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LMT 6.8SPC MRP Review.

20560 Views 46 Replies 14 Participants Last post by  lwrkeysfisher, 
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16" LMT 6.8SPC DI:
1. Brief Description:
16" Chrome Lined Barrel with a 1:10" Twist/6-Groove/SAAMI Chamber (Converted to SPCII Chamber). Carbine Length Gas System.

2. Break-in:
The first thing I did was convert the SAAMI Chamber to the SPCII Chamber. I also polished up the Bore with some Remington cleaner. I broke in the barrel with the Tubbs Final Finish Bullets (Sierra 135 Gr. SMK Bullets). I had no failure to feeds of any sort during break-in.

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.

Sierra 90 Gr. HP:
Brass: SSA.
Primer: CCI#41.
Crimp: Lee FCD.
OAL: 2.260".
Temp: 80.

28.6 Gr. of H4198:
Avg: 2885 fps, Lo: 2867 fps, Hi: 2898 fps, ES: 31, SD: 13

27.6 Gr. of AA1680:
Avg: 2769 fps, Lo: 2754 fps, Hi: 2783 fps, ES: 29, SD: 14
28.1 Gr. of AA1680:
Avg: 2827 fps, Lo: 2812 fps, Hi: 2842 fps, ES: 30, SD: 21

33.5 Gr. of TAC:
Avg: 2632 fps, Lo: 2619 fps, Hi: 2661 fps, ES: 42, SD: 18

Speer 90 Gr. TNT:
Brass: SSA.
Primer: Wolf Smal Rifle Magnum.
Crimp: Lee FCD.
OAL: 2.270".
Temp: 60.

28.1 Gr. of H4198:
ACCURACY: 1.286"
28.6 Gr. of H4198:
ACCURACY: 1.065"
29.1 Gr. of H4198:
ACCURACY: 1.058"
29.6 Gr. of H4198:
ACCURACY: 1.180"

31 Gr. of H322:
ACCURACY: 1.225"

Hornady 110 Gr. BTHP:
Brass: SSA.
Primer: Wolf Smal Rifle Magnum.
Crimp: Lee FCD.
OAL: 2.245".
Temp: 60.

25.3 Gr. of H4198: (5 rounds)
ACCURACY: 2.201"

29 Gr. of H322:
ACCURACY: 2.207"
29.5 Gr. of H322:
ACCURACY: 2.632"

29.5 Gr. of X-Terminator:
ACCURACY: 3.518"

Hornady 110 Gr. V-Max:
Brass: SSA.
Primer: Wolf Smal Rifle Magnum.
Crimp: Lee FCD.
OAL: 2.270".
Temp: 60.

25.3 Gr. of H4198: (5 rounds)
ACCURACY: 1.233"

28.5 Gr. of H322:
ACCURACY: 1.739"
29 Gr. of H322:
ACCURACY: 1.667"
29.5 Gr. of H322:
ACCURACY: 1.956"

29.5 Gr. of X-Terminator:
ACCURACY: 2.595"

Hornady 110 Gr. V-Max:
Brass: SSA.
Primer: CC#41.
Crimp: Lee FCD.
OAL: 2.260".
Temp: 80.

30.5 Gr. of TAC:
Avg: 2438 fps, Lo: 2437 fps, Hi: 2442 fps, ES: 5, SD: 2
ACCURACY: 2.050"

25.3 Gr. of H4198:
Avg: 2482 fps, Lo: 2469 fps, Hi: 2492 fps, ES: 23, SD: 12

Sierra 110 Gr. Pro-Hunters:
Brass: SSA.
Primer: Wolf Smal Rifle Magnum.
Crimp: Lee FCD.
OAL: 2.270".
Temp: 60.

28.5 Gr. of H322:
ACCURACY: 1.422"

Sierra 115 Gr. SMK:
Brass: SSA.
Primer: Wolf Smal Rifle Magnum.
Crimp: Lee FCD.
OAL: 2.270".
Temp: 60.

24 Gr. of H4198: (5 rounds)
ACCURACY: 1.076"

28 Gr. of H322:
ACCURACY: 1.033"
28.5 Gr. of H322:
ACCURACY: 1.549"

29 Gr. of X-Terminator:
ACCURACY: 1.964"

Sierra 115 Gr. SMK:
Brass: SSA.
Primer: CCI#41.
Crimp: Lee FCD.
OAL: 2.260".
Temp: 80.

