I took my barrel off for the first time, Yesterday, and discovered that my barrel bolt requires a 5/16" wrench, which, based on the info in this thread, means it is one of the "correctively machined" uppers. Terra indicated, in her post, that a mistake was made on these uppers, and the barrel bolt holes had to be machined for a larger bolt. This fact, on it's own, does not disturb me so much, but werra indicated that his new upper, which was correctively machined, would not work properly with his 6.8 conversion, even though his old upper worked fine, and his resolution appears to have been the acquisition of a replacement upper. I also noticed that my upper appears to have a thread insert in the barrel bolt hole. I guess all of these things, collectively, make be a bit concerned, so I have a few questions. I apologize, in advance, for my rapid-fire questioning, but I decided to try to address all of my concerns with one post, instead of several. I think many of these can probably only be answered by Terra, but anyone who can shed some light, please do so.
Were the barrel bolt holes the only thing that was abnormal, non-standard and/or correctively machined on that batch of uppers?
Why wouldn't werra's correctively machined upper work with his caliber conversion? Do I need to be concerned about the compatibility of my receiver with any caliber conversions that I might buy in the future? When you addressed werra's problem, you suggested he try his old bolt carrier. Was this just to determine if the new bolt carrier was malformed, or is it routine for a bolt carrier/bolt/barrel combination to have to be matched up to work reliably? Should I ask for a matched bolt carrier along with any future caliber conversions I order?
Does my upper have a thread insert in the barrel bolt hole? If no, then please disregard the remainder of my questions. If yes:
Are thread inserts used in the barrel bolt holes of all XCR uppers? If not, what am I lacking, in the way of relative strength or durability, by having a thread insert? I am worried about this because, if, and when, I acquire a caliber conversion, that bolt could be removed and installed on a routine basis, and needs to be tightened to a relatively high torque every time. If my threads are in any way sub-standard, I could be hastening the demise of my upper!
The insert appears, upon casual inspection, to be a bit more shiny than the upper. Is the insert steel or aluminum? If steel, was it plated or coated to prevent a galvanic reaction with the aluminum upper?
Were the barrel bolt holes the only thing that was abnormal, non-standard and/or correctively machined on that batch of uppers?
Why wouldn't werra's correctively machined upper work with his caliber conversion? Do I need to be concerned about the compatibility of my receiver with any caliber conversions that I might buy in the future? When you addressed werra's problem, you suggested he try his old bolt carrier. Was this just to determine if the new bolt carrier was malformed, or is it routine for a bolt carrier/bolt/barrel combination to have to be matched up to work reliably? Should I ask for a matched bolt carrier along with any future caliber conversions I order?
Does my upper have a thread insert in the barrel bolt hole? If no, then please disregard the remainder of my questions. If yes:
Are thread inserts used in the barrel bolt holes of all XCR uppers? If not, what am I lacking, in the way of relative strength or durability, by having a thread insert? I am worried about this because, if, and when, I acquire a caliber conversion, that bolt could be removed and installed on a routine basis, and needs to be tightened to a relatively high torque every time. If my threads are in any way sub-standard, I could be hastening the demise of my upper!
The insert appears, upon casual inspection, to be a bit more shiny than the upper. Is the insert steel or aluminum? If steel, was it plated or coated to prevent a galvanic reaction with the aluminum upper?
