Odd Velocity Variance

[AllenOne1]

I have a new 6.5 barrel, 300 plus rounds on it now. The velocity follows an odd pattern that I've not seen before. The first shot is very slow due to a cleaned and oiled barrel, this is expected. The next shot velocity is 40 fps faster than the expected average velocity, speed then begins to slowly walk down until it gets into a "normal" range. Takes about 10 rounds to stabilize and even then I'm getting higher ES than I would like to see.

Brass is annealed after each firing (AMP), chamfered & deburred, neck brushed, sized, mandrel, powder (Autotrickler), bullet seated. Case sizing and bullet BTO are very consistent.

Anyone seen this before?

I'm going to stop oiling the bore after cleaning and see if that makes any difference but I've done that for several years. Not sure what else to look at.

 

[RegionRat]

Sometimes there is a quick fix and sometimes this takes time to sort out. Keep an eye on the velocity and note how it responds to the shot count and cleaning over several sessions.

If you have a borescope, check the condition and type of fouling. Since you are troubleshooting, you will want to do a normal cleaning and at some point go nuclear if necessary, and that requires a borescope.

Keep in mind you may have several issues in play all at the same time or combining in the duration of the cleaning cycle.

Some velocity issues can also come from reloading issues, ignition issues, as well as fouling, but you have to keep an open mind and watch for all of them till you know for certain which ones are to blame.

 

[Emerson0311]

Are you cleaning to bare metal after each range trip?

 

[AllenOne1]

Are you cleaning to bare metal after each range trip?

No, I wouldn't call it cleaning to bare metal. Chemical cleaners and nylon brushes. There is always color along with a little carbon and copper that doesn't come out. No abrasives on this barrel at this point.

 

[Emerson0311]

No, I wouldn't call it cleaning to bare metal. Chemical cleaners and nylon brushes. There is always color along with a little carbon and copper that doesn't come out. No abrasives on this barrel at this point.

Your experience doesn’t seem to indicate a carbon ring. I would take the rifle home after a range visit and not touch the bore or chamber. Go shoot it another day while tracking the velocity of each shot to see if the pattern is still there.

 

[AllenOne1]

Your experience doesn’t seem to indicate a carbon ring. I would take the rifle home after a range visit and not touch the bore or chamber. Go shoot it another day while tracking the velocity of each shot to see if the pattern is still there.

That's a good idea. I normally clean after every shooting session so 30-50 shots then clean. Carbon ring doesn't seem to exist so don't think that is coming into play.

This barrel shoots small so am not ready to go nuclear as a fix at this point. I'll be double checking each step of my reloading process this week just to be sure nothing is flakey there as well.