30 Gr. of TAC:
Avg: 2361 fps, Lo: 2347 fps, Hi: 2385 fps, ES: 38, SD: 20
ACCURACY: 1.693"

24 Gr. of H4198:
Avg: 2322 fps, Lo: 2298 fps, Hi: 2347 fps, ES: 49, SD: 24
------------------------------------------------------

Factory ammo:

SSA 90 Gr. HP Tactical Load:
Avg: 2937 fps, Lo: 2904 fps, 2969 Hi: fps, ES: 65, SD: 21
ACCURACY: 1.536"

SSA 110 Gr. Pro-Hunter Commercial Load:
Avg: 2443 fps, Lo: 2415 fps, Hi: 2469 fps, ES: 54, SD: 19
ACCURACY: 1.555"

SSA 115 Gr. Enhanced SMK Commercial Load:
Avg: 2465 fps, Lo: 2450 fps, Hi: 2473 fps, ES: 23, SD: 7
ACCURACY: 1.860"

4. Conclusion:
1-3-09: So far, I have only had zero failures, but I only fired 80 rounds. I tested the SSA 115 Gr. SMK Tactical Loads and I didn't have any pressure signs of any sort. The brass is ejecting at the 1 O'Clock Position wih all of the ammo I tested, which is not good. I even switched to the H2 Buffer and it only helped out a little bit. I checked the headspace with the No-Go Gauge and the bolt closed, which is not supposed to. So either it is seriously over gassed, or there is a headspace issue.

1-5-09: I spoke with LMT today about the brass ejecting forward and I was told that it should eject from the 1-3 O'clock position. I also told them about the no-go gauge closing and I was told to check out the accuracy. If it is bad, they will replace the barrel.

2-11-09: I did send the LMT 6.8SPC barrel back to LMT and they replaced it. Turn-around time was approximately 1 week. I Reamed the barrel to the SPCII Chamber using the Michiguns SPCII Reamer and all of the ammo that I tested had no pressure signs. Today, I finally got the chance to finish test loading the 6.8SPC MRP Barrel. I can honestly say I am pleasantly surprised with the accuracy of the barrel. Even the Hornady 110 Gr. V-Max shot under 2MOA at 100 Yards. The winners were definitely the Speer 90 Gr. TNT with H4198 (no surprise), and the Sierra 115 Gr. SMK with H322. The only bullet that sucked ass was the Hornady 110 Gr. BTHP, which is very disappointing because I was hoping that it would be the most accurate. All of the other bullets were all under 2MOA, with the TNT and SMK right at 1MOA.
The only negative was that this barrel and most of the LMT 6.8SPC barrels are seriously over gassed. Even with the H3 buffer, most of the brass was ejecting at the 2 o'clock position. LMT uses the Hornady ammo as their test ammo, which is pretty weak compared to the SSA ammo, so that is most likely why their barrels are over gassed.

3-25-09: I recently sent my barrel to Harrison to get cut down to 14" and have the FSC30 permanently attached. This was mainly one to try to get the brass to eject at the 3-4 o'clock position since this barrel was so over-gassed. I recently got the barrel back and I went to the range today where I tested it out. With the H3 buffer, the brass was ejecting at the 3-4 o'clock position and the recoil was much less. I also tried some more loads with the H4198 (Hornady 110 Gr. BTHP, Hornady 110 Gr. V-Max, and the Sierra 115 Gr. SMK) and the accuracy was great. I only chronoed the Speer 90 Gr. TNT with 28.8 Gr. of H4198 (2872 FPS), which is the load I am taking to the class in April. I'm officially a happy camper. H, I love you man. (No ****).
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T
I am a bit confused you have a CM and SS that both shoot .5-.75 are these 6.8 MRP barrels or something else or dif caliber? I doubt anyone can say you will get that accuracy from a production barrel. I would cerintaly say get it converted to the DMR as it will make the last half of the throat whichc it is going to cut in be .0015 tighter which will give a better entrance to the rifling which is one of the two most cristical parts of accuracy from the barrel.

