Tuesday, August 25, 2015

Fix Your AR 15's Jammed Bolt Catch Assembly

I came to the end of a magazine of 5.56 and the bolt closed in the receiver, instead of being held open by the bolt catch. Hunh, that's weird, I thought wisely to myself, like a firearms professional, and had a look at the weapon. It turns out the catch had jammed and wouldn't rise to catch the bolt when the magazine was empty. What had gone wrong? I took bolt catch assembly apart to find out.

All Taped Up

It's not hard, tape up the receiver to stop it getting scratched, then tap out the roll pin that holds the assembly in place. Save yourself some aggro and use a roll pin punch. Pin out, remove the catch, its spring and its detent. Look at these items in wonder and inspect their various wells to check for Hillary's emails, or anything else that might have jammed the catch.

Bolt Catch Assembly. Don't Lose the Spring, or the Pin, or the Detent, or the Catch.

Inspection passed, reassemble the catch using a drift pin to hold it in place, I used a small punch, then test its movement. Notice that the catch is sticking and that it doesn't want to release when it's tapped into the receiver. Why?

Tap Out the Roll Pin

I had a closer look and saw that the face of the catch was fractionally proud to its inletting in the receiver, which produced friction and stopped the catch's movement.

Diamond Coat File and Blue Heeler

So I pulled the catch and filed the offending metal down with the diamond coat file on my Leatherman Wave. Not much, about the thickness of a piece of paper, 0.1 mm. Then I tested its movement to see if it was still jamming. It didn't, good result.

Get a Roll Pin Starter Punch, they're Helpful

Then put the spring back its hole, and the detent in the spring. Don't lose the spring and the detent by idly flinging them across your workbench, because if you do the bolt catch won't work. Next replace the catch, using a drift pin to hold it in place, and see if the thing works. It does. 

Use a Small Hole Punch as a Drift Pin

Keeping the drift pin in place, tap in the assembly's roll pin, using a roll pin starter punch to get it going, and finish off with a roll pin punch until the pin's in position. Test the assembly and note with a warm glow of inner satisfaction that the catch doesn't stick and jam anymore. Well done, hopefully the problem's solved.

To make sure, put the rifle back together again and place an empty magazine in its well. Pull back on the charger and release. Will the bolt catch move upwards thanks to the pressure of the magazine spring and hold the bolt open? Will your expert machining be vindicated? A moment of bated breath and... yes, it works.

And it Works

Congratulations, you are now a Bolt Catch Assembly Technician (BCAT).

With that in mind, I think I'd better go and range test this beast.

Gun rights,



LL said...

I think that we need to reclassify you to be the armorer of the Dallas Light Cavalry (Irregular) (Dismounted).

Job well done.

LL said...

PS - I noted a photo of Blue Supervisor helping you do all of that. And I noted that he didn't receive ANY credit.

LSP said...

It seems that I'm working towards an armorer's qualification, and all thanks to the good advice of the dog.

Thanks, Blue Skillset, for a job well done!

Unknown said...

Which part of the bolt catch is "the face of the catch"?

(This is my third try to post a question about this subject. I hope there isn't three posts showing!)

LSP said...

Alright there, Nevil.

The flat side that catches the bolt -- but, this post notwithstanding, I ended up getting a new catch. My "mod" worked for a while and then didn't; it was easier to get a new piece than keep messing with the old one... the original wasn't properly machined.

JJ White said...

LOL. Nicely written, I'll have to try this and see if I have the same issue. Mine is jammed SHUT against the receiver after the last round is fired. Note this is a Colt 9mm, but the principle is the same...

LSP said...

Good luck! I'm no expert but I'd recommend replacing the bca and see how that goes.

I ended up, ultimately, doing that with the one in the post. Problem solved.