View Full Version : SBR question best barrel 10.5 11.5 or 12.5
I want to put a SBR together to use with a AAC M4-2000 can. Just wondering what the thoughts were on the various barrel lengths available? What is the best length overall for this application to still allow easy movement, yet have good ballistics still?
I was looking to go with a gas piston upper also like the LMT MRP (I like the option to swap barrels quickly) or the LWRCi.
Thanks
I like 12.5" because you start losing velocity exponentially as you go to 10.5". Depends what your goal is. You can hit targets at longer ranges with a 12.5". 10.5" might look cooler, but ask yourself if the 2" reduction in muzzle length is really going to be that big of a benefit if you have to shoot an intruder inside your home, and what the likelihood of that happening is.
A Noveske 12.5" will launch a 55 grain round at ~2710 fps, and a 75 grain at 2530 fps.
A friend has a 12" LMT piston upper and I love it.
Ignoring your piston request, I'd opt for a 10.5" as a host for the M4-2K.
One issue you're going to have regardless of which of those lengths you choose is finding a piston operating system that will clear the teeth on the M4-2K mount to disassemble. Do your homework before hand if this is important to you (it would be very important to me).
One issue you're going to have regardless of which of those lengths you choose is finding a piston operating system that will clear the teeth on the M4-2K mount to disassemble. Do your homework before hand if this is important to you (it would be very important to me).
That's a non-issue with LWRCi. The M4-2000 fits a 10.5" LWRCi M6, M6A1, M6A2, and M6A3 just fine. The SPR/M4 fits a 12.7" LWRCi M6A1/A2/A3 with carbine gas blocks. These uppers were designed with AAC and SureFire cans in mind.
Here's an M6A2 with an M42K mounted (as found in this thread (http://forum.lwrci.com/forum/viewtopic.php?t=4345)):
http://i684.photobucket.com/albums/vv201/JSK_2009/DSC_0403.jpg
It may be a non-issue with the LWRCi guns, but it is not a non-issue across the board for all pistons and all cans. Pistons that are removed through the front of the gas block have a potential clash with the suppressor mount. I'm not talking about whether or not you can get the can on the gun, I'm talking about whether or not you can strip the piston with the suppressor mount still on the gun.
I edited my post as I didn't see the OP was also considering LMT. On those systems you WILL run into piston removal headaches with certain suppressor mounts. On the LWRCi, it's a non-issue.
Robb Jensen
10-11-09, 17:01
The 10.5" PWS DC10 is an option. It's piston, op rod and CH are attached to the bolt carrier with nothing coming out the front. However due to the rails being very close to the flash hider threads it probably won't work with a M4-2000. It would very likely work with a PWS YHM Phantom FSC556 and a YHM Phantom suppressor.
Last time I checked LWRC guns were less than perfect. And of course considering the price tag may not be within the reach of the average M4/M16 aficionado.
I edited my post as I didn't see the OP was also considering LMT. On those systems you WILL run into piston removal headaches with certain suppressor mounts. On the LWRCi, it's a non-issue.
A friend has a 12" LMT piston upper and I love it.
That's what I have. Haven't even had a chance to fire it yet.
I like 12.5" because you start losing velocity exponentially as you go to 10.5". Depends what your goal is. You can hit targets at longer ranges with a 12.5". 10.5" might look cooler, but ask yourself if the 2" reduction in muzzle length is really going to be that big of a benefit if you have to shoot an intruder inside your home, and what the likelihood of that happening is.
A Noveske 12.5" will launch a 55 grain round at ~2710 fps, and a 75 grain at 2530 fps.
A friend has a 12" LMT piston upper and I love it.
That is why I went 11.5 as a happy medium.
variablebinary
10-12-09, 02:43
My 10.5" LWRC M6A1 has been a real trooper.
It's been dunked in mud and snow, not cleaned for a thousand rounds or so, run hard suppressed (Halo), all with wolf, and it just wont choke.
The great thing about pistons is they tend to be less picky with short barrels, and junk ammo.
