Posted: 6/22/2011 8:13:20 PM EDT
Last week we had a fight stopper of a failure for the MRP piston operated upper. During a night training session, we had went through approximately 200 - 250 rounds of FEDERAL LAKE CITY M855 (SS109) when all of a sudden the LMT became a single shot rifle. No shells were extracted during the firing process. Upon inspection, I noticed that the piston rod was snapped in half.
Training session was effective over for the night. Took our ball and went home. Upon arriving home, we attempted to disassemble the piston assembly. The piston could not be removed from the barrel. I had to remove the entire barrel from the upper in order to beat the portion going through the gas block out of the weapon. The piston was snapped where the piston steps up and the spring is retained. The buldged area of the piston is normal. It's a small step to help retain the spring. At some point LMT added this to their pistons. 
A call was placed to LMT in the morning. Due to modifications to the barrel, LMT told us to go fuck ourselves and they wouldn't even listen to the issue or try to diagnose what was wrong. Modifications are as follows and were performed by ADCO. Barrel profile cut to .625" fore and aft of gas block. Barrel Shortened to 14.5" and a PWS Comp pinned in place. Gas port opened to shortened specification. Not really concerned about the warranty aspect. We purchased two replacement pistons for $30 dollars each. I'm used to getting the finger from companies after they've gotten your money. The pistons arrived today, and we went to reinstall the unit with the new piston and we found that the gas block itself has begun to separate at the rear collar. This was noticed when reinserting the piston, it was not aligning with the guide near the chamber of the barrel. This is what caused the piston to break. 
Wah, wah waaaah... We have another LMT MRP piston op barrel with the exact same modifications except I'm using a Vortex instead of the PWS. The gas ports were opened to the same diameter by ADCO. Mine has probably 3500 rounds through it, while his was just under a 1000. All factory ammunition has been used. This one is more of a cluster-fuck because once a flash suppressor is pinned on, you can't just slip the gas block over the brake. So another call has been placed to LMT today. Different tech support who didn't just give a FOAD answer. Asked for pictures, and will consult with the owner tomorrow. My guess is it'll be another middle finger, and a price for a new gas block. We'll see though. Not really bitching per se, just letting everyone know what your fate might be if you decide to modify anything. The issue could be a simple metallurgical problem. Perhaps there was a bad round somewhere? Nothing was noticed from any of the collected brass. d;']Dave[/span] |
| My GUESS would be a High pressure round, You can see where the gas block broke its right in the corner where there is little to no radius. Im guessing that popped first, which is why the piston snapped in half. As always, modifiicaton to parts does void wartrrantys though (LMT included) |
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Parts break, shit happens. I've been googling looking for other examples of this, and cant find anything. My guess is a hot round and faulty gas block. Its understandable that LMT isnt being very cooperative. play the modification game, pay the modification price. That's why I quit playing with cars. I only wish VW would have warrantied my VR6 after I installed the T04E turbo 
I would guess the barrel is trash now. I'm sure LMT uses a special jig to install the gas block at the proper location, which only they have. LMT probably wont want to attempt to pin on a new block to a barrel that already has groove from a previous block/pin. |
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No big worries if they won't warranty anything. I'm not all that concerned with that. I'm just looking to correct the problem so that the rifle is reliable. Mainly, I'm interested in hearing if the gas port is out of spec. Hopefully they'll just sell us a gas block to replace the fucked up one.
We went through all the brass that was fired during the session. None seemed to have signs of overpressure. Extraction seemed pretty consistent at about 3 o'clock. The lower was running a Spikes ST-T2 buffer and a Wolff XP Mainspring. Yep, modding shit can cause unforeseen problems. I never heard of this problem before either. |
| Got off the phone with LMT. They're issuing a letter that hasn't arrived yet. They said that the gas port was 48% larger than maximum allowable specification? So basically the barrel is trashed. Too large of a gas port allowed it to batter the gas block until it deformed and broke. |
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Quoted:
Got off the phone with LMT. They're issuing a letter that hasn't arrived yet. They said that the gas port was 48% larger than maximum allowable specification? So basically the barrel is trashed. Too large of a gas port allowed it to batter the gas block until it deformed and broke. Sorry, but I don't believe that to be true at all. We dont open any gas ports 48%; taking a DI from 16" to 10.5" isnt even a 48% increase. As said above, we dont open gas ports going from 16" to 14.5". Maybe LMT made the port too big originally(we seen LMT barrels that they did not drill ports at all, so its possible), but that still shouldn't cause a break. We'll have to start measuring the port sizes on new barrels that come in and see what we get for reference. If that is possible, that is a big reason to stick with DI. I've never seen a broken gas block, or gas tube on a DI AR. In regards of over gassing DI ARs - I've seen almost 48% size variance in gas ports in barrels of the same length from different manufacturers. |