View Full Version : Trim length tolerance?
Hey all,
For precision shooters, what is an acceptable range of tolerance for trim length? For example, I trim 223 to 1.75 and my tolerance seems to be in the .003 range or down to 1.747. Using WFT’s btw.
Interested to hear everyone’s thoughts.
Cheers.
Total neck tension and release of bullet from the neck include several factors. Case neck wall thickness, concentricity and consistent annealing will have more effect than .003" variance in case length, assuming you are not crimping.
I don't get that much variance using WFT so you might check whether the case holder that the shoulder butts up to is getting brass shavings in it. I periodically wipe it clean with a Qtip.
Since the WFT indexes off the shoulder, you want to make sure all the brass being prepped in that batch went through the exact same sizing die and setting.
It is also easy to get going a little to fast and remove the case before it is perfectly trimmed. I try to pause an extra second or two after I think it is done just to make sure the cutter is done.
Also, if you over chamfer or debur you might shorten the neck by a couple of thous.
gunnerblue
04-07-18, 18:19
I have not observed any change in accuracy from variances that small in trim length only. Neck tension and uniform neck wall thickness are more important. I am not a benchrest shooter so my definition of precision stops at 1/2 MOA.
When I use a WFT I get .001” variance in OAL but strive to do each case as consistently as possible, to include speed of the drill which I’ve found to have a big affect.
You are full length resizing and will have brass spring back variations in shoulder location. The good news is the ejector and the firing pin push the case forward in the chamber until the case stops when the case shoulder contacts the chambers shoulder.
The WFT trims off the shoulder and the case shoulder will always be in the same position in the chamber and the case mouth will be in the same position every time also.
Meaning the only variations will be the head clearance or the air space between the rear of the case and the bolt face.
Below the variations in the measured OAL will be at the rear of the case and not at the case mouth.
https://i.imgur.com/HK76WCp.jpg
Bottom line the distance from the case shoulder to the case mouth will be the same in the chamber.
https://i.imgur.com/RDNXFbN.png
Thanks for the responses! That's given me a couple of things to think about.
Yeah and that all assumes extremely good chamber and barrel and shooting technique to be able to notice such fine variations in the larger factors, let alone a slight case length variation.
I'm at that point where I get some inconsistency at times and I'm working to remove as much of that from the load as possible. That way, when the group or long range shot is off, I 100% know it's me rather than wondering if my load was a factor.
I've not found trim length to be a critical factor. I almost never trim .308 brass anymore. .223 is done on the giraud. Our riflesmith is a fan of leaving necks a little longer for more neck contact with the bullet. But I honestly don't know there's a difference.
ive found the dillon trimmer setup has tolerance of about +-.002 or .003.... nothing I get worked up about and still seems to provide sub MOA accuracy.
+/- .002 on my WFT, no issues as I can't tell the difference between groups of "varied" length brass and brass that is all exactly 1.750"
Hey all,
For precision shooters, what is an acceptable range of tolerance for trim length? For example, I trim 223 to 1.75 and my tolerance seems to be in the .003 range or down to 1.747. Using WFT’s btw.
Interested to hear everyone’s thoughts.
Cheers.
I compete in Short Range Benchrest, and I can tell you that as far as I and most other shooters in that particular game are concerned, the neck trim length really only matters for a few things.
1. If you are going to neck turn, your trim length needs to be identical because the neck turners index off of the case mouth. After you neck turn, it doesn't matter, so long as you...
2. Don't let the brass grow longer than the chamber.
Outside of BR there are some other factors enumerated here already by other posters.
As far as accuracy is concerned, it doesn't really matter.
The Little Crow trimmer instructions call for using your drill at high RPM. I have a corded drill that spins at close to 2000 RPM it seems. I had that same thing happen to me trying to make less noise at low speed while my kid was napping. You have to run that thing fast or shavings will collect in that shoulder area and give you variations.
NWP had a great post and covered it really.
I learned the hard way about different sizing dies set ups on my T7 a ways back.
I don't trim for 308 and rarely do 223. I figure I can shoot or I can worry about every minor detail down to the .0001. I'd rather shoot. But honestly, I despise reloading, even on my dillon 650.
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I don't trim for 308 and rarely do 223.
I rarely trim .308. And I only trim .223 because I have the Giraud and it chamfers the necks. The .223 brass doesn't usually trim much off at all unless it's once fired 556 stuff that's really long. After first trim, it's maintenance/chamfer.
I figure I can shoot or I can worry about every minor detail down to the .0001.
It's definitely a balancing act. I don't do anything that doesn't actually improve the ammo. All this depends on volume too. If you only load 50 rounds per week for one bolt gun, you can go balls out and nit pick every little detail. I have too many irons in the fire to be too anal about the ammo.
Read up on RCBS X dies, by Larry Gibson, as he extended the avg case life by 3-4X using them in 7.62x51 in a Springfield M1A.
I rarely trim .308. And I only trim .223 because I have the Giraud and it chamfers the necks. The .223 brass doesn't usually trim much off at all unless it's once fired 556 stuff that's really long. After first trim, it's maintenance/chamfer.
It's definitely a balancing act. I don't do anything that doesn't actually improve the ammo. All this depends on volume too. If you only load 50 rounds per week for one bolt gun, you can go balls out and nit pick every little detail. I have too many irons in the fire to be too anal about the ammo.Good to know. Your insight and common sense wisdom is priceless
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ubet, If you get any interesting results on your crimp tests, post them up.
ubet, If you get any interesting results on your crimp tests, post them up.Will do. I crimped my ocw test rounds last night. Need a break in weather and time to go try them. Then I will do a ladder test inside the node at 400yards. After I have my charge weight I will try 10 crimped vs 10 not and post.
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Skimmed the thread and not sure if anyone mentioned it but variation in your measured OAL after trimming will include variation from the sizing process as well because the WFT or similar indexes off the case shoulder. In my experience brass of different lots/headstamps/fire counts/etc will all size back a little differently, as much as 0.003” from what I’ve seen, even from the same die at the same setting. If you’re not aware of sizing variation you may have you’re chasing your tail trying to tighten up trim length variation.
I’ve been using CBC brass recycled from a case of 62gr I bought a few years back. I recently picked up some Lapua 55gr loaded ammo so once I get through those, I’ll rotate those into my precision loading.
Skimmed the thread and not sure if anyone mentioned it but variation in your measured OAL after trimming will include variation from the sizing process as well because the WFT or similar indexes off the case shoulder. In my experience brass of different lots/headstamps/fire counts/etc will all size back a little differently, as much as 0.003” from what I’ve seen, even from the same die at the same setting. If you’re not aware of sizing variation you may have you’re chasing your tail trying to tighten up trim length variation.
Yep. Same with the Giraud. Short of annealing and sorting off brass, You can't control it. So I don't bother measuring it or giving it any thought.
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