If I plan on getting a 12" SBR and adding a suppressor.
Am I better off getting a gas-piston system, or does D-I work well at that length with a suppressor?
Does a standard D-I system need an adjustable gas block in order to run a suppressor? (similar to the Noveske Switch block).
Really depends on how anal you are about cleaning. With the DI system and a can you get a lot more blow back into both the upper receiver and lower receiver, carbon build up and all kinds of junk. It shouldn’t hurt the operation as look as you keep up with the cleaning. The piston will naturally run cleaner with a can.
An adustable gas block may be good idea on a SBR 12" upper. The gas holes tend to be larger on the shorter barrels to insure cycling of the bcg. With the larger gas hole and more blow back with the can you may be overgassed. The adjustable gas black will help keep over gassing under control.
So an adjustable gas block isn’t necessary on a 16"+ direct impingement upper?
And a gas-piston sytem is beneficial in SBRs w/ a suppressor because there is less carbon buildup in the chamber?
An adjustable gas block on a DI gun + suppressor is there to preserve the timing of the action, not to reduce gas/particulate blowback. Since SBRs are more sensitive to timing issues, a 16" gun most likely would not need an adjustable gas block, although you might want to use one to reduce felt recoil. And if you want to use an adjustable gas block on a fighting gun, don’t get one of the blocks that require an allen wrench or similar to fine tune; these are for fun guns only since you can’t lock the adjustment. Think Noveske Switch Block or similar for hard use.
In addition, a piston will not reduce blowback by more than 25% or so. You will still get all sorts of gunk on your upper, lower, mags, ammo – you name it – because much of the blowback comes through the chamber. A piston does nothing to reduce blowback through the chamber.
The bottom line is this: if you want to shoot a suppressed gas gun, you have to be OK with more frequent and more thorough cleanings. There are some pics on this site of suppressed guns that have gone through carbine classes; they’re unbelievable.
I have yet to see evidence from a verifiable source state conclusively that piston operated ARs do anything better than DI ARs, even when running an SBR suppressed.
Personally, I think something like the Noveske Switchblock will do a lot more for you in this situation.
I’m not convinced of the superiority of Pistons either.
I’m sort of in the same boat as theoak. Except, I’ve been stuck for a while between purchasing a LWRC 12.7" M6A2 or a M6A3. The only difference is that the A3 has an adjustable gas block. Is there a justifiable reason as to why I should get the one with an adjustable gas block? I’ve considered the A3 because I do have plans for a suppressor in the future.
Is there some resource out there that can give evidence to show how much of a difference an adjustable block makes? I know it was mentioned previously that it was to better control timing. But, does anyone have an example to help people understand the benefits of a adjustable block?
The adjustable gas block is going to allow you to control how much gas reaches the gas key. Too much gas will cause a higher cyclic rate in a FA gun and increased recoil and wear and tear on your moving action components in SA or FA. That excess gas also burns off lubricants faster, causing more frequent PM’s on the working parts.
You can reduce some of the recoil, wear and tear and reduce the cyclic rate on your carbine by using a heavier buffer and/or a stiffer recoil spring. But these will not help with the excess gas getting the action dirtier and lube burnoff. For that you need something like a Switchblock for a duty gun or a JP adjustable gas block for a game gun.
As for the piston guns, remember that their design bleeds off excess gas into the piston housing. On a suppressed gun this may reduce the effectiveness of a can in lowering the overall sound signature.
to answer your questions, i personally have a 10.5" barrel currently running an m4-2000 suppressor. this rifle is setup as a direct impingement gun and it runs flawlessly. my gas block is a standard low profile one from troy. no switchblock or anything. gun works with zero problems. i cant personally speak of experience with a 12.5" barrel with a suppressor but i would imagine that it would run just as well or better than my setup.
I have fired a di 10.5 with a can and it gives you alot of gas blowback, but not anymore than i get on my 20" di with a can.
What benefit does a gas piston offer aside from having a cleaner chamber and running cooler in full auto?
The DI AR was not originaly designed for short barrel lenghts. There is a ton of info available on the net about all the technical issue (and potiential solutions) associated with this. It is also a bit of a controversal subject, like asking “the best handgun caliper for self defence” or " is the glass half empty or half full".
My experience has been the following:
DI short barrel uppers can have reliability issues. The shorter they are the more problems you can have. 10"-14.5" is usually a minor fix. less than 10" can get problemactic.
No matter what the brand or the quailty of the build, I have always been able to get any length DI to run reliably on Semi. Full auto is a different story. The shorter it is the harder it is to get it to run reliably on full auto.
Piston guns have there own issues. Every piston upper I have had has run reliably on semi or full auto. But, the shorter they get the more violent the recoil and the faster they run on full auto. FYI, I sold my piston uppers under 10" but kept the DI uppers under 10".
Supressors can mask alot of operational issues (can also help some) in a short system. A suppressor creates an entirely different impulse and alot more back pressure. Again semi is usually an easy balance adjustment full auto can be a problem.
I have never noticed a difference in terms of filth between DI suppressed or piston suppressed- in general, shooting suppressed is dirty business.
The one thing I have noticed without fail, is that a suppressed piston gun is noticeably louder than a DI gun. from my experience with SCARs, ACRs, and 416s.
My ideal suppressed AR would be a 12.5" with switchblock.
YMMV
It seems most people on this forum prefer D-I, and if anyone actually prefers a G-P it’s because they’re “cleaner”. I have never heard anyone say a G-P is more reliable or accurate.
Its because they are not more reliable or more accurate. Welcome to M4C;)
Stand corrected unless its a HK-416:p
Larry Vickers said that Delta went with the 416 because the short DI guns weren’t reliable enough for what they were doing. He said this was especially true when you were talking about full auto suppressed.
I would say that it depends on how much shooting you do.
The piston doesn’t know what to do with the extra gas any more than a DI gun does. So the extra carbon and such will get dumped into the chamber.
Being a SBR/Suppressor fan, I came up with my own solution. We went with a small gas port and a LMT enhanced carrier. We use the extra pressure from the can to cycle the weapon. Then what gas is left is expelled with the LMT enhanced carrier.
Doing it this way, reduced muzzle rise, felt recoil and my gun runs cleaner than a DI gun with NO can on it!
This concept has been proven to run 100% with over 5,000 rds fired.
C4
Grant is it safe to assume that you are running these in 5.56 caliber? Do you have any experience with a 6.8 Spec II 10.5" suppressed? That is the next build I am contemplating but don’t know what to expect.
Also, what barrels are you using to get the “small gas port”?
Yes, 556 only. I don’t care for 6.8 so I stay away from it.
I special order my barrels with the GP size we won’t (generally). We also have found a way to change the GP size in a barrel from what was factory spec’d.
C4
When shooting my AAC can on a 12.5" DI barrel, after 10 rounds the chrome BCG will look like 80-100 rounds of unsuppressed PMC Bronze .223. That’s how much dirtier they get.
I learned from Mike Pannone that there are several things you can do to enhance reliability in suppressed SBRs, such as…