Bearing Surface Comparators


August 19, 2009
Upgraded my Bearing Surface Comparator

BSC with Digital Indicator

I upgraded my David Tubb’s Bearing Surface Comparator by replacing the Dial Indicator with a Digital Indicator.  I went to my local Harbor Freight Store and purchased a Cen-Tech digital indicator with my 20% discount coupon.

Mearing Bullet Bearing Surface Lenght

The digital indicator makes the whole bullet measuring process seem easier and faster.  The digital indicator has enough travel that allowed me to zero the indicator at the bottom of its stroke and still read the bullets bearing surface lengths.  This will also allow me to compare different batches of bullets down the road.

Zeroing Bullet Surface Bearing Lenght


 
September 2005 Data Updated

I just recently received my Bearing Surface Comparator (BSC) from Superior Shooting Systems (SSS), David Tubb’s Company.  Prior to receiving this BSC, I ha
d been playing around with my Neal Jones 22 Rim Fire Headspace Checker to measure bullets.  I have two special inserts which allow me to measure 22 caliber and 30 caliber bullets.  I have measured 1000 bullets using the Neal Jones Tool, one 500 count box of 80 grain 22 caliber MatchKings and one 500 count box of 175 grain 30 caliber MatchKings.  Using the Neal Jones gauge, I was able to separate both boxes of bullets into distinct bearing surface length groups.  The measurement using the modified Neal Jones gage includes the boat tail length, so I decided to give David Tubbs Bearing Surface Comparator a try.  First to be processed through my new BSC were the same Sierra 30 Caliber 175 MatchKings bullets that I had separated into basically two groups using my Neal Jones Tool minus 100 bullets from one of the groups which I had loaded and was unable to recheck.

David Tubb's Bearing Surface Comparator
(bsc3.jpg)

The BSC is a pretty slick setup, easy to use and quick.  The BSC costs $134.95 for a single caliber set-up with dial indicator, plus $34.95 for each extra caliber insert.  The first bullets (400) I measured had been pre-measured and sorted using my modified Neal Jones 22 Rimfire Headspace checker with a 30 caliber bullet insert.  Using the David Tubb's BSC it was very easy to refine the separation on the 400 bullets into groups with 0.001 inch incremental differences in the bullets bearing surface length.

When I used the Neal Jones gage, I was able to sort the 500 count box of bullets into basically two piles.  When checking the bullets using the Neal Jones sliding scale, the group of bullets with the longer bearing surface length would only use the first couple of numbers on the scale with a few even too long to be measured.  On the other group of bullets with the shorter bearing surface length, the slide on the Neal Jones Tool would go all the way to the last couple of higher numbers and sometimes off scale.  So I just made two piles out of the box of 500 bullets.  Meanwhile I have used or loaded 100 from the group with the longer bearing surface measurement.   A couple of weeks later I measured the remaining 400 bullets again using the BSC.  I was surprised that I still basically had the same two piles.  All of the bullets that I measured with longer BS with the Neal Jones gauge were all within a couple of thousands and almost all that I checked as being a little shorter with the Neal Jones gauge also stayed in the shorter piles using the Tubb BSC.  That is all but five of the shorter ones, so I either measured five wrong or placed five in the wrong pile.  I will just say that I measured five shorter as being longer using the Neal Jones gauge.  After all it is pretty hard to measure a longer one short and that is my story which I am sticking to.

Measuring and Sorting
Using the BSC I separated the bullets by .001 inch increments. This was much easier and much more repeatable than using the Neal Jones gauge.  The two distinct bullet groups were 7 to 8 thousands apart and there was a .003 inch gap between the two groups.  Comparing the Neal Jones verses the Tubb BSC, the BSC is the clear winner and it beats my Neal Jones gauge hands down.  What is interesting and significant is that the variation I have seen so far all seems to be in the surface zone and not in the boat tail.  This is good news.  It would be a real pain to measure and sort every bullet by the spoiler length.

BSC Operating Tips
My setup includes a locator for the bullet insert or base unit you place under the dial indicator.  I happen to have a small strip of felt with adhesive on one side and stuck a little v-shaped felt locator on the surface plate to automatically locate the bullet insert under the dial indicator.  I drop a bullet into the base unit and then slide the two into the Felt-V which properly centers everything under the dial indicator.  Next I lower the indicator insert down on the bullet boat tail and slightly turn the lower base unit with bullet to get a reading.  The needle on the dial indicator settles right down to well under one thousand of total movement while slightly turning and that is when I decide which pile the bullet would be going to go into.  The BSC setup works great; it’s much easier and faster than trying to use a modified Neal Jones gage.

Added Handle
(bsc1.jpg)

One other thing surprised me with the BSC.  That is the set screw which holds the insert onto the dial indicator stem was the same size #6-32 set screw that is used on the Leupold Scopes Target Knobs.  Lots of the silhouette shooters replace these screws with a longer cap head screw and then never worry about striping the socket head on the set screw inside the scope knob.  I just happen to have a life time supply of these longer #6-32 hex cap head screws.  So the longer 3/8 cap head screw is used on my BSC also.  The longer screw makes a great little handle to raise and lower the insert.