Paulo have you now confirmed LMT is no longer making the gas ports the size of a manhole? If so do you know what the size is? Have you toght of using one of the adj gas tubes for yours. It might be better than the beating the parts are taking from teh very heavy buffer. It woudl allow for a carbine buffer and SSS spring which is a very nice setup.



The 18" SS barrels whaty gas port location are they using for the 6.8? middy carbine ?
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Tim_W said:
Paulo have you now confirmed LMT is no longer making the gas ports the size of a manhole? If so do you know what the size is? Have you toght of using one of the adj gas tubes for yours. It might be better than the beating the parts are taking from teh very heavy buffer. It woudl allow for a carbine buffer and SSS spring which is a very nice setup.

The 18" SS barrels whaty gas port location are they using for the 6.8? middy carbine ?
Click to expand...
Gene told me they only had a few more barrels in stock, so the next batch should have the proper gas port size. The current gas port size isn't as big as even I thought, but it is still too big. If they make a 6.8 Piston they will completely have to change the gas port location to the Mid length gas system, so I hope they change their barrel specs. I'm just glad that he actually listened.
Their 18" looks like it is also the carbine gas system. I told him the ideal gas port locations of all the barrel lengths.
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G
Sorry for the confusion. The barrels I mentioned are 5.56. I should have been clearer. They do very well with LE TAP 75gr OTM and 60gr BT under H335. 5 shot groups not ten shot groups like Paulo mentioned. .5" 10 shot group with an AR and I would have the ckeck my pants for a deposit...
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Biscuit,

got it thanks.

Paulo,

How big did you think big is for a gas port!?! The current ones were like .110" from my understanding!!!!! That is at a carbine location no less!!! The max rifle length 20" gas port I have seen in a 6.8 is .110" Carbine gas ports are normally 70% smaller than rifle port size. The normal Carbine gas port size for the 6.8 is .063-.-068 Middy .078-.093 , Rifle .093-.110. Trust me that is a huge port on the current LMT and I am very very glad they are changing it. It is going to soon be moot as they look to be changing as you said. That is other than for all the others like you that got stuck with these old ones. STAG has been replacing anyone's SAAMI barrel than calls and reports issues. LMTs issue IMO is worse I wonder if pushed if they would replace them for those that asked. Not that that woudl help you as you have the customizing bug :):)

I think it was not so much they were trying to get relaible function for HRdy ammo whihc I am sure they were but what I think really happened is someone made a major oopps and they ended up with 10-20K barrels will large gas ports. If you think about it the rifle gas port size is the same as it is. It would be very easy to accidentally drill the gas ports to that size by mistake. Nothing more than installing the wrong bit size in the mill or writing down the wrong size on the technical order request.. Then it was simply carried thru for all the barrels as they are done assembly line style

Did they say anything about the chambers? Are they going to stick with SAAMI? I know you had to be trying to get them to switch that for sure.

We really need to pressure them IMO and maybe someone will get thru. They have a very good piston system and make a very good AR in general. Their 10.3 uppers are considered to run the best of all the DIs which is hard to do over a huge volume. All their 5.56 get very high marks consistently. If they switch to better specs they will sell a hell of a lot more and being such a large company having them bigger in the 6.8 game woudl be a very good thing.

I can see how they could argue for the 10 twist as there are still others that use it. But SAAMI chamber its so overwhelming now........ 18" carbine gas also is just way out there. I can give them 16 as there is a case for it as you have made in the past but carbine in an 18"!?!Well glad they make that enahcned BCG casue its the prefect use for the carrier and bolt.

I realize they only use carbine and rifle port locations on their guns but still adding a middy gas port seems a much better answer than using a gas port location they themselves have come out with special parts to deal with in barrels with to much length after. That is how the entire enhanced BCG came to be. They were looking for ways to deal with the fact the carbine location used on the M4 was to close and extra duration and increased pressures were causing excessive wear and reliability issues. I remember reading the entire interview about all of it as it was part of the entire MRP upper system release. I still think the MRP is one of the slickest upper designs currently out there.

