Help with AR M4 Build

[gr8vfr]

I am considering building an M4.
I have a both pre and post ban options open.

I Have a Rock River lower and a Colt lower.
What are the differences between pre and post ban lowers.
Are they the same?
A builder just has to follow the rules for the date the lower was manufactured?

My Colt Sporter is pre ban about twenty years old.
I have no clue the age of the Rock River.
Will any upper interchange?

Thanks and post any questions which will aid to helping me find a solution.

:rockin:

[Circuits]

Colt Sporter 2 lowers have a large pivot pin. You'll need an offset pin to use most new uppers on it.

The Rock River is post-ban, so you'll need a post-ban compliant M4gery upper, and won't be able to use a real telestock if you build the M4gery on the Rock River lower.

[sfc ret]

some colt lowers also have a block in them...I don't know if your model does or doesn't, but if it does, you have one of 2 options..... mill it out or buy a bolt carrier that will allow it to go pass the block.

[kanewtervalve]

If both receivers are already complete rifles I would leave them as is because of resale value. You will be able to build a post ban M4 for less that $600 even if you buy a new stripped lower receiver. Just my .02.

[gr8vfr]

Yes... I have Rock River stripped lower and a Colt lower.
I didn't want to use the Colt assembled.
They look the same to me.

I wanted to weigh my options.
I can get either pre or post ban uppers.

Yes... I figured when all said and done I would have 650.00 invested using the Rock River...
However, I like the pre ban supressor and tele stock...