Tech Tip: Lapping the Inside of Seating Stems
Here’s a simple task you can do that will give your seater die a more perfect fit to your match bullets. You can lap the inside of the seater stem so that it matches the exact profile of the bullet. This spreads out the seating force over a larger area of the bullet jacket. That allows smoother, more consistent seating, without putting dents, creases, or sharp rings in your bullets.
This process is demonstrated here by our friend Erik Cortina of Team Lapua-Brux-Borden. Erik, one of the nation’s top F-Class shooters and a skilled machinist, explains: “Here I’m lapping my new seater die stem with lapping compound. I chuck up a bullet in the lathe and lap the inside of the seating stem. I put lapping compound on the bullet and also in the stem. You can do the same with a hand drill and bore paste. You can see in the piture below how much contact area the stem has on the bullet after being lapped. This bullet is a Berger 7mm 180-grain Hybrid. ”
READ Related Article on Polishing Seating Die Stems »
Q1: Is Lapping Seating Stems really necessary?
It can be helpful but it’s not necessary to make your seating stem an exact match to a bullet, particularly if you’re loading hunting or varmint rounds. But it is helpful to do some mild internal stem polishing. This should eliminate any ring (or dent) that forms on the bullet jacket during seating.
Photo credit Sierra Bullets.
Sharp edges on a seating stem can cause a ring to be pressed into the bullet jacket — especially with compressed loads that resist downward bullet movement.
Q2: Is there any down-side to the process?
Not really. However, if you shoot many different bullet types for a particular cartridge, you may not want to conform the stem aggressively to one particular bullet design. Lightly lap the inside of the stem to remove burrs/sharp edges but leave it at that. A light lap will prevent a ring forming when seating bullets.
Photo credit Sierra Bullets.
Similar Posts:
- For Better Bullet Seating — Try Lapping Inside of Seating Stems
- Improve Bullet Seating Consistency — Lap Your Seating Stems
- Polish Inside of Seating Stems to Avoid Ring Marks on Bullets
- TIP: Polish Seating Stems to Eliminate Ring Marks on Bullets
- Bullet Seating Advice — How to Avoid Ring Marks on Your Bullets
Tags: Bullet Seating, Erik Cortina, Polish Die Stem, Seating Die, Seating Stem
This is a better way to destroy the seating stem than improve it. Rotating a bullet against a non-rotating, hand-held stem is likely to create a cavity misaligned with the axis of the stem. Please, hold the bullet and rotate the stem.
I used the Wilson die body to stabilize the bullet in a dummy round. I partially seated my bullet leaving some extra stem above the micrometer so that it would turn freely and exert downward force on the bullet ogive. I put some diamond lapping paste inside the stem mouth and a drop of oil on the outside of the stem, then slid it down over the dummy round. The top of the Wilson stem is cut for a flat-head screwdriver. I chucked a long flat-head bit into my hand drill and turned the stem as I kept finger pressure on the base of the trapped dummy round. After 2-3 minutes of honing in this manner the bullet showed a full 1/16″ wide contact patch with the stem interior.