LowSpeedHighDrag

I use both a JP GMR-13 with a 16" barrel and another AR-15 with a TACCOM upper (5.25" barrel), and both Vihtavuori N320 and N350 powder. My results mirror yours using the slow powder. It works for a short barrel, but not for a longer one. Switching to the N350 for the JP rifle, I get much better results, with a vastly lower SD using a slow burning powder rather than the fast burning one.

Or needed to. ?

Could I accomplish the same thing by just putting a "shock buffer" on the rear cushion, under the head and, obviously, inside the buffer itself? Sort of like a 1911 or Glock shock buffer fitted to the end of the guide rod... FWIW, I actually like using the 2 stage setup, as I can tune it to the load I'm using to get just the right amount of resistance. Oh, and nice upper, BTW.

I'll second your comment on the circle/dot reticle. Makes fast shooting much easier, particularly for steel targets.

While you're at it, you might want to try switching the 510c to the center dot only and see how you like that. Press the minus button for 3 seconds and the reticle switches between circle dot and a dot only.

Interesting. I was running a Taccom upper with the Taccom 3 stage buffer, using a 115 gr bullet at around 132 PF, and found there was *too* much dampening. Didn't have enough force to reliably eject the spent case. Went back to the original 2 stage setup for the buffer (mine was before they started selling the 3 stage), set the adjustment to around the middle of pre-tension, and now it runs fine.

Excellent read. Thanks for posting.

Hmmm. May need to go back and retest 90 and 115 gr heads with HS6... Oh, and forgot to ask, what barrel length are you using?

Where did you get the magwell? I couldn't find it using a web search...

Thanks, I'll consider it part of "make ready."

Couldn't find this in the rules. What is the start condition for a laser or light, on or off?

Not trying to argue the point, just asking what's your reasoning?

I ran a red 510c at a Steel Challenge match this weekend, and had no problem with brightness in full sun. OTOH, one of the 510c's that I bought came with a battery that was severely run down, and needed to be replaced. That's the first thing I suggest trying. Also, as mentioned above, make sure you're running in battery mode and not solar/auto mode. Press and hold the "+" key for 3 seconds to switch between them.

I have the older model GMR-13, and it seems to like the 124 gr. heads quite well. My earlier testing seemed to favor the recoil using a slower burning powder (N350), but I'm going to go back and retest the various loads this week.

Interesting. What if the KNS pins had the screws set so that they weren't tight against the receiver, so the pins could still rotate? Would that eliminate the increase in pull weight?

Sorry, what kind of difference?

I'd like to see the load you use. Please post it here. TIA

I wouldn't show up with a bipod.

I have the JP 14.5 barrel + comp, and I like it, although I have no idea how effective the comp itself is because I can't remove it to test.

I picked up a Taccom ULW upper for the GMR-13, just for Steel Challenge. Wow, it's a lot lighter. The stock upper would probably be fine for USPSA, but is definitely going to slow you down when you need to make fast transitions. Looks like I'll have to see if I can get the special barrel nut tool from JP...

Sorry, are you saying that the JP barrel nut is non-standard? If so, which other handguards would be compatible?

Taccom makes a G10 handguard at 11.5" and a carbon fiber one at 14"

Thanks, I'll give it a try. After using the Taccom upper, I miss having a really light handguard.

I took a look at my GMR-13 upper to see if I could remove the handguard myself. It looks like there are screws accessible through the slots in the handguard. Would these screws need heat applied also?