Tips on Case-Trimming from PMA Tool
The folks at PMA Tool, makers of arbor presses, neck-turning tools, and other case-prep tools, offer some good advice about case trimming on the PMA Tool Blog. Here we reprint a PMA blog post that explains case trimming basics and helps you choose the right case-trimming tool for your needs.
Case Trimming Basics
Trimming the cartridge case to the proper length is a crucial step in case preparation that should not be overlooked or underestimated. The cartridge case or the rifle can be damaged, or even worse you get badly injured. In most instances cases should be trimmed after firing and sizing. Trimming new brass is necessary for a lot of wildcats and can be beneficial in some instances, but by and large, trimming new brass is not necessary for most situations (unless you are neck-turning). Cases should be trimmed after you have sized the case, because the expander ball on the decapping pin can (and will) stretch the neck. Those of us who neck size should get into the habit of trimming after sizing as well. This is a good rule of thumb to go by, and hopefully it will keep you safe during the reloading and shooting process.
There are so many case trimmers out there that work, deciding which one is right for you can be confusing. Even though I have trimmed thousands of cases, using about every method possible, I can’t answer the question of what case trimmer is right for you because of all the variables that may be involved. I can, however shed some light on the subject.
The two most popular designs of trimmers either index (1) off the base or the head of the case, (2) off the shoulder or datum line of the case. There are pros and cons to each and it all depends on what you are willing to live with.
Indexing off the Base (Case Head)
Let’s talk about the first one I have listed, indexing off the base, or the head of the case. The pros to this method are that you can achieve a very accurate over all length and that is after all, what it is all about. The cons to this method are that you can get some variation doing it this way. Let me explain, the base is not always square to the body or can be damaged during firing especially if it is fired through a military style rifle with a very aggressive ejector. These cases should be discarded, but sometimes they can be overlooked. This condition can lead to an over all length that is incorrect. The case head being out of square will be corrected upon firing, however that case will wind up being shorter than the rest of your cases, possibly creating a difference in the neck tension on the bullet. The more you can do to eliminate variables in your reloads the better off you are going to be. This method can also be very slow, and if the user gets careless the result will be a inconsistent over all length.
Indexing off the Shoulder (Datum Line)
The second method I mentioned, trimming off the shoulder or the datum line of the case, has its pros as well. I have found this to be the quickest of the methods and very accurate as well. After the case has been sized through the die the dimensions (particularly the headspace) of the cases are usually very uniform and exact, this allows the case to be trimmed by indexing off the shoulder. This method can be done very quickly, by hand, or by powering either the case, or the trimmer. You also don’t have to worry about the case heads being out of square with the body using this method. Generally the trimming time is cut in half, and this leads to greater focus on the job, without becoming careless. [Editor’s Note: The World’s Finest Trimmer (WFT) is one power device that indexes off the shoulder datum. It works fast and is very precise. The new WFT 2 Model with interchangeable trim chambers works with multiple cartridge types.]
Summary
The choice is yours to make. I hope that this was some help to you, whether you are looking for your first trimmer or looking to replace the trimmer you have. Just remember to always put safety first and accuracy second, and you will start making little bug holes in no time.
Similar Posts:
- Case-Trimming 101: Tips from PMA Tool
- Helpful Advice on Case Trimming from PMA Tool
- How to Trim Brass Like a Pro — Smart Tips from PMA Tool
- PMA Micro-Adjust Case Trimmer — Precise and Handy
- New Info Site and Case Trimmer Tool from PMA Tool
Tags: Brass, Case Trimmer, Forster, OAL, PMA Tool, WFT, Wilson
My vote is for the Giraud trimmer. Awesome piece of machinery.
I like the ‘worlds fastest trimmer’ but shoulders are rarely EXACT. Just measure em, you can see for yourself.
Such an approach throws you into all that fails with StoneyPoint type OAL tools..
I’m satisfied so far trimming to the case heads.
I suggest everyone interested read Matt’s original blog post at http://blog.pmatool.com/. We don’t insist or even recommend trimming your cases prior to neck turning. Cases grow and stretch at differing rates and trimming prior to firing at least once (fireforming) can amplify this variance. Unless you are forming brass for a wildcat or other cartridge that requires it, there is no reason to trim prior to firing once or twice (at least no other reason that we can think of).
I used a friends Worlds Finest Trimmer and was sold on this product.
Case prep is everything. I clean then, full length size and de-prime every case. Then I clean the primer pockets, trim, and chamfer necks in/out. I clean again and anneal all my cases every reloading.
Nat Lambeth
My crank trimmer gathers dust while my new Little Crow (.223 and .308} trimmers do all the work about five times as fast, at least. A lot cheaper then the power trimmers as well. I chuck mine in a 3/8 drill then put it in soft vise jaws and lock the trigger back. Away we go!