I put in a brand spanky new Young Mfg, M16, Sp1 Hard Chromed complete BCG,,out of 40rounds 3 had lightstrikes and never went off. Reloaded them and they went off.

The BCG is the only factor that has changed in my AR, I have never had any issue prior to this. The ammo was mix of Fiocchi and XM and Match Hornady.

I have seen this before, when there was a buildup of varnished lube in the bolt (you used a new BCG). I can promise nothing, but I would first disassemble the BCG and totally clean the bolt, maybe there is a buildup of lube from the chrome plater or something got in there. I would look the bolt over closely, then if it is clear, lube it well and reassemble it.
It's unlikely that your hammer spring went tits-up at the same time, but that would be the 2nd thing I'd look into.

I had a friend complain "your damned reloads wouldn't fire" and I looked at the rounds, there was hardly a ding on the primer. Pulled his BCG, cleaned the varnished REM oil out of the firing pin channel and proceeded to shoot the same rounds that had failed him. No problems after that.

I highly suspect since the BCG was brand new, it just needs cleaned well. Many manufacturers put a preservative type oily coat on new parts, I dunno about Young Mfg tho. It's worth the cost to check it out. Give that a try.

Other than the above you might have a out of spec chamber, head space issues, hammer issues, hammer spring issues, out of spec BCG, bad ammo, bad firing pin, burs in you bolt, etc..





Check the easy and cheapest first.Of course some of these issues are not related to a new BCG so ignore them.



Does it light strike when putting the original BCG back in there? Was there a new bolt with BCG?

Clean the new BCG.

Ok, ill strip it down and check it out

I dont have the original  BCG< sold it to fund the new one. lesson learned

Thanks everyone.

nvm

UPDATE

Stripped bolt down completely. scrubbed it, cleaned it, CLPd it.

Took it to the range today. Ran flawlessly.

I guess it needed a good cleaning and lubing but also need to mesh with the upper some more. Being chromed I figure it might be a little thicker.