Can I chop a 14.5" LMT MRP barrel to 12.5 for an AAC SP

MisterWilson · Post by **MisterWilson** » Thu Apr 10, 2008 10:19 pm

I can get the tax stamp taken care of, that's no biggie. My concern is whether or not I can simply take an LMT Monolithic Rail Platform barrel and cut that length back a bit. Besides being chrome-lined (Which may or may not be an issue depending on who you ask), they supposedly drill their gas port at a 45' angle from the bore.

Anyone ever done it before? More trouble than it's worth?

Gotta admit, it'd be pretty slick.

DevL · Post by **DevL** » Fri Apr 11, 2008 5:26 am

What is an AAC SP? You will still need to open the gas port no matter what angle it is or risk being under gassed.

markm · Post by **markm** » Mon Apr 14, 2008 10:43 am

One of the members on M4carbine.net replied that several of these were done by LMT for his outfit. If I remember correctly, there were no other mods done to get them to run good.

They were cut just past the 203 cut on the barrel.

Fletcher/AAC · Post by **Fletcher/AAC** » Mon Apr 14, 2008 12:22 pm

I had no problem cutting my 16" CL MRP 6.8 barrel to 11.5".

Ramius · Post by **Ramius** » Mon Apr 14, 2008 1:35 pm

I had a 16" MRP barrel cut down to just around 12.25" for the SPR/M4. No problems.

MisterWilson · Post by **MisterWilson** » Fri Apr 18, 2008 7:49 pm

Anyone else ever cut an MRP barrel?

Slick · Post by **Slick** » Fri Apr 18, 2008 11:18 pm

Yes, I had ar15barrels.com cut a 16" c/l 6.8 MRP barrel to 12.5" and it works great.

MisterWilson · Post by **MisterWilson** » Fri Apr 18, 2008 11:56 pm

Since the 14.5 has the carbine length gas system hidden under the handguards, I wonder if I could go to 11.5....

MisterWilson · Post by **MisterWilson** » Sun Apr 20, 2008 2:50 pm

Bump for more chopped MRPs.

cowboy7242001 · Post by **cowboy7242001** » Sun Apr 20, 2008 4:22 pm

Wow! I was just pondering the exact same setup. Glad to know it works.

trwalsh · Post by **trwalsh** » Mon Apr 21, 2008 10:06 pm

11.5" might be pushing it. Conventional wisdom is to give it about 3 inches or so in front of the rail to install the MITER mount and leave a little clearance for the can when attached.

How long is your MRP rail? Add ~3 inches or so from there.

MisterWilson · Post by **MisterWilson** » Mon Apr 21, 2008 10:18 pm

2.75 inches is what the miter mount requires.

MRP has a 9" rail.

What I want to know is how Ramius cut his barrel to 12.25" when the 16" middy has the gas block about an inch out in front of the 9" rail.

Ramius · Post by **Ramius** » Wed Jun 04, 2008 11:56 am

Actually have not measured exactly how long the sucker worked out.

I sent my MRP barrel to Noveski with instructions to cut it as short as possible for a SPR/M4. They were guessing it would be anywhere from 12 - 12.75" and it has shot very well.

MisterWilson · Post by **MisterWilson** » Wed Jun 04, 2008 12:30 pm

Interesting...I hadn't considered Noveske for that.

The folks at ADCO were the only other ones who didn't blink at the prospect of chopping an MRP barrel.

Another thing is that you've got the mid-length gas with the block out front...I'm thinking that I could probably go another inch or so shorter since I'd be cutting what was a 14.5 w/ carbine gas...

But then again, if I hold out another few months I could just buy a factory 12" pistol MRP barrel...

Decisions decisions.

tangodown911 · Post by **tangodown911** » Wed Jun 04, 2008 5:32 pm

MRP piston does not have enough barrel sticking out past gas block assembly. Looks to me to be about 1.5 inches?

MisterWilson · Post by **MisterWilson** » Fri Jun 06, 2008 1:32 am

I believe you're correct.

cowboy7242001 · Post by **cowboy7242001** » Fri Jun 06, 2008 9:58 am

tangodown911 wrote:MRP piston does not have enough barrel sticking out past gas block assembly. Looks to me to be about 1.5 inches?

Yep, not much room at all.

ArevaloSOCOM · Post by **ArevaloSOCOM** » Fri Jun 06, 2008 10:52 pm

I plan to cut my Bushmaster to 12.5 for my SPR/M4 can.

It seems to be the idle lenght

DevL · Post by **DevL** » Sat Jun 07, 2008 3:01 pm

I have a 9.125" rail and my SPR/M4 required 11.75" of barrel to clear the rail. I have a short gas block in the carbine position and that was not the limiting factor... the rail was. 11.5" on a 9" rail wont fit. It might fit if you could recess the suppressor slightly into the rail system but you still need enough room for the latch to be accessable. Many 9" rails (ones not designed to fit the standard front handguard retaining cap on a midlength gas system) are actually 9.125" or so in length.

Ramius · Post by **Ramius** » Thu Jun 19, 2008 3:20 am

I'd guess it is around 12.5" or so. It may be 11.75" The barrel was a standard 16" MRP barrel and I had it chopped as short as possible for the MRP carbine length forend. I won't be able to measure it for a few weeks.

Truth be told I don't really care how short it came out. What I needed was a carbine I can use while working around vehicles. I am for a barrel length that still produce reasonable velocities. If I wanted something really compact I'd go with an Uzi or a MP7

Okay, for mortals I'd go with an MP5K.

My next project will be a 16" or 14" 6.8SPC w/ a 6.8SPC SPR/M4. Have to do some reading on this one to figure out the best length.

Backout FH, about 1/16" ahead of the gas block.

Another shot of the carbine.

MisterWilson · Post by **MisterWilson** » Thu Jun 19, 2008 11:42 am

B E A Utimous!

John4045 · Post by **John4045** » Wed Oct 28, 2015 12:22 pm

Yeah, I know.

Any more chopped 16 or 14.5 MRP barrels? I'd like to cut a couple down to 12.5 or 11.5.

colblaster · Post by **colblaster** » Fri Feb 23, 2018 9:58 am

Posting in ancient thread.

I have a 12.5" MRP barrel with carbine gas, started as the 14.5" barrel.

ADCO did the work.

has been running great for years, both suppressed and unsuppressed (M4-2000 or 762-SDN-6).

With pretty much any ammo I throw at it.

This configuration is the go to setup for the MRP.

John4045 · Post by **John4045** » Sun Feb 25, 2018 11:27 pm

Thanks for the feedback. 12.5" hits the sweet spot. Way to keep the thread alive!

Can I chop a 14.5" LMT MRP barrel to 12.5 for an AAC SP

Can I chop a 14.5" LMT MRP barrel to 12.5 for an AAC SP

by request, photos on the Chopped MRP for SPR/M4

Re: Can I chop a 14.5" LMT MRP barrel to 12.5 for an AAC SP

Re: Can I chop a 14.5" LMT MRP barrel to 12.5 for an AAC SP

Re: Can I chop a 14.5" LMT MRP barrel to 12.5 for an AAC SP