How is bearing surface length measured for boatail bullets?

[Cassidy]

Some sort bullets by weight and by bearing surface length. How is bearing surface length measured for boatail bullets?

 

[dkhunt14]

I use a comparator. It is made for sorting bullets. Matt

 

[jlow]

I use the Hornady LNL comparator with two inserts and body for the bullet in question. With this method, you will not get the actual true bearing surface length since the bodies used have holes that are actually smaller in diameter than the bullet diameter at the bearing surface area, so the number you get is relative (to another bullet or batch of bullets). Not sure you can get absolute lengths as if you increase the diameter of the body to the diameter of the bearing surface, it will just slip pass as it has nothing to grip.

 

[JamesnTN]

I found a machine shop going out of business and bought one just like this one for 1/3 the cost of new.


http://www.amazon.com/Mitutoyo-Optical-Comparator/dp/B000R896BO/ref=sr_1_3?ie=UTF8&qid=1409708682&sr=8-3&keywords=optical+comparator

 

[jlow]

Yea, cheap - still $2,600! ;D

Seriously, it is a nice machine but I would not like to sort bullets with that puppy.

 

[4xforfun]

+1 on what jlow says. I have Bill Shehanes (D & B supply). it uses two comparitors and a dial indicator. What you are diong is sorting the bullets in reference to each other. I seperate to within .001. I could go as low as 5/10,000, but that is pretty nitpicky!!

I never toss a bullet unless it is flawed. Bullets that are way out get used as sighters-fowlers. Just sort and shoot in groups.

Good luck,
Tod

 

[Brians356]

Can anyone reference evidence that sorting bullets this way has a demonstrable effect on group size (starting with common "match-grade" bullets)?

 

[jlow]

I doubt it very much. Remember even if the bearing surface length change by 20 thousands (like I found in another post), that is only around a few percent compared to overall bearing surface length. The reality with reloading is unlike a laboratory experiment where we can keep almost all the variable constant and only change one at a time (and see what happens), some of the variable with reloading cannot be controlled. For example, things like temperature, wind, and even as simple things as case volume (unless you are willing to throw out most of your brass even buying only Lapua). I understand that everyone really is overwhelmed with the things one has to do in brass prep but these smaller variables if you don’t do your best to control them can add up which further muddies the picture.

 

[Brians356]

Probably the most consistently tiny groups ever recorded were shot using Remington 52-grain Benchrest bullets - unsorted.

I wonder how those Remington bullets from the early 1980s compare in consistency to today's custom bullets, or even to Sierra match bullets?

 

[Changeling]

I would put my money on the 52gr Sierra match ;D

 

[Brians356]

I would put my money on the 52gr Sierra match ;D

The 53-gr MatchKing?

 

[4xforfun]

I doubt it very much. Remember even if the bearing surface length change by 20 thousands (like I found in another post), that is only around a few percent compared to overall bearing surface length.

True...and 48 grains of powder is just like 50 grains...only a few percent off, right?? No big deal.

 

[dkhunt14]

I have seen differences at 1000 with less then a few thousandths. Matt

 

[jlow]

Matt - Not doubting you but did you check all the other parameters? The reason I asked is my recent episode with the Noslers 77 grain CC, I did see 20 thousands difference in bearing surface length, but there was also a different in the diameter of the bullet which resulted in 10 lb less seating force, and it's ojive which resulted in 4 thousands difference in seating depth.

 

[dkhunt14]

I checked the bullet and they were within a tenth. I also ran them through a bushing. They were also within 1/1000 of OAL. so the BC would be close. My Dasher didn't show as much difference as the 300 WSM did. All my testing was done at 1000 so I could see the vertical. I colored 5 bullets blue and five bullets red and shot them just like a match. 10 shots in 30 seconds under pretty decent conditions. MATT

 

[jlow]

OK. So did the ones with the shorter bearing surface length shot a little lower?

 

[dkhunt14]

I don't remember where they went. I just know the 210 VLD didn't go in the group. I think the shorter went low right. Now the Dasher shot the 105 VLD in a random group. So I don't believe a 6 is as critical. Matt

 

[BillPa]

I use the Hornady LNL comparator with two inserts and body for the bullet in question.

Same here...

A .002" under bushing on the ogive and a second on the heel to eliminate any variations of the base in the measurements.

Bill

 

[Cassidy]

Bill - so you are seeing, in the bullets you measured, a 0.009" range in the bearing surface area. It this range of bearing surface area from the same batch of bullets.

 

[deadwooddick]

Same here...

Bill

Interesting that a distribution "bell curve" isn't readily apparent.