bladeracer wrote:I've been shooting a case-life test.
Ten .223 cases, 26.5gn of AR2206H, Rem 7-1/2 primer, and Hornady 55gn SP bullet.
All ten were once-fired factory PPU when I got them. Pockets uniformed to depth, and chamfered, flash holes deburred inside and out.
I collet neck-size five and FLS five.
Trimmed to 1.756" each time, mouth chamfered.
The first load was a 52gn bullet swaged from .22LR brass on 27.0gn of AR2206H, but the bullets weren't reaching the target due to the velocity. I also didn't see much value in testing with loads hotter than I normally run so I changed to the 55gn and dropped it to a 26.5gn charge.
I shot them for the third time yesterday, which was the first time I did so over the chrono.
I put fourteen reduced loads through first at 1870fps to warm the barrel.
The neck-sized ran 3244 3244 3228 3244 3205 for a mean of 3233fps, and 20mm 100m group.
The full-length-sized ran 3341 3300 3308 3367 3316 for a mean of 3326fps, and a 22mm group.
Roughly 100fps faster, or 3% increase in velocity just from FLS instead of neck-sizing.
Has anybody else measured such a difference?
I'm wondering if the idea that FLS wears the brass out faster might not actually stem from them running higher pressures due to the reduced case capacity of full-length-sized brass.
Over three loads I'm seeing about .001" growth in the neck-sized and 0.0045" in the FLS'ed brass, but it seems to be reducing each time.
I assumed the lower case life is from wearing out the brass from a case hardening & thinning point of view, with the difference in pressure not being a big/or the biggest contributing factor (apart from to a point governing how much stretch the case undergoes), given that each time you are FL sizing, shooting & trimming you are causing it to flow & become thinner & more brittle...?
But to answer your question re the experiment,..A load i have chrono'd with a newish rifle has given me results along the lines of what you have found with velocities, although im still puzzled by them.
Its a 22-250 & the chrono results were...
Once fired & FL sized brass (being formed) gave me an average of 3560fps,...seated for a .020" jump.
The fireformed & neck sized only brass gave me an average of (3490fps)-3500fps....seated for a .010" jump.
points of difference that may be of interest...
*the obvious of the .010" jump between the two.
*There is only .003" MAX difference in the shoulder measurement of the cases (from FLSized to formed-with the FL Sized being from the die wound ALL the way down to the shell holder), but most of the cases are only .0015"-.002" difference in the shoulder measurement from FL sized to fully formed.-other rifles i have in same chambering are atleast .0045" difference in the shoulder to head length.
*it is a very short chamber compared to the other few 22-250 chambers ive measured.
*I didnt do an actual water volume test on the cases to see the volume difference of before & after being sized/formed to get a true constant to measure from.
*Although this particular rifle has a shorter chamber & therefor load density is higher than others i have, it seems to take hotter loads--ive gone 1 full grain above ADI max & still have not hit any pressure signs that i can tell.
Im surprised to see that much difference in velocity, with such minimal differences in the loaded cartridge, but then i've never experimented in the past to know what to expect.
60-70fps less looks like a big number on paper, but i guess its not much difference in real world terms--well at least i for one would not see the difference in results on a rabbit or a fox.
The man who knows everything, doesnt really know everything...he's just stopped learning...