New Colt 6920, something is wrong

[MadRabbit]

Few questions- 1) Could you do a function check normally prior to the disassembly/reassembly? 2) Will the bolt retract nomally if you let it slam home, but do NOT pull the trigger? 3) Is your bolt carrier key tight, screws staked, etc.?

[KL7]

Few questions- 1) Could you do a function check normally prior to the disassembly/reassembly? 2) Will the bolt retract nomally if you let it slam home, but do NOT pull the trigger? 3) Is your bolt carrier key tight, screws staked, etc.?

1) No, the bolt would stick right out of the box. That kind of prompted me to do the disassembly.
2) I didn't try that, I 'll do that tonight when I get home. I'll lock the bolt back and let it release.
3) The screws are staked and looking good. When I examined the bolt, I looked for any obvious places where it would be binding (scraped metal), but I didn't see anything around the gas key or screws.

The only area I see that actually looks like metal on metal contract is the inside of the gas key where it meets the gas tube coming from the front. I wonder if the key and the gas tube are smashing together and locking up. That might be why it takes both arms to pull the bolt back and unlock it.

[SA Friday]

Ya. This sounds like something on the BCG is binding like a mo-fo. Thus my question about the two most common assy errors that lead to BCG binding.

Try functioning the firearm in any fashion possible instead of just the standard function test and see if you can narrow down what is binding. But don't be suprised if it's all for not. If the BCG also binded in the other upper, I suspect the issue is specifically with something on thje BCG. My next step would be to decide if it was going back to Colt for repair or further tinkering. If you want to pursue further testing of the problem, break out the sharpie and see which surface the binding is coming from. (Note: white rain squirt bottle hair spray will remove the sharpie when resolved).

[MadRabbit]

I doubt that's actually the cause, if this is a new rifle straight out of the box what probably happenened is what's known as "tolerance stacking" The cam pin specs are X +/- .003" for example (I have no idea what the actual cam pin specs are), you get one at +.003" which is still within specs, but then the parkerizing goes on a bit too thick, and now your cam pin is +.005". End result is that when the cam pin stops it's rotation in the BCG as you pull back on the charging handle, your bolt is not completely unlocked yet. One of the reasons I asked about the gas key being securely attached. Just for $h!t$ and giggles, if you can get the BCG out try swapping just the cam pin from your other rifle. You could also try rotating the current cam pin 180 degrees and see if it improves things for you.

[KL7]

Well, I finally figured out the cause. Something is wrong with the colt firing pin.

1) I tried swapping just the cam pin between the two rifles. Same locking issue on the colt, but the Delton functioned fine with either.
2) Rotated the cam pin 180 degrees with the colt firing pin and colt cam pin. Same locking issue.
3) Swapped just the firing pin between the two rifles with all other items stock and now the Colt functions just fine. The Delton also works fine with the Colt firing pin.

Although the Colt is now fixed using the Delton firing pin (and the Delton works just fine with the Colt firing pin), I don't understand why the firing pin would bind up the BCG? I examined both firing pins and they both look straight, although the Colt firing pin looks like it is just a tad bigger. Maybe the Delton has looser specs for the BCG and firing pin size and the Colt is just a bit too tight? I'm guessing the Delton's smaller firing pin inside the Colt BCG allows just enough play to allow everything to function?

Anybody have an idea why just the firing pin would bind up the BCG?

Thanks for all the replies is helping me get this sorted out.

KL7

[BPTactical]

You probably have a M16 firing pin in an AR carrier. There is a slight difference in diameter of the "flange" on the firing pin. The larger diameter will hang up on the hammer. Take a set of vernier calipers and measure the flanges. If the Colt is slightly larger you have a 16 firing pin. Swap it out for an AR and go have fun.