Bolt Catch Issues (AR15)

[Mentiroso]

Troy upper mated to CMMG lower. Using stock CMMG parts kit and troy BCG.

The issue is bolt catch will not engage BCG in bolt-locked position or stay open after last round. My thinking is out of spec bolt catch, bad spring or slightly bent bolt catch roll pin.

What are your thoughts?

[Bravodigger]

Could be the magazine too

[xrayoneone]

This happened on a couple of my builds. One was caused by the spring one was a catch that was a little large.

Remove the upper and place an empty magazine in the lower. You should be able to see the bolt catch lift. If it lifts then it probably isn't a magazine or out of spec catch.

I would then remove the spring and check if the catch moves freely. If it doesn't I would file the catch until it fits freely.

If the catch moves freely I would then trim one coil from the spring until it works correctly. The spring should provide enough tension to keep the catch down until the magazine trips it. You don't want it too loose nor too strong.