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Posted: 5/5/2008 7:50:35 AM EDT
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I am planning on getting another upper for my Bushy lower. I have a standard 20" A2 upper and want a 16" M4 barrel. Is it ok to switch my bolt carrier group back and forth between the two uppers or should I get a new BCG with the new upper? Just looking to save a little $$ Thanks |
Don't obcess over it. If the barrel extention was installed correctly on each barrel there should be no problem switching bolts. (Unless the bolt is extremely worn) In which case it should have long headspace in the original weapon it was in. Always good to have a no-go headspace guage handy to do an initial check before using the bolt in a different barrel though. 
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When you put a bolt in there and fire it there is a certain amount of breaking in as the two parts wear against eachother. Eventually they will reach a point where all the rough edges are knocked off and the erosion is minimized. When you put in a different bolt in there the process starts over because the new bolt will have slightly different pressure points. Each time you move the bolt to a different upper the bolt has to wear in against a "new" receiver extension. The whole process accelerates wear on the locking lugs of both the bolt and the receiver extension because a bolt/barrel combination never reaches the point that they are really broken in. |
Good explanation. This is the only real reason to keep a dedicated bolt/barrel combination. Regardless, your rifle is not going to blow up. The military is adamant about keeping the bolt with the barrel. Why? They have a gazillion weapons to keep track of. There is no way they can keep a round count on each rifle. At least you or I might know, "I've fired 4 cases of Wolf through my Bushmaster carbine and 23 SA battle packs through my DPMS rifle." You can at least estimate the amount of wear on the rifle. The only way the military is going to be able to check the rifle for wear is with a Field gauge. If the bolt closes on a Field gauge, they try a new bolt. If it still fails, the rifle is sent to be rebarreled. (Personally, if a rifle's barrel is that worn, I'd chuck out the whole upper half, but that's just me.) I have swapped bolts and carriers among rifles during a troubleshooting session. |
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Conventional wisdom around here seems to be that it is okay to install a new bolt in a used gun, but bolts should not be routinely swapped. I have a new BCG tucked away as a spare; testhopped it in both my rifles with no problem. The TM says specifically not to swap bolts, and having a whole extra BCG is just an easy fix for the problem. BCs don't cost much. Moon |
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