x

[Snareman]

x

[mattmillerrx]

Thats what I do but I know some who do center to center.

[Snareman]

x

[jhm]

I use outer to outer, however you loose because of the caliber of the round, a 45 cal. bullet is going to make a larger group than a just as accurate 22 cal. will.   Jim

[Swampman]

The standard has always been center to center.

Using a dial caliper, the group size is measured at it`s two farthest points (largest outside diameter). The diameter of the bullet (in thousandths of an inch) is subtracted from that measurement to produce the true group size.

They also make plastic arbors that fit in the holes for this.

[bilmac]

Center to center. Otherwise these 30 cal benchrest boys would never report the size groups that they can shoot. A 45 shooter could never shoot a group tighter than .45" The edge of the bullet comes in to play when you are target shooting competitively. Then if the edge of the bullet cuts a scoreing ring, it counts as the next higher score. Some guys will shoot a large bore gun just to gain this advantage.

[Bart Solo]

It has been center to center since I was a kid at camp. 

[Graybeard]

Center to center is the standard BUT determing the center of a hole isn't the easiest task in the world to accomplish. So the way I do it is to determine which two shots of the group have the widest spread. I then measure from the same outside edge of them and which outside edge that is can vary depending on the group conformation as well as how clean the edges are.

If the spread is primarily latteral then use left or right edge of both never right edge of one and left of the other. If the spread is primarily vertical use top or bottom edges.

You can measure the extreme spread from furtherest points then subtract the bullet diameter and get the same number but ONLY if the bullet cuts a clean caliber diameter hole. Jacketed bullets seldom do that.

[Snareman]

x

[Don Fischer]

Absolutely center to center. But not being to good at math, there's an easier way. Measure from the outside edge to the inside edge of the two widest shots. That measure will be center to center without subtracting one bullet dia.

[trotterlg]

It also seems to be a common practice to measure a group depending on what will cover it, like a dime or a quarter, not too technical but anyone can lay a dime or a quarter on a target and see if the pattern is covered.  It also favors the small cals, but it is easy and getting 3 touching 44's is easier than getting 3 touching 17's.  Larry

[Graybeard]

Not really. With my .17 Fireball it's quite easy to get three touching at 100. I sure don't own a .44 that will do that.

[mattmillerrx]

I guess it depends on what you are measuring for.  I generally am measuring to determine which load shot the best out of the same rifle, so outside to outside is the easiest fastest method for this since I am comparing the same caliber. 

The few times I have shot for group size competing with friends we measure center to center which can be hard to determine as mentioned and of course gives you the best info for actual group size and in comparing bench rest matches involving various calibers.

I do like the dime/quarter, and for some of us, basketball references cause it can be done quickly and it also gives a good size reference in pictures that are posted.

I noticed you have just started reloading so outside to outside might work for you too if that is all you are doing, but if you are shooting any kind of match center to center is the way to go.  When I finally get set up to shoot in my ranges MBABR match I will measure center to center

[OLDHandgunner]

Always have done mine center to center.

[AtlLaw]

I don't think there is much doubt that the "official" (whatever that means) way of measuring groups is center to center.  This gives the distance between points of impact of the tip of the bullet, not the whole body, and is why bench rest shooters can shoot sub-caliber groups, and, in theory and for scoring purposes, it makes no difference what caliber they use.

I, on the other hand, am a hunter, not a bench rest shooter.  So while I still measure my groups center to center, I just lay my calipers on the target eyeballing the points at the center of the hole.  Close enough for Gub'ment work!     'sides, what's a few hundredths of an inch among friends... 

[bilmac]

I measure mine the same as Atllaw. I only measure to the nearest 1/8" and eyeballing the center is plenty good enough. Let the benchresters worry about the thousanths

[woodchukhntr]

I do the same as Atlaw, center-to center.  Either I estimate the centers, or measure from the outside of one to the inside of the other 2 farthest apart shots.

[Snareman]

x

[bilmac]

If he had wanted the higher score he should have shot a larger diameter arrow. Your buddy sounds like a democrat politician to me making up the rules as he goes.

[jhm]

It is just another one of those things MEN like to brag abt. the fuel economy their vehicle get, how much they get paid, how tight their riflw shoots, and darn I have forgot the other one!!!   Jim

[woodchukhntr]

I don't know archery rules, but there are several different methods of scoring with guns.  In one method the scoring ring has to be touched or broken, while in another the complete hole has to be within the ring.  But we are talking about group sizes and not scoring.  The center-to-center (ctc) method seems to be the one universally used as it does not take the caliber into consideration, so a 1/2" group is the same with a .17 or a .45.

[kiddekop]

The  group of WW2 vets in our gun club always measured center to center so my best 100 yard 5 shot 30-06 group is .234 inch with my glass bedded & leupold scoped Sako Finnbear  shooting 165gr nosler solid base bullets,58gr of imr 4831 with a cci lr primer.

[Snareman]

x

[jro45]

I've always measured Center to center. Sometimes if you get a flier it makes a big group.