How necessary is bottle neck case trimming?


January 5, 2013, 11:30 AM
I've watched a bunch of tutorials and read through instructions over the past several weeks and most say something about trimming cases.

I have thought about this for a while and I think I understand the idea. You want ALL your cases to be the same length for the caliber being reloaded.

BUT... on a bottle necked round for rifle, would it be better to resize/massage the brass back to the original length? Seems like say the brass is .010" over length, wouldn't a die be able to push it back to original length without having to remove material?

I've read trimming usually is done for the first reload. Not sure that's always the case but curious here or if that was just one loader's opinion.

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January 5, 2013, 11:35 AM
Your reloading manual gives you a max case length, and a Trim Too length, which is generally .010" under max as you noted.

Cases longer then MAX may jam into the end of the chamber and raise pressure, as there is not enough room for them to expand to release the grip on the bullet.

Cases get longer when you resize them.
There is no possible way a die can "push metal back where it came from" by pushing on the end of the case mouth.

All that could happen if they tried is the shoulder would buckle to relieve the pressure on the end of the case.

RCBS does make an X-Die that is said to prevent case length growth during sizing.
But I have no experience with them.

Yes, you should check case length after the first firing/sizing and trim if necessary then.

Then again after a few more firing/sizing cycles as they continue to grow.


January 5, 2013, 11:36 AM
I trim my cases or at least check length on every reload. Sizing only rests the shoulder. The very top portion of the neck is what you're trimming. Size first, then trim.

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January 5, 2013, 11:42 AM
You definitely want to watch length, but that said, I don't trim mine, at least yet. Almost all my brass has been fired 0-1 time, and this is something that tends to be a bigger issue with cartridges that are higher pressure and/or brass that has been fired more than I have so far. Of course having hundreds of rounds of brass and light shooting hobby tends to help, as does not loading too hot.

January 5, 2013, 12:02 PM
Keeping bottle neck rifle trimmed is important.

I measure all rifle cases after resizing but I only trim the ones that exceed the max length.

Trimming is not one of my favorite reloading chores and by trimming only the over length ones minimizes that task. Usually, about 25% to 40% need trimming at each resizing session.

There are various reasons that some folks like to keep all their cases trimmed to the same length.

January 5, 2013, 12:22 PM
Hope this isn't too far off topic, but the RCBS X die looks intereting, any reviews from the guys here?

Thanks, Mike

January 5, 2013, 01:06 PM
I trim mine when I feel like it. I am sure at some point case stretching would force me to trim but some brass I've fired 5 or 6 times and not trimmed.

January 5, 2013, 01:35 PM
I trim every time I reload my bottleneck. I like the accuracy I got when I did my workup, so I make sure everything is the exact same as I did it during workup which means trimming to the same length I did when I did the workup.

January 5, 2013, 02:37 PM
As noted, manuals give a maximum case length measurement and a trim-to measurement. Manual numbers ensure cartridges are safe to use per SAAMI regulated firearm chambers. Keeping in mind that SAAMI numbers realistically allow for some margin of saftey, it is likely quite safe to wait until case length just exceeds the manual maximum and then trim to 0.010 off maximum. The exception may be if you have a custom built firearm with a really tight chamber, in which case the only way to ensure safety is to make and measure a chamber cast. Making a chamber cast will also tell you if you need to use the manual maximum number to tell you when to trim because there are firearms that have larger (longer) chamber lengths than the maximum approved by SAAMI!

January 5, 2013, 02:52 PM
How necessary is bottle neck case trimming?


January 5, 2013, 03:07 PM
All chambers are a little different. You may be able to get away with a little longer neck, you may not.

I always "square" my necks up by just putting enough trim on them to get a nice bright ring that is perfectly even all the way around.

As the neck stretches it thins the transition from the neck to the shoulder.

Keeping the cases uniform in length does remove one more variable.

January 5, 2013, 04:43 PM
"..most say something about trimming cases."

Thing to remember about all that stuff the directions say to do; DO IT!

January 5, 2013, 05:41 PM
It is part of the process when reloading rifle rounds. In my view a necessary part of the process or it wouldn't be part of the process.

January 5, 2013, 06:16 PM
I almost always trim and chamfer at the first reload, so I know exactly where I started from. Also, the necks are not always square on factory rounds and trimming before the first reload will square them up.

It's usually 3 to 5 more loadings before I need to trim again. But I measure about 10% of the batch after every trip through the resizer.

January 5, 2013, 06:25 PM
I like my Redding form and trim die.I size and deprime in one station on a rcbs 2000 progessive,then run them up into trim die and you use a file to knock off whats exposed. Makes a nice flat cut,easier and more consistent than chucking up and turning on other cutters. I also have a "worlds finest trimmer" that you put in a drill motor in a vise,works good for high volume of 223. I also know some of my chambers are quite a bit longer than SAAMI max case lengths by using a simple Sinclair overall chamber length plug you put in an empty case,close action,remove and measure. I bought a hornady case prep trio electric tool that works good for chamfering and deburring after.I tried the Lyman case prep center,broke on third case.

January 5, 2013, 10:15 PM
I've used both the Lee trimmer set up, and the RCBS mini-lathe type trimmer. Both work well. Disadvantage of the lee is that you have to trim before seating primer.

I keep a "standard" for each case (in a left over Sierra bullet box) and simply set the RCBS trimmer using this. Takes very little time to whip in a case and if it doesn't engage the cutter, it is done. If it does, 2 or 3 turns is often enough.

Cases stretch if your rifle's bolt/chamber are longer than your case. The sides expand almost all the way to the back under the extreme pressure, and "grab" the chamber. Only at the web (thick) does the case not grab well. Thus the base of the case is free to move. If the case is smaller than the bolt/chamber, it is then going to stretch right at that point, a few mm forward from the base of the case. Thus, head separation. I've had it happen, and probably most active reloaders eventually do.

After my experience, I decided to set my Lee dies to VERY MINIMALLY compress the length of the case (set the shoulder back as little as possible). Lee advises turning the die in 1/4-1/3 turn (I think) beyond where it touches the holder. I would certainly go on the minimum end of this, and if the case can easily go into your chamber, even less. Thus you will get much less stretching and cases will last longer. I think you will need less trimming also (I seem to be doing less as a result). On one rifle I acutally made a casting (from a fired case) of the chamber/bolt and made mesurements to figure out how much for that individual rifle, I wanted to full length size the case. (This was a bit labor intensive and took a couple tries)

I would certainly either CHECK or go ahead and pop into the trimmer each time. There are some "template" length checkers, or you can even make your own from a thick piece of slightlyk flexible plastic, some shears, a caliper and some careful cutting. I used the plastic from a 5-gallon home depot bucket (after flattening it using a bit of heat).

Neck tension is key for rifle high accuracy. On one rifle, each trip to the range, my "zero" was dropping and inch or more as I reloaded the cases repeatedly. Groups were lousy. Then I learned how to anneal correctly (youtube) in a very very dark room, and all of a sudden that same rifle was shooting a very respectable 10-shot group much better than its previous 5 shot groups! Neck trimming is probably in that part also, but annealing every few reloads (if you're going for high accuracy) seems key to me.

Good luck!

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