BGC comparator help

[desert shooter]

I just received my BGC comparator and need a little help. I followed the directions that Bob sent with the tool and sorted just 1 box (100) bullets and ended up with 10 sub-lots of different measurements with a variance of 15 thousands between the lowest to highest measurement. I was wandering if those who use this tool end up with that many sub-lots as well and have that wide of a variance between their measurements? I did not clean the bullets as recommended because I was not sure what to use, Bob recommends carb/brake cleaner to clean the tool, but I did not feel comfortable using that on the bullets. What do you use to clean your bullets before measuring them, or do you measure them without cleaning the bullets? Also, how often do you take the tool apart to clean and lube the comparator and stem? Any input is greatly appreciated as this step of reloading is totally new to me and am wandering if I am doing something wrong.I have learned so much from the posts on this site.
Thanks
DS

 

[jlow]

Not to pull this thread too much off topic, but I have never used this tool but it has always intrigued me. However, Just looking at the photos at their website, I have always been confused.

The top photo shows the comparator with the dial indicator on top. I assumed that you just put the bullet inside and lower the tool over it to get a CBTO length. However, the second photo on the bottom shows a comparator attached to a dial caliper with a loaded round inserted. That cannot be the same tool as I cannot see how one tool would work in both situations.

Can someone comment?

 

[BoydAllen]

The tool is designed to do one job, measure the distance between where a seating die's stem would make contact with the ogive, and where the rifling would make contact. Variations in this measurement reflect differences in the shapes of bullets ogives that result in variations in distance from or into rifling of loaded rounds. Bullets ogives are formed with female dies. There is no interior support, so such factors as lubrication and differences in metal grain structure and hardness can result in small but potentially significant differences in ogive shape. If one shoots like with like, and makes appropriate adjustments for different lots, to maintain ogive to rifling relationship, then the effects of ogive variations can be minimized. Of course there are other sources for variation in seating depth that cannot be ignored. This tool can only address one. Another approach is to seat long, measure ogive (near to where the rifling will make contact) to head for each round, sorting them into groups that have like measurements, and then doing a final seating, readjusting for the requirements of each batch. Of course having a micrometer adjustment on one's seater makes this much easier, and none of this will fix a bad barrel, incorrect powder charge, incorrect wind flag read, or any of the other myriad factors that conspire to enlarge groups.

 

[desert shooter]

Thanks to all who replied.
Tom, It is a little tricky learning how to use the tool, but I will apply more pressure and recheck my results. Do you clean your bullets first and if so what do you use?
JLow- the website shows the BGC comparator on the top of the page and the tool that attaches to the calipers shown on the bottom of the page is a different tool altogether. BoydAllen gave a good description of the BGC purpose, I am just learning how to use the tool.
Thanks
DS

 

[jlow]

Thanks desert shooter - I kinda figured that but didn't want to be continued to be confused! ;D

 

[Joe Salt]

desert shooter us Alcohol to clean your bullets, I put the bullets in a little white bucket, stir them around the put them on paper towels and dry them off. When you are dunn look in the bucket and see the crud that is left.

Joe Salt

 

[Martin52]

Repeatable consistent pressure on the base of the projectilve when pressed into the BGC tool I have found is essential for reliable measurements, so you do have to develop a "feel" with this tool and for me it took a few sessions when sorting.

regarding variance, 0.015 does appear significant, it may be attributable to inconsistnet pressure.

I sorted 500 Berger 155.5 FB's yesterday and got a variance across the lot (except for one) of only 0.003.

I ended up with 6 batches each separated by 0.0005.

 

[TimP]

DS,

I would suggest that you just keep playing with the tool until you can get consistent measurements. I hold my tool in the palm of my left hand insert a bullet and push it in with my right thumb and out with my left index finger a couple of times using equal pressure watching the reading. I then sort my bullets into .001 sub lots and depending on the bullet manufacture typically don't have more than five or six with the majority of the bullets within two. Don't forget this is a tenth indicator.

I rinse my bullets with water, strain then roll them up in a towel and shake dry.

I sort .30 and 6mm bullets and typically only clean and lube when switching from one to the other. Which is every 1000 bullets or so.

Hope this helps, Tim

 

[desert shooter]

Thank you to all that have replied, there are so many good shooters on this site who are willing to help.