perhaps a dumb question.... How exactly do you measure group size???

[Grendel-Gene]

I admit this may be a dumb question.... but just what is the "official" way of measuring a group size?

Do you measure the distance between the two most separate shots in the group? If so, do you measure center hole to center hole or do you measure from the outside edges of those two most distant holes?

Just want to know how to do it correctly.....

Thanks

[LRRPF52]

Find the furthest from each other, and measure center-to-center, or far-side edge of one to near-side edge of another. Not far-side edge of one to far-side edge of the other.

[YutYut]

I was taught center to center of the 2 furthest shots.

[bwaites]

The most accurate way is to measure far side to far side of the two widest seperation holes, then deduct the diameter of the bullet. Thus....

Far side to far side equals 1.264 inches. Deduct the diameter of the bullet, 1.264-.264, and you have a 1 inch group.

LRRPF52's method is also accurate, but sometimes it is impossible to find the inside edge if two shots overlap.

Center to Center is impossible, because you are simply guessing where the actual center is, AND having to guess twice in the same measurement!

[YutYut]

Well put bwaites. I will use that method from now on. Theres also a computer program that calculates the group for you.

http://www.ontargetshooting.com/

[Texas Sheepdawg]

Well put bwaites. I will use that method from now on. Theres also a computer program that calculates the group for you.
http://www.ontargetshooting.com/

I am playing with the free version of that software. It is okay...

[YutYut]

Me too. I have the android version. Ill upload a picture

[YutYut]

it has its flaws but its pretty cool.

[sgt_murf]

The most accurate way is to measure far side to far side of the two widest seperation holes, then deduct the diameter of the bullet. Thus....

Far side to far side equals 1.264 inches. Deduct the diameter of the bullet, 1.264-.264, and you have a 1 inch group.

LRRPF52's method is also accurate, but sometimes it is impossible to find the inside edge if two shots overlap.

Center to Center is impossible, because you are simply guessing where the actual center is, AND having to guess twice in the same measurement!

+1 Use the same method except
On Service Rifle / Competition / Tactical weapons the groups are 20 shots using the furthest distance between the groups gives the best data.
On hunting arms usually 5 shot groups give the best as one usually does not fire more than that hunting (key word is usually)
Cuz when the load is dialed in the wind and elev side are pretty much the same unles the wind is blowing

[Grendel-Gene]

Thanks... I just wanted to be sure so that when I get decent ammo you dont think I am bragging!!! ha ha!!!

[bj139]

I recently measured a group from outside edge to outside edge and subtracted .264 for a .980 group.
I measured center to center and got a larger group.
I then measured a single .264" bullet hole and got .220". WTF?
Measuring edges seems no more precise than estimating center.
Look at post #8 above. The computer hole fits are no better than human judged hole fits.
A human programmed the computer hole fits so it should be expected.
I better stick with center to center. It is the most honest.
"Honest", I haven't used or seen or heard that word used in quite a while. I guess it has fallen out of favor. Sad.

[StoneHendge]

I recently measured a group from outside edge to outside edge and subtracted .264 for a .980 group.
I measured center to center and got a larger group.
I then measured a single .264" bullet hole and got .220". WTF?
Measuring edges seems no more precise than estimating center.
Look at post #8 above. The computer hole fits are no better than human judged hole fits.
A human programmed the computer hole fits so it should be expected.
I better stick with center to center. It is the most honest.
"Honest", I haven't used or seen or heard that word used in quite a while. I guess it has fallen out of favor. Sad.

For whatever reason, bullets usually make a hole smaller than its caliber. Perhaps the resident physicists can explain. I always measure the size of the holes getting punched by the particular bullet in the particular paper that day and subtract THAT from edge to edge.

[Randy99CL]

I saw a rimfire benchrest competition target where there were 5 bulls for a single (sighter) round each, then those 5 holes were measured and averaged to determine bullet hole diameter. Each target group on that sheet was adjusted accordingly.
Makes sense and probably the most accurate way of measuring groups with normal calipers and a magnifying glass.

[JASmith]

For whatever reason, bullets usually make a hole smaller than its caliber. Perhaps the resident physicists can explain. I always measure the size of the holes getting punched by the particular bullet in the particular paper that day and subtract THAT from edge to edge.

The bullet point tends to shove the paper aside. The effect is more pronounced at low impact velocities.

It is also the reason wadcutter bullets were very popular among competition shooters who used revolvers. Semi-wadcutters work almost as well and are more friendly to semi-auto pistols.

[Kswhitetails]

Because the paper or whatever the target is made of has enough elasticity to stretch rather than shear at the outside limits of the perforations, making holes that seem smaller on inspection afterward. Just like water reacts like a solid to a bullet at the speeds associated because it doesn’t have time to move out of the way and cannot compress. Cellulose materials on the other hand can compress, bend, and stretch, especially at high speeds. (Speed in this case referring to the short period of time in which the bullet interacts with the target)