Best bullet comparator design

[rlporter507]

Not looking for the best brand of comparator but wondering which design is better and WHY. A square hole, or a hole that has a Taper to match ojive?? The Area 419, SAC, and Sinclair tools have a taper, Hornady and Ugly Reloading are square.

 

[DngBat7]

Look up the Bob Green comparator on the forum. Or BGC comparator. Hands down the best. He does not make them anymore I don’t think, but usually you can find them used on here. It takes the important measurements that other comparators don’t.

 

[rlporter507]

I did thanks. found this

So determined that the best comparator contact point is bore diameter on the bullet. One thing is this video that is not mentioned, the Sinclair nut comparator i had was tapered at the hole. So his measurements are not correct. He measured the hole, not the larger dia. of the taper. I see on Brownells site, there pictures show one with a taper and one without. So he might have had an older one without the taper, so then his measurements would be correct.
So where I am at now sounds like bore dia contact point is best.
This must be what Area 419 is talking about in this video

being able to measure one style bullet, and having the same measurement for all bullets for that rifle. it would have to contact the bullet at the bore dia to do this. That's the 1 1/2 degree lead angle they have.
That's how I'm understanding it anyhow.
Still, wondering if a sharp hole edge or angle is best.

 

[RegionRat]

A square hole, or a hole that has a Taper to match ojive??

I think you are trying to contrast an edge contact versus a conformal contact surface?

Both can work equally well if the operator keeps the contact forces managed equally well.

In inspection or metrology labs, we would call these tools comparative since the edges on the Hornady style still have a break or chamfer. So they cannot meet the strict definition of a cutting plane at a hole diameter when being used on curved ogive shapes or conical case shoulders.

The friction and contract stress of both styles means you will need to "standardize" how much force you put on them. An area contact will typically be more repeatable than a line contact when inspecting a curved bullet surface, but with that said it doesn't matter in this context. The method is supposed to be comparative, not absolute, and for practical internal ballistics that is better than required when done properly.

Tool set ups that use low friction indicators, with controlled spring forces, tend to be better than hand operated ones because the contact forces are controlled better. That is not to say you can't do this by hand with a 6" caliper and the Hornady style tools, but you must be careful to get good results.

You can learn to use either style tool with some careful attention and dexterity. When we teach new techs, we hand them the GO-Gage or a steel dummy reference bullet to practice with till they gain proficiency and understand the contact pressure and friction issues. Once they have the hang of the tools on steel, we let them loose on brass and bullets.

If you use a "standardized" bullet that you keep for set-up tooling as a reference before every session, and zero your tools against it... you will start to get better results. Same thing applies to shoulder datum tools being zeroed against a Go-gage. YMMV

 

[rlporter507]

Thanks. I ordered the Area 419 holder for the caliper to get more consistency on the bench.
I have not been happy with my results from the Stoney point or Sinclair tools, this could be some of the problem. I'm still going to buy a better quality of comparator, just doing the research to decide which one.

 

[gunsandgunsmithing]

Best is probably a "barrel gizzy", made from the cutoff of your barrel using the reamer used to cut the chamber. It can be used for shoulder bump too, if he cuts the shoulder into it.

There's also this. I make these and they work great but the bbl has to be off. Super easy and accurate. Forgive the hillbilly accent and poor video but hopefully it's enough to give you the idea of how it works.

Finding the lands...Tool!

This is a tool I've used for years for different things, from finding the lands, checking shoulder bump, chambering barrels and even cutting cone depth with an attachment I have inside that contacts a "datum" or reference point from an old bbl that transfers to the new one when cut. Super simple...

forum.accurateshooter.com

 

[Dimner]

I don't think Bob Green is making tools anymore, is that right?

 

[rlporter507]

I don't think Bob Green is making tools anymore, is that right?

I googled him, and a site came up with the tool. didnt try to buy one, so not sure if he does or doesnt.

 

[Tesoro]

Honorable mention to the Hollands for speed and accuracy. They are up in a tiny town in the Oregon coastal range near me. But moving to Montana! State messed with them too much on their shooting range. Typical.