Thread: AR-15 from 9mm to 5.56???

Looking for some knowledge from AR builders out there. I have a SBR’d 5.56 AR that I bought already set up as a 9mm (mag block for Uzi mgs and complete upper) . I would like to put a 5.56 upper on it but need to know what parts need to come out and what can stay. I know that the mag block and upper need to go, but don’t know about the hammer, buffer & spring. Please advise.

Thanks for the info. I have the correct hammer so it looks like I am g2g

You need the "no notch" hammer for 9mm, either will be fine for 5.56. Check your buffer, many 9mm's use a longer buffer. Other's use a standard length buffer with some type of spacer (I've even heard of people using quarters). Both of these setups prevent the bolt from moving further than it needs to move (9mm) which can result in broken bolt catches. If you have a longer buffer or a spacer in the gun it won't allow the bolt to go back as far as it needs to go (5.56).

U should be gtg. I use my 9mm buffer with both uppers.