Bearing Surface

[dkhunt14]

Looks to me like the one that Mark King has right down to the printing on the box that the insert sets come in. ark has them made from some guy. John Buhay used to make them and sold to a lot of different guys. He took a new job a few years ago and couldn't use the machinery to make them anymore. He turned everything over to Mark. Matt

 

[savageshooter86]

would be interesting for the shooters who shoot small groups at LR to test the effect of bearing surface differences. Shoot some groups with mixed bearing surface lengths(variance +/- 10 thous or more and shoot against zero variance. See what it shows on paper 8)

I use Buhay Sorter and it works great

 

[bdale]

would be interesting for the shooters who shoot small groups at LR to test the effect of bearing surface differences. Shoot some groups with mixed bearing surface lengths(variance +/- 10 thous or more and shoot against zero variance. See what it shows on paper 8)

I use Buhay Sorter and it works great

That is the very reason I'm giving up on base to ogive measurement and going to bearing surface measurement cause the way i see it bearing surface would have more effect on pressure thus affect FPS and your POI, reason for asking how much variation in your measurements per lot was acceptable, got some good replies and info along the way :

 

[johara1]

Bearing surface is drag as the length changes so does the velocity. I can see it at 100 yds. let alone 1000. ES changes with trimming and pointing. If you don't think it matters don't do it because you don't have a gun that shoots good enough to see the difference. It is all about eliminating variables …….. jim

 

[deadwooddick]

No, the BS or bearing surface is the total area on the side of the bullet that contacts the bore,BTO or base to ogive is the measurement of the bullet from its base to the ogive or the area that first contacts the rifling.

Thanks, still seems to be a disconnect understanding BTO and BS, even w/ your clarification.

 

[spclark]

Thanks, still seems to be a disconnect understanding BTO and BS, even w/ your clarification.

Both are factors affecting the shape of bullets:

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.

Surface area vs. length: two different yet related dimensional characteristics; variations in one can and will affect the other.

Changes in BS will alter friction developed as bullets are fired.

Changes in BTO will affect how much of the mass of a given bullet is behind the point at which the bullet first contacts the rifling when fired. Relatively greater mass behind this point shifts the center of gravity rearward of the bullet's aerodynamic center. (If you've ever sailed a sailboat remember how the steering is affected by where the center of the sail is positioned relative to the mast and keel or lee board(s)?)

Also affects the depth at which each bullet is seated relative to others (which will add to or subtract from loaded case volume which in turn affects pressure curves).

In an ideal world every bullet would be exactly the same as every other bullet in a box. In reality the variations encountered in production make their way down to the end user. If your equipment and shooting discipline are sensitive enough to detect these variations, consistency of performance depends on how well you can "tune out" how these variations that will affect each round you fire.

 

[M14AMU]

Bearing surface is drag as the length changes so does the velocity. I can see it at 100 yds. let alone 1000. ES changes with trimming and pointing. If you don't think it matters don't do it because you don't have a gun that shoots good enough to see the difference. It is all about eliminating variables …….. jim

So....Hmmmm.....what you gonna do about the changing metallurgy within the jacket material?? Just assume that it's all the same?? I think not!

 

[Blaster-37]

For some reason I have had better repeatability with stainless comparators. John Hoover and Mark King have good ones. For bases I use optical comparators from Starrett and Mitutoyo. These measure the thickness of contact lenses and can be purchased used on ebay for 100.00+-. Hoover's gear works well with them. With a 0.01 mm gauge I get very good repeatability, even when I recheck the group a year later. I like that. For most of the high end competitors I know, bearing surface is that important.
We also point, weigh to 0.01 gr. Some of us even run them over our Junke to compare the jacket discrepancy. Every step requires volumes of info and time. The amount of hours spent on 1000 bullets is crazy. Then spend a bunch of time making perfect brass, loads, etc. This insanity is usually the result of having one flier take you out of a record. I don't believe people are born this way.
If you care this much about your gun, rest, etc. also then all you can blame is your skills. It's a choice.
If your not interested in a world record at 1000 yards don't start, you will quickly be certifiably crazy.

Oh yeah, exactly what does measuring the bullet base to bearing surface determine for accuracy or is it simply a lack of options to make the shooter feel better about his bullet sort?
greg

 

[Dos XX]

Blaster,
What do mean by " for bases". Are you talking about a handheld comparator for measuring the base of the bullet?

