Reverse Your Rocket Tool for a Smoother Inside Neck Chamfer
Want smoother chamfers on your case-mouths? Here’s a simple tip that can: 1) remove the sharp edge left by chamfering blades; and, 2) create a smoother entry for your bullets. Smoothing the inside chamfer can avoid nicks on your bullet jackets, and can also make bullet seating more consistent.
If you are using a 45° rocket tool on newly-trimmed brass, start your inside chamfer with two or three turns in the normal cutting direction. Keep the tool centered, and use light-to-moderate pressure — you don’t need to remove a lot of brass. After your cutting turns (which should reveal a shiny chamfer line), take out the tool, inspect the neck and remove any small brass chips or shavings.
Now here’s the secret — put your tool back in the neck and go in the reverse direction for a couple partial turns. Again, be sure to keep the tool centered and use a light touch. The reverse rotation of the rocket tool inside the case mouth will burnish and smooth the chamfer. Next you can make a quick spin with some fine steel wool held in your fingers. Don’t grind away — you do NOT want to get rid of all the carbon in the neck. As a last step we run a hand-held nylon brush in the neck for 2-3 quick passes to further smooth out the chamfer and remove any residue from the steel wool.
We think, if you use this procedure, your will find that your bullets seat more smoothly and consistently. That can improve accuracy and help avoid mysterious fliers.
You can use this same technique even if you prefer a sharper angle chamfer tool for your initial inside-neck chamfering operation. Reverse your tool gently a couple turns to burnish and smooth the cut. And always remove brass chips and shavings before you run the tool backwards (in the non-cutting direction).
Don’t Forget to Smooth the Outside Chamfer Too
You can also use the backwards rotation trick on outside chamfers to smooth and soften the sharp edge. A little steel wool, applied judiciously, can help here. If you are chamfering a large number of cases after trimming, you may want to tumble the brass in corn-cob or walnut media after the chamfering procedure. Tumbling further smooths the chamfer. You want a nice, smooth chamfer with no burrs or sharp edges.
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Tags: Case Mouth, Chamfer, Reloading, Rocket Tool
Never ran a cutting tool backwards and done anything good for the tool.
Editor: Terry, we appreciate your comment (Terry is the 2012 NBRSA Champion at 600 yards).
But the idea is not to drive the tool with heavy pressure in reverse direction. You are essentially just rolling the tool gently over the edge of the cut with almost no down pressure. I’ve done this for years with no ill-effects (on a forster rocket).
The problems I see most guys having is that they OVER-cut their chamfers or dig in the edge of the blade unevenly. Remember this is just brass… we are not talking about cutting steel with a chamber reamer. Other guys go in way too far with the deep-angle K&M, leaving a knife-edge on the case mouth, which is a bad result.
I agree with the previously posted comment. You don’t run drill bits, reamers, end mills, files backward without ruining them.
Although I usually get some satisfaction by giving the editor a hard time is he gets some little detail wrong, this time I am jumping in on his side (no disrespect to the machinists who have posted).
As an example of the difference between chamfering case neck IDs and other more normal machining operations, about 14 years back I wrote an article about several products that are sold by Holland Gunsmithing, including a chamfer tool that has a VLD angle, and three spiral flutes that are glass beaded, over their entire surface including what started out as conventional cutting edges.
Curious about this detail, I called Darrell and asked the reason for the unconventional approach. He told me that it was done to keep the edges from digging into the brass excessively, which the edges did when sharp. Skeptical, I tried it, and it worked perfectly, producing a smooth burnished chamfer, that was easy to control. Since then he has changed cutters, but I still have the old one, and it still does just fine.
The moral, sometimes things do not work just the way that you expect them to. Rules have exceptions.
Understand that I am NOT telling people to push hard with the tool. You are just rolling it lightly in reverse, maybe three or four, gentle 40-degree rotations, sort of floating over the chamfer. And remember we are also talking about a tool that costs about $16 bucks and will probably work better if it NOT ultra-sharp. As noted my Forster tool is working 100% fine after chamfering multiple 1000s of necks for a full decade. If I have to replace the tool after another decade of use, my tool cost will have been 80 cents a year, less than the price of one piece of Lapua brass. But the reality is that you will lose the tool to rust long before a little light back-spin is going to hurt it… at least in my experience.