Confused? barrel length and velocity

[Lynum Up]

I just returned from the range. I'm shooting 175gr SMK's out of a Savage 10fp w/ 24" barrel- 1 in 10" twist. The chrony showed 2600fps average. I then switched to a Rem.XR-100 w/ a 26" tube- 1in 12" twist and the velocity dropped to 2525fps average!? I thought the longer the barrel, the more speed? Maybe I'm talking apples to oranges here w/ two differant rifles and actions? The XR-100 (I just picked up) does'nt appear to ever have been fired, so I treated it as a new barrel and cleaned it after each shot, as when breaking in a new barrel. Would a new barrel cause this velocity drop?

 

[Erik Cortina]

Yes, some barrels are slower when new, then increase speed after 100 rounds or so.

But there could be other factors, such as chamber dimensions, freebore, etc.

 

[Erik Cortina]

Yes, some barrels are slower when new, then increase speed after 100 rounds or so.

But there could be other factors, such as chamber dimensions, freebore, etc.

 

[CPorter]

If the new barrel is rougher then friction will slow the bullet down. There is also a point of diminishing returns. The pressure starts dropping off and the power required to overcome friction increases with the cube of the difference in speed. That's part of the reason you don't see 5000 fps all that often despite better powders, metals, etc.

 

[TonyR]

In addition to all of the potential problems previously mentioned, you might also consider the possible effect of changing light levels on your chronograph. I have seen as much 100 fps changes during a string due to passing clouds, shadows from safety baffles and just the changing angle of the sun. I have since acquired a chronograph with Infrared screens which has given me more reliable readings.

 

[blawton]

Almost every single barrel that you put on or start shooting when its new will gain velocities as its being worn in. The friction reduces as you keep shooting it. There is also the bore diam along with bore configuration thats gonna change FPS alot as well. Every barrel is going to differ some if not a lot at times. You have nothing to worry about and the chrono being affected is a good point as well. You just cant beat a infra red chrono. good luck

bobby