Gunsmithing Help with LMT MWS 6.5CM

[svxwilson]

I have a LMT MWS in 6.5CM that I have been breaking in and running into issues with it in regards to factroy ammo and what I consider overpressure ammo/rifle combos.

Primers are popping and getting heavy extractor pin stamps with FGMM 130Berger hybrids, Factory lapua 123 scenar has primer cratering, pierced primers, and heavy head damage from extractor and extractor pin. Hornady factory 147 eldm partially popped primers and also had heavy head damage just like other cases.

When I used my labradar on the lapua factory rounds i was getting 24" barrel velocities from a 20" factory lmt mws barrel. So I loaded up some hand loads in alpha 6.5cm lrp brass with h4350 and 123 scenars. And found that near the beginning of book min i was seeing pressure signs and getting very high velocity (fps) for the charge weight.

This perticular MWS is using a SSA-E trigger, JP Low mass High pressure BCG (checked headspace with gauges and measured fired brass and its within spec) and H2 SCS. It also has a reduced size gas port with a eztune gas tube @ .089 to accommodate the low mass bcg and scs.

Should I try to slow the bolt down to keep it in battery longer by getting either a RCA adjustable gas key for the Bolt Carrier or get another tungsten weight for the SCS and effectively make it a H3? I believe the SCS already has the heaviest spring thats red/yellow.

Thanks for your time and thoughts,
svxwilson

 

[FCS]

Full mass carrier.
Heavier buffer.
Higher K buffer spring.
Adjustable gas block or gas key.

Yes, keeping locked up longer will resolve issues.

 

[Zak Smith]

The MWS stuff is not exactly standard, but if you have too much gas, the best solution is to have less gas. 0.089 still seems very large to me. On my AR-10's, I barely crack the adjustable gas system open to have them run right. I just set up an 18" 6.5 CM (RLGS) with a Seekins block and it was probably around 1/4 turn open to run perfect, suppressed.

 

[newguy2k3v2]

If it’s a factory Lmt barrel I think you’re fighting an uphill battle with the lightened bcg and rifle length gas system. Proof’s 20” barrel is a +2 and even they recommend a full mass bcg. Also I’ve found that the Lmt dual ejector bolt almost eliminates ejector marks vs a single. I know that doesn’t really explain the velocity. You may be lucky and just have a fast barrel.

 

[Junkman768]

you could just go full LMT. Its all built to go together. If you want JP, sell the LMT and go full JP. Both are great rifles. I own an LMT MWS 6.5 24"ss and I have messed around w my buddies JP 6.5cm 22". JP is little more accurate than my LMT and shoots softer. But my LMT NEVER jams and the JP is more of a race gun. if you must continue on this path of most resistance contact Dave WIlson sure he can get it fixed.

 

[svxwilson]

Update:
I emailed BRT and they sent a .082 tube. I also got a RCA adj gas key, and another tungsten weight making it a H3. That combo helped a ton! Did one at a time just to see the progression, but ended up with all 3. It shoots significantly softer and is not destroying brass or primers any more.

I noticed the feed ramps on the 6.5CM barrel is significantly different than the 308 SS LMT barrel. Here is a pic of a new Proof 6.5CM carbon barrel with the LMT 6.5CM in the middle and the LMT 308 on the right. LMT said the different feed ramps was to help a specific berger bullet to feed.

I was having issues with bullets jaming into the left feed ramp (including Berger 130s) . Got clearance from LMT to polish the ramps with cratex and now that problem is fixed and it feeds like butter now with its mirror finish.

 

[svxwilson]

you could just go full LMT. Its all built to go together. If you want JP, sell the LMT and go full JP. Both are great rifles. I own an LMT MWS 6.5 24"ss and I have messed around w my buddies JP 6.5cm 22". JP is little more accurate than my LMT and shoots softer. But my LMT NEVER jams and the JP is more of a race gun. if you must continue on this path of most resistance contact Dave WIlson sure he can get it fixed.

Thanks for the Dave Wilson recommendation, I have herd of him before.

I have complete JPs which is part of the reason I wanted them to share parts and LMTs BCG is vaporware and very hard to find right now. So I figured I could try this experiment and see if I could get it to work.

The JPs I have run like clocks. After initial adj gas adjustment they have never malfunctioned and their brass looks like bolt gun brass.
Just had an LMT MWS lower laying around and wanted to put it to use.

In the future if and when LMT BCGs become available again I may return it to its factory settings but if it keeps running like it is now after the last update of parts it may not need it.