Neck-Turning Tip: Match Your Cutter Angle to the Shoulder
When neck-turning cases, it’s a good idea to extend the cut slightly below the neck-shoulder junction. This helps keep neck tension more uniform after repeated firings, by preventing a build-up of brass where the neck meets the shoulder. One of our Forum members, Craig from Ireland, a self-declared “neck-turning novice”, was having some problems turning brass for his 20 Tactical cases. He was correctly attempting to continue the cut slightly past the neck-shoulder junction, but he was concerned that brass was being removed too far down the shoulder.
Craig writes: “Everywhere I have read about neck turning, [it says] you need to cut slightly into the neck/shoulder junction to stop doughnutting. I completely understand this but I cant seem to get my neck-turning tool set-up to just touch the neck/shoulder junction. It either just doesn’t touch [the shoulder] or cuts nearly the whole shoulder and that just looks very messy. No matter how I adjust the mandrel to set how far down the neck it cuts, it either doesn’t touch it or it cuts far too much. I think it may relate to the bevel on the cutter in my neck-turing tool…”
Looking at Craig’s pictures, we’d agree that he didn’t need to cut so far down into the shoulder. There is a simple solution for this situation. Craig is using a neck-turning tool with a rather shallow cutter bevel angle. This 20-degree angle is set up as “universal geometry” that will work with any shoulder angle. Unfortunately, as you work the cutter down the neck, a shallow angled-cutter tip such as this will remove brass fairly far down. You only want to extend the cut about 1/32 of an inch past the neck-shoulder junction. This is enough to eliminate brass build-up at the base of the neck that can cause doughnuts to form.
The answer here is simply to use a cutter tip with a wider angle — 30 to 40 degrees. The cutter for the K&M neck-turning tool (above) has a shorter bevel that better matches a 30° shoulder. There is also a 40° tip available. WalkerTexasRanger reports: “I went to a 40-degree cutter head just to address this same issue, and I have been much happier with the results. The 40-degree heads are available from Sinclair Int’l for $13 or so.” Forum Member CBonner concurs: “I had the same problem with my 7WSM… The 40-degree cutter was the answer.” Below is Sinclair’s 40° cutter for its NT1000 neck-turning tool. Item NT3140, it sells for $12.95. There is also a slightly more expensive 40° cutter for the NT3000 tool, item NT3340.
Another good way to approach this is to push the shoulders back .020-.025 on the unfired cases you’re going to neck turn. Then, just neck turn with whatever cutter your tool has..no need to be concerned about matching the shoulder angle perfectly…just turn back to the new neck/shoulder junction.
Then, to fireform the cases, seat the bullet firmly in the lands and use a good amount of neck tension. When you fire the case, the shoulder will blow foward and the neck/shoulder junction will be perfectly ‘blended’ as the brass takes the shape of the chambers neck/shoulder area.
To set the shoulders back, I simply use a shellholder faced off .020-.025. If you don’t have a lathe, you can do this on a bench grinder by using the side of the grinding wheel. It’s not imperitive that it be perfectly flat..just reasonably so…since you’re only going to use it to set the shoulders back.