Correct way to calculate group size

[M-61]

Bullet hole diameter on paper is almost always .015-.020 smaller than bullet

I have never heard of that. The paper certainly would make it easier or harder to get an accurate read.
My post# 15 was on IBS target. The one with 6 targets on it, what ever it’s actually called. My post was to show what that Ballistics-X program gives you.
Do I shoot targets like this every time? Yeah, in my dreams. But you can add whatever dimension you want to it ( I won’t), it’s still a nice way to get a group size. I have a couple that are a bit better and a whole bunch that are way worse. 21” 30BR. 34.0 4198 Bergers FB I’ve always been a 100 yard guy. Mainly because that’s what most ranges near me have been no matter where I lived.

 

[Old Navy]

I have posted this before but I will again. Turn your target over, push the peddles down and scotch tape them. Turn your target over and you will see the actual hole sizes.

 

[Alex Wheeler]

I have always used my calipers and measured the largest distance from outside edge to outside edge of the group and subtracted the bullet diameter to determine my group size.
I was reading a posting the other day and they subtracted a smaller number for their group. Specifically they used .290 for a 30 caliber.
Did I misunderstand their posting or is that standard practice?

Measure edge to edge if you dont have a group measuring tool. I have measured many 1000s. Edge to edge is the way to go unless its short range then you have to do math.

 

[Jayplace]

I checked the measurement of my target bullet holes and they do in fact measure about .010 smaller than the actual bullet. It's from a 30BR.
I used my calipers with a magnifying glass, so i'm sure it's close. The target was printed on 110lb card stock and cuts pretty clean.

 

[varget204]

CRAP!!! That makes my groupes even bigger.

Use Plastic Callipers lol & wear Sunglasses Helps

 

[Bottom Fodder]

I have posted this before but I will again. Turn your target over, push the peddles down and scotch tape them. Turn your target over and you will see the actual hole sizes.

But this is to simple/ easy, most people now days need to make it complicated

 

[jelenko]

For my own load development, depends on the target paper. For paper that leaves a frayed edge with powder residue, I eyeball center to center. Pretty sure I'm within a few hundredths of an inch.

I have some Caldwell targets that feel like plastic - they cut real sharp and I measure edge to edge.

 

[JEFFPPC]

Something important that has not been mentioned. Scoring for a match be it group or score should be done by one person as we all look and measure differently. Many years ago when I went to the IBS school Michelle Hart had 60 students and instructors measure a target with a 5 shot group. Not 1 person viewed the group as she did. Not 1 out of 60. Recently I took 3 targets measured by any person at a match and measured them. I average .035 bigger than they were scored. Perfect example why one person should measure. Your not measuring a steel block but a paper that can tear funny, have fuzzy ink lines, maybe damp or wet, then you take it home and measure it after it dried, many things that can alter how its viewed. I would be curious to have 60 phones with the Ballistics X app measure the same target in 60 different locations with different lighting conditions. Off all the above mentioned methods I like JimmyMacs the best. Of course everybody is standing outside the scoring shed clambering, " Hurry up, what are you doing in there? .......LOL.

 

[Olde Man]

For reference measure one of your fowlers on that target that you are using. It should compensate for different paper etc.

 

[Greg@wfcustom]

I have posted this before but I will again. Turn your target over, push the peddles down and scotch tape them. Turn your target over and you will see the actual hole sizes.

Plus 1 on ^this
Been doing it that way for 40 years, then I measure them with an "official" reticle attachment
on Starret Dial (non digital) calipers. Very repeatable by the way.
But then I've measured well over 60,000 NBRSA/IBS match targets since 2001!
YMMV
G

 

[PhilC]

Interesting read. I shoot cast competition and after struggling with petals started flattening them about a year ago. Cast leaves a grayish ring outside the hole so I've been using that for my "edge" and measure outside to inside. Adding a roll of Scotch tape to my range bag and will start using Jimmymac's method.