Velocity Creep

[tm7554]

So i'm working with a 7WSM EW Model 70. Not exactly a long range gun but it will have to work for now. I should also point out that i'm fairly new to hand loading.

My question relates to velocity. In all of my range sessions i've noticed velocity creep around the 3rd round. For a given load, the velocity will really climb. I'll start with the cold barrel around 3080 and end up at 3160 into the 3rd and 4th rounds. Is this common? Seems to be true for factory loads also. I'm thinking it's just the light barrel contour maybe as the 4th and 5th shot start to wander and I have to let the barrel cool.

 

[Lefty7mmstw]

how fast are you shooting your rounds?? Pressure will climb some as your barrel heats up but 80 fps is a bit much within a couple of shots.

 

[tm7554]

I'll shoot those 3 like a minute apart.

 

[Lefty7mmstw]

I'll shoot those 3 like a minute apart.

probably fouling settling in pulling your pressures up a tish. You may also notice a bit of gain from freshly cleaned to fouled if you leave any oil in the bore as lube will tend to drop pressure.
What's it shoot like fouled in?? If it's got a good sd/x and good accuracy then I'd forget about the first shot or two and run it.

 

[tm7554]

I do finish with an oiled patch when cleaning. So you are suggesting the lube could reduce pressure and yield the slower velocity correct?

 

[Lefty7mmstw]

What I am suggesting is you don't really worry about it as long as you know what's going on and can compensate for it. Your oil patch is slicking up the barrel for the first shot or two; do they fall in the group? If they don't you may want to hunt your rifle fouled, as many people do. A shot or two will suffice.

 

[SBruce]

I do finish with an oiled patch when cleaning. So you are suggesting the lube could reduce pressure and yield the slower velocity correct?

IME, an oiled or clean bore either one can cause both fliers and variable velocities. Not always with all guns, but definately does in some. I don't take the chance and always foul the barrel before any testing.

What I am suggesting is you don't really worry about it as long as you know what's going on and can compensate for it. Your oil patch is slicking up the barrel for the first shot or two; do they fall in the group? If they don't you may want to hunt your rifle fouled, as many people do. A shot or two will suffice.

+1, a shot or two maybe three, in the dirt if need be

 

[Mikecr]

It's normal