The group below is a .22 rimfire group and consists of five shots. It has caused some controversy over on the Rimfire thread, at least with one very upset poster who vehemently disputes the measurement between the two widest hole centers of .1915" as show on the calipers.

Since the guys on the benchrest forum should know something about measuring group sizes, please put your eye on the group and provide your best estimate of whether the group is closer to the measurement represented, or more like .300" as the irate poster estimates.

I realize that your frame of reference is limited, but the holes were made by a .22 LR, and the lines on the paper appear to be spaced 1/4".

Have fun:

I personally don't like the measuring tool. I prefer the Neil Jones tool that we use in BR. I think Saaed is measuring correctly, but I don't like the tool. It may be a good one, but I have reservations about it.

How could it be .191 when even one bullet is .224? r in w.

They measure the distance from center of the bullet hole to the middle of the furthest bullet hole or total width of the 2 widest bullet holes and subtract 1 bullet hole from it.

Can anyone dispute the FACT that if two bullet holes DON'T TOUCH then the GROUP MUST be larger than the diameter of one bullet?

How can this group be .191 when 2 bullet holes exactly touching would be .223 AND there are 2 bullet holes in that group which DON'T TOUCH AND have a clearly visible gap between them?

In fact the group will measure at least .26 and could be as much as .30 CTC.

Besides the obvious of using your eyes, one can use a tape, measure the lower left bullet hole and compare that measurement to the ".191" gap. On my monitor the bullet hole width measures almost exactly 1/2 inch or a tiny fraction smaller. The gap measures 1 5/32 inch. Hmmmmm, 1.15625 x .223 = .258 inch group and that is for the bottom 3 bullet holes, not the ones that are obviously not touching with the fartherest upper rt hole edge not visible. Now I'd be the first to admit that this is not an exacting method of measurement but I certainly KNOW that it means the group is WIDER than one bullet diameter.

In case there is any doubt, I'm the one who disputes the GROUP size of this and every one in the whole series that I have looked at. I came to these conclusions by simply looking at the relationships between bullet holes and comparing that to the "measured" group size. It can be roughly verified by the "measuring" I did above (which is the first time I've done it simply to prove the point because your eyes will tell you the measurements are not correct), but you eye and mind will get you closer to a real result than almost all of the "measured" groups.

Hey Cholly,
I'm not arguing against you. I don't like the measuring tool.

Butch:

I think that's a big part of the problem. I've never used one like that, but it seems obvious to me that it tends to obscure the edges of the bullet holes. No one, especially me, believes that Saeed is doing it deliberately.

Considering that there are not hundreds of groups to measure, the simplest way would be to simply lay a mic on the edges of the two outside bullet holes and subtract .223, all this done on a flat surface, of course. It might not be totally exact but it would certainly be within a thousandth or two.

I always thought it was outside to outside minus the bullet diameter.

Peg, Just what I said.

outside to outside won't get you a measurement within one or 2 thousands. .020 is close on outside measurements.
Its over 1/4".

I think you need to add half a bullet hole diameter to the number you show. If you had a two-shot group with zero gap between the two, like a figure eight shape, that group would measure; from outside to outside edge .448" (2x.224") minus one caliber, .224" for a .224" group.

I would hazard a guess, that your number, .191" is the space between the two outermost holes.

Add half the bullet diameter, .112" and you end up with a group that measures .303", pretty close to bglenn's estimate.

Rich

However you measure, outside edge to outside edge minus bullet diameter or center to center, it still comes up ~.191

quote:

Originally posted by Idaho Sharpshooter:
I think you need to add half a bullet hole diameter to the number you show. If you had a two-shot group with zero gap between the two, like a figure eight shape, that group would measure; from outside to outside edge .448" (2x.224") minus one caliber, .224" for a .224" group.

I would hazard a guess, that your number, .191" is the space between the two outermost holes.

Add half the bullet diameter, .112" and you end up with a group that measures .303", pretty close to bglenn's estimate.

Rich

I'm with Rich. I believe the tool gives the group a 1/2 caliber "credit" so to speak...that is not correct.

The tool measures the diameter of a bullet.

The group is about .22 I put a picture on one of the other "measure this group" threads.

Sorry, but I also agree it is impossible to have a group smaller than .222 unless the unless the outside holes are overlapping. That measurement is incorrect.

The caliper should be zeroed with the brackets completely closed and then set around the edges of the farthest two holes.

You can clearly see that the gap between the flat edges of the brackets is also larger than .222 I think the the caliper must have not been zeroed correctly.