MP5 Disassembled - Lower Troubleshooting

This guide is oriented specifically toward MP5 builds in 9mm. If you are using a G3/91, 33/53/93, 32, or similar, this guide may not be perfectly applicable as the exact troubleshooting steps may vary. We cannot guarantee functionality or reliability of Super Safety/ARC-Fire with non-AS Designs lowers and we cannot offer troubleshooting for Leber or Lee Sporting lowers.

Note: All products are recommended to be installed by a qualified gunsmith.

Utilize these steps after ensuring you are using mil-spec AR-15 parts in your lower AND that you are using 124gr NATO 9mm ammo (no 115, no 147, no +P, etc.). DO NOT use M16 FCG parts or “fancy” parts for initial testing (you can use upgraded hammers/springs/etc after you have it functioning, but we will not help troubleshoot those), the more generic, the better. The only exceptions to these rules are Geissele triggers provided by ASD or other SS sellers pre-cut AND/OR the ASD MP5 Hammer, we will help troubleshoot these.

• Issue: The trigger pull is very heavy in super safe/ARC.
  • Solution: Lightly sand the rounded corner of the trigger with 220-grit sandpaper. Only take off a little material, it shouldn’t take a lot to get it running smoothly. MAKE SURE you keep the round shape on the corner. After function tests pass, we suggest using 320-grit, 400-grit, and possibly one more higher grit to polish the corner without removing more than a surface amount of material.

• Issue: The trigger does not function in super safe/ARC. It either doesn’t allow you to pull it or it won’t release the hammer when the lever is fully forward.
  • Solution 1: Attempt to jiggle the super safety around the middle position slightly back and forth and see if the trigger is still prevented from being pulled. This can indicate the width of the tail of the trigger is a bit much (you can narrow this down some with a dremel/file) or that the safety detent hole is slightly out of spec (which aligns the super safety too far to one side).
  • Solution 2: Sand the rounded corner of the trigger with 220-grit sandpaper. Only take off a little material, it shouldn’t take a lot to get it running smoothly, but may take a few tries. MAKE SURE you keep the round shape on the corner. After function tests pass, we suggest using 320-grit, 400-grit, and possibly one more higher grit to polish the corner without removing more than a surface amount of material.

• Issue: The super safety cam is jumping positions during function checks or live testing without you pushing it.
  • Solution 1: Verify you are using a rounded safety detent and the round surface hasn’t flattened out too much.
  • Solution 2: Verify the safety detent spring is not crooked/bent/pinched and appropriate pressure is applied to the detent/cam (you should feel distinct tactile clicks when you move between positions). If the pressure isn’t sufficient, you can add some material under the detent or spring to compress it further. In rare cases, you may need to reduce the pressure by removing a coil or coils from the spring.
  • Solution 3: In extremely rare cases, the cam may be out of spec, please contact us.

• Issue: The trigger does not reset when you move the lever as far back as it can.
  • Solution 1: Verify the safety cam is in the middle position or the ARC-Fire selector is in the third ARC position, this is “super safe.”
  • Solution 2 (ARC-Fire Specific): This may indicate the ARC-Fire assembly is too "loose" inside and the reset point of the function is too far back to be properly actuated. Please contact us for a replacement part.
  • Solution 3: Trigger may be overcut, please contact us if you purchased the trigger from us.

• Issue: The trigger and hammer pins are “walking out” and you need to push them back in sometimes.
  • Solution: We recommend always installing Anti-Walk Pins on Super Safety kits. DO NOT USE ANTI-ROTATION PINS!!! Anti-Walk Pins are available from a variety of vendors.

• Issue: The safe position is not “safe.”
  • Solution: The trigger is most likely very incorrectly cut or something is not installed correctly, please restart installation from scratch and if it continues, please contact us

• Issue (ARC-Fire Specific): The selector is hard to move from Semi to ARC positions, but not from Safe to Semi.
  • Solution 1: Try replacing the detent with any mil-spec detent you have available.
  • Solution 2: The detent bar may be out of spec. If you would like to quickly check this, you can loosen the primary selector screw just a little, then re-test movement, if it's fixed the bar is out of spec. Please contact us for a replacement.

• Issue (ARC-Fire Specific): The selector is hard or "gritty" to move between all positions.
  • Solution: Try replacing the detent with any mil-spec detent you have available.