View Full Version : Is Gas-piston better than D-I for an SBRs with a suppressor?
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.
decodeddiesel
03-08-10, 09:57
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.
rrpederson
03-11-10, 06:31
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).
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.
Thomas M-4
03-13-10, 16:07
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
The Dumb Gun Collector
03-13-10, 16:08
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.
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).
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
http://img.photobucket.com/albums/v613/Tim_Orrock/Vickers%20Hackathorn%20M4C%20Class%202010/TD1/g-01-0016.jpg
Mike from Texas
03-17-10, 10:34
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
http://img.photobucket.com/albums/v613/Tim_Orrock/Vickers%20Hackathorn%20M4C%20Class%202010/TD1/g-01-0016.jpg
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"?
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.....
- using a chrome or Ion Bond bolt and carrier (cleaning is much easier and you get immediate visual indication of carbon fouling with chrome)
- making sure it's sprung/buffered properly
- using a good lube such as Slip 2000, or better yet, grease such as TW25B
- using good mags (a suppressed SBR with 3 or 4 rounds in the mag is a damn good way to measure how good or bad the mag is)
Mike from Texas
03-17-10, 11:52
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
Are these barrels available for purchase from you in 5.56 of course?
I'm still on the fence between 5.56 and 6.8. I REALLY don't need to jump off in another caliber, but the ballistics on the 6.8 Spec II look pretty good even in SBR form.
Magic_Salad0892
04-06-10, 04:24
I run an M6A3 12.7'' in 6.8 with an AAC M4-2000, M6A2 12.7'' with an AAC SPR/M4, and a KAC SR-15 E3 IWS 11.5'' CQB with an Ops Inc. 15th Model CQB MBS.
Of all of them I do prefer the LWRCi M6A3, for many reasons.
A - For some reason the recoil is more comfortable to me. (As is the weight, it's a bit heavier though. 3 oz. to be exact.)
B - My M6A3 is quieter than both of the others. (By 1 or 2 full dBs, when the gas system isn't off)
C - The carbon build up isn't caked on the bolt carrier like the KAC. (Still just as dirty.)
D - With the LWRC M6A3 I get the option to turn the gas off completely making it quieter due to the action not cycling.
E - I know I'm not going to have to swap bolt carriers every 2000 rounds with the piston system.
F - I can perform over the beach operations if need be. (I live in Oregon, there's a lot of water here.)
Over all. No you don't need a piston system, I can run my KAC a LOT and it'll be fine, I've ran my KAC 2000 rounds without cleaning it. (Had to swap the bolt carrier out after though, it was through it's life span anyways.) It functioned okay.
I prefer the piston system though, for the reasons stated.
And if somebody says ''I'm not impressed with the piston system.'' bring up two things.
Service life, and OTB. (Over the beach)
Actually, OTB can be done with some DI guns if you live in a wet state.
(Oregon, Washington, Virginia (Virginia gets a lot of rain right?)
B - My M6A3 is quieter than both of the others. (By 1 or 2 full dBs, when the gas system isn't off)
Did you sound meter this or are you just speculating? Just curious how you came up with the measurement.
E - I know I'm not going to have to swap bolt carriers every 2000 rounds with the piston system.
.
. [snip]
.
I've ran my KAC 2000 rounds without cleaning it. (Had to swap the bolt carrier out after though, it was through it's life span anyways.) It functioned okay.
Can you clarify the "swapping bolt carriers" comment for me, please? How many rounds did your KAC carrier have total before you needed to replace it? What symptom or wear evidence led you to believe the carrier needed replacing? Lastly, if you could describe the type of use the KAC carrier experienced that would help better understand how it came to needing replacement.
Thanks in advance for your additional info. I like knowing expected life of certain items compared to what I see in my own guns.
Take care,
Mark
Are these barrels available for purchase from you in 5.56 of course?
I'm still on the fence between 5.56 and 6.8. I REALLY don't need to jump off in another caliber, but the ballistics on the 6.8 Spec II look pretty good even in SBR form.
No, not currently.
C4
Magic_Salad0892
04-09-10, 12:38
Did you sound meter this or are you just speculating? Just curious how you came up with the measurement.
Yes I sound metered this.
Can you clarify the "swapping bolt carriers" comment for me, please? How many rounds did your KAC carrier have total before you needed to replace it? What symptom or wear evidence led you to believe the carrier needed replacing? Lastly, if you could describe the type of use the KAC carrier experienced that would help better understand how it came to needing replacement.
Thanks in advance for your additional info. I like knowing expected life of certain items compared to what I see in my own guns.
Take care,
Mark
Swapping Bolt Carriers: Needing a replacement bolt and bolt carrier - end of service life.
I think it had like 5-6 thousand or so. I don't exactly remember how many rounds it had through it suppressed but it had a lot. More than half.
Wear or evidence that it needed replacing: I'm looking at it right now. Honestly I think I could shoot it more, but it looks like it has been shot more than it has, this is because I've shot it a lot suppressed, through a short barrel, and because the gun as a whole has seen a lot of abuse.
How was it used: Shot a lot suppressed.
Also: The KAC bolt carrier has a longer service life than any DI carrier I've ever used. It's amazing.
