AR pistoll!!! I haven't found anything about it to suck.
I'm curious, what would lead you to state that they suck?

There are more build options available in a pistol than an SBR, why have those SBR restrictions? For a stock? A stock which imo, isn't even necessary for a close qtr combat /range toy, weapon.

Quick target acquisition and follow up shots with a cheek weld on a buffer tube pad, works amazingly well with the right muzzle device. Flaming pig, Lantac Dragon etc, all make these short barrel AR's very manageable shooters.

Pay for a trust, pay for the tax stamp, pay for an unnecessary stock, pay for an engraving, paperwork to move your SBR out of state.

I feel like the SBR suck, far outweighs any AR pistol suck.

 

[outrider58]

I absolutely love my AR pistoll!!! I haven't found anything about it to suck.
I'm curious, what would lead you to state that they suck?

There are more build options available in a pistol than an SBR, why have those SBR restrictions? For a stock? A stock which imo, isn't even necessary for a close qtr combat /range toy, weapon.

Quick target acquisition and follow up shots with a cheek weld on a buffer tube pad, works amazingly well with the right muzzle device. Flaming pig, Lantac Dragon etc, all make these short barrel AR's very manageable shooters.

Pay for a trust, pay for the tax stamp, pay for an unnecessary stock, pay for an engraving, paperwork to move your SBR out of state.

I feel like the SBR suck, far outweighs any AR pistol suck.

Because they can't be used like SBRs?