Last round bolt hold open


If you have any doubts in your ability to perform the following actions, stop immediately and seek assistance from a qualified gunsmith. If you need clarification on any of the steps below, please contact us to speak with a member of our support team.

Always wear proper personal protective equipment (PPE) including adequate eye protection when servicing a firearm.

The last round bolt hold open (lrbho) relies on a number of different components to function correctly. If any one of these components become damaged it can cause the lrbho to become inoperable. If your lrbho feature is malfunctioning check the following:

  • Verify you are using a good condition OEM Glock magazine. Magazine springs can wear out over time. If one magazine fails to hold the bolt open, try using an alternate OEM Glock magazine.
  • Verify you are using factory ammunition and not reloads or re-manufactured ammunition.
  • Make sure the lower receiver has our lightened bolt catch spring installed. If you purchased one of our complete firearms it came preinstalled. If you purchased one of our lower receivers or receiver sets, this spring was included in the small bag located inside the receiver box.
  • Verify you are using the correct buffer and spring. See our Buffer and Buffer Spring page for our recommendations.
  • Verify you have the correct cycling distance.
    • Manually lock the bolt to the rear and leave the charging handle extended.
    • Pull the charging handle rearward until it stops and measure the distance traveled. It should be roughly a minimum of 1/4".
    • If you have a shorter distance, the bcg is not traveling far enough to actuate the lrbho.
  • Verify you can manually charge the gun with an empty OEM Glock magazine, and the bolt holds open.
  • With the upper receiver completely removed, insert an empty OEM Glock magazine and verify the bolt catch lifts completely up.
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