Case Trimming: Reloading Trimming Overview
At some point during your handloading journey, you’re going to start asking: Is case trimming important…and is it necessary? Do I need to trim my cases? What kind of trimmer should I invest in? How do I trim my cases?
If you’ve had questions like these, read on for a comprehensive overview of case trimming and the reloading process.
From choosing the right location on your bench to using the right hardware, we’ll cover everything you need to get reloading.
The Why Behind Case Trimming
During each firing of your firearm, the brass cartridge expands to fill your firearm’s chamber. This expansion process eventually lengthens your brass. Similarly, as you’re resizing your spent brass cases on your reloading press, this process of working the brass lengthens the case.
Do I Need to Trim My Cases?
Simply put, no. After a number of reloads, your will grow too long and be out of specification for your needs. Your cases might not reliably feed in your magazine, chamber in your firearm, or fall outside of the max case length specified by your reloading data/manual. At this point, you’ll either need to trim your cases to get them back to the right length, or trash them.
Keep in mind that the case growth is more significant in the first few reloading cycles, after that, case growth generally tapers off and the reloader can achieve more firing/reloading cycles before case trimming is required.
How many times can you fire a case before it lengthens and you’ll need to trim it? Depends on the firearm, your intended use for the ammo, your specific load, and other factors.
Intro To Handloading: Trimming The Casing, Chamfer & Deburr
RCBS® Trim Mate Case Prep Center
Trimming Factors
Several factors come into play when it comes to case trimming including; reloader’s preference, case growth after firing, case growth after re-sizing, cartridge type being loaded, i.e., straight wall (handgun) or bottleneck (rifle), crimping vs no crimping and lastly, reloading consistency.
Bottom line – trimming comes down to case length. During every reloading session, the reloader needs to measure the case length after re-sizing. If your cartridge case measures over the max case length specified in your reloading manual, then you have two options; trim the case below max length, or discard the brass.
How Much Do I Trim Each Case? What Trim Length Should I Trim To?
Some reloaders will trim only a few thousandths off the case length after every re-sizing to maintain the same case length for every reload, as well as to maintain consistency. Some reloaders will not trim until they absolutely need to, then they will trim to a length .010”-.020” below SAAMI max case length, continue their firing/reloading cycle until case length is at maximum, then they will trim again.
An easy starting point, trim a few thousands shorter/slightly below the SAAMI specified max case length. Some reloading data sources also specify a recommended trim length. You can find this information in your reloading manual or on reputable websites like Hodgdon’s Reloading Data Center
Cartridge Type & Case Growth
If the reloader is reloading straight wall or handgun cartridges, the case growth after firing and re-sizing is generally small enough to where the cases do not need to be trimmed.
On the other hand, the reloader may be shooting higher pressure rifle cartridges that grow approximately .005” after firing and another .005” after re-sizing, growing the case length to the point where it is over maximum case length and may not chamber in your firearm. In this case the reloader has no choice and would need to trim, to bring cartridge case length back to specifications and allow for cartridge to chamber.
Crimping: If crimping cartridge cases is required and the reloader is concerned with accuracy, then case trimming is a must. If case lengths are not all the same length, the reloader will get more crimp on longer cases and less crimp on shorter cases. This will affect accuracy, due to inconsistent crimping. If case length variation is excessive, as it may be with cartridge cases from different lots, different brass manufactures, different reloading cycle, etc. it is possible to cause damage to the cartridge from over crimping where the body of the case or base will become deformed and bulged from applying to much pressure during the crimping operation.
How Do I Trim My Cases?
You’ve decided to trim your cases. You’ll need to pick up the right equipment. You can trim manually, with a slower hand driven process or you can trim on a powered/electronic trimmer.
RCBS offers both manual and power case trimming options, as well as various accessories.
Manual Trimming
Trim Pro-2 Case Trimmer
For reloaders trimming a smaller number of cases or just learning the trimming process, a manual trimmer is a good place to start.
The Trim Pro-2 Manual Case Trimmer, comes equipped with a universal case holder to fit cartridge case head diameters ranging from .250” to .625”. The adjustable case length bushing allows user to adjust trim lengths to within .001”. Simply insert case into shell holder and advance cutter into case, while manually rotating cutter shaft until travel is stopped by adjustable trim length bushing.
RCBS also sells a converter kit, allowing you to use a drill to power your manual trimmer.
Powered/Electronic Trimming
Trim Pro-2 Power Case Trimmer
For handloaders wishing to trim a high volume of cases or speed up your process, take case trimming to the next level with the Trim Pro-2 Power Unit. This trimmer comes equipped with a universal case holder to fit cartridge case head diameters ranging from .250” to .625”. High torque, low RPM motor with self-feeding mechanism that automatically feeds the cutter head into the case, once the handle motor handle is released, allowing the user to conduct other reloading tasks while the trimmer is doing its work. The Trim Pro-2 Power Trimmer also includes an adjustable bushing to allow user to adjust trim lengths to within .001”.
Trimming Accessories
If you’ve landed on powered trimming, you can speed up both your case trim and case prep processes with an RCBS 3 Way Cutter. These cutters not only trim the case to length but also chamfer the inside and deburr the outside of the case mouth.
VLD 3-Way Cutter
The VLD 3-Way Cutter uses carbide inserts ground to tight tolerances. Trims, chamfers and deburr’s case mouth in one operation, so no need to chamfer and deburr case mouth after trimming. All three cuts are performed with the carbide inserts. One carbide inserts trims and chamfers the case mouth, while the other deburrs the outside of the case mouth. The inside Chamfer cutter is set up to produce a 11° Angled chamfer to accommodate modern, high BC bullets. The VLD 3-Way Cutter will accommodate calibers ranging from .22-.50 Cal.
Trim Pro 3-Way Cutter
Trims, chamfers and deburr’s case mouth in one operation, so no need to chamfer and deburr case mouth after trimming. This 3-Way Cutter uses special pilots, i.e., not standard pilots, for the inside case mouth chamfer and the inside chamfer is at a 45° angle. The Trim Pro 3-Way Cutter will accommodate calibers ranging from .17-.375 Cal. This cutter uses case hardened steel for cutting not carbide. However, a replacement 3-Way Carbide Cutter Head is offered for this cutter.
Replacement Carbide Cutters
To speed up the trimming process even more, RCBS offers carbide replacement cutters to use in place of the standard case hardened steel cutters that come with both the Trim Pro-2 Manual and Power Case Trimmers.
Trim Pro-2 Power Unit
For those who currently have a Trim Pro or Trim Pro-2 Manual Case Trimmer it’s not too late to upgrade to a full-blown Trim Pro or Trim Pro-2 Power Case Trimmer. Simply mount the manual case trimmer to the Power Unit base plane, remove the cutter shaft handle from the manual trimmer and attach the cutter shaft to the power unit. Now you’ll have all the benefits of the Trim Pro-2 Power Case Trimmer.
Final Thoughts on Case Trimming
If you’re handloading, you’re looking to save money and improve the quality and accuracy of your ammo. Trimming helps you accomplish all these objectives by making your brass last longer and be more consistent. Regardless of the gear you choose for your case trimming, RCBS has you covered.
Invest in the right tool, learn to use it well, and let precision guide your handloading success.
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