Trimming the bottom of bullets

[LC Tikka]

Does anyone trim the bottom area when preparing bullets and chasing high level accuracy.
As the shot pressure acts only on the bottom of a bullet to push it down the barrel, then if the bottom area is not square and concentric with the bullet centreline, wouldn't the bullet be pushed off its axis as it travels down the bore resulting in some imbalance. Also as this bullet leaves the muzzle the gases would escape uneven, as with a poor crown.
This is something I would never check or do, as I am not into absolute accuracy, although it does seem to be important.
When making quality reloads there are many things checked, indicated, trimmed, weighed, sized, measured and modified. Correcting any error in the bullet bottom area that takes all the force may just be the edge in making your reloads better.
LC

 

[BoydAllen]

The shape of bullets is pretty much determined by the pointing die and the punch that pushes the core and jacket assembly into the die. No, no one that I know of has taken this approach, and I have read everything on accuracy that I could lay my hands on for years. I would look elsewhere. There are enough things to do, that we know work, for a shooter that is new to the accuracy game to learn and do, to keep a fellow fully occupied for some time.

 

[Immike]

Does anyone trim the bottom area when preparing bullets and chasing high level accuracy.
As the shot pressure acts only on the bottom of a bullet to push it down the barrel, then if the bottom area is not square and concentric with the bullet centreline, wouldn't the bullet be pushed off its axis as it travels down the bore resulting in some imbalance. Also as this bullet leaves the muzzle the gases would escape uneven, as with a poor crown.
This is something I would never check or do, as I am not into absolute accuracy, although it does seem to important.
LC

Interesting thought, this is a concern with the large flat based bullets shot from muzzle loading slug guns and most of them use a gas sealing wad and straight starters to avoid the problem. This is the first time I have heard this in center fire. We are at the mercy of the mold or cutting tool in this case. Have you found them to be out of square? With a boat tail would it do anything for it? Interesting question.
This problem is in print in with a diagram in Ned Roberts book.

 

[bheadboy]

gas checks have long been used on case bullets to provide aflat base and tight seal, I doubt jacked bullets can be improved upon.

I have made 53/70 gr 224 and 6mm with carbide dies and they are extremely true.

Bob

 

[sailhertoo]

I've always wanted to set some bullits on an optical comparator and see just how different they are from each other.

 

[Lapua40X]

There are a lot of theoretical discussions on this and other forums about "trimming" bullets in one way or another. I rarely find anything in these discussions about how their "trimming" affects the radius of gyration (essentially rotational stability). Choosing to remove material from a bullet means choosing to alter its original center of gravity. Frankly, I opt for buying quality bullets over trying to imagine I have either the skill or the equiplment to trim a bullet's base to tolerances closer than those produced by today's factory equipment.

 

[300 RUM]

I cant say I have spent hours checking the bottom of a jacketed bullet, but I did one time look into this subject. I used a perfectly cut 90 deg angle gauge and simply sat the bullet on it, then looking to see if the body lined up with the vertical side by use of a back light. I have also machine a block with a drilled hole .309 for .308 bullets with a cross cut through the drilled portion. I then could drop a bullet in to the hole and look at the bottom to see how much was touching or if there was an angle.


In the short the bottom of the bullet at least "Berger's" are the best part of the bullet!

 

[jonbearman]

With the amount of pressure when seating the core into the jacket,I think it would be the least part to worry about.I seriously doubt the base would be out of spec unless the die was imperfect to start with.Worry about the ogive and have a cup of coffee! LOL I would worry about sizing and seating and the sorting of your bullets to be the first priority.