Home Forums Hunting & Shooting Ask The Gunwriters Book velocities

Finally got to run some loads over my new chronograph, was a little shocked with my 22-250. I am shooting the Speer 50 SP, I am using the same case, primer, and even a Rem 700 with a 24 inch barrel. My question is, running a max load of Varget, I was only getting an average of 3548, when the manual shows just shy of 3700. The extreme spread was 38 fps. This load shoots great, primers are not flattened out at all, just a little disappointed in the velocity. I understand all about variances in barrels, temp and pressure altitude, this just seems like a lot of difference.

Is this a case where you hear about folks using a chronograph to exceed book loads to meet book velocities? This load shoots good enough that I am not going to mess with it. I've just had this question running thru my mind the last couple of days.

At 500 yards, the difference in trajectory for your FPS vs. book FPS might be about 4"... not worth many tears.

A lot of the book velocities and pressures are derived from test barrels which are often cut to minimum chamber specs. The smaller chamber will produce lower pressures and velocities than a "typical" chamber will.

There are all sorts of other variables, such as the capacity of the brass, seating depth, the characteristics of your particular jar of powder, and the length of your rifle's throat.

If you're really curious, you can stick a PressureTrace on it.

Ummm Denton
I do believe that you ment that the smaller chamber will produce HIGHER pressures & velocities than a typical barrel.

Hawk
I've seen 270fps difference with the same lot of ammo, by simply changing the throat (and it cost me an inch of barrel to get rid of the slophole that was in their). Typical chamber with oversize throat, 2725 average, match chamber and minimum diameter throating, 2998 (Nosler has reported the same loading at 2995 to 3007 depending on issue # of the manual).

Probably the two biggest factors are throat dimensions and powder lot. I have seen velocities vary over 8% just from switching powder lots, though that much is unusual.

My bad.

You are right, of course.

We all get our fingers crossed up, and can't see what we're typing, every now and than. I know I do it on a regular basis.
I think most people knew what you were meaning t to say

Just a little caution. Too many people look at the primer for pressure signs!! In a rifle with proper to tight tolerance for headspace you can run WAY over design pressures before the primer will show flatening. A round that has been neck sized only and fired in the same rifle again that shows a flattened primer is probably too hot.

Wayne

Yup. I once ran a series of pressure tests in an instrumented rifle. Then I popped the primers out, and used a binocular microscope to put them in order from roundest to flattest. The order did not correlate all that well with the measured pressures. It's only a very, very rough indicator.