BC numbers.......before and after -More info
Jul 6, 2011 16:00:17 GMT -5
Post by Richard on Jul 6, 2011 16:00:17 GMT -5
Below is an excerpt from the Benchrest Central Forum...600/1,000 section.
Dave happens to be a personal friend of my, an accuracy gunsmith and fellow competitor. We live only 30 mi. apart and have traveled to matches together. He has been building benchrest rifles for well over 20 years. He is presently affiliated with Accuracy International fitting and chambering their tactical rifles on his newly acquired (two years ago or so) CNC lathe. He sells a small gadget that allows you to trim the meplats on your bullets by hand with a fixture that has an END mill. The end mill is equipped with a stop so you can uniform all the tips on your bullets. While this does somewhat enlarge the meplat, it does cut them to a uniform diameter. In long range shooting this relates to uniform BC's for lower ES's which translates to less "vertical". He has also played with inserting plastic tips and doing some testing for both Sierra and Hornady. As you can see from the below post on BR Central, trimming/uniforming the meplats did slightly lower the BC by .003 but then adding the plastic tip increase the BC by 3.1%.
Just thought this might be of interest as we are dealing with improving BC on the .40 cal. bullets.
benchrest.com/showthread.php?75519-BC-numbers-before-and-after
Richard
Dave Tooley
Location Gastonia, NC
BC numbers before and after
I stated a couple of weeks ago that I would report accurate BC numbers in regards to meplat trimming and pointing. Below are numbers for a 30 cal. bullet over 200 grs. with the BC averaged between 500 and 1200 yds.
Stock G7 BC .289
Conservative meplat trim G7 BC .286
Pointed G7 BC .298
Trimmed and pointed G7 BC .297
Pointing increased the BC 3.1%
That's inline with the testing I did for Sierra by installing plastic tips in their MK's.
Dave
Charles E
Super Moderator
Thanks, Dave, that's most interesting. Did you get E.S./S.D. data for BC, like when you did the tests on the tipped bullets?
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07-06-2011 Dave Tooley
No I didn't. It was a long day of testing. The first five hours dealing with a virus in three different computers. When we got rolling it was a couple shots then on to the next load before something bad happened. While not a large sampling the numbers are accurate.
After having identified the importance of meplat uniformity years ago and testing and observing all the goings on with pointing I now believe that pointing greatly reduces the influence of the meplat. I have done things at extreme distance we could only dream of 18 years ago.
Dave
Dave happens to be a personal friend of my, an accuracy gunsmith and fellow competitor. We live only 30 mi. apart and have traveled to matches together. He has been building benchrest rifles for well over 20 years. He is presently affiliated with Accuracy International fitting and chambering their tactical rifles on his newly acquired (two years ago or so) CNC lathe. He sells a small gadget that allows you to trim the meplats on your bullets by hand with a fixture that has an END mill. The end mill is equipped with a stop so you can uniform all the tips on your bullets. While this does somewhat enlarge the meplat, it does cut them to a uniform diameter. In long range shooting this relates to uniform BC's for lower ES's which translates to less "vertical". He has also played with inserting plastic tips and doing some testing for both Sierra and Hornady. As you can see from the below post on BR Central, trimming/uniforming the meplats did slightly lower the BC by .003 but then adding the plastic tip increase the BC by 3.1%.
Just thought this might be of interest as we are dealing with improving BC on the .40 cal. bullets.
benchrest.com/showthread.php?75519-BC-numbers-before-and-after
Richard
Dave Tooley
Location Gastonia, NC
BC numbers before and after
I stated a couple of weeks ago that I would report accurate BC numbers in regards to meplat trimming and pointing. Below are numbers for a 30 cal. bullet over 200 grs. with the BC averaged between 500 and 1200 yds.
Stock G7 BC .289
Conservative meplat trim G7 BC .286
Pointed G7 BC .298
Trimmed and pointed G7 BC .297
Pointing increased the BC 3.1%
That's inline with the testing I did for Sierra by installing plastic tips in their MK's.
Dave
Charles E
Super Moderator
Thanks, Dave, that's most interesting. Did you get E.S./S.D. data for BC, like when you did the tests on the tipped bullets?
--------------------------------------------------------------------------------
07-06-2011 Dave Tooley
No I didn't. It was a long day of testing. The first five hours dealing with a virus in three different computers. When we got rolling it was a couple shots then on to the next load before something bad happened. While not a large sampling the numbers are accurate.
After having identified the importance of meplat uniformity years ago and testing and observing all the goings on with pointing I now believe that pointing greatly reduces the influence of the meplat. I have done things at extreme distance we could only dream of 18 years ago.
Dave