I have a Colt lower with the sear block and would like to be able to use my Colt full circle carrier without altering the sear block. I put it in the upper and it seems to be fine, no contact with the sear block. Any info would be greatly appreciated, thanks John

If I am not mistaken the answer is no, you can not.  The reason why you have the half moon carrier is so there is clearance between the BLOCK and the bolt.  If you use it with the full circle bolt, you could risk injury or destroying your weapon.

Max

That is what I thought but I have the clearance, it does not hit the block at all, I think the block is just so you can't convert to full auto but not 100% sure.

I use a full circle (RRA Enhanced) in my sear blocked lower.

The shape and design of the rear of your carrier have nothing to do with the block on your lower. The only thing the block on the lower does is prevent you from easily drilling a hole in it to accomodate an auto sear and pin.

You can use a full circle carrier in any upper in conjunction with a blocked lower. The full circle's only function is to trip the auto sear off of the tab on a full auto hammer and release it to strike the firing pin after the bolt has fully seated back into battery. A half moon carrier does not have this portion on it and therefore can not trip an auto sear.

That is why, if you install an auto sear in a non-blocked lower, you will still need a full circle bolt carrier along with a full auto hammer, trigger, disconnector and selector switch for the rifle to function properly.

You asked me what time it was and I told you how to build a watch but there ya go.

Thanks, that's what I thought but wasn't sure. I appreciate the help, take care and happy holidays.

Actually, the Colt sear block (if it is the type that has a section sticking "up" into the upper receiver, when the rifle is assembled) prevents the use of a FULL AUTO bolt carrier.  While the "full circle" BC (semi-auto bolt carrier) SHOULD work, you should make sure that it doesn't make contact with that little piece of the sear block that sticks up inside the upper receiver.  Quote from the patent PDF:

That's from the patent PDF available on [url]http://www.biggerhammer.net[/url]

Here, we need to make the distinction between a "full-circle" BC, and a "full-auto" BC.  In the following drawing:
[img]http://www.ar15.com/content/docs/AR15-M16Parts/boltCarrier.gif[/img]
you'll notice that the full-circle BC will NOT hit the factory autosear, OR a DIAS trip.  the full-auto one will, since the closed portion extends more toward the bolt.

If you have a full-auto BC in your rifle, your upper and lower will NOT WORK together, provided you have a sear-blocked lower.  If you have a "full-circle" BC (second in pic above) you _should_ be just fine.