I wanted to bring my extra 20" upper along to the range to use with my M4 clone. So I wanted to know would I have a problem with the rifle not functioning properly because of the gas system differences between the M4 barrel and a 20" barrel. Since the M4 uses a difference buffering system then an A2 stock I wanted to ask here if I would get a cycling problem if I use the 20" upper on the M4 lower.

Thanks, for looking and all replies.

Leadfoot,

I was wondering the same thing myself a little while ago and found out that it doesn't matter as long as the spring, buffer and tube all match. In other words, either all parts are for a collapsible stock or all parts are for a fixed stick. Here's where I got the info from:

[url=http://ar15.com/forums/announcement.html?b=3&f=66&id=187][b]Combinations of barrels and buttstocks[/b][/url]

Matt_B, thanks for the reply. I thought there might be a difference due to a shorter tube in the 14.5" upper. I just wanted to make sure that the 20" would cycle a round correctly with the shorter buffer system in a collapsible stock than the standard A2 buffer system in an A2 stock.

I have fired my 20 inch upper on my Carbine lower without a problem, I kept the short (also heavy) buffer and spring in the carbine.