Don’t Over-Chamfer Your Necks — Bullet Damage Can Result
Shaving bullet jackets is a problem reloaders encounter from time to time. It can be caused by excessive neck tension, burrs on the case mouth, or over-aggressive chamfering that leaves a ragged edge on the case mouth. Larry Medler discovered some rounds where the bullet jackets were getting shaved. Diagnosing the problem, he found that this was caused by his outside neck chamfer. He was using a powered screwdriver to rotate the case, and over-cutting plus tool chatter was causing the case neck to roll inwards. This created a thin, sharp edge that actually cut into the bullet jacket as the bullet was being seated.
Larry has a Load Force 250 measuring instrument that records the dynamic bullet seating force and displays the results on a computer screen. Larry noted that spikes in seating force were associated with the cases where the bullets were shaved. Inspecting the cases, Larry realized what was happening. Chamfering the outside after doing the inside allowed his tools to cut too much. Combined with tool chatter, this actually created a sharp, ragged edge that rolled inward towards the bullet: “I discovered I had rolled the case mouth rim inward while deburring the outer edge. When deburring the case mouth on the outside edge, every now and then I could hear some tool chatter. The effects of this chatter really show in the picture.”
The above chart shows the dynamic bullet seating force for the bullet with the shaved jacket. Note the large initial force used to cut and scratch the bullet outer surfaces. The final seating force of 47 pounds is just before the Wilson Seating Die bottoms out and the force on the load cell jumps. The chart below shows normal bullet seating force.
As a fix, Larry decided to reverse the neck deburring operations. Now he deburrs the outside first. This reduces tool chatter and prevents the edge from rolling over, because the neck thickness has not been thinned by inside chamfering. While Larry uses a powered screwdriver to speed his case processing, the lesson applies to those who chamfer manually as well–do the outside first and never overcut.
Remember, you simply want to remove burrs and create a slight chamfer. You don’t want to thin the brass significantly at the case mouth. This is why it is important to be very careful when using a deep-angle cutter such as the K&M inside neck chamferer. Click HERE to read Larry’s full report on neck chamfering, with more details on use of the Load Force 250 measuring instrument. Using device such as this, or a K&M arbor press equipped with a seating force gauge, will help you diagnose problems with your neck tension and reloading procedures.
Similar Posts:
- Neck Chamfering and Bullet Jackets
- Reverse Your Rocket Tool for a Smoother Inside Neck Chamfer
- Tools to Chamfer INSIDE of Case Necks — Various Angle Options
- Neck Chamfering Tools–Assortment of Angles Available
- Inside Chamfer Tools — Sorting Through the Options
Share the post "Don’t Over-Chamfer Your Necks — Bullet Damage Can Result"
Tags: Brass, Bullet Jacket, Chamfer, Larry Medler, Necks
I’ve been using the K&M inside taper neck reamer for years, turning by hand, or with the cutter shaft mounted to my Forster case trimmer, and I’ve never experienced anything like the pictured cases. I take a very light outside cut with the “rocket ship” de-burring tool, followed by another light inside cut with the K&M to the recommended depth of 1/32″. Flat-base bullets start into the case mouth without any undue pressure required, and certainly without the extreme damage as shown. Maybe the pictured results are one of the reasons I never use any type of a power tool. Works for me.
I discovered the importance of “gently” using a VLD rebutting tool when working with moly coated bullets. Almost no matter what you did with a 45 degree debarring tool, the moly coating was damaged. The seating force required when using a VLD rebuffing tool is almost always less.
Chucking one of the hand held VLD tools in a drill is quick and gives a much better “feel” than doing them by hand in my experience.
Even where there is no obvious visible damage to the bullet, one has to be suspicious of damage to the core when the seating pressure is great.
I’ve been happy with the RCBS 3-way cutter for the inside chamfer, outside chamfer and trim all in one motion type thing for awhile. Maybe there is some thing to it after all and it’s not just some gimick.
I have never seen a neck so damaged in my life. I am sure this was overdone to prove a point, but if this is a common event in your reloading procedure, you might consider getting glasses and taking a valium.
I needed this article! I have had trouble with my 6.5 BPC cases shaving bullets from the start. (though less severely and more evenly than shown.) I too use a screwdriver and do the outside last! I recently started using the deeper/larger part of the Lyman M-die to open the mouth a bit more. it seems to fix the shaving but I am getting uneven tension (I can feel it now.) I need a bushing die but I might have to settle for a new chamfer right now. (It shouldn’t take too long to get the bucks for a FLbushing die from C&H though.) Thanks!
This is why you ALWAYS outside chamfer first and then do your inside chamfer second. about any load manual printed in the last 50 years mentions this. Pretty basic stuff.
I think this was probably done by the fingers in a lee die. And i never seen anything like it either. Im sure a regular sizer or seater will not do this.
Varmint al has some great tips on using steel wool to smooth out and ridges left by cutters.