Rim thickness on .22s is something I see discussed ad nauseum, but I've yet to see an experiment of meaningful sample size verifying the theory that it improves accuracy. This is probably better to test with cheaper ammo that presumably has a higher variance in rim thickness. Consider grabbing a bulk box, and sorting into "thickest 20%, thinnest 20%, and median 40%". Shim the bolt to match the headspace of the median average, then shoot sets of groups containing 1) the thickest and thinnest ammo mixed together and 2) the median ammo. Would be very curious to see the results from such a procedure, the more groups the better!
I agree. I definitely plan on doing testing in the near future, but I'm busy preparing for nationals at the moment. Some preliminary testing that I have done shows improvement in group size when I shim the bolt to tighten the headspace from its normal 0.0435 to the 0.0405-0.0395 range for Eley ammo which has a rim thickness of 0.039-0.038 I think there are a few tests to do. One would be to test ammo sorted by rim thickness for groups and SD/ES vs a random selection. This would most apply to bulk ammo like you suggest since most of the match ammo I have seen from Lapua and Eley has at most a 0.001 extreme spread in rim thickness. The other test that comes to mind is matching the rim thickness to the headspace of the rifle via bolt shims to see if there is an improvement. The issue, as you point out, is getting a large enough sample size to make the results statistically significant. I need to dust off my old statistics textbooks and design the experiment and then find a calm day or book an indoor range to do the testing.
@@CopperStarPrecision Right on, man. +1 on doing it indoors to isolate the effects of weather. Probably ought to chrono everything to isolate the effects of varying velocity, too... Looking forward to a video on this if you ever get around to it.
@@CopperStarPrecision Also, there's some redneck science claims I've heard from another channel ("STKO") and I'm curious if they hold any bearing among the competition crowd: 1) Humidity's effects on powder burn and chamber fouling have a larger effect on accuracy than any lot-to-lot variance would, and lot-tested ammo doesn't necessarily consistently perform the best in different humidity than what it was initially tested in. 2) The ratio of contact-bearing surface on the bullet to the width of the grooves in rifling has the largest effect on a given barrel's ammo preference (ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-fNCyOCaWo00.html). Not really seeing these mentioned anywhere outside his channel, and his process isn't exactly scientific :) Was wondering if there's any merit to either of these.
Shimming rim thickness all depends on the chamfer of the rifle's chamber. Save your money from "rabbit hole" gauge prices and detail the rim thickness to your rifle... It does require more work☹ 223 case is great for comparing different brands of ammo... Old school
Lot testing will always be key, but matching the headspace to rim thickness can usually give you a better starting point for a specific brand of ammo. My MTR headspace is 43-43.5 thou and it likes SK/Lapua which makes sense. I've never found any Eley ammo that shoots well since the rim thickness is closer to 39 thou. If I wanted to shoot Eley I would need to shim the bolt for tighter headspace.
Thanks for the video! How concerned are you with touching brass, and wax coating, on the rounds as you measure? Does that coating even matter? New to precision 22lr and enjoy watching your channel.
The lubrication on the bullet does matter and varies between brands of ammo, but I'm not terribly concerned of touching it as long as I'm not rubbing it all off on a paper towel or something. Some ammo is very dirty and you might have to make sure your measurement tools are clean to avoid false measurements.
@@CopperStarPrecision Are you stung the lube on the brass (as opposed to the lead bullet) matters? If so, perhaps you can explain in a future video. I don't think it really has any impact on peformance but maybe I'm missing something.
