MP-A2 Radial Delay Modifications

MP5 Mag Receiver Set required modifications

To use a CMMG Radial Delay action with your MP5 receiver set, you will need to modify the bolt as follows:

  • File material from the bottom two lugs of the bolt. These are the two lugs that interface with the top round in the magazine. The exact amount required depends on the fit between your receiver, magazine, and action. Between 1 and 2 hundredths of an inch is a good place to start: i.e. reduce by approximately 15% of their factory length.
  • Slightly round the rear of those same lugs. As the bolt travels rearward, it will scrape the top round in the magazine. Slightly round the sharp edge where the two lugs first touch the round when the action cycles.
  • That’s it. Use dummy cartridges to test chambering and ejecting rounds. The MP5 mag feeds from both the left and right, so be sure to test both sides by using two rounds. If the bolt carrier binds or requires excessive force going over rounds forward or backward, take off slightly more material and/or round the rear of the lugs more.

Glock Mag Receiver Set Adjustments

If you have any issues with your glock mag receiver set, try the following:

  • If the bolt catches on the top round in the magazine too much, adjust the magazine over-insertion stop down. This is done by loosening the two screws on the side of the receiver above the magwell and repositioning the over-insertion stop.
  • If the magazine still sits too high, the magazine catch can be filed down slightly. Make very small adjustments and check the fit and function each time. If you drop the mag too low the bolt will fail to pickup a round.