9MM AR Troubleshooting

The 9MM AR platform requires some specialized rifle parts to function reliably and prolong longevity of the hardware. Unfortunately though sometimes the best researched plans do not uncover shortcomings of the AR and in this case the 9MM AR. The quickest way to find problems with a weapon is to simply shoot it and shoot it a lot.

The purpose of this page is to aid you with 9MM AR troubleshooting.  Basically your gun stopped shooting, something doesn’t fit or worst of all your gun experienced a hardware failure. If you have any experience to offer send us a message.

9MM AR Broken Bolt Stop | 9MM AR Broken Bolt Catch

9MM AR Broken Bolt Stop | 9MM AR Broken Bolt Catch

Without question the biggest malfunction 9MM AR shooters experience is a broken bolt stop, broken bolt catch. As far as I know this only applies to 9MM AR rifles, SBR’s, carbines and pistols who use a 9MM specific AR bolt catch. Colt AR6951 Bolt Catch is the only dedicated 9MM Bolt Catch that I am familiar with.and know of. CMMG and Rock River Arms also offer 9MM AR specific bolt catches.

The purpose of the special 9MM Catch is to allow the bolt hold open feature to function with the Colt 32 Round magazines, their clones and modified UZI magazines.

There is a couple reasons for this common issue of a broken bolt stop, broken bolt catch with the 9MM AR platform. Keep reading below.

Note: When discussing the 9MM AR the assumption is made that the shooter is utilizing a carbine length buffer system

Two Reasons a 9MM AR Bolt Catch Breaks

Reason One – A 9MM AR Bolt is shorter than a milspec AR-15 Bolt Carrier Group. This unfortunately allows the 9MM bolt to travel further down the buffer tube than necessary. This over-travel condition allows the 9MM AR Bolt to travel too fast in the forward direction causing premature failure of the bolt catch.

Reason Two – The blow back nature of the 9MM AR recoil system provides the 9MM bolt with some serious energy and velocity. This energy and velocity combined with the over travel condition of the bolt cause premature failure of the 9MM AR Bolt Catch.


Fix and Prevent 9MM AR Bolt Catch, Bolt Stop Failure

Fortunately the solution and prevention are pretty easy. A different 9MM buffer is needed and possibly a higher quality buffer spring. Some thrifty and clever shooters have added spacers, five stacked quarters etc in their buttstock, added weights to their buffers and made modifications to the buffer to increase it’s overall length and weight. In my opinion this is less than ideal. I prefer a more professionally engineered solution that is simpler and has less parts.

Solution Part One – The  Colt 9mm buffer is 3.300″ long. This is often too short. When the thickness of five stacked quarters .345  is added to the length of the Colt 9mm buffer we conclude our 9mm buffer needs to be approximately 3.645″ long! Now if you look at the 9mm buffer specifications below you will notice that most 9mm AR buffers are longer than the Colt or RRA which are the traditional standards. The longer buffers reduce the amount of travel available to the bolt.

Solution Part Two – Some shooters have reduced recoil and improved reliability buy using a 9mm AR buffer that in addition to being longer than standard 9mm AR buffer it is also heavier. Once again look at the chart below and compare the Colt and RRA buffers to the other manufacturers listed.

Solution Part Three – I have learned over the years that all AR-15 recoil springs are not created equal. Use a quality recoil spring.

Conclusion – To prevent a 9MM AR Broken Bolt Catch select a 9mm AR buffer that is at least 3.600 inches long and weighs more than 5.5 ounces. My personal preference is the Hahn and Heavy Buffers offerings. If you recoil spring feels week replace it with a Wolff XP or from another reputable manufacturer.

9MM AR Buffer Specifications

  • COLT 9mm SMG Buffer SP62913 - Length 3.300" , Weight 5.5 Ounces
  • CMMG 9mm Heavy Buffer 90CA9B4 - Length 0.000", Weight 5.3 Ounces
  • Yankee Hill Machine 9mm Buffer YHM-925-A - Length 3.600", Weight 5.9 Ounces
  • Spikes Tactical ST-9X 9mm Buffer SLA009X - Length 3.700", Weight - 8.5 Ounces (No longer produced)
  • Blitzkrieg Components 9mm Hydraulic Buffer - Length 3.900", Weight - 6 Ounces
  • Rock River Arms 9mm Buffer 9MM0107 - Length 3.250", Weight 5.5 Ounces
  • Hahn Precision Pistol Cartridge Buffer 9mm Buffer - Length 3.6875", Weight 7.0 Ounces
  • Heavy Buffers 9Q Buffer - Length 0.000, Weight 8.5 Ounces (No longer published but much longer than the Colt 9mm buffer)
  • Heavy Buffers 9QT Buffer - Length 0.000, Weight 12 Ounces (For SBR's and Full Auto) (See Above)
  • New Frontier Armory 9mm Buffer - Length 0.000, Weight 8.0 Ounces
  • New Frontier Armory 9mm Buffer - Length 0.000, Weight 10.0 Ounces
  • VLTOR A5 H4 Heavy Buffer - Length 3.995, Weight 6.83 Ounces
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