Correct way to calculate group size

[Jayplace]

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?

 

[Bill Norris]

Different paper thickness and texture will leave different size holes. This is where the lesser number comes into play if I understand correctly.

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?

 

[Bc'z]

Inside edge of 1 hole to outside of the other will give you your center to center
Edit... unless they go into 1 hole!!!

 

[Jayplace]

Inside edge of 1 hole to outside of the other will give you your center to center
Edit... unless they go into 1 hole!!!

I would agree with that. However, I'm shooting a 30BR and hopefully, I don't have to many inside holes.

 

[Lucky Shooter]

I'mprimarily a .224 shooter who loves bugholes.

A .224" bullet and good target paper will make a single hole diameter of about .200".

Subtracting .200 from the group's outside edge to outside edge will produce
a fair group size-----not full precision but easy enough for a fun shooter.

I haven't done this for 20 cal and 6mm bullets but think this method would
just as well.

Very simple for approximate group sizes------fun is where you find it.

A. Weldy
























ke

 

[newbieshooter]

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?

NECK BUSHING TEST 30BR

^^^^^^If you get the best tune with a particular neck tension, you may or may not see better results from changing the neck tension. Looking at the horizontal group, I would bet that is more due to the load being out of tune for that particular neck tension, or gun handling one.

forum.accurateshooter.com

 

[jimmymac]

Measure a bullet hole. Dial your electronic caliper to that dimension. Zero the caliper then start measuring out to out. Done.

 

[lotech]

I've measured actual bullet hole size in copy paper and target paper. They are smaller than actual bullet diameter. I've found the best way to measure groups to obtain useful information is by using a ruler graduated in tenths and twentieths. Such measurements are repeatable, while caliper measurements seldom are.

 

[M-61]

I found that Ballistic X app to be the best for me. No more calipers.

 

[JFrank]

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?

Are you scoring targets at an event or just evaluating your own performance ?
Just a follow up- if you’re scoring for a match then get some help but if you are just looking at your own targets, it’s not that critical.

 

[Jayplace]

Are you scoring targets at an event or just evaluating your own performance ?

I'm doing it to evaluate my own groups for load development. However, I would like to be able to compare what i'm doing with what I see posted for matches for comparison also. I understand my shooting conditions may not be the same as what they had, but it gives me something.

I would like to measure the proper way and have a fair comparison to what others are doing.

 

[Jayplace]

I found that Ballistic X app to be the best for me. No more calipers.

I don't know what the Ballistic X is, other than an app. How does it measure groups without calipers or some type of physical measuring device?

 

[jelenko]

I don't know what the Ballistic X is, other than an app. How does it measure groups without calipers or some type of physical measuring device?

https://bulletin.accurateshooter.co...alculates-shot-group-size-from-target-photos/

 

[Jayplace]

I've measured actual bullet hole size in copy paper and target paper. They are smaller than actual bullet diameter. I've found the best way to measure groups to obtain useful information is by using a ruler graduated in tenths and twentieths. Such measurements are repeatable, while caliper measurements seldom are.

I don't think I can read read a scale that accurately any longer. When I was younger, I could barely read a machinist scale marked in 1/100 graduations.

 

[M-61]

I don't know what the Ballistic X is, other than an app. How does it measure groups without calipers or some type of physical measuring device?

I don't know what the Ballistic X is, other than an app. How does it measure groups without calipers or some type of physical measuring device?

Ballistic-X is an app that I think cost $9.00
I’m the last person to ask how it works. Take a pic of your target. Go to the app. Select the target, enter range, caliber, and mark it for 1”. Enter your shots. It will give a lot of information including group size.
There is much better info on this than what l wrote. I’m probably the least knowledgeable person with this type of item. However the fact I can get to work speaks volumes of its simplicity. Here’s an example of what you get:

 

[Jayplace]

https://bulletin.accurateshooter.co...alculates-shot-group-size-from-target-photos/

Ballistic-X is an app that I think cost $9.00
I’m the last person to ask how it works. Take a pic of your target. Go to the app. Select the target, enter range, caliber, and mark it for 1”. Enter your shots. It will give a lot of information including group size.
There is a much better info on this than what wrote. I’m probably the least knowledgeable person with this type of item. However the fact I can get to work speaks volumes of its simplicity. Here’s an example of what you get:

Thanks for your reply.
The phone and I don't get along well so maybe if you don't understand it, but it works for you, I may have to give it try.
For the most part, my phone gets used as a phone.

 

[M-61]

Thanks for your reply.
The phone and I don't get along well so maybe if you don't understand it, but it works for you, I may have to give it try.
For the most part, my phone gets used as a phone.

Me too! Not a single thing with this stuff is natural to me. The fact that I succeeded is actually remarkable. Once I got it down it was perfect. I take a photo of my targets and they are in my ‘album’. When using the app I select it from there and no matter how many times I made mistakes it’s easy to recall the photo and start again. Screwing up does not loose the target.

 

[varget204]

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?

Bullet hole diameter on paper is almost always .015-.020 smaller than bullet. The Solution measure one of the bullet holes,6MM usually around .220-.230, 204 ruger around .185-.190

 

[Jayplace]

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

CRAP!!! That makes my groupes even bigger.

 

[lotech]

It's important to note that some photograph or cut out these groups to keep as a remembrance and show to others. Certainly nothing wrong with that if the groups are measured accurately. With a caliper, it's very easy for the shooter measuring his own group to add a slight advantage, but hopefully most don't do that.

Using a caliper measurement, even if it can't be repeated, makes the group look more impressive and adds considerable effect vs. a "dull", useful, and repeatable group size measured to the nearest tenth or twentieth of an inch with a ruler.