wyrmzr
08-28-2014, 08:09 PM
I managed to have some down time today, along with lots of rain. So, I got time to slug the barrels of my S&W M&P .40 and my 300 AAC barrel.
The .40 turned out well; the measurement was .402 at the rifling, which is what my cast bullets have been dropping at. If I add PC to that, I should have a great setup. I have fired about 20 of those cast with LLA, and they fire and cycle great, but could use some more lube (a bit of leading at the end of the barrel).
The one that surprises me is the 300 AAC. It came out at .308, which isn't an issue, but.... As I pushed the slug down the barrel, at about the halfway point, I got a couple of inches where it simply slid with almost no force. So, about midway down this barrel, the diameter is larger than at both ends. I'm not certain yet, but the diameter may even be smaller at the throat than at the other end of the barrel. I'm going to slug again to confirm this, but it did give me resistance back after the couple of inches of no resistance.
I'm thinking that if the barrel is slightly larger in the middle, that may not be as much of a problem as if it's large at the muzzle. But, it does make me wonder if that will affect accuracy (I can get 1 MOA with this barrel, have fired a few hundred rounds through it). If the muzzle is OK, but the throat is really small, should I try fire lapping to ensure it's broken in, or maybe just fired a whole lot of jacketed rounds through it to break it in?
Looking for any ideas/suggestions. The barrel, for now, is temporarily out of service as I build a new upper for it; I went to .223/5.56 on this rifle by moving to a bull barrel.
The .40 turned out well; the measurement was .402 at the rifling, which is what my cast bullets have been dropping at. If I add PC to that, I should have a great setup. I have fired about 20 of those cast with LLA, and they fire and cycle great, but could use some more lube (a bit of leading at the end of the barrel).
The one that surprises me is the 300 AAC. It came out at .308, which isn't an issue, but.... As I pushed the slug down the barrel, at about the halfway point, I got a couple of inches where it simply slid with almost no force. So, about midway down this barrel, the diameter is larger than at both ends. I'm not certain yet, but the diameter may even be smaller at the throat than at the other end of the barrel. I'm going to slug again to confirm this, but it did give me resistance back after the couple of inches of no resistance.
I'm thinking that if the barrel is slightly larger in the middle, that may not be as much of a problem as if it's large at the muzzle. But, it does make me wonder if that will affect accuracy (I can get 1 MOA with this barrel, have fired a few hundred rounds through it). If the muzzle is OK, but the throat is really small, should I try fire lapping to ensure it's broken in, or maybe just fired a whole lot of jacketed rounds through it to break it in?
Looking for any ideas/suggestions. The barrel, for now, is temporarily out of service as I build a new upper for it; I went to .223/5.56 on this rifle by moving to a bull barrel.