I feel like I am beating my head against a wall with this thing.

I've sent it back to LaRue Tactical once already, but it returned still having the same issues, albeit they occur less frequently.

Here is a summary of what was going on before I sent it back to the factory:

After changing the barrel on my 7.62 PredatOBR from a 16" to a 20", and changing from a SureFire Flash Hider to a LaRue Tranquilo Muzzle Brake, it is short stroking. Sometimes the bolt doesn't come far enough back to pick up a round, sometimes it picks up a round, but doesn't chamber. It will not lock back on the last round.
I have shot it with the gas block in the un-suppressed and supressed position. The suppressed position predictably made the problem worse, with the bolt often not cycling at all.
I shot it with both the factory LaRue magazines and M3 20 rd Pmags, two of each. The Pmags preformed slightly worse than the factory mags, but the problem was present with both.
It has the factory buffer tube, factory H2 buffer, and factory red spring. The barrel nut is torqued down properly and everything seems installed properly.
The gun and BCG had about 650 rounds on them before adding the 20" barrel. I shot about 80 rounds of federal GMM 175gr and 100 rounds of federal XM80CL. The problem was about the same between the different loads.

The action (BCG, buffer, spring, & trigger) are all bone stock from the factory.

It does have a Phase 5 extended bolt release, but everything functioned fine until the barrel was changed and the muzzle brake was added.

I was instructed to send the rifle back by LaRue customer service for troubleshooting.


Fast forward a couple months to today.

I have the rifle back.  LaRue put a new BCG in the gun and cleaned it up really nice.  I take care of my weapons, but they sent it back looking like a brand new gun.  They also swapped out the used mags I sent in and sent it with brand new magazines.
They said that they ran through all the ammo I sent them and tried some of their own and couldn't get it to malfunction as I described.

I went to the range to give it a try, and started by firing suppressed.  My LaRue M308 Tranquilo suppressor recently came in, so I started with that.

On the PredatOBR's "suppressed" setting, I experienced a couple failures to feed on the first magazine.  I decided to switch it over to the "unsuppressed" setting, and once I did, it ran fine (That's with the can attached, and the gas set to unsuppressed---technically that's incorrect).

Intrigued by this, I unscrewed the suppressor and tried a few rounds unsuppressed.
I chambered a round, sighted, squeezed, and *bang*.  It fires.  I sight in and squeeze the trigger a second time.... *click* ... nothing.

The bolt didn't strip another round off.  I ran through the rest of the magazine, and the problem continued every few rounds.  It seemed most pronounced when the magazine was full, but would continue at seemingly random times.

Is it the buffer/spring? Is it the gas system?  I have no idea...

Just to recap, I did not experience ANY of these issues prior to adding the muzzle brake and going back and forth between the 16" & 20" barrel.

I am not having a "hurrdurr I'm done with LaRue" moment.  They've treated me well through the whole ordeal with courtesy and professionalism.  
I have a LaRue 5.56 Stealth SBR that runs like a clock.  It's an absolute pig.  It runs any ammo I put through it, suppressed and unsuppressed.

This problem is only present in the .308 rifle.

I am going to give LaRue another call, but if I can't get a hard fix, I'm seriously considering removing the muzzle brake, replacing the factory A2 flash hider and dumping it for a KAC SR-25 or LMT MWS.

Any input is appreciated.




ETA:  LaRue came through!


I got off the phone with LaRue, and they are going to exchange the rifle.

After running through a LONG check list of how the gun is set up and what it's doing, they're going to replace it.  

Mark LaRue got involved, and I'm happy to say that he and his staff really came through on this one.  I've been trying to get this thing to work for almost 3 months now, and it was starting to feel pretty hopeless.  

I'm extremely satisfied with how they handled the situation.

IIRC, if the red spring doesn't work, step one is to switch to the white spring.  If that doesn't work, I'd try a lighter buffer.  I have a tOBR 20" factory and have no issues suppressed or unsuppressed, I can pull it when I get home and look at the spring.buffer combo.

BTW - I'm assuming your shooting quality ammo.

Shooting both Federal 175gr Gold Medal Match amd Federal XM80CL.

I appreciate it.

Definitely a gas and/ir buffer issue. I've seen this tons if times on AR15s and other 308 ARs including AR10s.

My guess would be too heavy of a buffer/spring combo. That's one thing i didn't like about the LaRue design, was no rifle length buffer system, just the spacer on their carbine. If they have one, I'm unaware.

I bet the gas port on the 20" isn't enough, plus you have the heavier spring or buffer in. Like above said, try a lighter spring and buffer. I wouldn't give up on it yet.

When you sent it in, did you send the whole rifle, or just the upper?

The whole rifle was sent back.  

I will call LaRue, but regardless of what they say, I'll try some different buffers/springs before sending it back.  I really don't want my rifle gone for another couple weeks if I can avoid it.