 

[johara1]

Bearing surface is drag as the length changes so does the velocity. I can see it at 100 yds. let alone 1000. ES changes with trimming and pointing. If you don't think it matters don't do it because you don't have a gun that shoots good enough to see the difference. It is all about eliminating variables …….. jim

So....Hmmmm.....what you gonna do about the changing metallurgy within the jacket material?? Just assume that it's all the same?? I think not!

I'm comparing bullets with in a lot, on the bearing surface length. So metallurgy change of the jacket is not an issue……. jim

 

[johara1]

Blaster,
What do mean by " for bases". Are you talking about a handheld comparator for measuring the base of the bullet?

He is referring to the granite surface plate the unit sits on, go to any machine shop and you will see a large granite surface plate not SS. to check for surface flatness ……. jim

 

[Blaster-37]

I like the all stainless highly accurate Mitutoyo or Starrett Comparator Stand. I get more repeatable results from these than the granite stands, no offense John. Here is an example:
http://www.ebay.com/itm/STARRETT-COMPARATOR-0001-INDICATOR-STAND-/271113621014?pt=LH_DefaultDomain_0&hash=item3f1fa18e16
I have got 3 of them for around 100 each, some for my friends.
greg

 

[Dos XX]

I was thinking that Buhay / King / Hoover unit comes with a small granite base?

I think I feel myself moving further down the rabbit hole.

 

[Joe Salt]

I've been playing with the Buhay comparator for a number of years and yes there is a difference in BS going down the barrel. But every time I change lot numbers the BS changes, I have the number written down that shot the best in my rifles. So if by chance I get close, say 2 thou. of that number I'll buy all I can get of the Lot #. so call it pressure difference or is it the twist in the barrel that BS likes. ??????

Joe Salt

 

[Blaster-37]

I actually use one like this with a flat circular base.

http://www.ebay.com/itm/STARRETT-No-25-B-0-25-0-DIAL-INDICATOR-with-STAND-and-case-/271534869200?pt=BI_Tool_Work_Holding&hash=item3f38bd4ad0

Make sure your good micrometer has enough through to check zero with the gear touching on each other from time to time. These have a very heavy base. I personally like the top handle for fast bullet processing. Up and down with one hand and change bullets with the other. You can set it down on the bullet without cutting into the jacket. Just a slight wiggle and you have an accurate repeatable bearing surface.Bearing surface sorting is a breeze with these.
I don't know why I get better repeatability with these than the granite base. I have both. I need absolute repeatability to 0.01mm now or next year. it will make you smile. I usually put my own micrometer on them. Hoover's gear locks right on the micrometer and the base is perfect. Alot of machinist/shooters make their own stainless bases. I like John's Stainless bases just fine for my 6s and my 7s. Be sure to keep them clean.
greg

 

[DennisH]

I wish I had better pictures, but following are pictuers of the actual bearing surface. I thought it might help. I measure by bearing surface and it seems I shoot a little more accurate with them. I also trim the meplats, plus weigh them after cleaning.

Another picture showing bearing surface.

 

[Blaster-37]

Thanx Dennis, great visual aids.

 

[Catskinner]

With respect to bearing surface, whats the consensus on base of bullet pressure ring diam contributing to pressure. like 0.30835 to say 0.30875 what say you bad or ok except for loading bullet in case?

 

[johara1]

I shoot a.2437 pressure ring and a .2432 shank but my free bore diameter is .2438. Only problem i have is you don't have enough spring back to hold the bullet if you plan to shoot them in to the lands………. believe me this is fact…… jim

 

[M14AMU]

Bearing surface is drag as the length changes so does the velocity. I can see it at 100 yds. let alone 1000. ES changes with trimming and pointing. If you don't think it matters don't do it because you don't have a gun that shoots good enough to see the difference. It is all about eliminating variables …….. jim

So....Hmmmm.....what you gonna do about the changing metallurgy within the jacket material?? Just assume that it's all the same?? I think not!

I'm comparing bullets with in a lot, on the bearing surface length. So metallurgy change of the jacket is not an issue……. jim

You're comparing bullets within a Lot for consistency to wring as much accuracy as possible from your rifle....and I'm saying that within ANY LOT of bullets there is a possible change of metallurgy which possibly would counter-act efforts toward maintenance of accuracy!!