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This message has been edited. Last edited by: dwd1985,

I own both DI and piston 5.56 MRPs. The DI is great, but I really love the LMT piston system. The MRP is already on the heavy side, so I don’t feel like the weight difference of the piston is a big deal on that particular rifle. For you, the downside is going to be the cost of a piston BCG. If you go DI it’s only the cost of the barrel.

Cost of new BCG aside, I would say piston based on my own preference, even if you weren’t going to shoot it suppressed. But that’s not a cheap BCG.

10.5” MRP DI barrel is $459 at LMT; the 12” piston conversion kit, which includes the BCG, is $879. That might decide it for you.

quote:

Originally posted by dwd1985:
There is a 10.5” DI option, as well as a 12” piston option. Any thoughts on which one I should go with? I have a SilencerCo Chimera in jail that I will he switching back and forth beywwwn the .300 and 5.56 barrels.

I have the MRP 12" piston upper. There is very little room (1/4" or less) from the rear of the threads to the piston plug, so any suppressor quick mount that reaches back behind the threads would be problematic.

quote:

Originally posted by henryaz:

quote:

Originally posted by dwd1985:
There is a 10.5” DI option, as well as a 12” piston option. Any thoughts on which one I should go with? I have a SilencerCo Chimera in jail that I will he switching back and forth beywwwn the .300 and 5.56 barrels.

I have the MRP 12" piston upper. There is very little room (1/4" or less) from the rear of the threads to the piston plug, so any suppressor quick mount that reaches back behind the threads would be problematic.

My major concern. When I looked into it long, long ago, there were a number of mounts that wouldn't work with the 12" piston.

I went with the 11.5" DI.

Mounting any SWR or Silencerco Supressor w/ the ASR Mount on the LMT 12" MRP Piston upper is not an issue as the Supressor is well in front of the rear of the threads. The larger 'potential' issue is whether there is sufficient clearance on the OD of the Muzzle Device to remove the Piston Plug for cleaning.



SWR Specwar 5.56 - ASR Mount w/ Trifecta RS Flash Hider

I have a DeadAir Sandman-S that should be released from jail any day now (check cashed on 4/28/18) so I can't say for sure, but I believe the Supressor is mounted further down/back on the mount with the KeyMo system. I'm sure a phone call to DeadAir could confirm the details on the Muzzle Device OD as well as the inline location of the Supressor w/ the KeyMo mount.

I'd actually be interested to know those details as well as well as I'm not 100% sure which Supressor I'll be using/mounting on my LMT 12" MRP Piston SBR either!

OK, you got me thinking and I decided I had to know right now! I retrieved my LMT Piston SBR (along with an unmounted Silencerco ASR Flash Hider) and my Brown & Sharpe dial caliper to take some critical measurements....Here's what I found:

Standard LMT Flash Hider OD = 0.862"
Silencerco ASR Flashider OD = 1.109"

Eyeballing it, there is approx. 3/32" clearance from the Std. Flash Hider when removing the Piston Plug/Op Rod. Conclusion: Basically, any Muzzle Device with an OD < 0.956" should work with the LMT 12" MRP Piston upper!

That said, the ASR Ring on the Silencerco Mount is located approx 1/8" further away from the Piston Plug, which allows for a bit more tolerance (wiggle room/angle) to remove the Piston Plug. I'm confident that worst case, if the Piston Plug is separated from the Piston/Op Rod during removal, it will clear the Silencerco Mount! Here's the trick - It's possible to reach in thru the opening in the quad rail to hold the Op Rod in place while removing the Piston Plug separately. I'm doing this on an already clean (and obviously cool) weapon, so it might be a little more tricky if the piston was dirty, but it should not be an issue.

Here's a pic of the KeyMo mounted Nomad on rifle showing it does not extend beyond the base of the Muzzle Device/Mount....And as you already know, the KeyMo is compatible with the SilencerCo® Chimera!



Regardless of how you plan to mount your Supressor, I'd say you're GTG with the LMT 12" MRP Piston upper!

Finally got the call....Sandman-S outta' jail and in my possession!

