As long as you're consistent I don't guess it matters too much. Most the people I know try a center to center measure. I usually do outside to outside. But that's just when I'm shooting alone. I figure the outside of the hole is the hest out so if you're keeping that inside where you want it it's all good

Largest dimension outside to outside converted to hundredths, minus the bullet diameter is the way it will be done if you ever compete in rifle disciplines, not sure about pistol as I have never competed with one. I have had many groups in the .3's and a few in the .2's over the years with rifle. The last comp I went to was won with a .187" group! There have been a couple of zero groups scored, but not many.


EX- 5 shots measures 3/4" outside to outside 3/4" = .750

.750 ( group size in hundredths ) minus .308 ( bullet diameter ) = .442 group size


As you can see 3/4" groups will get you nothing in a rifle comp. I generally have to get into the low 3's to get in the money, and the 1's or 2's to win.

The only way you can compare accuracy of different calibers is by using center to center measurements.

Using outside when comparing a .22 group that measured .35 outside to a .45 group measuring .45 would yield a misleading conclusion.

My method therefore is use of C/C values.

Originally Posted by TOF

The only way you can compare accuracy of different calibers is by using center to center measurements.

Using outside when comparing a .22 group that measured .35 outside to a .45 group measuring .45 would yield a misleading conclusion.

My method therefore is use of C/C values.

That is why the big bores are so dominant in rifle competition, and the reason I switched to a .338 edge for competition. The 6 and 6.5 mm have far better ballistics, but you are giving up almost a full hundredth of an inch by using them. Now when it comes to the limited class I always shoot my 6.5x.284, or my 7mm RUM. If I could ever figure out a way to get a .458 win out to a thousand yards thats what I would use in the unlimited class, and I would win every event based on the 2 hundredths advantage I would have before I sent the first round downrange.

The problem with center to center is that most groups in competition are one ragged hole, pretty hard to find 1 center, much less 2!

Originally Posted by tropicmaster

That is why the big bores are so dominant in rifle competition, and the reason I switched to a .338 edge for competition. The 6 and 6.5 mm have far better ballistics, but you are giving up almost a full hundredth of an inch by using them. Now when it comes to the limited class I always shoot my 6.5x.284, or my 7mm RUM. If I could ever figure out a way to get a .458 win out to a thousand yards thats what I would use in the unlimited class, and I would win every event based on the 2 hundredths advantage I would have before I sent the first round downrange.

The problem with center to center is that most groups in competition are one ragged hole, pretty hard to find 1 center, much less 2!

unless you can cover all your shots with a 50 cent piece and give somebody 35 cents in change you still need practice