The symptom:  Load magazine, charge, BANG!  Pull the trigger for shot #2 = *click*
Why click?  No round is in the chamber.  No bullet stuck on the feed ramp or a stove pipe.  So, I re-charge, bang, bang, *click*

Here’s the best part: this is ONLY with an H&K Hi-Reliability magazine.  USGI = no problem.  Now I also must confess I have an MGI RRB in there as well as an IMSI spring.

The combination of ultra-stiff spring and RRB makes for tough job for the BCG to drive it back.  So I eliminated the spring and just stuck with the MGI Rate Reducing Buffer.  I shot 200 or so rounds.  And just to be sure EVERY DAMN TIME I went to the H&K mag it didn’t want to play ball.

The ONLY way the H&K wasn’t going to give me a hard time was if both the buffer and spring were back to stock.

Even having 26 rounds in the H&K didn’t help.  I would drop in a USGI with MagPul Gen2 follower loaded up to a full 30 rounds and NO PROBLEMS.  God bless those $10 USGI mags.

About all I can surmise is the fact that a USGI mag seem to be more tolerant of end-users adding heavy buffers and trying out different buffer springs.

Definitely sounds like short stroking, but I can't recall ever hearing it being a mag issue.  Interesting.

I have a 16" carbine with an H buffer that won't run with HK Mags (FTF though).  It runs fine with everything else.

Stephen

what ammo, barrel length, gas length?  the mgi, heavy spring in a 5.56 seems like overkill.  most people just run a midlength with heavy buffer.  if it ejects fully but doestnt feed, sounds like mag.  if it was short stroking, it wouldnt fully eject.  which is more beneficial, the hk mag or mgi buffer/hvy spring?

assumed hvy spring.

Quoted: what ammo, barrel length, gas length?  the mgi, heavy spring in a 5.56 seems like overkill.  most people just run a midlength with heavy buffer.  if it ejects fully but doestnt feed, sounds like mag.  if it was short stroking, it wouldnt fully eject.  which is more beneficial, the hk mag or mgi buffer/hvy spring? assumed hvy spring.

Ammo:  Black Hills blue box 55gr FMJ
Barrel length: 14.5"  1:7 twist
Gas: Carbine

The hvy spring I would agree is overkill so I removed that out of the equation.  Bushy tends to overgas just a little and the H-Buff makes for a smooth ride.  I know what's causing it, just want to know what it's called.  :)

height=8

Quoted: It sounds like the spring in the HK magazine is weak and not feeding the next round up in time.  I've seen the same symptoms from old worn USGI magazines.  A new magazine spring fixes them right up.

+1

My guess would be the HK mag spring is Extra Power, thus adding to much friction to the carrier bottom causing a short stroke. A short stroke can eject the fired case and still not be far enough back to pick up another round.

I've never been convinced that HK AR-15 mags are "high reliability".

Krauts wouldn't know “high reliability” if it was staring them in the face.  Ever own a German car?  High performance, yes.  High reliability, no.

When I surfed HKPro forums in the past, one of the number one problems I saw people report were weak magazine springs in their HK pistols.  The fix was to switch to Wolf springs.  I could easily see that problem occurring in their AR-15 magazine.  I have a few HK AR mags, the feed lips bend too easily, and they weigh too much.  One mag gave me all sorts of issues when I tried to run it in my friends FS2000.  To me a standard USGI (Okay Industries preferred) mag with magpul follower, is a better alternative.

Quoted: Quoted: what ammo, barrel length, gas length?  the mgi, heavy spring in a 5.56 seems like overkill.  most people just run a midlength with heavy buffer.  if it ejects fully but doestnt feed, sounds like mag.  if it was short stroking, it wouldnt fully eject.  which is more beneficial, the hk mag or mgi buffer/hvy spring? assumed hvy spring. Ammo:  Black Hills blue box 55gr FMJ Barrel length: 14.5"  1:7 twist Gas: Carbine The hvy spring I would agree is overkill so I removed that out of the equation.  Bushy tends to overgas just a little and the H-Buff makes for a smooth ride.  I know what's causing it, just want to know what it's called.  :)

with a carbine gas system you should be getting enough gas.  make sure the gas blockand carrier key are tight, gas rings arent aligned, and buttstock screw is tight.  try diff ammo.  sounds like failure to feed with the hk mag.