I can confirm the following critical dimension:

DeadAir KeyMount Muzzle Brake - Max OD = 1.081" (Mounting Shoulder at the base of the threads)

Hope this helps!

Sooo, whatcha' gonna' do? Piston or DI? Inquiring minds want to know...

Just to follow up, I discovered there are some differences between the Key Mount Muzzle Brake and Flash Hider from Dead Air. As you can see from the pics, the 'Mounting Shoulder' is located further away from the base of the threads (and Piston Plug!) on the Flash Hider, which should allow for a bit more tolerance (wiggle room/angle) to remove the Piston Plug. So there you have it...

There are two positions on the Piston Plug, 'FIRE' and 'SUPP', so yes, the LMT 12" Piston System does have a Suppressed mode/setting.

This message has been edited. Last edited by: nhracecraft,

I have both and they are both good. Mine are both set up the same except for the color of the furniture, and accuracy wise I can't tell the difference... the piston one is more nose heavy but somewhat easier to clean.



-Tom

quote:

Originally posted by nhracecraft:
There are two positions on the Piston Plug, 'FIRE' and 'SUPP', so yes, the LMT 12" Piston System does have a Suppressed mode/setting.

My 12" MRP piston upper (purchased directly from LMT in Sept. '09) has no SUPP marking on the plug, just FIRE. The instructions show rotation 90 degrees for removal, and that's the only other position. It appears the design evolved over time.

quote:

Originally posted by henryaz:

quote:

Originally posted by nhracecraft:
There are two positions on the Piston Plug, 'FIRE' and 'SUPP', so yes, the LMT 12" Piston System does have a Suppressed mode/setting.

My 12" MRP piston upper (purchased directly from LMT in Sept. '09) has no SUPP marking on the plug, just FIRE. The instructions show rotation 90 degrees for removal, and that's the only other position. It appears the design evolved over time.

Interesting 'henryaz' - My LMT 12" MRP Piston was purchased in late Nov. 2011 and definitely has 'FIRE' and 'SUPP' settings.

While I do have a PDF of the earlier CQB Piston Manual (dated/created 12/5/08), it makes no reference to any settings (assembly and disassembly only). The later 'Rev. A' version of that manual (dated/created 8/8/11) does have a section on the 'Operation' of the Piston system, referencing the 'FIRE' and 'SUPP' settings. FYI - This is the same version of the manual currently on the LMT website.

I also have printed copies of the MRP Weapon System manual (Rev. D & Rev. G) that were supplied with my LMT's, and both reference Operation of the Piston system in the 'Suppressed and Non-Suppressed' modes. There is NO printed date reference in the manual(s), however I do have a PDF of the 'Rev. F' version of that manual (dated/created 8/8/11). Rev.F is the version currently on the LMT website.

OP - Hope this helps. I'm sure a call to LMT will confirm the current Piston System details with certainty...

quote:

Originally posted by henryaz:

quote:

Originally posted by nhracecraft:
There are two positions on the Piston Plug, 'FIRE' and 'SUPP', so yes, the LMT 12" Piston System does have a Suppressed mode/setting.

My 12" MRP piston upper (purchased directly from LMT in Sept. '09) has no SUPP marking on the plug, just FIRE. The instructions show rotation 90 degrees for removal, and that's the only other position. It appears the design evolved over time.

I have both the old style plug and newer style. The old style had one setting of fire but you could rotate 180 degrees to make the rifle a single shot that required manual charging. I kind of like it. The newer is marked FIRE/SUPP
I don't notice much difference but the hole on the Suppressed setting is smaller so I guess it does decrease gas.
I don't find it to be over gassed in the FIRE position so I just leave it when shooting suppressed.

From the LMT website: "The MRP is the rifle length receiver designed for 14.5″ barrels up to 20″ barrels..."

https://lmtdefense.com/parts/l7ra1a

FYI - The barrel length info re: the 'MRP (Quad Rail) Upper Receiver' also applies to the 'MLR (M-LOK) Upper Receiver' and the 'SLK (Smooth) Upper Receiver' as well!