New barrel=less velocity?

[outerlimits]

rebarrelled my open gun and added one of bob L's pro sx comp (bob, it's sweet). anyway, immediately noticed a drop in velocity. chrono keeps proving the point. my load was 8.2 of n350 using 115 hp montana gold bullets.

old barrel got me to 1,470+ fps...new barrel gets only 1,428 fps. the only differences are the old barrel had about 20K rounds thru it, and was a heavier comp. both have TJ holes in them.

can i assume the difference is that the new barrel is tighter (i.e. it ain't shot out)? anyone experience this before?

[rhino]

No two barrels are alike! I'd guess that it's either the bore or chamber or both being a little looser.

[L9X25]

I have an unscientific method that I use to determine if a bore is too small (tight) or too loose (worn out) for a given projectile. Look at the velocity of a group of bullets over the chrono. If the general trend is that the bullets are fastest at the begining, and generally slow down as the barrel gets hot, you barrel is likely on the loose side for the projectile that you are shooting. If the velocities get faster as you shoot, your barrel is likely tight for the projectile that you are shooting.

Some folks (including Wil Schueman) recommend that you shoot a projectile that is .001 to .002 larger than the bore diameter, even with jacketed bullets, for the best gas seal (least wear) and best accuracy.

Obviously the best and most accurate way to find out about your barrel is to "slug" the barrel and find out the true bore diameter.

Leo