Measuring Groups

[twidle]

Besides Sinclair who else makes a device for measuring groups.

 

[scout1]

twidle, the magic devices I believe you are seeking are a ruler or a set of calipers. Take the most extream outside to outside measurement and subtract the calliber you are shooting.

Example- 100 yrd five shot group measured outside to outside is .750 or 3/4' subtract .308 if that is the calliber you are using and you arrive at your center to center group of .442'

I hope this helps and saves you the money you will spend buying something that does a simple subtraction problem for you.

 

[gambleone]

Yes twidle, what scout1 said. There's no need to buy any expensive item in order to get an accurate measurement. Make sure your lighting is adequate.

 

[NateHaler]

twidle, the magic devices I believe you are seeking are a ruler or a set of calipers. Take the most extream outside to outside measurement and subtract the calliber you are shooting.

Example- 100 yrd five shot group measured outside to outside is .750 or 3/4' subtract .308 if that is the calliber you are using and you arrive at your center to center group of .442'

Subracting the bullet diameter is not precise. The holes are typically smaller than bullet diameter, which I realize might be counter-intuitive, but the more precise method is to measure center-to-center of the outside-most two shots.

 

[Toby Bradshaw]

To measure groups as they would be measured in competition, you need the right tool for the job -- calipers with a plexiglas window that has the common bullet diameters etched in it, with a rubber foot to pin one of the caliper jaws while the other jaw is moved to the other end of the group.

Go to a bechrest tournament and you'll see how it's done and what equipment is required if you need precision to 0.001'.

If you just want to know group size to within a few thousandths, measure the diameter of the black ring produced by a single bullet in your target,it will be smaller than the nominal bullet diameter), measure the diameter of your group outside-to-outside, and subtract the measured bullet diameter.

Toby Bradshaw
baywingdb@comcast.net

 

[AlNyhus]

If you haven't seen Charlie Hood's 'Quick Estimator', take a peek. They are really slick.
Hood Quick Estimator

Hart also makes the atachment that fits on a standard dial caliper to measure groups.

If you're using a dial caliper to measure the groups, you need to subtract the diameter that your bullet makes in the target paper, not the actual bullet diameter. Most .308 bullets will make a hole about .290-ish depending on type of paper, backing material, etc.