MV related to barrel life

[Dunraven]

What typically happens to MV as a barrel approaches the end of its expected round count? Can this be used to predict the end of a barrel? Have a 6XC barrel where I used MV of 2925 last 2 years. This year the same load shot high enough that the program had to be modified to nearly 3100. Barrel has over 2300 rds. Thx.

 

[Sheldon N]

Normally as the barrel wears the muzzle velocity slows and the gun will eventually start throwing fliers and not group as well.

If your barrel is now suddenly going over 150 fps faster that's concerning and a sign of excess pressure. Couple possible causes for increased speed come to mind. One would be a carbon ring that is crimping the bullet/case causing the pressure to build excessively before the bullet releases. Another might be that your brass is too long, same net effect of crimping bullet in case and preventing release. Last option I can think of might be that you just changed lots of components and went from a very slow lot of powder to a very fast lot of powder. 150fps for a lot to lot change would be higher than I would expect though.

If I were in your shoes I'd be cleaning the barrel and attempting to get rid of any carbon ring. Might need a borescope to confirm, or you could just do some of the cleaning regimes out there for carbon rings. My own approach is using CLR soaked patch in the throat and a bronze brush.

 

[_Raining]

Did you confirm your zero? From reading your post it sounds like you are not actually measuring your velocity but making assumptions based on elevation needed to dial to a distance.

 

[Dunraven]

Confirmed zero before last match but will check it again . Cleaned barrel, I thought thoroughly, this winter with eliminator and wipe out. Could try it again. The carbon ring ideas sounds plausible. Have not changed powders in a year. Brass is trimmed after every firing. Have not checked chrono readings lately. What seems most important is that elevation poi is accurate at distance(starting at 450, n this gets me pretty close out to 950 here). I don't really care what the chronograph says, if it doesn't coordinate with the ballistics solution. Don't know any other way to do it.

 

[_Raining]

Well aside from small imperfections in the chronographs results, you typically want to true by using the real MV and then changing the BC. In the real world things degrade, including any of the tooling used to make the bullets. So the BC listed on the box isn't going to be perfect. We can't measure BC but we can measure MV so you want to true the BC not your MV unless you have no way to getting access to a chronograph. Also note that there will be small error in your scope tracking, this is very difficult to measure because you need exact measured distance to the target and you need the target to be squared up to you, you can't be shooting at an angle or if you are then you need to take that into account when doing the math etc.

Also note that getting rid of a carbon ring is not easy, you can search it up on the hide. Chances are the things people suggest to get rid of one is not something you did with normal cleaning.

 

[Dunraven]

I asked that question once about whether BC or MV should be changed in the program. Got no answer then. If I understood the Kestrel .instructions, a difference in elevation poi was measured in mrads(or moa), as either plus or minus. Then the kestrel program automatically adjusted MV. That's why I started adjusting MV until I got the correct poi. Adjusting bc does make sense. All part of the journey out here.