Boy that sure sounds like a gas issue. If I had to diagnose, I'd probably start by pulling the gas block off & check the size and/or alignment of the holes, or possibly replace the whole thing altogether. After that would be replacing the gas tube itself (I assume this is a DI rifle) in case something got blown into it when it was new.

Barring a fix with all that, I'd then go down the line to the buffer/spring combo as already suggested above. I find it hard to believe that changing a simple muzzle device would have caused that much of an issue, seems coincidental.

Best of luck, they're still great rifles.

Wondering who installed the gas block on the new barrel?

I would check the alignment of the gas port to the gas block and make sure there are no obstructions.


ETA:  While I also have a Phase 5 on my LaRue 762, and it works fine, the Phase 5 could be causing your LRBHO issue.

Quick question and please excuse me as i dont know much about Larue rifles. Did the gas tube length change going from a 16 to 20 in. Bbl?

2.5 years and 11 posts?   Nice to see ya' Rock Star!

The gas block came installed on the barrel.  

http://www.larue.com/762-predatobr-barrel-cartridge

The gas tube on the 20" is rifle length and the one on the 16" is mid length.

Seems from what you are saying the gun needs a little more gas.maybe a hotter load?
.
You could also ge with a lighter spring.
The only other option I can think of is to inlarge the gas ports slightly to let more gas into the action.the larue switch block uses two ports as I remember so you may have to enlarge them both,somthing i would let the mothership do if it were me.

Pete

When it does fire, where does the brass eject to?  2 o'clock, 4 o'clock?

Don't think this is an issue but are you running the bcg wet with CLP?  On my Tar Heavy, I had to run it good and wet for the first few hundred rounds to break in.

I spoke with a LaRue rep yesterday, and I've got a list of things to go do on the range and observe.  
From there, I'll get back in touch with LaRue and see where to go from there.

What exactly do they want you to try? Given your symptoms, it's obviously undergassed for the current setup. There's not a whole lot of things to really check. Either you have an issue in the gas system itself (gas port too small, misaligned block, bad gas block entirely, bad tube, or gas key loose) or the buffer/spring combo is just too heavy. Change the spring and buffer and you'll likely be just fine.

I told them I'd like to avoid sending it back to the factory again if possible.  

I am going to try firing only one round in the magazine to test the bolt locking back.  I'm going to swap the red spring for a white spring, I'm going to remove the phase 5 lever and reinstall the factory bolt release, and take notes on what the rifle is doing.

These are a variety of steps we discussed to potentially avoid me having to send the rifle back again.  I will likely have to wait until friday or saturday to get out and run the tests, and I'll report back.

Once you change the bolt catch back to factory, I'd suggest you add the buffer into the mix.  I got home really late last evening so I couldn't check mine, but I suspect your 16" included the H2 buffer to compensate for the gas port pressure on that carbine length gas system. I believe my factory 20" has a regular weight buffer.  White spring, then buffer. You may also have to move back to the red spring with the lighter buffer. Good luck.

I'm on the page with everyone else. Lighter buffer and spring.

Checked my factory 20", it has a regular buffer.

Thanks.  Do you by chance have a scale to weigh it?

What about your spring?

Is it red? White?  Something else?


Thanks again.

Check the gas key. Look for leakage around the key. Then proceed to the springs and buffer. You are correct in only putting one round at a time in the mag while testing.

I'll strip it down and weigh the buffer tonight.

I have the red spring and normal weight buffer.

Thank you.

Well.... that doesn't bode well for me, because I have the same buffer/spring combo.

I'll still try some other weights/spring types, but this has definitely got me irritated.

ETA:  Defender3, are you using a rifle length buffer & tube?
I'm using a 7.62 carbine buffer & tube.

Rifle length buffer and tube, and an AR10 rifle length spring.  

I thought you said you have an H2 buffer?

Sorry, yes, it's a H2 buffer in a 7.62 *carbine* tube.

Back from the range.

Switched to Sprinco White Spring

Shooting with the gas block set to suppressed, with the Tranquilo attached:

Magazine 1  
20 single shots fired (as in, loading one round at a time into the magazine), 12 failures to lock back, 2 complete failures to eject (empty shell case still in chamber).

Magazine 2
20 single shots fired (again, loading one round at a time into the magazine), 10 failures to lock back, 1 complete failure to eject.

Both magazines filled to capacity would have a failure to feed every 2-4 rounds.  I shot both magazines this way twice.


Shooting with the gas block set to **unsuppressed**, with the Tranquilo attached:

All shots fired, no malfunctions


Shooting with the gas block set to un suppressed, with **no** Tranquilo attached:

10 single shots fired (again, loading one round at a time into the magazine), 10 failures to lock back on last round.



I contacted LaRue again, they are ready to take the rifle back again.  I said I want to try one more thing (I just didn't have time to today); I'm going to change out the 7.62 carbine buffer tube for a rifle length buffer tube, rifle buffer, and Sprinco green spring.

If that doesn't work, it's going back to the factory and we'll see where we go from there.

Persistence will pay off in the end.

FWIW, I'd suggest you test to the lowest level, no suppressor until you diagnose and get it working.

