Bearing surface tolerance

[JAWZ]

When measuring bearing surface with a comparator guage what do you consider acceptable?

Anything uner .01 of the mean or average ?

Eg. .972----.966 Is this an acceptable difference?


Thanks guys.

 

[boomtube]

Not real sure I understand what you mean. ??

 

[royinidaho]

JAWZ,

Here's what I do.

Just finished measuring a set of 26 Long Range Bullets.

I'm a bit finiky and have a funky measurement system (Sinclair Nut style and an inexpensive dial caliper. Thus lots of measurements and checking to get confidence in any one measurement.


Any bullet under 0.64" or above 0.642" gets tossed in a common bin to be shot as a comparison to the more consistent bullets.

I don't expect to see a difference much under 800 yards. As the bearing surface variations increase it may be assumed that extreme velocity spread increases and become more of a consideration as distance increases.

 

[JAWZ]

I have been measuring 50 300gr smk in 338 and have them 10 from .965 - .968 and 40 from .971 -- .973 in bearing surfce length.

Is the .008 difference between the .965 smallest and the .973 acceptable or should i seperate thm into 2 groups .

Roy you are working on a .002 tolerance correct ?

 

[Boss Hoss]

Roy----I go .001 on mine. Sometimes sorting 1000 SMK's I will have 8 piles some with 450 some with 4. I load everything the same because all of my rifles are built to the same tolerances by the same person who prefers to do it that way and it is the most accurate and I agree plus it is not wise to argue with the Master LOL!!! The only difference is that with the smaller piles I will use them for foulers and sighters as there may not be enough to load for a match or enough to load 100 rounds for a hunting lot which is my minimum to fool with.


Now-----everyone who reads this must understand that in order for this to make a meaningful difference there are many other thing in the process that must be done absolutely correctly or this will be for naught. It is absolutely a necessity to use a tool that will give you consistent and correct answers every time such as the Buhay tool. So don't think you can do this for instance using total length of the bullet by measuring from the base for example. The true bearing surface must be known in order for this to be of any value.


Roy----I know you are doing it correctly but some who read this might think hey I can just measure the base of the bullet and go from there.

 

[royinidaho]

JAWZ, yep +/- 0.001" or 0.002" overall. I'd do +/- 0.0005 as does Boss Hoss, but my equipment is pretty much crap. Plus I shoot only rocks and aminals which are a little more forgiving than putting the calipers to a group on a target.

Boss Hoss - yes I'm striving to measure actual bearing surface. With the tools I'm using I have to determine, as accurately as practicable, an average boat tail length, then measure ogive to base the do the math. As part of my overall process its working well but as I extend the range beyond my current confidence distance I'm going to have to upgrade some equipment.

 

[JAWZ]

Thanks for the advices guys.

I am measuring mine using twin comparators 1 on each side of my callipers.

 

[royinidaho]

Thanks for the advices guys.

I am measuring mine using twin comparators 1 on each side of my callipers.

That's a good way to do it.

 

[Boss Hoss]

The Buhay Tool will get you the readings you need to obtain consistent readings every single time.

 

[Kevin Thomas]

Boss Hoss,

Haven't seen the Buhay tool before. Got any info on it?

Kevin

 

[Mikecr]

http://www.davidtubb.com/tcom_images/reloading/bsc_instructions.pdf