MP5 Assembled - Live Fire Troubleshooting

Utilize these steps after following all the Lower and Upper Troubleshooting steps above.

• Issue: <5 rounds are fired before a LPS (Light Primer Strike) or hammer follow occurs and the charging handle needs to be pulled again.
  • Solution 1: Test different ammo. Some ammo has very hard primers or is too weak to properly reset the hammer.
  • Solution 2: Replace the hammer spring with an "extra power" hammer spring from Wolff (30095).
  • Solution 3: If these steps do not resolve the issue, please contact us.

• Issue: Failure to extract or eject. Can result in issues such as one live round and a spent casing in front of the bolt carrier at the same time OR casings getting caught in the ejection port or in the cocking lever joints.
  • Solution 1: The most common issue here is underpowered ammo that will not adequately cycle the ejector lever with enough force to kick the spent casings out of the gun. We STRONGLY recommend 124GR NATO 9MM ammo for all initial testing/cylcing and troubleshooting (we use Remington 23718 for our in-house testing, but we see plenty of success with other brands too). DO NOT USE SYNTECH 150GR (OR OTHER UNDERPOWERED SUBSONIC ROUNDS) WHEN TROUBLESHOOTING.
  • Solution 2: Check ejector lever function and for any signs of damage (chipping or breaks). Ensure there is not too much side-to-side wobble and that it can move freely up and down.
  • Solution 3: If you are using a K model (especially when suppressed), you may need to replace your locking piece with an 80-degree or 90-degree to slow the rate of fire. If you are running underpowered ammo (especially 147gr+ subsonic ammo), you may need to go to a higher degree locking piece. All of this varies based on the exact host, bolt gap, ammo, suppressor, etc. used and may take some trial and error.
  • Solution 4: As a last resort, we would replace the following parts in order: Extractor spring, Extractor, Ejector Lever. We recommend using H&K branded parts despite the steep additional costs. After replacing these,  If it continues, test other ammo, suppressors, etc. as it may simply be too much or not enough bolt velocity.

• Issue: The lever snapped in the first 100 rounds.
  • Solution 1: Please review the Dry Fire troubleshooting steps again.
  • Solution 2: The hardening of the lever may have been incomplete, we will replace the lever, please contact us.

• Issue: The rate of fire is far too high! Full size exceeding ~950RPM or K size exceeding ~1200RPM.
  • Solution 1: Verify you are not using overpowered ammo (i.e. +P or high velocity). You should be utilizing 124gr NATO 9mm with no suppressor for all baseline troubleshooting. Suppressing will increase the rate of fire, so we recommend verifying good function without the suppressor first, then move to suppressed and adjust as needed.
  • Solution 2: Replace the locking piece to a lower degree version.
    • Full Size Models - Use the 100-degree locking piece in 99% of applications. Most OEMs use a 100-degree, but if you cannot verify, you may order one from RCM, PTR, etc. they are interchangeable between brands.
    • K Size Models - Use the 80-degree for fulltime suppression with high powered 147gr loads. If you shoot both suppressed and unsuppressed, you should use the 90-degree locking piece (we generally recommend this overall for K models). If you shoot solely unsuppressed, you should be fine to use the 100-degree locking piece (various OEMs use 100-120 degree locking pieces for the K models).
    • SD Models - Use 115 or 120-degree locking pieces, either should be fine.

• Issue: Failure to feed.
  • Solution 1: This can indicate an issue with your mags. Genuine HK mags are the best starting point for troubleshooting the mags.
  • Solution 2: Test a different kind of ammo. Flat nose ammo is notoriously difficult to feed in MP5s, you should utilize round nose ammo only (hollow point is hit or miss).
  • Solution 3: This can also indicate an issue with the mag catch position resulting in the mags sitting too high or too low or at an angle. Replace the mag catch with an HK brand mag catch.
  • Solution 4: Some stocks/braces/endcaps may be too tight and cause binding at the rear of the firearm, preventing return of the bolt fully forward (or at a minimum reducing bolt velocity significantly).

• Issue: The slip trip broke within X amount of rounds (X < 5,000).
  • Solution 1: This can indicate an issue with bolt velocity being far too high. We strongly recommend reading the above troubleshooting step discussing rate of fire being too high.
  • Solution 2: This can also result with certain braces/stocks/endcaps. Look at the inside of your stock/brace/endcap and see if there are any marks/indents/damage from the slip trip slamming against it. If this is occurring, you may need to clearance that area to allow a little more travel or install a buffer tube to prevent full travel.
  • Solution 3: Contact us, we will replace the slip trip the first time it fails prematurely.

• Issue: I've followed the whole guide and it still doesn't work!
  • Solution: Buy a HK SP5. (J/K, contact us)