[paulosantos]

A. INTRO:
I finally got my LMT 5.56 Piston Upper on 1-2-09 and I had the chance to take it to the range on 1-3-09. I'm not going to bore you with pictures or tell you how clean the upper was or how cool the BCG was to the touch after several hundred rounds. I think most of you guys already know the benefits of a Piston AR. What I have always wondered was the accuracy of a Piston AR. This is my very first Piston AR. The one thing that I have always wondered about the Piston AR's was the accuracy. Everytime someone asked a Piston owner about the accuracy of their AR, most of the replies were, "This is a Combat Rifle." So I decided to test it out myself.

B. 16" LMT 5.56 Piston Upper:
1. Brief Description:
16" Chrome Lined Barrel with a 1:7" Twist. Midlength Piston System.

2. Break-in:
Before going out, I checked the Chamber with the PTG 5.56 Reamer to make sure that it was indeed a true 5.56 Chamber, which it was. I then polished up the Bore with some Remington cleaner. I broke in the barrel with the Tubbs Final Finish Bullets (Sierra 77 Gr. SMK Bullets). In the first 30 bullets, I had approximately 10 Short Strokes, which was not a surprise since I used a very light load with H322 with the 77 Gr. SMK Bullets. The remaining 20 bullets used during the break-in period all feed fine.

3. Accuracy Results:
Support Used: Harris Bi-pod and rear sandbag.
Optic: Swarovski Z6i 1x6 scope set on 6x.
Trigger: WOA Tuned RRA with Superior Shooting Springs.
Range: 100 Yards.
Shot Groups: 2 10 round shot groups.

Hornady 55 Gr. FMJ:
Brass: Winchester.
Primer: Wolf Smal Rifle Magnum.
Crimp: Lee FCD.
OAL: 2.220".
Temp: 30. (70 during chronoing.).

24.5 Gr. of X-Terminator: Avg: 2885 fps, Lo: 2861 fps, Hi: 2911 fps, ES: 50, SD: 21
ACCURACY: 1.823"
25 Gr. of X-Terminator: Avg: 2954 fps, Lo: 2898 fps, Hi: 2982 fps, ES: 84, SD: 33
ACCURACY: 1.945"
25.5 Gr. of X-Terminator: Avg: 3005 fps, Lo: 2982 fps, Hi: 3023 fps, ES: 41, SD: 19
ACCURACY: 1.903"

25.5 Gr. of Benchmark: Avg: 2965 fps, Lo: 2936 fps, Hi: 2989 fps, ES: 53, SD: 19
ACCURACY: 1.307"
26 Gr. of Benchmark: Avg: 3021 fps, Lo: 3005 fps, Hi: 3089 fps, ES: 41, SD: 20
ACCURACY: 1.335"

23 Gr. of H322: Avg: 2761 fps, Lo: 2726 fps, Hi: 2789 fps, ES: 63, SD: 23
ACCURACY: 1.095"
23.5 Gr. of H322: Avg: 2826 fps, Lo: 2772 fps, Hi: 2855 fps, ES: 83, SD: 32
ACCURACY: 1.922"

25.5 Gr. of H4895: Avg: 2891 fps, Lo: 2849 fps, Hi: 2943 fps, ES: 94, SD: 34
ACCURACY: 2.531"
26 Gr. of H4895: Avg: 2985 fps, Lo: 2949 fps, Hi: 3023 fps, ES: 74, SD: 26
ACCURACY: 1.585"
26.5 Gr. of H4895: Avg: 3049 fps, Lo: 3016 fps, Hi: 3079 fps, ES: 63, SD: 24
ACCURACY: 1.978"

25.5 Gr. of Varget: Avg: 2784 fps, Lo: 2721 fps, Hi: 2855 fps, ES: 134, SD: 56
ACCURACY: 2.015"
26 Gr. of Varget: Avg: 2859 fps, Lo: 2842 fps, Hi: 2892 fps, ES: 50, SD: 20
ACCURACY: 1.413"
26.5 Gr. of Varget: Avg: 2928 fps, Lo: 2898 fps, Hi: 2969 fps, ES: 71, SD: 31
ACCURACY: 2.423"

Hornady 55 Gr. FMJ:
Brass: Winchester.
Primer: CCI #41.
Crimp: Lee FCD.
OAL: 2.220".
Temp: 80.

