BCM gas block size?

[Dollar]

If I changed the gas block on a 16" middy, what size gas block would I need? Is it a .750?

Also I read online that there would be difficulty taking out the pins on the front sight post, whats the details on that?

thanks

[Josh3239]

Depends what profile your barrel is. Lighterweight profiles are .625, government or M4 profile would .750 and heavy barrels are .926. A 16'' midlength is usually .750. Where did you get your barrel? Do you know the countour?

I have knocked many FSBs off barrels because I hate those things. I have knocked off somewhere around 7 of them. Just need a punch and a hammer. Some come off in less than 5 whacks and other require a serious beating. Shouldn't take to long though. Only on 1 pin (not FSB, just 1 pin) was it so stubborn that I had to drill out. If you have arms and a couple of bucks for a punch and a hammer at home you can do it. You do have to know that all muzzle devices will have to be removed though.

[2zero9]

Not really trying to revive an old thread or thread jack but my search has been futile.

I received a BCM 14.5" middy upper as a gift and I want to change out the the FSB, but I'm not sure what low pro gas block size to get. How do you determine the gas block size? Do you use calipers? Are there other ways to measure without calipers?

Any help would be appreciated.

[Josh3239]

Again it depends on your barrel profile. I am guessing it is .750, the standard and most common. But if it is a heavy profile or HBAR is it .925. If it is a lightweight or pencil barrel it is .625.

Caliphers cost $10. But I know times are tough. You can wrap some tape measures around the area of the barrel with the gas port. Or you can try a straight ruler perpendicular to the barrel, though that is probably the roughest way to do it.

[ar15barrels]

I want to change out the the FSB, but I'm not sure what low pro gas block size to get. How do you determine the gas block size? Do you use calipers?

Measure the diameter of the barrel with calipers between the two "legs" of the FSB.

It wil either be 0.750" or 0.625".
Your calipers may be off a couple thousandths either way, but that is most likely just your skill in using them...