Once their 10.5" Mk18 come back in stock at Bravo or others and the prices are normal I plan on picking one up as I have been wanting one for a couple years now. That will be my main 5.56 setup as really I am 6.8 specific but want to be covered given I have a good stash of cases and bullets. A perfect rifle for hunting for my 10 year old daughter as well.:)
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Tim, Gene told me the gas port size and it is in the .08" range. No matter what size it is, they are waaaaaay over gassed. They set up their barrels with the older Hornady ammo which was under powered. Gene also said they got some SSA ammo in to test out.
They actually have several 556 barrels with the Mid length system and if they ever make a 68 Piston, it will have to be Midlength, so I hope they change their specs on he barrels since the have to change their barrels anyway.
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G
I drink the LMT Kooolaid but found them very rigid to deal with. Good guys, they talk to you and answer questions with knowledge. I wouldn't think they will budge unless high sales numbers are a given. Hell, in 2006 my department switched over to LMT's for patrol and SWAT. They wouldn't accept a purchase order! They made us send payment up front. That's a pair!

I would kill for a real deal 6.8 barrel for my MRP.

BTW: "Rigid" is not a slam. I just think they have som many orders to fill inc mil contracts the numbers of 6.8 buyers just don't demand immediate attention.

I STILL WANT 1 THOUGH!
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paulosantos said:
Tim, Gene told me the gas port size and it is in the .08" range. No matter what size it is, they are waaaaaay over gassed. They set up their barrels with the older Hornady ammo which was under powered. Gene also said they got some SSA ammo in to test out.
They actually have several 556 barrels with the Mid length system and if they ever make a 68 Piston, it will have to be Midlength, so I hope they change their specs on he barrels since the have to change their barrels anyway.
Click to expand...
Agreed. If they go with the mid on the 18 and change the chamber along with the changes expected with the gas port it will defiantly more them way up form the bottom of the list. It woudl be nice especially when the get the piston out to be able to recommend it. As I said I have always been very happy with their 5.56 stuff. All of them.
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BISCUT said:
I drink the LMT Kooolaid but found them very rigid to deal with. Good guys, they talk to you and answer questions with knowledge. I wouldn't think they will budge unless high sales numbers are a given. Hell, in 2006 my department switched over to LMT's for patrol and SWAT. They wouldn't accept a purchase order! They made us send payment up front. That's a pair!

I would kill for a real deal 6.8 barrel for my MRP.

BTW: "Rigid" is not a slam. I just think they have som many orders to fill inc mil contracts the numbers of 6.8 buyers just don't demand immediate attention.

I STILL WANT 1 THOUGH!
Click to expand...
I have found this too but it has more I think to do with who you talk to and how you approach it. I remember calling and you could tell the tech I was talking to was getting ready to take a bit out of someone form all the Q&A he must have done that day. I realizing this switch to a empathetic position and cracked a few jokes about dumb customer and and their demands and teh such. After than he was willing to jaw with me longer than I had time to. Answered everything and then some. Sent me a part I needed overnight that he had told me when I first called woudl not go out for a week or more . Now that I have a product out there and seeing some of the emiails I have gotten, although most have been very good etc, I can see how at a size company like that you could really get to where you become rigid with things. But still a cusotmer is a customer adn you shoudl alwsy tyr to treat them as though they are special and you appreacaite the fact they have put trust in you and your prodcut to choose it. It sure can be challenging sometimes though:)
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Paul, do you have a date code on when the newer barrels were used? Mine was from late Jan 09, I have not tested it and would prefer to just send it back if it is problematic out of the box...

Is there any word on LMT upgrading barrels anytime soon?
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C
Paulo and Tim,

I'm back and I just posted over at TOS concerning the LMT and 6.8 SPC. You can read what Dave Fortier and I both have to say here:

http://www.ar15.com/forums/topic.html?b=3&f=121&t=441671&page=5&#4055086

I hope I stated my case alright. I know that I suggested some ideas that you guys might not agree with, but please just read my reasoning and also Dave's report from Black Hills Ammo and Mr. Karl Lewis at LMT.

Take care and will sign off for a while again.

