Case trimming, just how much does trim length affect accuracy?

Shooting Supplies : Ammo - Reloading - Firearms - Optics - Accessories
phillips321

phillips321

Well-Known Member
Hi guys,

Using the hornady quick trim for my 3 calibers I never get consistent trim lengths.

Im reloading for my .243 currently for example and am getting the following:
Before - After
2.060 - 2.035
2.050 - 2.037
2.057 - 2.039
2.054 - 2.039
2.060 - 2.040
2.056 - 2.035

~0.05 range. I assume this is fine and nothing to worry about?

Thanks in advance
 
Generally speaking that is fine and will not impact performance unless you are literally after minute of gnat at 1000 paces.

That said, the inconsistency would annoy me when a decent trimmer should get it bang on every time. I use a cheapo zip trim (disposable item that breaks every coupla thousand cases) and a lee case length gauge. It is bang on every time.

But anyway, you are fine to crack on. As long as you are within min and max tolerances, the odd thousandth is fine.
 
phillips321 said:
Hi guys,

Using the hornady quick trim for my 3 calibers I never get consistent trim lengths.

Im reloading for my .243 currently for example and am getting the following:
Before - After
2.060 - 2.035
2.050 - 2.037
2.057 - 2.039
2.054 - 2.039
2.060 - 2.040
2.056 - 2.035

~0.05 range. I assume this is fine and nothing to worry about?

Thanks in advance
Click to expand...
What’s the tolerance of your callipers?
 
All I need is something that won’t affect MoA accuracy, as that’s all I can shoot on a good day anyway 😉
 
I cant see how thats going to affect accuracy in any way to be honest.

I dont even measure mine - I just run them through the trimmer (Lee) on an electric drill and thats it, I just assume its correct. Some of them trim off nothing, some a little bit and some quite a lot. Both my main stalking rifles will stick everything on your thumb nail at 100y easily with my home loads.

I always assumed you trim just to make sure everything will chamber correctly as the brass stretches.

Do also bear in mind we're talking about 1mm of variance between the shortest case and the longest one - I really cant see how thats going to affect anything much.
 
jax ,s post is a valid one as well cheap calipers could be out more than the cases. as long as they are in spec as above mine all get trimmed the same.
 
stubear said:
I cant see how thats going to affect accuracy in any way to be honest.

I dont even measure mine - I just run them through the trimmer (Lee) on an electric drill and thats it, I just assume its correct. Some of them trim off nothing, some a little bit and some quite a lot. Both my main stalking rifles will stick everything on your thumb nail at 100y easily with my home loads.

I always assumed you trim just to make sure everything will chamber correctly as the brass stretches.

Do also bear in mind we're talking about 1mm of variance between the shortest case and the longest one - I really cant see how thats going to affect anything much.
Click to expand...
1mm of extra resistance and next tension could have an impact on accuracy of it didn't then people wouldn't bother crimping or next turning etc

whether or not it's noticeable in every rifle or to every shooter remains to be seen.
 
Old melv said:
Just under 2 thousands of an inch can't see this affecting much and as said above whats the accuracy of your calipers and measuring technique.
Click to expand...
If that’s +/- 0.002” tolerance and the OP’s callipers are the same, there’s .004” of the .005” variation originally listed.
 
I always thought the case length was more of a pressure thing. Exceed the max length and you end up crimping the brass in the barrel when chambering. This can possibly increase pressure beyond what is expected.
 
I suspect that of the case-prep tasks, inconsistent neck-tension will have a bigger impact on shot-to-shot accuracy than 50 thou' neck length difference between cases.

And apart from case prep, consistent charge weight metering, consistent COAL, and concentric projectile insertion probably all have more impact on accuracy.
 
I only ever trim cases that I've FL resized. Can't remember the last time I trimmed one otherwise. I just fireform, neck size and re-load. Accuracy seems fine. Am I a bad person?

FN
 
Fabnosh said:
I only ever trim cases that I've FL resized. Can't remember the last time I trimmed one otherwise. I just fireform, neck size and re-load. Accuracy seems fine. Am I a bad person?

FN
Click to expand...
Not too bad, just a little naughty. One big benefit of trimming is that it enables you to get a good and consistent crimp. Based on your post, you are not a crimper, trust me, you don’t want to go down that rabbit hole on this site.
 
zambezi said:
I suspect that of the case-prep tasks, inconsistent neck-tension will have a bigger impact on shot-to-shot accuracy than 50 thou' neck length difference between cases.

And apart from case prep, consistent charge weight metering, consistent COAL, and concentric projectile insertion probably all have more impact on accuracy.
Click to expand...
I know we're talking about a few thou here, but doesn't having different neck lengths have an impact on neck tension? Longer neck having more grip thus affecting tension?
 
Jelen said:
I know we're talking about a few thou here, but doesn't having different neck lengths have an impact on neck tension? Longer neck having more grip thus affecting tension?
Click to expand...

Impact yes. I just think it is less.

I was just thinking mathematically: If a total case neck is 220 thou in length, 50 thou is sub 23% of that length. So a small difference in neck tension must have a larger impact than removing 23% of the surface area.

Plus, if you do an internal chamfer, you further negate the grip imparted by the last 20 thou or so.
 
phillips321 said:
Hi guys,

Using the hornady quick trim for my 3 calibers I never get consistent trim lengths.

Im reloading for my .243 currently for example and am getting the following:
Before - After
2.060 - 2.035
2.050 - 2.037
2.057 - 2.039
2.054 - 2.039
2.060 - 2.040
2.056 - 2.035

~0.05 range. I assume this is fine and nothing to worry about?

Thanks in advance
Click to expand...
A trimmer that indexes on the shoulder will give you more consistent neck lengths. On a more significant note, I would be concerned that your fired cases are significantly over max case length of 2.045 inches.
Regards
JCS
 
jcampbellsmith said:
A trimmer that indexes on the shoulder will give you more consistent neck lengths. On a more significant note, I would be concerned that your fired cases are significantly over max case length of 2.045 inches.
Regards
JCS
Click to expand...
Shooting a Blaser R93, I FL size every reload. The rifle shoots well, if I do my part with 87vmax I can get 0.5MoA. The 243 case head spaces off the shoulder I think so im not sure how fired case length is a problem? (Please enlighten me, I'm a more or less self taught reloader so if there's a safety/danger issue I'd like to know )
 
phillips321 said:
Shooting a Blaser R93, I FL size every reload. The rifle shoots well, if I do my part with 87vmax I can get 0.5MoA. The 243 case head spaces off the shoulder I think so im not sure how fired case length is a problem? (Please enlighten me, I'm a more or less self taught reloader so if there's a safety/danger issue I'd like to know )
Click to expand...
Once upon a time I observed a Blaser 243 owner blowing primers. His cases were too long and the case mouthes were being nipped by the leade. This created an over pressure situation that was resolved by trimming correctly.
Regards
JCS
 
jcampbellsmith said:
A trimmer that indexes on the shoulder will give you more consistent neck lengths. On a more significant note, I would be concerned that your fired cases are significantly over max case length of 2.045 inches.
Regards
JCS
Click to expand...
Aren’t the 1st column figures after FL resize hence the need to trim ? Although 2.045” is Max case length for .243, I trim to 2.035” and the op 2nd column although inconsistent are all under the 2.045”.
 
charlieboy-shooter said:
Aren’t the 1st column figures after FL resize hence the need to trim ? Although 2.045” is Max case length for .243, I trim to 2.035” and the op 2nd column although inconsistent are all under the 2.045”.
Click to expand...
Yeah that's correct, column1 is after a FL resize, column2 is after trimming.
 
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