Case trim cause accuracy issues?

[Smoketheclay]

I load 6.5 creedmoor. Case trim length per the book is 1.910. Max per the book is 1.920

I loaded trimmed between 1.9110 and 1.9130

All other things equal, how much of an FPS change or deviation would be caused from the difference in trim length?

 

[Huskydriver]

I have no empirical data to say for sure one way or the other as far as the 2 thousands of an inch in trimming length but I am confident that you would def see an accuracy change with neck tension. If you are not annealing, you are not going to get the same amount of neck tension over the life of the brass and would guess is where your accuracy change is occurring all other things being equal. I dont stress trimming to a perfect thousandth as much as I do getting run out and neck tension consistent, I have plenty of hands on experimentation with those two variables to show me that they greatly matter to downrange consistency. Dont get me wrong I try to trim my brass the same but 2 thou in length has not made or broke my performance on target.

 

[Lunchbox27]

IMO you're over thinking this unless you're shooting benchrest, and even then... I have never seen anything that would make me go OCD over it. If your SAAMI spec minimum is 1 and your max is 10, trim to 5 and shoot! Hell, I don't even trim every time anymore. So long as I am under the max, I load and go.

Neck tension and run out is a different story as Huskydriver already mentioned.

 

[Supersubes]

You could be anal about trim length if you want, but as soon as you inside chamfer the necks, you’re right back to having several thou variance across the cases.

 

[Milo 2.5]

Zero your caliper, now open it to .002". Ask yourself that question now.
I had 3 x fired Dasher brass, I had jumped through hoops finding the perfect neck tension, the final step being a partial neck size. Anyway, I borrowed a friends AMP because I wanted it annealed, with the brass being softer now, my solution was to not chamfer the necks this go. I didn't do a head to head test, but the load came right back or better than it was.

In retrospect, I should really go back to work because I have way too much free time to even contemplate this type of horseshit.
The story gets even better because I bought a K&M arbor press and inline Wilson seaters to measure this fiasco, and sized, prepped brass produced the most uniform numbers that I've seen on any you tube vids of the system. I knew this going in, I could feel it on my coax and saw the results downrange. So I primed and powdered a tray of 50 cases, now my numbers were garbage, because now my bullet is contacting powder in the case. The press and dies sold in under 2 hours.
I guess when I read the instructions for the dies, the light bulb should have came on. Not verbatim, but they said, use an arbor press to seat bullets, if you do not have one, a poly tipped or rubber hammer will do just fine.

Edit: I'm not saying you should not pay attention to detail, small details can make a load. 4-5 yrs ago. it was the rage to tell new reloaders,"you cannot shoot the difference", < do that 10 times with the varying processes we do, you're not going to be interested in shooting anymore. But trim length here is miniscule.

 

[lightman]

I seriously doubt that you will see any measurable difference in your scores or group size with that difference in length. But I try to keep my case length closed than that. I also uniform the primer pocket and deburr the flash hole on my hunting or match ammo. This may all be for nothing in a factory rifle with a few mods but it makes me feel better about my ammo.