Barrel Speed Up

[Josh06]

I have never really noticed a barrel speed up like others have but I think I just had it happen yesterday. I was working up a load for another rifle and brought my 6.5cm that I plan on shooting in hunter matches this year to shoot some groups to make sure I'm at power factor (had picked a load right at 380k). I shot 5, 5 shot groups and it was very consistent until I got to the 5th group. These are shots 100-124 on the barrel.

Group 1 - 2588, 2586, 2583, 2589, 2594 - Avg 2588.2, ES 11.3, SD 3.8, PF 380.4k
Group 2 - 2584, 2578, 2592, 2585, 2584 - Avg 2585, ES 14.3, SD 4.5, PF 379.9k
Group 3 - 2571, 2587, 2583, 2603, 2583 - Avg 2587.3, ES 32.4, SD 10.5, PF 380.3k
Group 4 - 2585, 2587, 2583, 2581, 2597 - Avg 2587.2, ES 15.5, SD 5.5, PF 380.3k
Group 5 - 2599, 2621, 2606, 2606, 2602 - Avg 2607.4, ES 22.6, SD 7.8, PF 383.2

I realize its not huge increase but when I compared the 5 groups it really stood out. Could be statistical anomaly but I think I found the exact moment the barrel sped up with shot 2 of group 5.

 

[Chesterrose79]

Probably what happened. Barrels speed up up to 200 rounds give or take. I would load up 5 more groups and shoot. That will eliminate the chance of it being an anomaly.

 

[toddcdozer]

Ummmmm I'd look at some other reason for that increase. A barrel speeds up reasonably gradually by smoothing out. I can't comprehend that happening on one shot out of hundreds. Id be careful and look at other potential causes such as heat or even chrono issues sunlight etc

 

[Shane Lindsey]

Your speed up will be significantly more noticable. Like 60-80 FPS at least.

My 22" 300 PRC barrel went from 2767 FPS with 58 rounds down the barrel to 2827 FPS with about 120 rounds on the barrel.

 

[Josh06]

Your speed up will be significantly more noticable. Like 60-80 FPS at least.

My 22" 300 PRC barrel went from 2767 FPS with 58 rounds down the barrel to 2827 FPS with about 120 rounds on the barrel.

So maybe this is just the start of the speed up and will stabilize sometime over the next 50-100 rounds

 

[lancetkenyon]

Also, note it was the last group of the day...as temps were warming up I assume.
Not knowing what powder you are using, and where/when you were shooting (I assume Ft Worth area?) and what temps were, just throwing out another possibility of some powder temp stability as temps rose.
Ammo maybe sitting in the sun for the last group?

 

[Josh06]

Also, note it was the last group of the day...as temps were warming up I assume.
Not knowing what powder you are using, and where/when you were shooting (I assume Ft Worth area?) and what temps were, just throwing out another possibility of some powder temp stability as temps rose.
Ammo maybe sitting in the sun for the last group?

Cold north wind and the air temp was mid 60's, cooling off the barrel and suppressor fully between groups. Late afternoon and temp dropped while at the range. Ammo was in the shade/wind so it was probably cooler on the last group than the first. Load is Staball 6.5, Lapua SRP Brass with CCI 450.

 

[lancetkenyon]

Cold north wind and the air temp was mid 60's, cooling off the barrel and suppressor fully between groups. Late afternoon and temp dropped while at the range. Ammo was in the shade/wind so it was probably cooler on the last group than the first. Load is Staball 6.5, Lapua SRP Brass with CCI 450.

Well, there goes that theory...