02-06-2014, 02:07 AM
haustinv Wrote:I didn't know that Mega machines their upper to be heat/chill fit to the barrel. I always put things together multiple times test fitting everything till I get it right. Might say I have a little OCD issue.This is my problem, I chilled my barrel in my freezer which I keep at -10 (I'm an HVAC Contractor and do it because I can. :o ) When I tried to put it on the Mega upper it would only start maybe by about a 1/16 of an inch. If I heat the upper they will probably mate up but how will I ever get them apart.? I'm used to press fits but that's usually with steel parts that can take the force of pressing them on or off without damage. I'm concerned with this aluminum/steel situation though. As I have only changed barrels on my other factory built AR's with their much less precision fit. I'm apprehensive with this my first scratch build. Please anyone want to jump in on this and fill me in. Is there some trick I need to know, am I being overly cautious?
I have used numerous MEGA SBU's and the fit is special I would say. All I do is use my heat gun, for shrink tube but gets to 500 degrees. You just move it around the front of the upper for about 5 minutes not directing the heat in one area. The Aluminum heats up, expands and then just insert the barrel (no freezer required). Before it cools, put the barrel nut on and tighten so it draws it together. Once it cools it is locked tight. If you remove the barrel nut you wont be able to pull it apart. You will need to heat again in the same fashion but use a dowel or perfectly round piece of aluminum rod to help tap it out once heated. It does work, I have removed them using this block that fits in the upper receiver. http://www.midwayusa.com/product/819480/...uctFinding
Anyhow, once together you might not ever need to remove it. Plan ahead...