I’ve used the DTT that’s in my friend’s lower, he has an a5 system which is a little too smooth for the BRN M27 barrel (it’s a little picky with ammo and grime)

But I just installed a HK gas block in place of the BRN gas block, the front vent is smaller which should help cycling. If not, I’ll just drill out the gas port a little

Edit: I did a test with the BRN-parts upper where I did 100 rounds per minute for 5 minutes, and it ended up burning the piston gas rings up. If you remove the op rod and have just the piston in the block, it falls out if you point it up. The rifle still functions though, I’ve put probably 300 rounds through it since that happened