Originally Posted by Varmint Hunter
I shoot all of my loads over an Oehler 35P chronograph. Without exception, every gun I own will shoot slower with a clean barrel. Presumably, no fouling results in lower friction which causes decreased pressure and less velocity.
On average, it takes about 3 fouling rounds (sometimes more) to get velocity up and groups stable and predictable.
I also noticed that the chronograph can give different velocities, on different days, with identical loads, fired from the same rifle. I believe that this is caused by varying light conditions on different days but I'm not sure. I have seen loads vary by close to 100 ft/sec over several weeks of testing. For whatever it's worth, I did send the chronograph back to Oehler for testing and/or calibration but they said everything was right up to specs when they received it.
Roger that. That Oehler 35 if probably giving you very good data - it's top of the line in chronographs.
When I clean my bores, not with a dry patch
, I mean clean back down to the bare steel, I have at times noted substantially lower velocity on the first clean bore shot. It was an eye opener to me, and helped explain why one should always enter the field to engage an animal at long range with a fouled bore. I figured it out when I took two different rifles to the range that I had already collected MVs for. When I fired the first shot out of the first rifle and saw how low the muzzle velocity was, I thought I had made an error and undercharged the case with powder. The next shot jumped up about 100 fps and fit right into the normal velocity range.
Low and behold the very same thing happened when I fired the first shot out of my second clean bore rifle. At that point the
Now - I will say that all barrels seem to be different and I don't see a 100 fps reduction in MV from all of my cleaned barrels. Some barrels aren't much different clean bore to fouled bore. But if I see any trend, it's that my clean bore shots trend toward slower MVs than the fouled bores.
? I have read that the carbon coating layed down in the fouled bore presents less friction to the bullet traveling down the bore than the bare steel itself. I wouldn't bet my life on this being the cause, but that's one explanation I have read most commonly in the past.