Barrel slugging -5 groover- What is a guy to do?

[Paddy]

Trying to slug a 300aac barrel I have and it's proving tougher than I imagined. I pounded a ball of 000 buckshot through it and got a clean impression. But, the grooves are very faint on this barrel, and of course there are 5. So, my calipers tell me upon repeated measuring around the diameter either .305" or .306". Seems a bit tight?

Anyway my initial research indicates that accurate measurement of odd groove bores requires special equipment. I have some things, I don't have a V block. I have mics, dial indicators, and good calipers. Help!

 

[Paddy]

Precision dowel placed in a v block, dial indicator zeroed on that, then replace with slug and measure multiple points?

 

[bluetopper]

I never slugged a barrel in my life and I get absolutely no leading in anything I shoot.
Get you some .308 and/or .309 bullets and try them out.

 

[Paddy]

I'm casting my own and they are coming out .308/.309 possibly due to the alloy shrinking but then I'm powder coating them which increases size so I was just trying to figure the best thing, since in a perfect world I'd be sizing these bullets after powder coat and I can have them end up any size I want theoretically.

I don't have a V block so what I just did was prepare a piece of angle held like a v and then zeroed the indicator on a tool that measured .312 in the mics and replaced that with the slug. So then I was able to measure the difference in diameter, and I slowly moved the slug to measure many points. It came back -.009 - .0115 so I take from that my groove depth is .0025" and the OD is .303". However when simply measured with the calipers it came back .305-.306 so I'm a bit confused on that. I guess having the diameter supported on two points throws off the OD calculation, but the groove depth seems fairly accurate so if I take my smaller caliper measure of .305 and add one more groove it comes out .3075" which seems plausible.

 

[Schwing]

you will get more accurate results using a micrometer but I would be inclined to follow bluetopper and size a few in each size and test them for fit and reliability.

 

[clearcut]

IMHO powder coat size to .309 and check for key holing.

CC

 

[Paddy]

Schwing, I have a mic but how does it give a more accurate reading if the object isn't even number grooved? The challenge here is measuring an odd number of sides.

 

[Paddy]

Apparently the v block method can't be done with 90° blocks. So custom blocks need to be made.

 

[ku4hx]

I never slugged a barrel in my life and I get absolutely no leading in anything I shoot.
Get you some .308 and/or .309 bullets and try them out.

This^^^ Your bore will tell you which it likes best. Slugging just creates a known starting point that may lessen the workup to the "right" size.

 

[Paddy]

Okay granted, but at this point I'm more just concerned that I can't measure a 5 sized thing than I am about the question of why measure in the first place!

This is the best attempts I've seen at doing it the "right" way

http://castboolits.gunloads.com/showthread.php?119952-how-I-measured-a-5-groove-bore

 

[mongoose33]

Trying to slug a 300aac barrel I have and it's proving tougher than I imagined. I pounded a ball of 000 buckshot through it and got a clean impression. But, the grooves are very faint on this barrel, and of course there are 5. So, my calipers tell me upon repeated measuring around the diameter either .305" or .306". Seems a bit tight?

Anyway my initial research indicates that accurate measurement of odd groove bores requires special equipment. I have some things, I don't have a V block. I have mics, dial indicators, and good calipers. Help!

Good question. My Ruger GP100 has 5 grooves as well, and I never found a good way to assess the slug.

I reverted to just shooting different sizes to see what worked best.

Interesting link, Paddy--he's measuring a slug from a GP100.

 

[Paddy]

Yeah, now let's see if we can put our thinking caps on and apply some of that math. It's been a while since I was in geometry. Never did take trig because I thought I'd never need it. Guess I was wrong haha

 

[boom boom]

From CastBoolits forum talking about 5 Groove 686 Revolver barrel slugs,
Principle is the same. Haven't tried them with my British rifles though as not firing cast thru them yet.

http://castboolits.gunloads.com/sho...on-5-groove-bore&highlight=odd+measure+groove