I would like to see a myth busters thread on whether .003" inch variance in OAL actually affects accuracy to any measurable degree
1KPerDay, take a step back and look at the "totality" of reloading variables.
- And the tests were conducted using same headstamp brass. With mixed range brass, I get about .005" OAL variance.
Please note, it's not the FINISHED OAL that determines holes on target rather CHAMBERED OAL (after bullet setback) and STACKING OF RELOADING VARIABLES.
So while .004"+ OAL variance may not translate to significant change on group size, add to this bullet setback variance and powder charge variance (We all know even better metering powders vary by .1 gr which is going to be my next myth busting thread), now you have STACKING of reloading variables that could be measurable on target.
I would suppose that could, or would depend upon the case volume and powder used.
And if you are using a powder measure that drifts, you have another reloading variable that could stack.
When I shot USPSA matches, we did many comparison tests. One of the tests was shooting our different match loads (different bullets, powders/charges, primers, OAL, crimp, etc.) in the same pistol to see if we could see difference on target. When my match loads got comparable/smaller groups than other match loads, they got curious.
They were surprised to find out I was loading my match loads on Pro 1000 with pre-resized brass. Back than I was using Montana Gold FMJ/JHP bullets and Winchester primers along with WST/Titegroup/W231/Universal/WSF powders and many other shooters used the same components.
So we went to different shooters' houses and examined their equipment and reloading practice with calipers and scales in hand. What we found out was some of the powder measures drifted as much as by a few thousandths during a reloading session. Let's say you start out with 4.0 gr charge but the powder measure drift ends with 4.2 gr. If you factor in the normal powder measure drop variance, you could be reaching into your ammo bag and grab two different rounds with almost 3.9 gr charge and 4.3 gr charge loaded in the same magazine. This variance WILL show on target.
What they found with me was since I was using fixed volumetric hole Pro Auto Disk, my powder charge drops could not drift even after 1000+ round reloading session and all the rounds you grab from the ammo bag would have the normal powder charge variance of .1 gr. Of course while I used mixed range brass, I did use pre-resized brass which, as shown in recent myth busting thread, produced OAL variance of .001".