The folks at PMA Tool, makers of arbor presses, neck-turning tools, and other case-prep tools, offered some good advice about case trimming on the PMA Tool Website. Here we reprint a PMA article 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 updated WFT 2 Model and WFT Big Boy feature interchangeable trim chambers to work 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.
Story Tip by EdLongrange. User Submissions are welcome.
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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.
Story Tip by EdLongrange. User Submissions are welcome.
Share the post "Tips on Case-Trimming from PMA Tool"
Now through April 6, 2012, Sinclair’s Stainless Micrometer “Ultimate Trimmer” system is on sale for $159.99. That’s a $20.00 savings off the normal $179.00 price. This unit comes complete with micrometer cut-length control, stand, Shark Fin clamp for the case-holder, and a stainless Wilson cutter housing. NOTE: Caliber-specific case-holders are sold separately.
The Sinclair Micrometer head allows reloaders to easily adjust trim length in .001″ increments with an adjustment length of over 2″. The micrometer features easy-to-read, engraved unit markings and may be locked in place. The Ultimate Trimmer can trim cases from 22 Hornet up to 416 Rigby.
The Sinclair Stainless Ultimate Trimmer comes with Sinclair Mounting Stand and handy Shark Fin Clamp. This system makes easy work of installing and removing your trimmer case holder in a smooth “swing-arm” motion. The Shark Fin trimmer clamp secures the case head firmly against the micrometer adjustment head for a quick and accurate, chatter-free trim. NOTE: We have found that you will get the most accurate, repeatable trim lengths if you set the shark fin to a firm tension and do NOT hold the case-holder with your hand — let the Shark Fin clamp do the job. The video below shows how to use a Wilson case trimmer (with micrometer, stand and Shark Fin).
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We saw a cool new product at the Forster Products booth. Forster has introduced a new 3-in-1 Carbide cutting tool that works with all existing Forster case trimmers. This unit does three jobs at the same time. It trims the case to length, it puts a 14-degree chamfer on the INSIDE of the neck, AND (last but not least), it cuts a 30-degree chamfer on the OUTSIDE of the neck. It does this all quickly and efficiently — in a matter of a few seconds. We tested the new tool ourselves on a few cases. The tool is solid and well made. The carbide cutting tips do perform a very clean cut. Be aware, however, if you have turned your necks already, you may have to reset the blade positions before you start trimming your brass.
Forster’s CFO, Robert Ruch, demonstrates the 3-in-1 case trimming/chamfering tool in the video below. As you can see, the tool turns very smoothly (no chatter) and the job is finished in a few seconds. The actual cutting time, per case, is just a few second. The tool has an MSRP of $70.00, but we expect it to sell for around $50.00 at major vendors. It can be fitted on Forster trimmers and other hand lathes with a .490″ shaft diameter.
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The Sinclair Stainless Ultimate Trimmer comes with Sinclair Mounting Stand and handy Shark Fin Clamp. This system makes easy work of installing and removing your trimmer case holder in a smooth “swing-arm” motion. The Shark Fin trimmer clamp secures the case head firmly against the micrometer adjustment head for a quick and accurate, chatter-free trim. NOTE: We have found that you will get the most accurate, repeatable trim lengths if you set the shark fin to a firm tension and do NOT hold the case-holder with your hand — let the Shark Fin clamp do the job. The video below shows how to use a Wilson case trimmer (with micrometer, stand and Shark Fin).
