Case trim length

[PoisonIvyMagnet]

I'm shooting a Marlin levergun in 30-30. Looking at case specifications, drawings show the max case length to be 2.039". Lyman's cast bullet handbook shows the trim-to length to be 2.029“, and the 0.010" trim from max looks to be the norm for most cartridges. Is this pretty standard for you folks? Just how far back can you trim before you start seeing problems?

[EDG]

I like my brass to be the same length as my chamber when shooting cast loads.

The .010 short practice is mostly a jacketed bullet convention. If you know how long your chamber is you can use a case that is the same length as the chamber. When FL sized cases are fired they get shorter. When resized they get longer. Always check them after they have been resized and trim so you do not get a case that it too long for your chamber. If you cannot measure your chamber (it is easy to do usually) just use the length recommended in the manual.

I have some military rifles such as a 6.5X53R Dutch Mannlicher that have chambers longer than the lengths specificed for the brass.
The brass is supposed to be 2.110. The chambers are 1mm (.040) longer at 2.150 inches. These cases I make at 2.150 and fire form. After sizing I trim to a uniform length of 2.145 for subsequent firing.

[pworley1]

All the manuals are for the shortest and weakest actions that might be used. Your rifle could be longer.

[PoisonIvyMagnet]

Thanks guys. With the manuals I've picked up and forums I have read, I've found little discussion about trimming brass to length. Didn't know if you have to trim to different lengths for different purposes (such as cast vs jacketed). With my Marlin I've found that the 165gn ranch dog bullets I casted either have to be seated down past the crimp groove, or they jam into the rifling pretty hard. I recently started trimming the brass down shorter on some cartridges, which lets me seat to the crimp groove and chamber much easier. Wondered if I may have been using the wrong cartridge length, or if trimming down too far might cause me some issues that I haven't considered. With smaller 110gn jacketed rounds for light plinking, full length brass at 2.039" wasn't a problem.

[EDG]

You can run into the problem you describe with short or no throats and fat nosed bullets that are too large to ride on top of the lands.

If you trim your brass you will create a gap between the end of the case and the end of the chamber neck. Then you may have lead that expands into the gap between the end of the case and the end of the chamber. I run into that will several of my rifles. When I extract an empty case, a ring of lead comes out stuck to the case mouth. A full length case will prevent that sheared off ring of lead or will minimize it.

The best way to deal with this issue is to use a bullet with a nose that will fit the land diameter. You can try trimming a few cases and see if your loads are still accurate. You might look for a lead ring on your cases or worse - lead rings left in your bore and chamber.


Thanks guys. With the manuals I've picked up and forums I have read, I've found little discussion about trimming brass to length. Didn't know if you have to trim to different lengths for different purposes (such as cast vs jacketed). With my Marlin I've found that the 165gn ranch dog bullets I casted either have to be seated down past the crimp groove, or they jam into the rifling pretty hard. I recently started trimming the brass down shorter on some cartridges, which lets me seat to the crimp groove and chamber much easier. Wondered if I may have been using the wrong cartridge length, or if trimming down too far might cause me some issues that I haven't considered. With smaller 110gn jacketed rounds for light plinking, full length brass at 2.039" wasn't a problem.