01-13-2014, 03:35 AM
maverick5582 Wrote:I finally remember where I had seen this little bit of information:
Barrel Contour: You want some meat on the barrel. Between the upper receiver and the gas block don’t go real thin with a barrel (we like 1″ diameter if it’s workable weight-wise). When you touch off a round and the bullet passes the gas port, the gas system immediately starts pressuring up with a gas impulse that provides vibrations and stress on the barrel, especially between the gas block back to the receiver. A heavier barrel here dampens that. Staying a little heavier with barrel contour through the gas block area and out to the muzzle is good for the same reasons. ARs have a lot going on when you touch off a round and the gas system pressures up and the carrier starts moving (all before the bullet exits the bore) so the more things are made heavier and rigid to counteract that the better — within reason (I’m not advocating a 12-lb barrel).
Well like I just read from LRRPF52, every manufacture does things different.
JP Rifles uses .650 under the hand guard on there Grendel between the upper receiver and the gas block so who really knows. They do use there thermal dissipation to stiffen the barrel as they note on the link below.
http://www.jprifles.com/buy.php?item=JPSM6.5G-22M8
http://www.jprifles.com/1.4.5_hs.php
As far as contouring, I talked to my machinist and he has blanks that are 1.5" from one end of the blank to 1.25 at the other end. All contouring and cambering is done after rifling and he doesn't do any stress relief. According to him its not needed and he has done lots of barrels in all kinds of lengths. He makes Silencers and all kinds of custom SBR rifles so a 5lb barrel blank turns into a 1.5lb or less barrels sometimes.