I recently acquired a BCM 11.5" pistol. Upper, lower, BCG, gas block, charging handle are all BCM marked. The barrel has zero markings anywhere. I have removed the handguard and cannot see any markings. Can anyone help me identify if this is a factory barrel, or a replacement barrel on a factory gun? Any help would be greatly appreciated.

Pictures in links

https://www.imghippo.com/i/jxpLj1716161340.jpg
https://www.imghippo.com/i/STX2e1716161461.jpg
https://www.imghippo.com/i/GCW661716161500.jpg
https://www.imghippo.com/i/xycqZ1716161546.jpg

That looks like the ELW profile, which are marked in front of the gas journal per the pic on their website. Is the gas journal .625" in diameter?
It's hard to imagine it wouldn't be marked, but stranger things have happened. I have also not found another barrel with the same profile and lack of shoulder at the gas block journal as the BCM ELW.

BCM claims this was a factory gun based on serial. Although they are saying it’s not their barrel due to no proof marks. I have looked all day and I can’t find a barrel other than BCM with that taper either.

Could it be a cut down? Did BCM say what barrel length it was originally?

I wondered the same but BCM only makes the ELW in 11.5" (carbine gas), 14.5" (Midlength), and 16" (Midlength). That's definitely a carbine gas system.