Yes I sound metered this.
Interesting results, I've never experienced a piston gun that wasn't noticeably louder than a same barrel-length DI gun...
If you're using that meter you mentioned in the other thread, it maxes out at 130 dB, which is generally lower than the SPL from a 5.56 gun suppressed... Plus, the gunshot is too quick I think for it's 500 ms response time.
To be accurate, you really need a meter and mic that are specifically built to handle the levels and duration of a gunshot... unfortunately, they cost around 50 times more than the SL-4013.
FWIW
Magic_Salad0892
04-10-10, 12:36
I didn't use my SL-4013 on that sound test, as that was done before I bought mine.
I'm actually only using this until I can find something more fitting. Money isn't really an issue, I just needed a meter fast, because I'm in the market for good .45 and .40 sound suppressors.
Jason, any recommendations for a good meter and mic?
I think it had like 5-6 thousand or so. I don't exactly remember how many rounds it had through it suppressed but it had a lot. More than half.
That is interesting. I have bolts and carriers with a lot more rounds through them than that and much of the use has been full-auto fire with a 11.5" barrel hosts. I have one Sabre Defense barrel that has specifically been shot to try to get a 50K documented round count through it. We've been using that barrel for over two years now and use it frequently for LE demos. We let them run the gun as hard as they can do it using their ammo. The round count through the gun is well over 30K rounds at this point. It is still using the original bolt and carrier. I can't say the same for the gas tube, gas rings, cam pin or firing pin retaining pins though.
Go figure. Perhaps I just got lucky. :)
Thanks for the extra info. Take care.
Mark
Magic_Salad0892
04-12-10, 15:15
Were you using it suppressed, full auto?
Yes. I have an AAC M4-2000 with 20K+ rounds through it that was used most of the time with the Sabre.
The first time that suppressor was shot was when we were stress testing the (then) new Blackout mounts. We destroyed an older (but then current) Phantom mount through full-auto testing with that particular rifle. When the mount failed the M42K that was on the gun also was destroyed. The next day we put a new Blackout and brand new M42K through more than double the abuse that failed the Phantom mount. So, the very first weekend I shot that rifle we put 2500 rounds of VERY HARD use full-auto through the weapon. After that I used that weapon in several classes and then almost weekly at LE demos.
A friend gave me a Beta mag as a gift and I even ran a few Beta full-auto dumps through the weapon. Well, I didn't but I let friends do it. All Beta dumps were with a suppressor attached.
That is why I was more than a little surprised when you were replacing KAC carriers at only 5-6K rounds. It is also why I asked how you knew there was excessive enough wear on the bolt/carrier to warrant replacement. You never really answered what signs of wear were on those parts and I'd still love to know if you would be kind enough to post some extra info. Even pictures would be great if you could swing that. I like knowing how things got to a point of failure (or close to it). :)
Thanks,
Mark
Magic_Salad0892
04-12-10, 23:37
Sorry I don't own a camera so I can't post pics.
I have replaced the springs, and now have a Crane O-Ring, black extractor, and 5 coil extra power extractor spring.
I will put the (Not bad, but more than I am comfortable with) worn bolt back in the gun, and run it to the point of failure. Here I go.
It will now be the gun I take out instead of my trusty M6A3. ;D
It looks at 8 (I put 1000 through it today) thousand rounds what a normal bolt (BCM, Colt even) looks at 10 thousand rounds unsuppressed.
The signs of wear that I mentioned before, was a small fatigue crack on the bolt face. (Now gone. Or I don't notice it.)And I was having failures to extract after 5000 rounds.
I'll post an update at 10 thousand rounds, and every 2 thousand after that. Until failure.
I will be comparing it to my LWRCi bolt. My 5.56 gun has about five thousand rounds through it suppressed, with no signs of wear whatsoever. No carrier tilt to speak of.
Also, it's nice to know that my AAC M4-2000 will go through 20k rounds fired, even full auto mag dumps and still be functional. Thanks for doing that so I don't have to.
Yeah, the M4-2000 will take a lot of abuse but make no mistake after the abuse I've put it through you can see significant erosion in the core.
I forgot about extractors. I probably replaced the extractor on that high round count bolt once or maybe even twice. I'd have to check my logs to be sure. Same with the extractor spring. Oh, you might also try #60 o-rings. For me they work just as good as "Defender" or other high priced rings. They don't last quite as long but very, very close and you can get them for pennies each.
Mark
Magic_Salad0892
04-13-10, 15:30
Where can you get them that cheap?
Does your AAC still offer significant sound reduction?
How many decibels do you think?
I will also replace the gas rings, I may have worn those out.
Where can you get the #60 o-rings? Just about any hardware store. I get mine in a bag of 20 or 30 at Home Depot for maybe a buck or two.
Yes, that M42K still is very quiet. It is a bit louder than a new one but not too much. I have not sound metered it.
On the gas rings I extend the bolt from the bolt carrier and stand it on a table. If the weight of the carrier isn't supported by the bolt (and gas rings) the rings are shot and I replace them. That is an easy way to look for worn rings.
Take care.
Magic_Salad0892
04-13-10, 20:34
Much appreciated. :)
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