How do I Measure Group size

[rchouser]

I see people posting about shooting .30 groups and even some .20 groups with their 6mm BR and Dashers etc. Are these being measured across the size of the hole? I am shooting 5 shot groups that will measure about .40" at the longest point in any direction, but, the best I've ever done is about .37" for 5 shots.

What started me thinking about this is that my bullet is .243" in diameter, so, anyone shooting .20" groups is putting 5 shots into a hole smaller than the bullet caliber.

Please someone enlighten me because I know there is something about this group size measurement that I don't know. Also, I am 65 this year so chalk it up to just another old guy question.

thanks rch

 

[Keith Glasscock]

What is being discussed is the center to center distance of the farthest apart holes in the group. in order to do that, most people tend to subtract the basic bullet diameter from the edge-to-edge outside measurement of the group.

Thus:

group outside to outside of 0.5" would be

0.276" for a .224" bullet
0.257" for a .243 bullet
0.192" for a .308 bullet
0.0 for a 50 cal

Also remember that some will post in MOA. 1 MOA = 1.047" @ 100 yards (makes a .201 group sound better (it's a .1!). I don't bother - I just post in inches.

 

[joshb]

Hey! Lots of old guys, here! Some of us ask the same question again, cause we forgot we asked it before. Now, if I can remember where I left my reading glasses, I could accurately measure groups. I usually don't post my group sizes. Too humiliating.

 

[bheadboy]

if the distance at the widest part of the "holes" in your target is .370, you would then subtract the dia of the bullet you fired, realizing the paper will spring back slightly after the bullet passes, actually measuring the "black ring" around the bullet hole is closer as that is powder rubbed off the bullets sides as it passes


so if .370 and you shot a 22br, the .370 - .224 and you have a group of .150"

Bob

 

[TAJ45]

As stated, most folks use the bullet dia as a subtraction constant. However, some disciplines require a single shot to be on the paper so that when measuring groups, an exact example will be "calibrated" to give a more exact measurement. This is in .22 rimfire iirc.

However, many will mention that for more reporting accuracy, something less than than the actual diameter of the bullet should be used as the paper will "spread" somewhat beyond the tear giving a more satisfactory (ego wise) measurement.

It don't amount to squat unless you're in competition. I just usually subtract .2 for my groups shot with a .224 and .220 for the 6mm. dAs far as a black smudge beyond the tears, my eyes don't discern that with the cf rounds. However that is what I go by when scoring the BE targets, rimfire and center fire as they usually leave a pretty good grease/lead smudge.

Like I said, it doesn't really matter much at all. It is what it is.

 

[rchouser]

TAJ45, I agree that it is not so important, but, when I am reading posts and trying to judge what my rifle is doing relative to everyone else, this will give me a point of reference and also allow me to communicate what I am doing accurately.

Busdriver and bheadboy, when I use my 6BR and shoot a 5 shot group that is 1 big hole and using my calipers measure the widest part of the hole at .4, then this would be described as a .16 group? This would be subtracting .24 from .4.

Is this common reporting?

thanks rch

 

[JohnKielly]

I use this program at home:

http://www.ontargetshooting.com/download.html

 

[bheadboy]

rch,

close enough for Gov work, unless you are in comp. as stated above, the bullet actual dia may be .2435 etc. so in matches and champ shooting a test shot is fired to give the dia of the hole per the shooter bullet used.

Bob

 

[mikecr]

With some paper a bullet hole is smaller than cal (this is pretty common), so you would subtract less than cal from a group in that paper. Like TAJ45 mentioned, you should fire a fouler off to the side for reference of what to subtract from grouping width.
You know if the gauntlet's been thrown, and the next beer comes from either your cooler or another bench.

I knew someone who would fully flatten out a 100yd group, subtract full cal diameter, and declare the group in MOA..
If he had a group flattened to 0.5" width, he'd subtract 0.243", which is 0.257 IPHY, but 0.245 MOA.
If he had subtracted a flattened reference hole of 0.220" instead of 0.243", he'd have 0.280 IPHY, which is 0.267 MOA.
Now what in diddly hell does .245 -vs- .267 MOA mean?
Well, to a guy flashing around a wallet group, I guess it means <1/4MOA :

 

[TAJ45]

Mikecr - I love it !!!