25.6 Gr. of Benchmark: Avg: 3124 fps, Lo: 3115 fps, Hi: 3137 fps, ES: 22, SD: 11
26.5 Gr. of Benchmark: Avg: 3180 fps, Lo: 3152 fps, Hi: 3205 fps, ES: 53, SD: 18
ACCURACY: 2.170"

26.5 Gr. of H4895: Avg: 3115 fps, Lo: 3093 fps, Hi: 3137 fps, ES: 44, SD: 22

25.5 Gr. of TAC: Avg: 2929 fps, Lo: 2904 fps, Hi: 2943 fps, ES: 39, SD: 16
ACCURACY: 1.688" (5 Rounds).
26 Gr. of TAC: Avg: 3002 fps, Lo: 2982 fps, Hi: 3023 fps, ES: 41, SD: 20
ACCURACY: 1.813" (5 Rounds).
26.5 Gr. of TAC: Avg: 3072 fps, Lo: 3051 fps, Hi: 3093 fps, ES: 42, SD: 18
ACCURACY: 1.599" (5 Rounds).
27 Gr. of TAC: Avg: 3107 fps, Lo: 3090 fps, Hi: 3122 fps, ES: 29, SD: 13
ACCURACY: 2.032" (5 Rounds).

Hornady 75 Gr. BTHP:
Brass: Winchester.
Primer: Wolf Smal Rifle Magnum.
Crimp: Lee FCD.
OAL: 2.250".
Temp: 30. (70 during chronoing.).

22 Gr. of H322: Avg: 2558 fps, Lo: 2520 fps, Hi: 2583 fps, ES: 63, SD: 25
ACCURACY: 1.119"

22.5 Gr. of H4895: Avg: 2420 fps, Lo: 2406 fps, Hi: 2428 fps, ES: 22, SD: 8
ACCURACY: 1.122"
23 Gr. of H4895: Avg: 2450 fps, Lo: 2424 fps, Hi: 2487 fps, ES: 63, SD: 24
ACCURACY: 1.701"
23.5 Gr. of H4895: Avg: 2525 fps, Lo: 2501 fps, Hi: 2549 fps, ES: 48, SD: 22
ACCURACY: 1.517"

23 Gr. of Varget: Avg: 2395 fps, Lo: 2372 fps, Hi: 2420 fps, ES: 52, SD: 21
ACCURACY: 1.537"
23.5 Gr. of Varget: Avg: 2477 fps, Lo: 2460 fps, Hi: 2492 fps, ES: 32, SD: 11
ACCURACY: 1.306"
24 Gr. of Varget: Avg: 2524 fps, Lo: 2510 fps, Hi: 2544 fps, ES: 34, SD: 15
ACCURACY: 1.704"

Hornady 75 Gr. BTHP:
Brass: Winchester.
Primer: CCI #41.
Crimp: Lee FCD.
OAL: 2.245".
Temp: 80.

22.5 Gr. of Benchmark: Avg: 2683 fps, Lo: 2666 fps, Hi: 2704 fps, ES: 38, SD: 16
22.8 Gr. of Benchmark: Avg: 2690 fps, Lo: 2666 fps, Hi: 2710 fps, ES: 44, SD: 20
23.1 Gr. of Benchmark: Avg: 2705 fps, Lo: 2682 fps, Hi: 2737 fps, ES: 55, SD: 22

24 Gr. of H4895: Avg: 2704 fps, Lo: 2661 fps, Hi: 2737 fps, ES: 76, SD: 39

Nosler 77 Gr. BTHP:
Brass: Winchester.
Primer: CCI #41.
Crimp: Lee FCD.
OAL: 2.245".
Temp: 80.

22.5 Gr. of Benchmark: Avg: 2650 fps, Lo: 2629 fps, Hi: 2682 fps, ES: 53, SD: 21
22.8 Gr. of Benchmark: Avg: 2656 fps, Lo: 2635 fps, Hi: 2682 fps, ES: 47, SD: 18
23.1 Gr. of Benchmark: Avg: 2691 fps, Lo: 2677 fps, Hi: 2699 fps, ES: 22, SD: 9

24 Gr. of H4895: Avg: 2699 fps, Lo: 2682 fps, Hi: 2732 fps, ES: 50, SD: 22

Sierra 77 Gr. SMK:
Brass: Winchester.
Primer: CCI #41.
Crimp: Lee FCD.
OAL: 2.245".
Temp: 80.

