New Recce 5 on a factory KAC 11.5 MOD2 upper. XM193, KAC H2 buffer. Going to try different mags tomorrow, I was using two old pmags. Anything else I should check? Seems odd for a 11.5" with a can to short stroke.

UPDATE

Still at the range but on a break posting results. I took four types of new mags to test. Factory SR-15 Knights 30, Lancer Warfighter 30, PMAG30 Gen3 and PMAG30 Gen 2. Each mag had three trials of three rounds. All mags passed by locking the bolt back after the final round with the exception of the Magpul Gen2 PMAG30. The Gen2's failed all three trials. Both mags from yesterday were Gen2 PMAG30's.

I also had a range officer video the ejection pattern but he did not get a good angle. The black rifle rest is just between 1&2 O'Clock of the ejection port. You can see a couple of the rounds strike the black rifle rest. The rifle is ejecting brass consistantly in the 2 O'Clock direction. No real observations of majorly deformed brass or anything out of the norm. Other than that she is good to go. Thanks for helping out and with the suggestions as always.

Is it locking back and functioning well unsuppressed?

Might be too much gas and too fast of a cyclic rate suppressed if the rifle is working correctly unsuppressed.

JPK

It is functioning perfect unsuppressed, yeah I'm Hopeing it is mags or a different buffer will fix. Changing the gas system on a KAC upper more or less the new mod2 gas system they have in it would be a bummer

I did a little Googling and it seems some guys are finding pretty heavy buffers work best in the KAC 11.5". I'm an advocate of fixing gas problems at the source, which would be the gas block,  but I believe the KAC gas blocks are a tight press fit and pinned as well, which would make it tougher. Since they must anticipate their uppers being suppressed, I wonder why manufacturers, especially top of the line manufacturers don't just include an adjustable gas block.

Edit: A little more Googling and I sure understand why you don't want to mess with the MOD 2 gas system.

Btw, another fix if the issue is too much gas would be the Gemtech Suppressed BCG, which has a quick and easy adjustment for suppressed and unsuppressed shooting.

How's the IR Defense MK II working out for you?

JPK

Sounds overgassed.

Contact KAC, see what they say.
I'd prob go with a heavier buffer though.

No, they have a proprietary E3 bolt/extension.
Though technically a mil-spec bolt should work in the extension, it's not something I'd go experimenting with personally.

Referring to the Gemtech not being a ready fix?

That is what i figured as far as messing with the MOD2 gas system. On the gemtech side not sure how the E3 bolt would function within the carrier although from my understanding the KAC carrier itself might be to mil-spec but I really do not know. I figured try different buffers if the mag thing does not work out tomorrow. The MKII thermal is great and lots of fun. Been using it as a spotter for white tail this year.

Yes, it's not a ready fix.
KAC upper has proprietary parts.

KAC's bolt carrier is a standard milspec carrier, so there is no reason why a Gemtech SBC wouldn't work as long as one used the E3 bolt.

See original post

Definitely over gassed suppressed, but if it's running reliably you found your issue.

A rifle cannot be properly gassed unsuppressed without being over gassed suppressed. With 2:00 ejection suppressed you are near as good a compromise as you can be without some adjustment mechanism, I think. The Gemtech would be a great addition, then you can select suppressed or unsuppressed gas flow quickly and easily. But no imminent need.

Glad it worked out!

JPK

Yeah me too. The can is dedicated so I am going to try a heavier buffer and or spring to get it optimal

An important question might be, "Is the lower dedicated to that upper?"

JPK

that it is

The Gemtech SBC works fine in KAC uppers. I have used it in my Mod 1 16" upper and Mod 2 11.5" upper without any issues, although ultimately I decided to go back to the standard carrier in the KACs and I put the Gemtech SBC in my 10.5" LMT.





 

What he said. I have noticed that you may need to go down a buffer weight for reliable function though. Otherwise, I like mine a lot.