Keep a log that can be sent back with the rifle, but, just my opinion, this isn't a LaRue issue, I think it's the buffer/spring combo from the rifle originally being a carbine versus what it is now, a rifle length gas system.

We know it worked with the 16" barrel and carbine length gas system, carbine length spring and H2 buffer.  If it's now short stroking with the 20" rifle length gas system, but with the same spring and buffer, we have a good place to start.

1.  Reinstall the 16" and test for function with the same loads.
2.  Install the 20" and test with the same loads.  If it's short stroking, replace with the white spring.
3.  Test the white spring, if it's still short-stroking, replace the H2 with a normal weight buffer and the red spring.
4.  Test with the normal weight buffer and red spring, if it's short-stroking, replace the red spring with the white spring and retest.
5.  If it's still short stroking, then replace the carbine buffer with a rifle length buffer, rifle length spring and normal weight buffer.
6.  Retest and repeat the steps with all possible spring and buffer combos.

FWIW - If you have the ability, ditch all the testing and move directly to removing the carbine system and go directly to the rifle system to do your tests.  Ensure you have a rifle length spring and rifle buffer.

I am leaning toward preferring the fixed, rifle stock anyway with the longer 20" barrel+suppressor.

I will be adding the rifle stock (Magpul PRS), rifle tube, buffer & green spring in the next couple days and test again.

I honestly don't want to waste anymore ammo messing around with the carbine stock system.

I will report back when done.

If I read your test results I don't think you said you changed the buffer.  That's the first thing to try.  An H2 is supposed to slow everything down.

I didn't because I don't have another carbine-sized buffer on hand.  I did try the red and white sprinco springs.


Today I went to the range and this time tried a rifle length tube with an AR10 buffer and sprinco green spring.

Same set of malfunctions:  lots of failures to feed, a few failures to eject, all with the gas block set to suprressed and the tranquilo attached.

Isn't the tranquilo supposed to have less back pressure/blowback? Could that be the cause?

Have you checked to see if the gb is clogged?

Pop the pin out, take out one tungsten weight and reassemble less that one weight.  Test fire and report back.

Order some tungsten weights and play with that yourself. Knock out the roll pin to swap them out.

This video maybe insightful for you on buffer weights:

Very interesting info.  Thanks for that.

I got off the phone with LaRue, and they are going to exchange the rifle.

After running through a LONG check list of how the gun is set up and what it's doing, they're going to replace it.  

Mark LaRue got involved, and I'm happy to say that he and his staff really came through on this one.  I've been trying to get this thing to work for almost 3 months now, and it was starting to feel pretty hopeless.  

I'm extremely satisfied with how they handled the situation.

Please update when you receive the replacement and provide us with an update on if it works better for you.

I will.

I anticipate it will be a few weeks, but I have this thread in my subscriptions and will come back to it.

seriously? Holy shit.


I'm not saying you have done anything wrong so don't think that but damn. They are swapping out a rifle you modified (yes I know you used their stuff to do it), never even crossed my mind they would do that.

That is awesome

I wonder if they are going to scrap it or find out why it's acting stupid.

The PredatOBR was designed and marketed as being something that could have user-changeable barrels, so in that aspect I wouldn't go so far as to say I "modified" it.

"Reconfigured" would be a more accurate description given the context.


The gentleman at LaRue said they will likely have their engineering department take a look at it, but when they will isn't clear.

He said they don't really have a policy on this sort of thing, and handle this stuff on a case-by-case basis.  But basically it came down to the fact I was using their product, and that product wasn't performing correctly.

They more than made it right.  

I am very grateful to be able to do business with such a company.

you know what I mean, I'm not busting your balls

I dont think I'd consider utilizing one of the key features of the rifle (user changeable barrels) with OEM parts to be modified. Glad to see they're helping you out OP!

It's all good.  I'm just glad it got taken care of.

They said this one will be tested and verified with a Tranquilo suppressor before it leaves the factory.

Here's to hoping the new rifle performs properly.

Received the new OBR today.

I have to attach all my widgets (optic, PRS stock, ambi safety, iron sights, bipod, sling mounts)  and then take it to the range.

I likely won't have time for another week or two, but I'll keep everyone posted once I make it out there.

Hopefully it's so undergassed that you aren't beating the rifle up by shooting it suppressed in the unsupressed setting.

I wouldn't do that. Doesn't need exponential wear.

Finally got to the range.

I only had an hour to shoot, so I put 75 rounds through the gun.

Everything is performing flawlessly.

I didn't do my best on the groups because I was in a rush, but I am supremely confident in this rifle.

I shot it suppressed, unsuppressed, with the scope, and with irons.  I know it needs more rounds on it before dubbing it "100%", but these early indicators give me a great feeling about it.  Absolutely zero weird gas/feeding issues.

I'm immensely satisfied and thankful for how LaRue handled the whole situation.

that's awesome. I'd love to know the root cause of the problem with your old gun.

Glad to here!