Chrono Question

[Blacktail]

I just purchased my first chrono and have only been loading a couple months. I having some difficulty working up consistant loads with the 7 mm stw. But my question is i set it up about 10' from the muzzle. with 72.5 to 73 gr of IMR4831 and 140 TSX or Accubonds getting average of about 3180 fps. I know that should be faster just curious if the chrono is 10 ' away how much does it effect the muzzle velocity reading. This this makes any sense at all..

[J E Custom]

If you have a chronograph with a proof channel it will tell
you what your loss per/foot is ,If not I would guess at your velocity
your only losing about 8 to 10 ft/sec.

I had to build a blast shield for mine because the shock wave would
cause an error in velocities on some of the big bores unless I
moved the screens way out.

The blast shield is nothing more than a 2x4 frame with a piece of
plywood 1/2x3'x3' with a 3''x6'' vertical slot at the matching height
of the screens.

The down side is more noise.

Placed 3 or 4 feet in front of the muzzle,this allows you to set the
screens 5 feet from the muzzel.

The only other reason for setting the screens close is that it gives
you a larger window to shoot through.(Multiple targets with out
moving the screens.

I hope this helped
J E CUSTOM