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Is constant case trimming necessary? This is what I found.

marchboom

Many of us use the "trim-to" measurement in the reloading manuals to correctly size our cases. But how many of you have actually checked to see if trimming was actually necessary? I recently obtained a borescope to see if I was cleaning my barrels properly. Then I chambered a fired case and inserted the borescope. On the .223 the trim-to length is 1.750". The case I inserted measured 1.775" and the borescope showed that the case could have been another .020" longer before there was any interference.

I checked 3 other .223 rifles and it revealed that the cases really don't have to be trimmed until they get much longer than the recommended max length. Therefore, I'll keep on checking the case OAL but I probably won't be doing much trimming.

Anyone else allowing their cases to get longer than the "max length"?
 
I set my Henderson trimmer to slightly longer than trim-length, and then trim every case after sizing and before seating. I don't do this for "trim length" per se, but rather because the Henderson puts an absolutely gorgeous Chamfer and Deburr on the case, and because it's powered it's a relatively easy step for me. Staying near the trim length is just kind of along for the ride.
 
marchboom said:
Many of us use the "trim-to" measurement in the reloading manuals to correctly size our cases. But how many of you have actually checked to see if trimming was actually necessary? I recently obtained a borescope to see if I was cleaning my barrels properly. Then I chambered a fired case and inserted the borescope. On the .223 the trim-to length is 1.750". The case I inserted measured 1.775" and the borescope showed that the case could have been another .020" longer before there was any interference.

I checked 3 other .223 rifles and it revealed that the cases really don't have to be trimmed until they get much longer than the recommended max length. Therefore, I'll keep on checking the case OAL but I probably won't be doing much trimming.

Anyone else allowing their cases to get longer than the "max length"?
Click to expand...
Yes, been doing it for years. Find a case with a long neck, drill out the primer pocket and see where it is. I try to minimize the area for a carbon ring to form. This does require checking cases for length every time you reload. I just run them in the preset trimmer as part of my brass prep. But as a short answer while trim every loading may not be necessary, measuring in some way is in my opinion. Long neck is a safety issue.
 
Last edited:
marchboom said:
Many of us use the "trim-to" measurement in the reloading manuals to correctly size our cases. But how many of you have actually checked to see if trimming was actually necessary? I recently obtained a borescope to see if I was cleaning my barrels properly. Then I chambered a fired case and inserted the borescope. On the .223 the trim-to length is 1.750". The case I inserted measured 1.775" and the borescope showed that the case could have been another .020" longer before there was any interference.

I checked 3 other .223 rifles and it revealed that the cases really don't have to be trimmed until they get much longer than the recommended max length. Therefore, I'll keep on checking the case OAL but I probably won't be doing much trimming.

Anyone else allowing their cases to get longer than the "max length"?
Click to expand...
I believe the space in the chamber is always much longer than the trim length for safety reasons. The SAAMI blueprint verifies this.
 
I never use the loading manual 'trim to length' measurement. I measure the chamber length on my chamber and trim to .010" under that length. I trim so cases are all within plus or minus one thousandths of each for best neck tension consistency. I clean the carbon ring after each shooting session.
 
marchboom said:
Many of us use the "trim-to" measurement in the reloading manuals to correctly size our cases. But how many of you have actually checked to see if trimming was actually necessary? I recently obtained a borescope to see if I was cleaning my barrels properly. Then I chambered a fired case and inserted the borescope. On the .223 the trim-to length is 1.750". The case I inserted measured 1.775" and the borescope showed that the case could have been another .020" longer before there was any interference.

I checked 3 other .223 rifles and it revealed that the cases really don't have to be trimmed until they get much longer than the recommended max length. Therefore, I'll keep on checking the case OAL but I probably won't be doing much trimming.

Anyone else allowing their cases to get longer than the "max length"?
Click to expand...
I like to keep my cases to the same length, though it's not really necessary, especially when trimming to a shorter length. The main reason I like have my case always at the same length is so that with any carbon ring build up does not put any pressure on the case mouth. When I FL size brass the OAL increases, like with my .308 cases, it can easily be .003 - .004. If my cases start out at 2.005 and I can go to .015, that leaves several reloads before I'll need to trim. . . but, I don't like the neck sitting on carbon ring. Having the cases at the same length also helps with consistent blowby as the neck releases the bullet (related to seating depth issue).

In addition to this, I typically load my cases long, so I do like to get my case OAL longer that I can have more of the bearing surface contact with the neck. If the case neck is long into the chamber neck area, there's not a lot of room to let the case neck grow. Also not a large area for carbon ring. When case necks are that long, it's a good idea to keep the case's OAL, trimmed to length.
 
^^^^^^^^ If the brass is of many different lengths the neck tension will be more or less depending on how long the neck is. More length = more area of contact with bullet and more friction between the neck and the bullet, less neck length means less. If they are all the same the amount of neck tension will be closer to the same with each case.
 
ebb said:
^^^^^^^^ If the brass is of many different lengths the neck tension will be more or less depending on how long the neck is. More length = more area of contact with bullet and more friction between the neck and the bullet, less neck length means less. If they are all the same the amount of neck tension will be closer to the same with each case.
Click to expand...
I agree. I'm just going to allow the cases to lengthen until they get to 1.770" and call that my max length. I'll keep a close eye on it.
 
Several years ago, I purchased a Sinclair chamber length gauge which is inexpensive and easy to use.

I measured the actual chamber length of all my rifles. Even applying Sinclair safety factory, I cut my trimming down to well over 50%. For some rifle, I have never had to trim. The gauge takes the guess work out of max case length.
 
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