Lathe Style Case Trimming

Written by Sierra Bullets Ballistic Technician Philip Mahin

Today, we will be discussing lathe style trimmers. Specifically, I have been using a Redding 2400 with a micrometer top but this could apply to a number of others also. Mine has been a very accurate trimmer capable of 0.001” repeatable lengths but it did take a learned technique to get there. For starters, I had to mount it on the side of my bench but there was a reason for that though. Consistency is the key when it comes to this type of trimmer because it works on the principal of screw threads tightening a collet around the rim of the case and more or less pressure on the handle will cause the case to be long or short from the stopping point. It was easier for me to tighten it down correctly when the case was sitting on the correct ledge in the collet using gravity to keep it there. At the same time, I could hold the keeper button with my left thumb and tighten the turn handle with the same amount of pressure every time with my right. I also started pushing the case upward with the handle before I tightened it, touching the case mouth to the cutting blades to keep it forced all the way into the collet. As long as I kept the shavings cleaned out of the collet with a nylon bristled brush, this method would seat the case correctly every time.

LabeledTrimmerAnother issue that might come up is the case neck being a little snug around the pilot. It is easy enough to chuck the offending pilot into a shop lathe and polish it down a bit. This will help the cases glide around it and possibly keep from binding up the works. If you get a case stuck on the pilot, you will be disassembling the whole handle area and removing the pilot from the cutter to separate the two. Thank goodness a 45ACP case is small enough that I could find a punch to fit through the flash hole and ease it out carefully. I also took this time to clean the interior of the handle and grease everything because shavings are collecting in there. One of the other gentlemen here mentioned that he also uses just a hint of Imperial Sizing Die wax on the pilot just to keep this from happening but of course this will need to be removed before any powder or bullet is introduced to the case. As you can see in the picture, I have the supplied extension attached to the cutting head to use with short cartridges like a 45ACP. This can be removed for use with a 243, 30-06 or even longer cases up to 3 ¼” or so.
The trimmed case will have a significant burr on the inside and outside of the mouth if you needed to remove a fair amount of material. This burr on the outside is no problem when trying to remove it from the pilot, but the one inside could cause it to hang up slightly. When I first started using it, my torque on the handle wasn’t as uniform as it should have been and some cases would slip out of the collet.  But not to worry, I just slipped it back over the rim and tighten it enough to pull the case free. These burrs are easily removed with a hand tool but don’t take off too much material, just enough that you can’t feel it anymore. The 45ACP as do others, rely on the case mouth to headspace properly so a little goes a long way. Cases with a bottle neck may need a little more removed from the inside to help ease a bullet into the mouth when seating it but only enough to keep from peeling its jacket. One last thing before I go, it is best to trim your cases after they have been sized because they will grow in length from before to after. Sometimes it may be a little more than others but when you put a set of calipers to it, you’ll know what I mean.

Have fun shooting and be safe.

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3 Responses to Lathe Style Case Trimming

  1. littletoes says:

    Interesting, but some of the problems you list are not apparent with the use of a Wilson type of trimmer. The case is held from the body, and there is no collet to ride inside of the case mouth. Fully equipped with all the goodies that Sinclair sells will get you a very good case trimmer.

    Good Shooting!


  2. bobd67 says:

    I agree with “littletoes” as far as the Wilson trimmer. Most all of my cases are trimmed using a Wilson. There is one exception, the 460 S&W Mag. The Wilson 45 Long Colt case holder (Q type) doesn’t work well due to the length of the 460 case and at last check Wilson doesn’t make a case holder to handle the 460. My only option was to resort to my Redding trimmer. I had trouble using the Redding pilot on the 460 case possibly because they were Nickel plated (not sure, only a guess). To remedy the problem I ran the cases through the expander die without flaring. Problem solved. When I measured the difference between the pilot and the expander I found the difference to be less than .0005″. I’m wondering if this would work with the other calibers for those who use the Redding trimmer and experiencing problems with a tight pilot..


  3. Pingback: Equipment for the Beginning Reloader | Sierra Bullets

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