"I guess it means <1/4MOA" - good one.

Having never been to backward about being forward, I had a "big time" boob surgeon, I think - well MD anyway, tell me about his 3/8" groups out of a production rifle. Even though he'd invited me to shoot at the range he belonged to, I pulled out of my target bag of shot and virgin tgts some true .375" 5 shot groups out of a 22-250 BVSS repeater with Starkes.

I mentioned that those would caliper the 3/8s allowing .200 for bullet dia. He was quiet for a while. If he wasn't the type to wave his wallet around, I'd have let it slide.......but just couldn't bring myself to do it. We all have our failings and I surely have mine.

 

[tdogg]

I use this program at home:

http://www.ontargetshooting.com/download.html

This is what I now use. Kind of archaic GUI but it works and is a great way to save your targets for future reference.

Cheers,
Toby

 

[Webster]

If you use official NBSRA targets they are made with a special paper that gives cleaner holes. The edges are not as raged.

 

[Mozella]

I use this program at home:

http://www.ontargetshooting.com/download.html

This is what I now use. Kind of archaic GUI but it works and is a great way to save your targets for future reference.

Cheers,
Toby

Yeah, "On Target" is a bit clunky, but it's cheap and really does a nice job of accurately measuring my targets. If, like some guys, you come out to the range with your $600 AR and are happy hitting a paper plate half the time at 50 yards, then you don't worry about such things.

However, once you get down below 1/2 MOA, and especially below 1/4 MOA, measuring precision with any accuracy gets pretty darn difficult. A coin or a carpenters tape ain't gonna' cut it. Some sort of process to scan and computer-score 5 shot groups is required when it gets down to sorting the fly s**t out of the pepper.

Plus On Target software produces all sorts of other useful measurements, including Mean Radius (they call it "Average to Center") which is a real PITA to calculate manually.

 

[NorCalMikie]

If you can cover your 5 shot group with a dime, you don't need no stinkin "On Target". 8)

 

[Mozella]

If you can cover your 5 shot group with a dime, you don't need no stinkin "On Target". 8)

Well, I suppose if you're satisfied with dime sized groups, you may be right.

But plenty of us frequently shoot 5 shot groups which can be covered by a dime. That's only barely less than 1/2 MOA at 100 yards for a .223. When you're fine tuning a charge weight or seating depth in an attempt to get down to the rarefied atmosphere approaching 1/4 MOA, that's exactly when you most need some kind of computer program so that you can measure and fully understand what you're looking at.

 

[Link]

I use targets copied off the net so after I get home I put a piece of scotch tape over the front of the hole or holes and push the paper back in from the rear. When viewed from the front the bullet always leaves a black circle on the paper. This seems to be a true indicator of where the edge of the hole is. Then measure. Good enough for me.

Link

 

[RGRobinett]

I use targets copied off the net so after I get home I put a piece of scotch tape over the front of the hole or holes and push the paper back in from the rear. When viewed from the front the bullet always leaves a black circle on the paper. This seems to be a true indicator of where the edge of the hole is. Then measure. Good enough for me.
Link

I like this!

As for MOA, Inches - unless participating in a registered group tournament, it doesn't much matter - let's see, at 1,000 yards, 0.047" times 10=0.47" . . . I don't know anyone who can tell/shoot the difference. If shootin' beyond a few hundred yards, it's necessary to check and correlate "click"" values/range finders anyway . . . Now, during a registered BR group event, .047 would be, "the end of the world", as many events are won/lost by the artifacts of division, where actually, the result is/was a statistical tie, where a remeasuring of the groups would/could result in a change of placement. Group measurement just isn't that precise. RG

 

[1shot]

I was privileged to attend an advanced 3 week rifle program for experienced designated riflemen. (We all know what I'm saying here right?) The instructor eventually became one of my closest friends and he is the most dry humored SOB on the planet. One of his favorite sayings was Well gee whiz (add you name here) that a fine group. You should have no trouble covering it with a garbage can lid". Totally off topic which I apologize, it just reminded me of the look on the students face when he learned a very terse lesson in life.
Lloyd