22.8 Gr. of Benchmark: Avg: 2668 fps, Lo: 2645 fps, Hi: 2682 fps, ES: 37, SD: 14
23.1 Gr. of Benchmark: Avg: 2685 fps, Lo: 2661 fps, Hi: 2710 fps, ES: 49, SD: 21
------------------------------------------------------

Factory ammo:

Hornady 60 Gr. V-Max TAP-FPD:
Avg: 2777 fps, Lo: 2766 fps, Hi: 2789 fps, ES: 23, SD: 11
ACCURACY: 1.528"

Hornady 75 Gr. BTHP TAP-FPD:
Avg: 2554 fps, Lo: 2525 fps, Hi: 2574 fps, ES: 49, SD: 18
ACCURACY: 3.021"

HSM (Hunting Shack Munition) 60 Gr. V-Max:
Avg: 2678 fps, Lo: 2645 fps, Hi: 2704 fps, ES: 59, SD: 23
ACCURACY: 1.402"

HSM (Hunting Shack Munition) 69 Gr. SMK:
Avg: 2574 fps, Lo: 2559 fps, Hi: 2588 fps, ES: 29, SD: 11
ACCURACY: 1.697"

M193:
Avg: 3127 fps, Lo: 3108 fps, Hi: 3152 fps, ES: 44, SD: 18
ACCURACY: 2.346" (7 rounds)

4. Conclusion:
1-3-09: So far, I have only had the 10 Failures which were during the break-in. I believe those were due to the weak loads and not weapon or magazine related. I'll keep updating as I do more accuracy testing in the upcoming days. So far, the accuracy is OK. Recoil is typical of any 5.56 AR that I've shot. The recoil with H322 was practically nill. I did check for Carrier Tilt and did observe some marks inside the buffer tuber, which I checked prior to shooting and there weren't any. It does not seem bad at all, but I'll keep an eye on it. I also noticed that the oprod is slightly bent. I'll call up LMT and ask them about it.
1-5-09: The carrier looks the same, so it looks like the carrier tilt has leveled off. I spoke with LMT today about the bent oprod and they said it is normal. So far I am very impressed with the accuracy.
1-15-09: Total of approximately 1K rounds so far with no problems.

 

[rcrandall]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

Good report, thanks!

 

[constructor]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

You are through,
I wish I had the time you do and the money you spend on reloading supplies
when you get a minute, would you post some photos of the piston system?

 

[paulosantos]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

You are through,
I wish I had the time you do and the money you spend on reloading supplies
when you get a minute, would you post some photos of the piston system?

I am not even close to being through. I was at the range from 10-3PM and I left because it was fucking cold and the stupid target kept falling apart on me. :lol: :lol: I'm going back tomorrow to finish up the 5.56 testing and back on Monday to start the 6.8SPC accuracy Testing. What are your thoughts on the ejection with the 6.8SPC MRP Barrel?

Pics coming up shortly.

 

[BillBond]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

My 6.8 LMT MRP with the original buffer and spring ejected to 1 o'clock.

It took a Wolff spring and a H3 buffer to get it to 3 o'clock.
I tried Slash's Tungsten buffer which is even heavier and it ejected to 2:50 o'clock.

8)

 

[paulosantos]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

My 6.8 LMT MRP with the original buffer and spring ejected to 1 o'clock.

It took a Wolff spring and a H3 buffer to get it to 3 o'clock.
I tried Slash's Tungsten buffer which is even heavier and it ejected to 2:50 o'clock.

8)

Damn. :shock: :shock: :shock:

 

[paulosantos]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

It is hard to tell on the picture, but the Oprod has two gas rings on it, which I thought was interesting. And the Oprod is slightly crooked, which apparently is normal from reading about it from other guys that have one. It is almost as crooked as my...

 

[dasu]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

sweet. now who the blank has MRP uppers in stock? dennys has the gas piston kit.

 

[paulosantos]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

sweet. now who the blank has MRP uppers in stock? dennys has the gas piston kit.

I got mine from West Coast Armory.

 

[dasu]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

price?

 

[IPSC_GUY]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

What is the recoil impulse on the piston set up like?

I am NOW kicking myself in the ass as I had a carbine length MRP that I SOLD before buying the rifle length MRP... before the piston system was out. I didn't know that they were planing to design the things to ONLY work on Carbine length uppers, CRAP ! ! !

