Bearing Surface Measurement Visual

[dixieppc]

I have noticed some threads in this forum where there was confusion between the difference in measuring base-to-ogive and measuring bearing surface of a bullet.

I then had an idea on how to show what the measurement of bearing surface is. Using my .243/6mm caliber attachment bushing insert set for my David Tubb BSC,

I used a Berger 105 hybrid darkened with a magic marker to show the contact points that the BSC touches off on.

Looking at the picture you will notice a shiny ring on both ends of the bullet close to where the bearing surface begins at the boat tail and in the vicinity of the ogive at the point.

Now, a lot of people have been asking what the length of their bearing surface should be when measuring it. It is not the numerical length of the bearing surface you are after, it is that the distance between those two shiny rings be the same from bullet to bullet. When using a bearing surface comparator, you're looking for consistency in the length between the two shiny rings from bullet to bullet, not what the actual length of the bearing surface is.

There have been some arguments about that you can get the same level of consistency sorting from base-to-ogive measurements which can be set up to do less expensively than bearing surface measurements. I personally do not think that you can get the same level of consistency sorting from base-to-ogive measurements that you can from bearing surface measurements.

I could be totally wrong about any of this. I've been totally wrong about many other things in life. I just thought it would be neat to have some visual aid that shows what a bearing surface comparator is measuring for those that are confusing measuring bearing surface with measuring base-to-ogive.

Regards.....

 

[47WillysGuy]

I use the same method. I sorted a SMK 190gr Match lot of 500 and found projectiles went from .530 to .541 of an inch of bearing surface length. Never tested them to see what the vertical difference, but makes the confidence level a bit higher for me. Anything to help accuracy.

German Salazar has more info on measuring bullets. A good read.

http://riflemansjournal.blogspot.com/2010/09/reloading-measuring-bullets.html

 

[amlevin]

I use the same method. I sorted a SMK 190gr Match lot of 500 and found projectiles went from .530 to .541 of an inch of bearing surface length. Never tested them to see what the vertical difference, but makes the confidence level a bit higher for me. Anything to help accuracy.

German Salazar has more info on measuring bullets. A good read.

http://riflemansjournal.blogspot.com/2010/09/reloading-measuring-bullets.html

I read his article. His conclusion was that there was no accurate way to measure the factors that matter therefore he doesn't sort.

 

[mikecr]

The German Salazar article is not about bullet bearing. It's about his issue with potential seating errors while not individually verified(assumed). He's right, there are errors, but there is no valid reason not to measure every round and verify that they're correct anyway.
What would solve his issue is a BGC(Bob Green Comparator).

dixieppc's right about bearing comparison being different than base-ogive comparison.
But what remains in consideration is that neither measurement is credible until the datums are qualified. That is, ogive radius and base angle. Add to this the lack of evidence that bearing itself even matters.

 

[dmoran]

^^^^^ Good reply.....^^^^^

Comparator(s) hole sizes are smaller then the bullets shank/bearing diameter, there for are qualifying to that diameter.
The bullet shank/bearing also is in between those diameters, and the variance at points A & B are what is being measured. Then like Mike stated: "Add to this the lack of evidence that bearing itself even matters."

 

[Joe Salt]

I measure B.S. also but like Mike and Donovan said seating depth and Diameter play a big part. But make sure your seating stem is the right size for the bullet you are using, and when changing Lot# of bullets make sure the Diameter is the same. Also I stress if you want consistent seating depth lub the inside of your necks. Or you will be galling the bullet and not get consistent seating.

Joe Salt

 

[MrUnderwood08]

As I see it there are several relevant measurements that could be used to sort bullets.

Common ones:
1. Weight
2. Bearing surface between two equally sized datum points (as pictured)
3. Base to upper datum line (transition of ogive to bearing surface)

BUT...
A commonly misused term is ogive. The ogive is the area on the bullet forward of the upper datum line. (The curved portion of the bullet leading to the meplat). Additional datum lines could be established in the curved portion of the ogive (like where seating stems tend to contact) and within the angle of the boat tail. Using a comparator that is smaller than intended for the caliber any two combinations of these datum lines could provide potentially relevant data.

In SMK bullets seating with a redding micrometer seater I seat to longer than intended measure and adjust to the correct length. In doing so I have seen 2-3 specific and different ogive shapes in the same lot. I believe this is because three machines were making the bullets that were then combined. This was in .30 175 gr SMKs. Using sorting methods I believe I could break a lot that contains three distinct shapes into their respective groups.

Hope this makes sense.

Daniel

 

[dmoran]

^^^^^ Great input Daniel....... ^^^^^

And your 1st post here on top of it !.!.!
Welcome aboard,
Donovan

 

[amlevin]

Additional datum lines could be established in the curved portion of the ogive (like where seating stems tend to contact) and within the angle of the boat tail. Using a comparator that is smaller than intended for the caliber any two combinations of these datum lines could provide potentially relevant data.

A friend I shoot with has created a 'tool' he uses to check seating depths. It consists of piece he's cut off his barrel blank and chambered using the same reamer as he uses to chamber the barrel. It is then cut off so when it's placed on the end of a finished cartridge the finished end aligns with the shoulder/neck junction on the case when the depth is correct (bullet against the lands).

Taking this idea forward, one could use an item like this only cut off more so the boat tail of the bullet would be revealed. Then machine a similar "tool" that fits the boat tail and use the two to measure bullets.

A little lathe work and these pieces would fit in the Hornady comparator adapter for use with calipers.