The Results Were Remarkable
The picture and table below show more of my bullet sorting results using the BSC.  The picture shows the results of sorting some 77 grain 22 caliber MatchKings.  The picture shows the little cups which I placed the measured bullets into.  In front of each cup is a Post-it with the dial indicator range written on it.  The little cups are small enough that I may weigh a cup full of bullets on my digital scale and get the bullet count per cup by just dividing the results by the bullet weight.  This little trick was devised after I finished sorting and put the first (400) 175 Seirra MatchKing bullets away.

Cups used for measured bullets
(bsc2.jpg)

The 175 & 77 Gr. bullets in the table below were not presorted using the Neal Jones gage an
d both are also the remaining portion of a 500 count box of bullets.  After playing around for a while I decided to use the shortest bearing surface length as the base measurement and relate all others as plus to the base measurement in .001 inch increments.  This will allow easy comparison between different lots, calibers, and brands of bullets.

Relative Bearing
Surface Length
175 Gr. 30 Caliber
Sierra MatchKing
77 Gr. 22 Caliber
Sierra Matchking
80 Gr. 22 Caliber
Sierra MatchKing
Shortest = Base Length
3
3
40
Base Length Plus .001 in.
15
12
132
Base Length Plus .002 in. 29
0
74
Base Length Plus .003 in. 1
0
80
Base Length Plus .004 in. 11
2
2
Base Length Plus .005 in. 38
15
0
Base Length Plus .006 in. 92
207
16
Base Length Plus .007 in. 17
27
Used
Total Checked
206
266
344

Both the 175 grain and the 77 grain samples in the table above show one predominate group with a slightly longer bullet surface bearing length and a second smaller group with shorter bearing length.  Loading and shooting the sorted bullets separately surely can not hurt anything or make things worse.  In the third column sample are the remaining bullets from a 500 count box that were presorted using the Neal Jones gage.  This box of 80 grain bullets also had two or more distinct groups.  When I load the sorted bullets, I just start at one end.  I also shoot them in the same order so shot to shot variations in bullet bearing surface length are minimized.  I have loaded some of the bullets with the longer bearing surface length and this box had a greater spread than shown.

The 400 Sierra 175 grain MatchKing bullets that I first measured and not shown on the table were from another box with a different lot number and that box also had the similar type of two distinct BS length groups.  So my initial results of sorting with either the Neal Jones gage or the more accurate BSC both yielded similar results, i.e. there were two distinct bearing surface lengths in each box of bullets.  One must wonder about the affect of differing bearing surface lengths may have on muzzle velocity standard deviation and accuracy.  I conclude sorting by bearing surface length surely can not make things worse and this may be one important step in reducing those so called flyers.  After all David Tubbs does it.

Conclusion: The Tubb BSC Works Well and Achieves Important Results
My bottom line for the BSC is that it is easy to use and gives very repeatable results.  I found the BSC is about five times faster to use than my modified Neal Jones gage and the modified Neal Jones gage is in all probability about twice as fast as trying to use a vernier caliper with a couple of bullet comparator insert devices attached to it.  I can have two pills in the cup while you are reading the vernier caliber.  The actual amount of benefit that is gained by this additional step (and the time spent doing it) are opened to question.  Sometimes the time involved with activities such as these may be as useful as range practice.  Mental conditioning is also part of the shooting game and the reloading process may be incorporated into this mental conditioning process.  So while doing some of these seemingly meaningless operations, cleaning primer pockets, turning necks, etc. with little or no measurable benefit, if one thinks about or dwells on those good shots of the past and dreams of great shots in the future, then the time may not be wasted at all but may actually be good mental “R&R”.  The BSC process also fits into my way of thinking, if you can separate a big pile of something into smaller meaningful piles, using some sort of valid measurement technique; it has to make things better.  Whether this additional step in the reloading process produces measurable accuracy gains or not is yet another story.  But we do know that many very successful shooters sort their bullets by bearing surface length, and their results in competition strongly suggest sorting does enhance accuracy, particularity at long range.

So far I am very happy with my BSC and only wish that David Tubbs never told me that the BSC coul
d be used on loaded ammo!  That’s just what I need, yet another to sort ammo I thought was ready to go.

Sierra 223 Caliber 80 grain MatchKing Bullets Sorting Results:
The table below shows my results from sorting Sierra 223 Caliber MatchKing Bullets using David Tubb's Bearing Surface Comparator.  The shortest bearing surface length is the base length and others are in plus one thousandth increments.  Note: there seems be be two or three distinct groups.  I expect to see a little shift if the data when repeating the same batch because the set up is not exactly the same each time.

Bullet Lot Number
 Base 
 +1 
 +2  
 +3  
 +4  
 +5 
 +6  
 +7  
 +8  
 +9  
 +10 
 +11 
 +12 
 +13 
 +14 
 +15 
 +16 
Total
Checked
00158895252626 - 7/05    
19
54
8
3
20
51
101
106
94
31
0
7
10
0
1


505
00158895252626 - 9/05
8
46
14
0
5
33
83
112
95
93
2
5
5
3
0
1

505





















































































































Click here - link to the Modified Neal Jones Gage which indicates similar results sorting SMK’s into distinctive groups.

Click here - link to David Tubbs BSC.

Click here - link to my Blog with more articles and BS.



Larry Medler
anyrange@comcast.net



Rifle Silhouette Shooting

Silhouette Ballistics

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Released - January 16, 2005
Revised - August 19, 2009