Anyone use a COLT Sporter or Match Lower with a Grendel

[LRRPF52]

Biggest piece of information missing is the ammunition.

What ammo are you shooting?

I have built and test-fired quite a few 20” 6.5 Grendels, including ones with AA, Satern, Lilja, Bartlein, and some other barrels I’m not thinking of right now.

All have had .094” ports, which is no different than .096” in practice. (The 3rd decimal is in the weeds.)

I have tested with 5.2oz AR-15 rifle/Rifle RET/Rifle spring, A5/A5 RET/longer spring, H2 buffer/Carbine RET/Carbine Spring, H Carbine/Carbine, and 2.9oz carbine buffers.

All of them fed, chambered, fired, extracted, ejected, and cycled through the entire cycle of operations repeatedly without issue.

The 2.9 oz carbine buffer set-ups seemed to have a little more 3 o’clock ejection and felt faster with cyclic rate, but not too much difference.

H2, A5, and Rifle set-ups seemed to work more ideally.

If your ammo is a light load, that will do it with the RLGS and .09x” port. 90gr TNT factory ammo even is hard to get to run in RLGS 20”.

107gr SMK not pushed hard enough could also cause short-stroking/failure to lock on LRHO.

Another possibility is an inefficient bolt carrier with loose fit to the bolt’s gas rings.

Do the bolt gas ring tests, both of them, and see if it collapses.

1st test is fully assembled bolt, bolt extended, set face down on flat surface. If it collapses, you have a loose carrier/bolt flange and gas ring set-up.

Next test is just the bolt in the carrier without the cam pin, firing pin, and FPRP.

Not all carriers are created equally, and the 3 bore inner diameters are critical for optimum gas pressure containment for the operation of the system: