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The bolt catch in my AR-45 broke over the weekend. The casting on it looked porous, so I assumed it was a bad part. However, after asking the question on my local CO gun forum I was informed that pistol caliber AR's tend to have bolt overtravel, causing the heavy bolt to slam into the bolt catch too hard when it comes back forward. This is why the PCC Carbine kits come with a spacer, or some kits come with longer than average buffers. My pistol caliber AR lowers both have A2 stocks, and I was not able to find a pistol kit for those when I built them. They both went together without a spacer.
On the advice from the other forum, I filled the space so the bolt goes back a little less than a quarter inch past the bolt catch. I used quarters, but a pre-made spacer or a piece of delron would have been good too. I have not yet replaced the broken bolt catch, but do have a parts kit I can rob of the part. I did test sear and trigger functionality, verifying the bolt goes back far enough to reset the trigger group properly.

It's a relatively common problem I was unaware of.
 
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The bolt catch in my AR-45 broke over the weekend. The casting on it looked porous, so I assumed it was a bad part. However, after asking the question on my local CO gun forum I was informed that pistol caliber AR's tend to have bolt overtravel, causing the heavy bolt to slam into the bolt catch too hard when it comes back forward. This is why the PCC Carbine kits come with a spacer, or some kits come with longer than average buffers. My pistol caliber AR lowers both have A2 stocks, and I was not able to find a pistol kit for those when I built them. They both went together without a spacer.
On the advice from the other forum, I filled the space so the bolt goes back a little less than a quarter inch past the bolt catch. I used quarters, but a pre-made spacer or a piece of delron would have been good too. I have not yet replaced the broken bolt catch, but do have a parts kit I can rob of the part. I did test sear and trigger functionality, verifying the bolt goes back far enough to reset the trigger group properly.

It's a relatively common problem I was unaware of.
Well, that explains something we were trying to figure out at the gun show. Someone had put some really nice leather spacers in an AR that got traded at the show, and we couldn't figure out why. I'm not an AR guy, so the best I could give the guy showing it to me was an, "I'll be darned." The spacers were perfectly machined to fit the space, and didn't look like someone's quick fix.
 

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Conversely, my 9mm AR had problems initially with not stripping rounds from the mag or engaging the bolt catch. The heavy buffer I had installed was a bit too long and needed to be be trimmed down a bit to make it all work.
The pistol caliber ARs need to be tuned individually.
 

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New Frontier Armory 9MM/40S&W Buffer Spacer (joeboboutfitters.com)
AR-9 Buffer Spacer for use with 9mm/.40 AR style firearms and standard carbine length buffers

  • US Made with engineering grade polymer
  • Use when running a carbine buffer with a 9mm/.40 cal blow back system instead of buying an expensive 9mm buffer
  • Helps lessen chance of breaking bolt catches by limiting the rearward travel of your 9mm/.40 blow back BCG
  • Helps speed up cycling by shortening overall (necessary) bolt travel when using the shorter rounds/shorter BCG
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Just a shock buff concept like used in a 1911. Same problem that killed the Marlin Camp Carbine in 9mm and 45 acp. It gives a little cusion but shortens the travel like the quarters or leather or commonly use dowel rod. Just looks better. Even a cut piece of pec pipe should work.
 
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