AR 9mm Feeding Woes

[shadowrider]

Anybody had any luck with with JHP ammo? Here's my build:

Zombie Defense lower with M4 cuts.
CMMG mil spec LPK
KAK Gen2 pistol tube w/Sig brace
Wilson Arms 7" barrel
CMMG enhanced ramped bolt
Hahn block (inserted from below)
Metalform Mags
Wolff extra power carbine spring
Rock River 9mm buffer
Using quarters for a spacer but they seem to have no effect on feeding, same problem with no spacer.

Using Remington 115 JHP factory is a complete no-go. 3 in 5 rounds will nose dive and the stout spring pushes the bullet back so far it's a guaranteed kaboom, that's if it will even chamber because the case is so bulged. Running basically any FMJ or even hard cast lead RN 125 grain bullet handloads and the gun runs like a raped ape, I haven't had a failure to feed yet no matter how fast I crank them off. It's like the energizer bunny with RN. I figured that the Remington JHP would run if any HP was going to because it's HP cavity is so small and the profile is very close to a RN profile. I'm kinda stumped. Are JHPs just not going to run? Hopefully this week I get to try some Speer Gold Dots and Hornady Critical Duty but I'm not holding out a lot of hope.

[jack crab]

I am also using a Hahn bottom block on mine. Out of a half dozen or so different loads run through the rifle, both HPs and FMJs, 115 and 147 gr, and regular and subsonic, it hates Federal American Eagle 147gr FMJ subs. The AE is a truncated cone profile while all the others are are rounded in some form or another. However, the AE runs great in pistols.

[Mad Machinist]

Go back to standard spring and loose the quarters......establish a base line...the extra power spring can increase bolt velocity coming forward that it make the round nosedive causing the issues you have.........

[HardToHandle]

Is the Hahn block sitting too low or the bolt stripping rounds with more contact on the top of the case?
Also would want to reduce that bolt spring pressure... Never seen that kind of force on a 9mm to batter cases.

Not pertinent to the OP, but my LWD lower has been perfect with HPs.

[U&A]

I have a CMMG MK9 PDW in the 9MM pistol version. make note that I do not have many round through it yet so it will get better over time but this is what Iv noticed so far.

FMJ's

I have noticed that it will run 100% on any FMJ that is 124gr or heavier. I have only found 2 brands of 115gr FMJ so far (and have just started shooting it) that it doesn't run 100% with and that is Pierce 115gr FMJ ammo (http://www.piercemunitions.com/ ) and Blazer 115gr FMJ aluminum. With the pierce I get a very hard jam on every other round almost. With the blazer aluminum I get a jam maybe 1 out of 30. With both rounds it is because it does not have enough power to cycle the bolt all the way back. I have never had a problem with the same "lot" of ammo in any of my handguns.

JHP's

I have not found a JHP that will not run good in the gun. granted, I have not run any of the lower end JHP yet and I also have not shot a JHP that was lighter than 124gr. the "carry" ammo that I have in it now is the 135gr Critical duty +P. I have a few hundred of that through it and have not had an issue yet. I think the hotter (or heavier) the round the better it will run for you. at least that is how mine is running.

One thing I tried is to take my shoulder out of the equation. Since my shoulder is absorbing some of the recoil I fired off a few round with the sig brace firmly butted up against the front of a heavy shooting bench. That made the difference that I was looking for witch concluded that the gun like hotter or heavier rounds.

sorry for the blabbering and hope I helped at least a little.

Edit: I also polished the odd looking feed ramp that they put on these guns. I don't know if it made any difference buy it cant hurt.

[shadowrider]

Thanks for the replies. I still haven't got to fire any other HP loads but I do have somewhat of an update.

Mad Machinist, I'll keep your suggestion in mind as there might be something to it. Still to be determined.

HardToHandle, the Hahn block appears to fit like a glove with very little up/down play when captured by the mag release. All appears to be kosher there and it's staying clamped securley too.

U&A may be onto something with bullet weight. I have been able to run several hundred rounds of my USPSA minor 147 grain TC cast lead load through it and it runs just as good as the 125 grain load. As in I have yet to have a failure of any kind. If it had a giggle switch, I could run mag dump after mag dump with them. So I'm thinking that the 115 load just didn't have enough juice to run. Both of these cast bullet loads, but especially the 147 just dribble the brass over the side of my 3 gun pistol. I had an instructor ask what they were and he said they sounded like "bunny farts", but they run this AR perfectly, so I think it's either a bullet weight or OAL thing at this point. I was sure the TC profile "gamer load" would make it choke, but it's the Energizer Bunny with them.