I've been wanting to do some rim thickness testing for a while.
I primarily wanted to see if it's possible to get much improvement out of some of the cheapest ammo.
So I bought three bricks of Remington Cyclone ($6 a box) and spent about four hours measuring rim thickness on 1000 rounds.
Thickness varies from 38-thou to 46-thou.
For comparison, 200rds of Eley Tenex all measure 38-thou - 100% of them, but they're five times the price of the Cyclone.
Remington Cyclone - 1000rds:
0.038" 30of (3%)
0.039" 87of (8.7%)
0.040" 265of (26.5%)
0.041" 287of (28.7%)
0.042" 224of (22.4%)
0.043" 43of (4.3%)
0.044" 35of (3.5%)
0.045" 20of (2%)
0.046" 9of (0.9%)
So, very roughly, more than half of them only vary by 0.001". Three-quarters of them vary by 0.002", and 90% vary by 0.004". The remaining 10% vary by as much as 0.008".
Although it was getting quite dark, the wind had died away completely, so I ran out, set up some targets and shot some initial groups at 50m off the bipod.
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Bottom centre was just zeroing with the 41-thou, because they're the largest batch. Then I shot the top left and centre 10-rd groups with the same 41-thou batch (with a small scope adjustment between them). The second group is 41mm across, which is not bad for my Ruger with the Cyclones (the very best group I've managed with them is 68.2mm at 100m for 10rds).
Then the lower left 10-rd group with the 42-thou batch.
And finally, the upper right 9-rd group with the 46-thou, and lower right 10-rd group with the 38-thou. If you were to overlay the two right-side groups, that should be an indication of the worst case with unbatched ammo, although it was very dark by then which may have affected my grouping. The 38-thou group is 51.5mm, and the 46-thou is 61mm (or 44.5mm ignoring the extreme flyer). Interestingly, overlaying both still measures 61mm with the flyer (and 51.5mm without the flyer) meaning, if I'd fired all twenty rounds at the one target they would've dropped into the same size group anyway (even with the flyer).
I still have a brick left so I can top up them back up to 1000rds, and then I might have a look at batching the three main batches by weight as well.
I'm also curious if it might be possible to compress the rims so that all of them are 38-thou, and whether that might make any difference. Could be interesting doing that experiment
This very preliminary test does seem to indicate some potential for improvement, possibly as much as reducing groups from 51mm down to 41mm. While that could be considered significant, it is offset by the expense of having to buy a lot of ammo, put in a lot of time batching it all, and then end up with perhaps 50-75% of it (at best) showing that much improvement. I'm inclined to simply spend a bit more for a more accurate munition.
Also, it may be significant that although the Cyclones are very cheap, they shoot quite well in my Ruger, better than average. I might have seen more improvement if I'd used something like the Sellier & Bellot Standard which is priced similarly, but shoots around 100mm at 100m. I don't particularly want to buy three bricks of ammo that I already know doesn't group particularly well in my rifle, but I may still do this anyway just for the experiment.
My initial conclusion is that I don't think the very early results warrant the effort involved. At least not with the Cyclones in my Ruger. The effort would be far more effectively put into shooting as many different ammo types as you can find. It would certainly cost more, but it would show real, and measurable, improvements.
Has anybody else done something similar?