What causes a slow barrel?

[AndyW]

I have 2 guns that are the same caliber cut with the same reamer, same twist barrels- 10 twist,one is 1" shorter w/ sporter contour,25") and the other is a varmint contour,26") both bullets .010 into the lands and there is a HUGE difference in velocities with the same load. The Caliber is 6mm AI. 230 fps difference between the guns. Maybe the 1" barrel difference is worth 30-50 fps of the difference? Any ideas why such a big difference?

 

[treeman]

andy the slower barrel is probably larger either in grove dimention or bore . the tighter one is probably faster because it makes more pressure. just a guess on my part.______treeman

 

[Rustystud]

There could be many factors. Two identical barrels made from the same lot of steel. The same drill, reamers, stress releiving, button and lapping. Same reamer, brass primers, powder, bullets, seating depth, etc. will shoot a little different period.
Rustystud