Bearing Surface

[bdale]

Thanks guys got all the info I needed and then some :

 

[Brians356]

BS is the surface area at the major diameter, the part that contacts the bore.

BTO is the distance measured from the base end to where the diameter of the ogive will first encounter the barrel's rifling.

What is the difference in diameter (if any) between the BOT and BS comparators' bores?

 

[JHardy]

Matt is correct. I have a lot of experience with Mark King's comparator. In fact, I used one to measure the base to ogive of 25,000 bullets for the United States Palma Team in their prep for the Nations and World Palma Championships.
the fixture the bullet enters is key. If it is crap, the measurement will not be consistent. Mark's fixture is very good and smooth.

I have mine set up to measure with a .0005 dial instead of a .001. Just the way I like to do precision work.

Jim Hardy

 

[spclark]

What is the difference in diameter (if any) between the BOT and BS comparators' bores?

Depends on the tooling you use.

I suppose the least doubt-prone method would be to have a device that mimics a given chamber's lead.

 

[Brians356]

What is the difference in diameter (if any) between the BOT and BS comparators' bores?

Depends on the tooling you use.

I suppose the least doubt-prone method would be to have a device that mimics a given chamber's lead.

Ok, let me start again this way: Are you equipped to measure both BOT and BS? If so, do you use the same comparator(s)? If not, why not, and what's the difference?

 

[spclark]

Ok, let me start again this way: Are you equipped to measure both BOT and BS?

Me? No, at least not to the same degree of precision others here may be capable of obtaining.

If so, do you use the same comparator(s)?

For seating depth purposes as well as measuring BTO dimensions I use what used to be called Stoney Pointe (now Hornady LnL) bushings. I know there are more purpose-designed devices for measuring BTO but for my needs the Hornady bushings have been adequate.

If not, why not, and what's the difference?

I tried measuring BS with a pair of identical bushings but because these differ in internal bore dimensions from that of the major diameter of the bullets I use (where the bearing surface is) there's no real precision in it. I've heard of folks wiping a Sharpie on bullets then dragging them sideways across a piece of paper which then leaves a trail of ink in width roughly corresponding to the length of the bullet's bearing surface.... Not being a machinist but familiar enough with the principal behind optical comparators I suspect that such would be the device-of-choice for truly reliable measurements over time.

 

[Brians356]

Thanks.

I use the Stoney Point for any bullet-related measurements.

Maybe someone who does both BTO and BS measurements will step in and detail the comparators used. There has been a lot of discussion of different fixtures involved, but nothing about the I.D. of the comparators.

 

[dkhunt14]

I don't have anything to measure the ID accurate enough. I use the Stoney point to keep track of loaded rounds and steel wool and check the marks on a bullet to see how my throat is doing. By writing that measurement every time I load, I can see how much my throat moves from season to season. You can't use the gizzy to measure because it is the worst. The lead that the reamer cuts and the ogive of the bullet gives you varying Measurements. It takes no pressure change at all to vary the numbers. If you don't want to buy the stand and make your own you probably can call Mark and get the inserts you need for your caliber. Matt

 

[Brians356]

You can't use the gizzy to measure because it is the worst. ...If you don't want to buy the stand and make your own you probably can call Mark and get the inserts you need for your caliber.

What's a "gizzy"?

I am not interested in measuring BS, unless and until I understand the comparator(s) used for that purpose. I'm still looking for details - from someone.

 

[Brians356]

I found the "gizzy":

"short dummy chamber done with your reamer to a scrap of your bbl"

 

[johara1]

It's called a stub and is used to measure how much you set the shoulder back ( head space)…… jim

 

[Brians356]

It's called a stub and is used to measure how much you set the shoulder back ( head space)…… jim

Sure, I know what a barrel stub is for, just never picked up the "gizzy" moniker, what is that derived from (if anything)?

 

[Joe Salt]

brians356 The Buhay comparator will do BS & BTO i check them both ways sometimes to see if they differ!

Joe Salt

 

[Brians356]

brians356 The Buhay comparator will do BS & BTO i check them both ways sometimes to see if they differ!

Joe Salt

What's the I.D. of the comparator for a 6mm bullet (or what have you)?

 

[spclark]

...just never picked up the "gizzy" moniker, what is that derived from (if anything)?

I'm guessing it's a corruption of the slang 'gizmo' http://en.wiktionary.org/wiki/gizmo

 

[Joe Salt]

brian I'm not great at measurements but the 6.5 I have is 263.5 and the 30 cal. is 307.5 hope that helps. Well I should have used my pin gages but used calipers if you need more exact I'll do it tomorrow.

Joe Salt

 

[Raythemanroe]

What shows up more down range, BS sorting, Base to ogive, Overall length, Weight sorting or what is the least effected down range?




Ray

 

[Brians356]

brian I'm not great at measurements but the 6.5 I have is 263.5 and the 30 cal. is 307.5 hope that helps. Well I should have used my pin gages but used calipers if you need more exact I'll do it tomorrow.

Pin gauges, at your convenience, sir. Pick one caliber or the other. If you only have the "go" or "minus" set, what's the largest gauge you can insert? Thanks!