Colt rifle question

[lavey29]

I have a pre-ban Colt rifle and the lower has that fixed sear block in place not the pinned one. The original Colt bolt carrier also seems to have a cut out in it which I guess was probably to be used with that pinned in sear block. Is there any problem or reliability issue to switch out the upper to a updated mid length version. The new upper does not have that cut out in the carrier. They are both small take down pin holes. Thanks for the help.

[m16]

It will be fine.

The only time you need an open bottom carrier is when your lower has a sear block that sits higher than the top edge of the lower receiver.

[lavey29]

Thanks that is what I figured but wanted a confirmation

[hyperrex8]

I have the same rifle and I bought a m16 auto bcg!! Just cut the block down and getting it down flush our a lil lower to the lower receiver! That's what I did

[REDdawn6]

There are walk throughs on ar15. Com forums on taking that block out also. Wouldn't have to worry about it at all.

[lavey29]

I dont have that pinned in block that sticks up just the integrated internal block that Colt puts in their rifles just in front of the buffer but it does not protrude above the edge of the lower receiver.