Meplat Trimming - from the base or ogive?

[thefitter]

Lets try this again!

Most meplat trimming systems that I have found index off the ogive.

Giraud
Sincalir
Hoover

The Whidden which uses the Wilson case trimmer indexes off the base.

Which is the best way to go? I posted a thread in another forum and this came up.

"... the bullet OAL is a part of the BC calculation. Trimming to a consistent OAL should, in theory, help make for more consistent BC from bullet to bullet - especially if they are pointed afterwards..."

At first I was not sure because we always worry about measuring at the ogive. However in this case I think that if the bullets over all dimension is the same then the BC is the same. And as long as your ogive is always the same distance from the lands then you are golden. It does not really matter where the base of the bullet is in the case +/- .001

I think therefore that the trimmer that creates bullets with the same BC at the start is the way to go. Then you measure your seating at the ogive. Right? Wrong? Sort of?

 

[Bob3700]

Re: Bullet pointing - from the base or ogive?

What makes you believe that the Whidden die indexes off of the base?

The die uses a Forester BR Seating die. The die insert points the bullet based on the shape of the ogive. That is why John has different inserts for different design ogives. While the system does push the bullet from the base, the insert has the specific point profile ground into it.

The variable when pointing bullets is the Bearing surface. As the BS varies, you have to adjust the die to compensate for this change in length or you can collapse the point of the bullet.

If you sort your bullets for BS length and then point them, you not only increase/uniform the BC of the bullet but you also uniform the muzzle velocity and therefore the vertical on the target.

You will only begin to see these effects at 600 yds but they really come into their own at 1K.

Below those ranges, all the extra work is probably not noticeable on the target.

Bob

 

[thefitter]

Re: Bullet pointing - from the base or ogive?

Sorry I wrote the header wrong. I meant meplat trimming. I'm tired.

 

[mc223]

I meplat trim from the ogive. I use a home made trimmer similar to the Sinclair in a drill press.

I messed around with trimming bullets to a uniform length from ogive datum line to the base for a very short time. Too many other variables to be able to detect any gains or losses

 

[TonyR]

I use the Whidden tools to trim the meplats and then point the bullets after sorting by bearing surface. Theoretically, trimming and pointing should be seperable processes but I have found that the trimming process often leaves a little burr that is hard remove without creating different problems with the meplats. The pointing die gets rid of this burr very neatly so my process is trim-point-trim. Bryan Litz told me to expect less benefit from pointing as the bullet diameter increases. My experience has been consistent with this advice. The effect on BC is easily noticable with the 6mm while it just seems to reduce fliers with the 7mm. I also believe that trimming and pointing may be more beneficial with Berger thick jacket bullets than the thin jacket bullets. Berger is actualy recommending that thick jacket 6mm bullets be pointed but I believe that it also applies to the larger sizes.

 

[johara1]

I use a hoover set up and i found it to work very well, trimming is measured off the ogive. I measure the bearing surface even as Bryan Litz says this is not a true way to judge a bullet and that ogive to base is the best way to judge them.
Pointing i think does change the BC. the percentage would depend on the size of the meplats. Off the bench at 1K it is more noticeable than on the ground in a sling, with the dasher SD is low i even had zero's ES. was 3 and all ways single digits. At 1K vertical is gone, now i only have to deal with my mistakes and the wind.......jim

 

[TonyR]

Jim,
I was at the Berger SW Nationals last week and Bryan talked about a study of bearing surface comaparators he is doing and he is skeptical about some of them; however, I don't believe he has concluded, yet anyway, that none of them work and he doesn't seem to be willing to talk about his findings until he is done. I have personally given up on the back-to-back comparators on a dial caliper and gone to the John Buhay JB Comparator. I like it because the measurements are repeatable for the same bullet while the other method would frequently give a different result for the same bullet. And I have proven, to myself at least, that bearing surface is well worth measuring given some of the extreme variations I have found in the same box of bullets from several manufacturers.

 

[johara1]

Tony, I had a batch of Berger that shot all over the place so i checked the bearing surface with a tubb set up and they were .050 difference in a hundred but if you check them from ogive to base they were very close.Bearing surface is drag,bearing surface also changes pressure. What i'm getting at is this has a direct bearing on vertical.
I proved it to myself at 500 to 1K, BS was held .001,meplats trimed and pointed. Necks were turned primer pockets were uniformed and i don't weigh cases or mess with the flash holes. The gun shot in the mid to low 1's at a hundred over good wind flags at 500 over good flags it shot under .600.
I started shooting 1k last year and a little success,but at 67 i have more to deal with than the wind....jim

 

[TonyR]

I agree completely with everything you've said, Jim, including the part about being 67. My best friend will be getting a new hip this week and I will be getting a cataract removed later this Spring. Maybe I'll finally see what I am shooting at???

 

[LRPV]

I realize that this is an oldy but it was the most relevant search result to my question and unless I missed it, the question never got answered.
So...

What is the best form of meplat trimming, from the base or from the ogive? I realize that to some these are loose terms at best for describing the anatomy of a bullet but I hope you get my basic idea.

Jason

 

[hoverp]

Real simple, call John Hoover, go to his website, find the number. Great guy and has a wealth of know how, behind years of competition.

After talking to him I bought both the pointer and meplat trimmer.

Awesome.

 

[bozo699]

Good read.