Starting  to pull whats left of my hair out, had a .308 with an un-threaded barrel, it never ever once had an issue  - took barrel out and got it threaded , put brake on - reassembled (and I've done loads) same gasblock same tube same everything. here started my issue. Rife acted seriously over gassed (yep just FGM 168gr) only holding bolt back on the first couple of rounds - then overriding the catch on the next couple - said @#$%^&@(@ - put back in range bag - went home and took apart, checked everything again - noticed serious scarring on the BHO catch and a "chunk" out of the bolt.
Catch:


Bolt:



What I have tried:

Its a les baer barrel nonstandard size gas block , so left original gas block on, replaced catch and used  JP 308 bolt after checking headspace was good  - used an mgi  adjustable gas tube , which provided some relief but any more than but was back to misbehaving by round 25, stopped , changed out original buffer for a heavy JP silent capture spring assembly, went down to the lightest spring (this reduced recoil) but did not fix the bolt hold open issue , added a bolt carrier with the sun devil adjustable key on it , tweaked ithe gas a bit and it started to hold open again , worked fine for approx 30 rounds then SOSDD again, stopped and the following pictures are where I am at :

New Bolt Catch:




Bolt :

 
Being that it ran like a raped ape before I got the barrel threaded - I am running out of ideas - 
Any suggestions welcome.

Thanks

just curious, Magpul mags?  if so, it's been posted about how the bolt catch doesn't get elevated very high on LRBHO, there's room for Dremel improvement, on the mag follower, but no idea why it worked before and not now, unless it was just waiting, slowly chipping away, and now it's gone (the engagement).

Nope KAC mags for that very reason

I think you'd want a heavier spring.  Call JP, Theyve always been extremely helpful when I am using their components and need help on a recoil system issue.

The initial chamber of the brake is likely causing enough back pressure to increase your cyclic rate, or something else has happened with the gas system and recoil system to allow excessive cyclic rate.

What brake is it?

Is this a 24" Les Baer?

Details on the buffer, spring and buffer tube combo?

It is a 20" Les Baer - the brake is a Thunderbeast CB (threaded on the outside for a Ultra 9 suppressor, I have not used the suppressor yet due to the issue I am having) 

Buffer tube is the original rifle length tube , fitted with the original magpul prs stock ( the one with the longer front piece for large frame clearance) . Buffer is JPSCS H2 version , spring is the lightest one out of the pack of three - and I have tried them all - goes from sharpish cycling to OK , just rides over the catch and damages things. Note , I have also tried the original spring buffer combo, which produces approximately the same combo as the JPSCS with the heavy spring, so not good.

   

I would look at an adjustable gas block, especially if you plan to run a suppressor in the future. If you're getting too much gas now, you'll be way over the top with a can in place.

Been there done that - their suggestion was use the lightest spring - which I have tried . Heavy spring increases bolt carrier speed on return to battery

I have to ask, only because I've seen it before, you ARE using the correct length buffer and space, right?
If you think you're still overgassed i would suggest trying a RCA adjustable gas key to tame it down, it did wonders for my 16" LR308 build.

The Sun Devil key does the same thing.

Ah, must have skipped over that part

Insert each empty mag in the lower and make sure the bolt catch is fully engaged.

Get a BHO from CMMG.  The BHO you have is hitting your upper and not getting up in front of the bolt like it should.

That's a possibility if something is out of spec.

This is what is hurting my head - the original BHO in the op was never touched / removed nada, only when the chunk got take out of it did I change it ...and  wait for it , I used a CMMG BHO which when looking at the lower with a mag in, is higher that the original BHO measured and plenty strong enough to take a chunk out of a bolt lug - can a spot of tig fix the bolt, I wonder ?  , I am beginning to suspect the brake has raised the gas pressure ( as suggested by LPPR52) such a large degree, that I should take the brake off and then see where I am at, also the entire rifle never had a threaded barrel to start with so I could be farting against thunder here especially with the non standard gas block  - thinking I have changed so many parts I am going nuts.

It's not a bad idea to go back to your last known good configuration and change one part at a time to figure things out..

So went I back to basics - surprise surprise, in the original configuration with the original BHO catch , bolt engagement is minimal, to the point about increased back pressure, potentially enough increase in cyclic rate to ride over the BHO catch,

Original config


And to @touchracing - absolutely hitting the upper always did , just never noticed , so I relieved the BHO until  it fit without interference on the upper ,

CMMG BHO relieved



and now it has a decent lock on the bolt and functions

Glad you figured it out and fixed it.  Never fun to have one that doesn't work quite right and causes other issues as well.

I was wondering (last night, after reading your posts) about the bolt catch since it seemed to barely be contacting, but only because I had an AR15 one time that had issues with the bolt catch spring and detent dragging in the hole in the lower.  I got it all put together and the bolt catch would stick/hang in the up position after being very hard to move into the up position.  Had to take it all apart again and use a drill to open of the hole in the frame that the spring/detent move in.

Feels good to figure things out and fix them, doesn't it.  Also feels good to have a rifle you can depend on again.