How about LMT MRP gas piston. Do you think that would clear the suppressor mount. I like the idea with the LMT and the ability to quick change barrels.
How about LMT MRP gas piston. Do you think that would clear the suppressor mount. I like the idea with the LMT and the ability to quick change barrels.
I stole this pic from TOS. I found it by doing a google search of "mrp piston AAC". It shows that the piston cannot be removed with the flash hider attached to the gun and the owner corroborates this in his posts. The owner posted that LMT told him it was not a big deal as the piston rarely needs service. Personally, this would not suffice for me, but it may work for you or be acceptable to you.
http://i134.photobucket.com/albums/q111/rob_s/gun%20stuff/SUC54186.jpg
thread I stole the pic from. (http://www.ar15.com/forums/topic.html?b=3&f=118&t=394685&page=13)
Completely unacceptable. One I get my mount set up and rock setted in place, I'm not interested in removing it again.... and then rezeroing my gun and haveing to re-check my POI shift with the can mounted.
Completely unacceptable. One I get my mount set up and rock setted in place, I'm not interested in removing it again.... and then rezeroing my gun and haveing to re-check my POI shift with the can mounted.
Agreed
KimberMike
10-13-09, 16:12
I have the Adams Arms kit on a 11.5" upper. This upper also has an AAC 18-tooth mount for my 762SD. All it took was a little bit of time and patience with a grinder, then a little bit of spray paint, to make the piston removable. It didn't take much to create the clearance. I can get some pictures if anybody wants to see.
Mike
I have the Adams Arms kit on a 11.5" upper. This upper also has an AAC 18-tooth mount for my 762SD. All it took was a little bit of time and patience with a grinder, then a little bit of spray paint, to make the piston removable. It didn't take much to create the clearance. I can get some pictures if anybody wants to see.
Mike
I was also thinking about doing the same thing with my PWS QD YHM attachment. Pics would be appreciated.
KimberMike
10-13-09, 16:36
Here's the pics.... if you would like more or different angles, just let me know.
Mike
http://i139.photobucket.com/albums/q292/motofox9/DSC03343.jpg
http://i139.photobucket.com/albums/q292/motofox9/DSC03346.jpg
http://i139.photobucket.com/albums/q292/motofox9/DSC03347.jpg
http://i139.photobucket.com/albums/q292/motofox9/DSC03349.jpg
Ahh.. I see. Looks pretty good and solves the problem at hand. Good job. :cool:
Frank Castle
10-13-09, 17:17
I stole this pic from TOS. I found it by doing a google search of "mrp piston AAC". It shows that the piston cannot be removed with the flash hider attached to the gun and the owner corroborates this in his posts. The owner posted that LMT told him it was not a big deal as the piston rarely needs service. Personally, this would not suffice for me, but it may work for you or be acceptable to you.
http://i134.photobucket.com/albums/q111/rob_s/gun%20stuff/SUC54186.jpg
thread I stole the pic from. (http://www.ar15.com/forums/topic.html?b=3&f=118&t=394685&page=13)
Rob,
You didn't read the entire thread. Some enterprising souls have figured out how to remove the piston. Still not the greatest solution as it will no doubt result in POI/POA shift- but it may not be an issue if piston removal does not need to occur on a regular basis.
Rob,
You didn't read the entire thread. Some enterprising souls have figured out how to remove the piston. Still not the greatest solution as it will no doubt result in POI/POA shift- but it may not be an issue if piston removal does not need to occur on a regular basis.
Yeah, I don't consider this much in the way of an option, which is why I didn't post it. At least it's an MRP so it's just two screws.
You will need to pull the barrel, hold the op-rod itself with one hand and pull it to the rear separating the gas regulator & op-rod into two pieces. Then just turn & tip the gas regulator and it will clear the teeth of the flash hider mount then allow the op-rod to run forward under it's own spring pressure and it's out too!
What about cycle reliability with a short barrel and a suppressor? I have heard issues with the gas system. What about using an adjustable or different gas tube?
Thanks
Robb Jensen
10-16-09, 06:57
What about cycle reliability with a short barrel and a suppressor? I have heard issues with the gas system. What about using an adjustable or different gas tube?
