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Question about case trim length

25K views 9 replies 8 participants last post by  LDBennett 
#1 ·
I have noticed that most reloading data contains a "maximum case length" and a "case trim length". Should I always trim the cases to the "case trim length" before loading them? For example, I am hand loading 270 win. The maximum case length is 2.540 and the recommended case trim length for most loads is 2.530. Most new cases are closer to 2.540. Should I trim them to 2.530 before loading them for the first time?

Thanks, Ron
 
#2 ·
I will say that it would be entirely up to you. If you did trim them then it may be a while before they stretch enough to have to be trimmed again. As for me, if the length is not over the maximum length, then I generally don't mess with them. If you are going to neck size them only, then they are fine as they are.
 
#3 ·
If you are approaching the lands (and actually can), the trim might make them a bit short if it's a marginal reach. May be leave them a bit longer if necessary but under the max. You can get closer to lands but still have enough neck to hold the bullet. If it doesn't matter to you, then trim away.
 
#5 ·
There are a couple of things to consider, Ron. If any of the new cases are over the spec length, you should trim them. But even if they're not, you might want to, just to make the length uniform for the crimping stage of the reloading process. If you rely on the built-in crimp of the bullet seating die in your set, it will apply a crimp at one specific height above the shell holder, and if the cases vary in length by much, that can affect the resulting ammo performance.

But if you have the Lee Factory Crimp Dies for your rifle setup, the length of the case is a lot less critical. It still matters, of course, but because this die applies a crimp radially rather than axially, there is little risk of crushing the case neck if the crimp is set too tight.

As GD mentioned, you might buy some time by trimming now, rather than waiting until individual cases stretch enough to require trimming. But to my way of thinking, trying to make perfect that which can never be perfected is an exercise in futility; load 'em and shoot.
 
#6 ·
OK guys, thanks for the replies. I have not been crimping my hand loads. I do have the Lee factory crimp die, so I could do it, but i have read lots of pro and cons about crimping, and I have decided (for the moment) to forego crimping. I'd like to hear more opinions about it though!

By the way, just brought home a new Browning A-bolt in 270 win. Beautiful piece of shootin' iron. Can't wait to break it in. Nice wood stock. Much nicer to look at than my composite Weatherby Vanguard. Hope it shoot as good as it looks.

Ron
 
#7 ·
I never trim new brass. I shoot it as is except I de-burr the case mouth inside and out. On the first reload I randomly pick out ten once fired cases from the lot. If any of them are beyond the maximum listed in the manuals the whole lot gets trimmed to the listed trim-to length. Subsequent reloads get the same process.

The range the brass must fall in is between the maximum case length in the manual and the trim-to length also in the reloading manual. But do not trim or make a judgement to trim until the cases have been sized. Sizing pushes the brass all around and measurement must be made after sizing. If the case are in the correct range any crimping will be uniform enough.

It is not necessary to crimp reloads for bolt guns if fed one at a time. If the magazine is filled and then shot the recoil might effect the set cartridge overall length of those cartridges riding in the gun during firing. Guns that load cartridges end to end must be crimped. Semi-autos must be crimped as cartridges in the gun get a pretty rough ride. The last thing you want to happen is for the bullet to recess into the case from recoil. That can greatly increase pressures during firing.

For rifle cartridges the best thing since sliced bread is the LEE Factory Crimp Die. I am NOT a LEE fan but this device works so well on the cartridges that I set my LEE hate aside and use the FCD regularly. It the die gets sticky in its operation you may have to take it apart and smooth the working surfaces of the collet to remove the galling caused by LEE's inability to understand that similar metals run against each other gall the metal's surface. But the die is worth the effort.

LDBennett
 
#8 ·
IMHO, Lee dies are crap! I'll just leave it at that.

The first thing you should do is get the "actual" measured length of your chamber. That will tell you how long your brass can get before you have to think about trimmimg.
Examples: Two different 6 BR chambers. Max trim length of the brass is 1.560. Actual "measured" length of both chambers is 1.585. So there's about .020 over max trim length before you need to start thinking about trimming brass. What it comes down to is you pick and choose when you want/need to trim your brass.
Depends also on what type of resizing die you use. Full length with the "button" will pull the necks longer with every stroke. Shoulder bump and neck size dies won't work the brass as much.
I have BR brass that has been shoulder bumped and neck sized 25+ times and still doesn't need trimming. Still going strong with no issues.
 
#9 ·
This is an interesting one! Except for the Lee FC, which I have zero experience with, I believe I agree with about everything everyone has said. They're just different ways to skin the same cat.

I believe I agree with Mikie most. One needs to know what their chamber actually measures. With SAAMI specs I expect most newer rifle chambers fall within the allowed tolerances and as you are working with a nearly new 270 WCF you should be fine. But such isn't always the case. Were it an old rifle a chamber cast would be a must. With a wildcat or custom rifle you were working with the dimensions from the gunsmith for the reamer would be required to determine max and trim to length. But those are just my opinions and worth what you paid for them.
 
#10 ·
If you have a modern rifle from a popular manufacturer (not a custom gun) no such chamber measurements are required. The manufactures build the gun to industry agreed to chamber specifications. The case specifications in reloading manuals take that into account.

Bumping the shoulder of the case and other advanced techniques are not for the new reloaders. They need to follow the instruction in there reloading manual to the letter if they expect non-frustrating success in making good ammo.

The risk in "measuring" the chamber is knowing how to do it correctly to get the real size. Get it wrong and let the cases get too long and you are in trouble. It is not that it can not be done successfully but it is that done wrong and it is dangerous. It is not for the uninformed or anyone new to reloading. If you follow the specs in the reloading manuals and size before you trim you will not get into trouble. Be safe!

LDBennett
 
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