Proper way to measure a group

S

sct

New member
Can anybody tell me the proper way to measure your bullet groups? I couldn't remember for sure. Thanks alot.
Steve
 
Bullet groups are measured from the center of a group of shots (normally 3 or 5)from the same distance. Normaly if you can place a quarter in the center of the group and you eather touch or cover all of the holes you are shooting about a 1 inch group. This is also the best way to zero your scope is to shoot a group of rounds (not just one) and then adjust the center of the group to the bulls eye. Then shoot another group to confirm. Using a good solid rest this should take about 3 or 4 three shot groups.
 
Groups are measured from center to center. Since you can't find the EXACT center of a group. You measure outside to outside at the farthest point. Then you subtract the caliber. Example: Let's say you shout 5 shots. You take the target home and grab your dial calipers and the two holes that are the farthest apart, measure 1.25 inches, and your shooting a .308 or 30-06. You subtract the caliber from this for your group size. 1.25-.308=.942 Your group size is .942, under 1 inch and subminute of angle.
What if you were shooting a .50 bmg, and you shot 5 shots into one hole. EXACTLY one hole. You would measure .50 and subtract .50 and give you a PERFECT group of 0.
 
Correct me if I am wrong Jack but the correct way to measure a group is to first measure the hole in the paper that the bullet leaves. This hole will be from the outside edge of the black smear to the other outside edge of the black smear. You then measure the holes (fartherest away from each other) from outside of said black smear to outside of said black smear, then subtract yout first measurement.

Most bullets will not leave a hole in paper that will be the same size as the bullet diameter there fore if you subtract the actual bullet diameter you are getting a false group size.

Now I know that this is extreme but the question was how to do it correctly. While the method that Bluedeacon will get you danged close (and the one that I use also) it allows for a fudging of actual size /ubbthreads/images/graemlins/wink.gif For casual shooting it isn't going to matter but in competition it does.....James L.

just being a smart alleck Bluedeacon /ubbthreads/images/graemlins/wink.gif /ubbthreads/images/graemlins/wink.gif /ubbthreads/images/graemlins/wink.gif
 
James L.
You are correct. You can only subtract what size hole the bullet makes in the paper, not the actual bullet diameter. There can be a large difference in hole size with different papers.

The only time you need to measure outside to outside and subtract hole size is if you have a one hole group. Most groups can be measured from the outside of one hole to the inside of the other hole furthest apart. That is the same as center to center, no subtraction needed.

Jack
 
In the varmit Calibers I prefer 5 shot groups and in large game 3 shot groups . I use the measure outside to inside and leave out the math. Also as I recal actual MOA is 1.046 but doubt anybody really cares were that number comes from but if you do I will post it.
 
Let me guess/??????? It comes from longitude measurements, It is the measurement of a degree at one hundred yards?????????? Just purley guessing on this one as I can't recall the "exact" definition.

Since most shooters out there (I would guess 99.9 %)lack a way to meanure .046 " they leave the .046 off and shorten it up to 1".

That measurement increases by itself every one hundred yards? . Example.. at two hundred yards it would be 2.092"..At 300 it would be 3.138" on out to 1000 yards (which is the most common long range shot) to 10.460" All of which equal MOA or one minute of angle.....

Those two measurements when put on paper can get confusing also. The symbol " means inch to us but on a map it means minutes

The symbol ' means feet to us but in the context of longitude markings it means degrees. Such as 14'- 6" would mean 14 feet and six inches to us but when put on a map it means 14 degrees and six minutes.. (that one used to tick me off in school)

That is why most people say a "one inch group at one hundred" instead of the correct term of "one minute of angle" at 100 yards

Did I get it right????? Just guessing on some of it as it has been a long time since I tried to recall it out of the depths of my empty head. :eek: /ubbthreads/images/graemlins/laugh.gif .....>>>>>>>>James L.

(Edited 3.152 to the correct measurement of 3.138. I never said I could add /ubbthreads/images/graemlins/wink.gif )
 
Ok so I was wrong , MOA is 1.047197546 The formula is as follows .
360 degrees in a circle and each degree contains 60 minutes and so each circle contains 21600 minutes of angle .
as a result 1 minute of angle is 1/21600 of a given circle .
The circumfrence of a circle in inches = 2x radius of a circle in inches x pi or.
2x(100x36)x 3.1415926=22619.4467.
since one MOA = 1/21600 of a circle 22619.467 inches in circumfrence one MOA would be (1/21600)x 22619.467 =1.047197546

Or if you use a trig caculator it is tan .016666 x 3600

So if you work the formula you will find 1 MOA at 200 yards is 2.0943950942


I am sorry but somebody just had to ask.
 
Pretty good powers of reasoning and deduction there James /ubbthreads/images/graemlins/laugh.gif I made a career out of chasing down bad guys like that /ubbthreads/images/graemlins/laugh.gif (One time when it was just a "little" off we got a S.W.A.T. team to raid this retirement home....)oh never mind /ubbthreads/images/graemlins/laugh.gif
 
SCT, There is another accepted (though outdated) method of measuring group size, the string method. A string is used to measure each hole's distance from the center of the target. Each measurement is added and the total is the group's string. This was the conventional method of measurement in the 18th & 19th centuries. It is where the term shot string comes from. It has fallen from use, I think, because it is less convienient. QJ /ubbthreads/images/graemlins/smile.gif
 
Jack,
Now I'm confused, in measuring a single bullet hole in competion, do you measure the outside edge of the black hole, or just the actual hole itself? I'm talking about one shot. It's just that not so long ago I lost a round because the black touched the line but the actual hole didn't. This was just a bunch of good old boys playing around seeing who could get the closest to the bullseye.
 
ninehorses
You been had.
Shooting at a target with scoring rings, anything that touches the ring gets the higher score. It doesen't even have to go into the ring just be tangent to it. For a normal bullet hole a "plug gauge" is used to judge if it touched or not. The plug gauge is full diameter, but will center in the hole so give a pretty accurate idea of what touched.

If a bullet is tumbling and goes through the target sideways, any part of it touching the scoring ring, gets you the higher score.

How to score targets is spelled out in amazingly minute detail in the rule books. As it needs to be. There are more protests lodged about scoring than any other facet of competition. Finding enough competent scorers to handle a big match can be hard. And heaven forbid rain during the match. Wet targets are a nightmare to score.

Jack
 
LOL - When I looked at the thread topic and saw 15 replies, my thought was "How can it take 15 replies to explain how to measure a group". As Paul Harvey would say, and then there's the "Rest of the story".

Very informative thread.

Dave
 
Originally posted by sct:
[qb]Can anybody tell me the proper way to measure your bullet groups? I couldn't remember for sure. Thanks alot.
Steve[/qb]
Click to expand...
SCT,
For us weekend shooters that all sounded pretty complicated.
For purposes of discussion among "the guys", just measure the distance between the centers of the bullet holes on the furthest apart bullet holes of a group.
 


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