BTW Paulo, still love my LMT MRP CQB Piston. I was talking with Gene last month and discussed with him the possibility of a piston 6.8 and in his words, they aren't even beginning to look at it. If I get my finances straightened out, I told him my plan to have Mike Rock make me a blank, buy a 556 piston kit (barrel and BCG), and send them off to Harrison with my upper and have him play around with it. To me, all it would take is to do the math with the gas port size..........556 DI vs 556 Piston and 6.8 DI vs whatever for 6.8 Piston. Sounds too simple and probably is, but it is a start!!! Anyway Harrison would be able to use the 556 Piston barrel extension for the new 6.8 LMT piston he would build for me. Just some thinking outside the box!!!
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Since the 18 inch barrel has a carbine gas system I figured it was a perfect reason to cut it down to a carbine length barrel.

I had mine cut down to 14.5 inches and had a Vortex pinned on by ADCO.
Then reamed the chamber with a Michiguns reamer and it now will handle SSA combat loads.
It still took an H3 buffer and heavy spring to get it to eject to 3 oclock.
Next I will try a F/A carrier to see if I can get it closer to 4 oclock.

:cool:
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BillBond said:
Since the 18 inch barrel has a carbine gas system I figured it was a perfect reason to cut it down to a carbine length barrel.

I had mine cut down to 14.5 inches and had a Vortex pinned on by ADCO.
Then reamed the chamber with a Michiguns reamer and it now will handle SSA combat loads.
It still took an H3 buffer and heavy spring to get it to eject to 3 oclock.
Next I will try a F/A carrier to see if I can get it closer to 4 oclock.

:cool:
Click to expand...
I'm using the H3 buffer, SSS SPrings, and the LMT Enhanced carrier and it is still ejecting at the 2 O'clock position. I ordered some AA1680 Powder to see if it will help since it is a very fast powder and it should help some. When I shot the SSA 90 Gr. Sierra HP tactical Loads, it was ejecting at the 3-4 O'Clock position.
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d90king said:
Paul, do you have a date code on when the newer barrels were used? Mine was from late Jan 09, I have not tested it and would prefer to just send it back if it is problematic out of the box...

Is there any word on LMT upgrading barrels anytime soon?
Click to expand...
You still have the older one. LMT Still has some of the current ones in stock, so after they sell these off, then the next ones will have the proper gas port size. It will be at least a month or so before they get the new ones.
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paulosantos said:
You still have the older one. LMT Still has some of the current ones in stock, so after they sell these off, then the next ones will have the proper gas port size. It will be at least a month or so before they get the new ones.
Click to expand...
Thank you for the heads up. Do you think they would be willing to exchange a unfired barrel for the new one?

Is there any word if they will be going to a 1/11 barrel in the future?
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d90king said:
Thank you for the heads up. Do you think they would be willing to exchange a unfired barrel for the new one?

Is there any word if they will be going to a 1/11 barrel in the future?
Click to expand...
They will most likely exchange it, but who knows when the new ones will be available. I don't think they will be changing to the 1:11" twist anytime soon.
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paulosantos said:
They will most likely exchange it, but who knows when the new ones will be available. I don't think they will be changing to the 1:11" twist anytime soon.
Click to expand...
Do you think the new barrel will be worth having? Maybe I should I just convert the MRP to a .556 barrel???? I would hate to have to do that because I already have a MRP in .556...
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d90king said:
Do you think the new barrel will be worth having? Maybe I should I just convert the MRP to a .556 barrel???? I would hate to have to do that because I already have a MRP in .556...
Click to expand...
Their 6.8SPC barrels are actually good shooting barrel, but you have to stick with the lower pressure rounds and most of them are over-gassed. If you have one that isn't over-gassed and get it converted to the SPCII Chamber, it will be a "good" barrel, but not as good as the 1:11"/4-Groove/SPCIIChambered barrels. It is up to you. I'm happy with mine FOR NOW. I'd at least try the one you have and see how it shoots.
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Equalizer_2
For the DI MRPs that are over gassed couldn't you use an adjustable gas block? Brownell's has them for $70-$80.

Just a question from someone that knows very little.
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Equalizer_2 said:
For the DI MRPs that are over gassed couldn't you use an adjustable gas block?
Click to expand...
Don't think it would work because the MRP gas tube is straight...

:cool:
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T
The MRPs need a special gas block and they do not have enough room for a typical adjustment valve to fit in there. Easier woudl be a adj gas tube. That stil take might a bit of tweaking but is doable. There are other ways to fix this as well. You can pin the old gas port closed and redrill the port or if still 16" drill it at the middy.
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