Measuring c-t-c distance for 2 holes

[jpretle]

Can someone post the correct procedure??
Thanks,

 

[ridgeway]

Put a pin in each hole, measure outer tangent points and subtract each pins radius if they are different sizes. If identical, just subtract diameter

 

[jpretle]

thank you

 

[Ggmac]

Similar but , same size holes , inside of one outside of other . No math needed . Remember only same size holes

 

[Dud]

Put a pin in each hole, measure outer tangent points and subtract each pins radius if they are different sizes. If identical, just subtract diameter

This but you can further confirm doing an inner tangent measurement and adding radi.

Of course that requires a caliper with good inside and outside jaws.

Depending on how things stack up, you might find a few 0.001"s of slop in the measurement. You can either split the difference or eliminate the slop to get really accurate.

 

[STOMP442]

Ge the Ballistic-X App. Simple as taking a picture with your phone. I haven't measured a group with calipers since I bought the app. Makes it really quick nice and easy and you can have it overlay as much info or as little as you want right on your photo.

 

[Dusty Stevens]

Ge the Ballistic-X App. Simple as taking a picture with your phone. I haven't measured a group with calipers since I bought the app. Makes it really quick nice and easy and you can have it overlay as much info or as little as you want right on your photo.

Have you tried to see if that works on bolt holes?

 

[tobnpr]

^^^^
Never once occurred to me that the OP was measuring group sizes on a target...

 

[Dusty Stevens]

^^^^
Never once occurred to me that the OP was measuring group sizes on a target...

Wonder if he really is measuring targets? And if he is who would trust a gunsmith to do it

 

[Dud]

Yeah, if I had my gunsmith measuring my targets, I would be breaking records for sure.

 

[TAJ45]

Itsa funny how the mind can get on a track...
Having just read/looked at the mill, stock, end mill running at 500+ rpm (guess), I was "in the shop" and was putting gage pins or drill bits in the holes and doing the math for the ctr to ctr distance.
I too never thought about group size.

However, PUHLEEZE dont use bullet dia in your math if using outside to outside. I usually add abt .030" as the paper always "closes up" from the stretching/piercing by the projectile.
E.G. if I have .835 w my calipers, outside to out side, I'll subtract .214 for a 6mm round, or .195/.200 for a .224. This is just a generalized attemp to allow for a known discrepancy. Nothing to obsess over.

 

[jpretle]

It is 'bolt holes', I was measuring.