Oh well, I spent 20 years in the Marines cleaning DI M16s so I at least know how to do it well.

On the 6.8 closing on the NO GO gauge... that is worrisome. Excessive head space?

IPSC_GUY
SIERRA II ALPHA

 

[paulosantos]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

What is the recoil impulse on the piston set up like?

I am NOW kicking myself in the ass as I had a carbine length MRP that I SOLD before buying the rifle length MRP... before the piston system was out. I didn't know that they were planing to design the things to ONLY work on Carbine length uppers, CRAP ! ! !

Oh well, I spent 20 years in the Marines cleaning DI M16s so I at least know how to do it well.

On the 6.8 closing on the NO GO gauge... that is worrisome. Excessive head space?

IPSC_GUY
SIERRA II ALPHA

I had a worse one before. This one at least takes a little force to close. It honestly feels like a regular DI. With the H4895, Varget, and X-Terminator powder, the impulse is noticeably more than the H322 and Benchmark powder.

I ordered a 9mm buffer and an enhanced BCG for the 6.8SPC barrel, so hopefully it will eject the brass more at the 3 O'Clock Position.

 

[paulosantos]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

price?

$1500.00

 

[IPSC_GUY]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

Interesting, I had heard that the MRP piston system felt better than most piston systems out there. So does LMT have any plans to do the 6.8 in a piston system? Maybe with a 1 in 11 twist barrel with a SPC II chamber?

Is the ejecting of the brass more forward a problem or indicative of a problem? My 6.8 throws them back to the very outside edge of the brass deflector where as the 5.56mm barrel threw them to the very inside of the brass deflector.

SPEAKING of which who makes a brass catcher for a flat top upper?

IPSC_GUY
SIERRA II ALPHA

 

[BillBond]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

It seems backwards that the oprod is offset on the piston gun
and that the gas tube on a DI gun is straight.

8)

 

[dasu]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

what does the crooked op rod do? is it offset to fit in the gun? would that help with carrier tilt?

 

[paulosantos]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

Interesting, I had heard that the MRP piston system felt better than most piston systems out there. So does LMT have any plans to do the 6.8 in a piston system? Maybe with a 1 in 11 twist barrel with a SPC II chamber?

Is the ejecting of the brass more forward a problem or indicative of a problem? My 6.8 throws them back to the very outside edge of the brass deflector where as the 5.56mm barrel threw them to the very inside of the brass deflector.

SPEAKING of which who makes a brass catcher for a flat top upper?

IPSC_GUY
SIERRA II ALPHA

The brass with the 5.56 Piston is going out at 3-4 O'Clock. While the 6.8SPC MRP barrel is ejecting almost forward at the 1 O'Clock Position. It usually means that it is overgassed. Ideally, you want the brass ejecting at the 3-4 O'Clock position. I did order a 9mm buffer and an enhanced BCG, so hopefully that will help. If not, it is going back to LMT.

I spoke with LMT about the 6.8SPC PISTON and they haven't begun testing them yet, so it will be a while. It would be nice if they changed the specs, but since I had absolutley no pressure signs with the Tactical Loads on mine, I'm not worried.

 

[paulosantos]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

what does the crooked op rod do? is it offset to fit in the gun? would that help with carrier tilt?

I have no idea why it is crooked. I'm calling them up tomorrow and I'll ask them.

 

[Clint]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

what does the crooked op rod do? is it offset to fit in the gun? would that help with carrier tilt?

I have no idea why it is crooked. I'm calling them up tomorrow and I'll ask them.

I bet they wanted to get the piston centerline as close to the barrel centerline as possible.
This would tend to minimize the barrel bending moment ( i.e. lever arm ).
It would also allow fitting more/most forearms.
The bend would then be a necessary evil to allow the op rod to match up with the gas tube centerline at the receiver.

Crooked puts more internal stress on the rod, which tends to make it bend more.
The same applies to panhard bars and drag links on a lifted 4x4.

 

[BillBond]

Re: LMT MRP Review. 5.56 Piston Upper & 6.8SPC.

what does the crooked op rod do? is it offset to fit in the gun? would that help with carrier tilt?

My guess is, so the gas block assembly will fit under the standard MRP rail.
I had an ARES conversion for a while and the op rod was straight but the gas block assembly would not fit under a standard handguard.

8)