Thanks
Adjustable gas tubes suck, the Pigtail sucks, the Fatboy gas tube sucks. Adjustable gas blocks belong on game/match guns. That said the Noveske switchblock is quite nice. The switchblock has two settings, full or suppressed and works well.
If not using the Noveske switch block it's really best to build the gun one way. Meaning to make it run only suppressed or make it run only unsuppressed. Otherwise it's a compromise both ways, too much gas when suppressed and too little when non-suppressed. The problem is that no body wants it this way as they want to be able to switch back and forth.
Adjustable gas tubes suck, the Pigtail sucks, the Fatboy gas tube sucks. Adjustable gas blocks belong on game/match guns. That said the Noveske switchblock is quite nice. The switchblock has two settings, full or suppressed and works well.
If not using the Noveske switch block it's really best to build the gun one way. Meaning to make it run only suppressed or make it run only unsuppressed. Otherwise it's a compromise both ways, too much gas when suppressed and too little when non-suppressed. The problem is that no body wants it this way as they want to be able to switch back and forth.
Or go piston. Shorty piston suppressed works just fine.
Robb Jensen
10-16-09, 11:49
Or go piston. Shorty piston suppressed works just fine.
That's a pretty general statement
I work on ARs daily and see just as many if not more broken piston SBR ARs that have problems running suppressed.....
No Bananas
10-16-09, 23:40
That's a pretty general statement
I work on ARs daily and see just as many if not more broken piston SBR ARs that have problems running suppressed.....
I don't doubt you, but I'm curious to know (and I'm sure the OP is too). What common problems do you see with the piston uppers? Any brand in particular?
parishioner
10-17-09, 00:27
I don't doubt you, but I'm curious to know (and I'm sure the OP is too). What common problems do you see with the piston uppers? Any brand in particular?
Curious as well as I thought that was one of the main benefits to having a piston SBR (being able to run suppressed with ease).
Robb Jensen
10-17-09, 07:29
I don't doubt you, but I'm curious to know (and I'm sure the OP is too). What common problems do you see with the piston uppers? Any brand in particular?
Just off the top of my head thus far:
Shifted gas blocks (not pinned), cracked gas blocks, worn out upper receivers (looked like someone took a bastard file to them), lower receiver extensions so worn from it's carriers tilt that the gun wouldn't run, lose carrier keys, broken/bent op rods, broken op rod springs, lose barrel nuts, broken bolt.
This experience is mostly with POF, Adams Arms, LWRC and a few others. I've seen very few problems with PWS, LMT, the newer LWRC guns seem to be running better than ever.
That is one of the fallacies of the piston argument, as many of these makers start out with inferior materials in the base gun, have their customers do their R&D, and make "updates" to the design as people complain.
Robb Jensen
10-17-09, 07:36
That is one of the fallacies of the piston argument, as many of these makers start out with inferior materials in the base gun, have their customers do their R&D, and make "updates" to the design as people complain.
Exactly.
What's sad is when you ask most people 'why a piston gun?' the answer is about 99% of the time 'because it's easier to clean'. :(
That's a non-issue with LWRCi. The M4-2000 fits a 10.5" LWRCi M6, M6A1, M6A2, and M6A3 just fine. The SPR/M4 fits a 12.7" LWRCi M6A1/A2/A3 with carbine gas blocks. These uppers were designed with AAC and SureFire cans in mind.
Here's an M6A2 with an M42K mounted (as found in this thread (http://forum.lwrci.com/forum/viewtopic.php?t=4345)):
http://i684.photobucket.com/albums/vv201/JSK_2009/DSC_0403.jpg
Nice setup! I like the DE Elcan.
I know a guy who runs a KAC can on a LWRC M6A2 10.5'' with no problems at all.
If you are going SBR you might as well go the 10.5, it's the shortest you can go without worrying about baffle strikes. In fact AAC will void the warranty if you run their can on any barrel shorter than 10.5. If you are worried about distance get a 16''.
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