Today we compared tumblelube vs. loverin lube grooves, and tumblelube lube vs. my favorite Rooster HVR.
TC with 27" Green Mountain barrel for 357 mag, sloppy throat. Unless otherwise stated, all loads used a 160 gr. spitzer, sized 0.360", oven treated wheelweight, Winchester Magnum Small Pistol primer, 17.9 gr. WW296, 1.830" - 1.840" COL. The bullets are seated just off the rifling but not actually engraving. All targets at 100 yards.
First up, my standard load for this barrel, except I tweaked it a bit, partial sizing the cases instead of full length sizing. I was hoping that partial sizing might reduce the standard deviation -- though that did not happen. The 17.7 grain load was slower in the partial sized case so I upped the powder charge to 17.9 grains, just enough to restore the normal 2000+ fps velocity.
I had intended to test all loads with 3 five shot groups and then calculate the mean radius for all 15 shots. However, as you can see on this target with the HVR Loverin bullet, the center of the group shifted slightly as I moved from one bullseye to the another. Maybe the way I held the rifle changed slightly? In any event, the shift was enough to throw off the mean radius if I combined all 15 shots, so instead I calculated the mean radius for each 5 shot group and then averaged the three. That's not the right way to do, it but it was the best I could do to salvage this test.
-- 2012 fps, 0.94% standard deviation, no better or worse than the "old" standard load.
-- 0.54" average mean radius, 0.31" average standard deviation.
-- 1.61" average MOA
-- no fouling visible to the naked eye
So how does that compare to the tumblelube version, when using the same HRV lube? Well, the tumblelube bullet with HVR shot about the same. Since the three 5 shot group thing didn't work out, I tried a single 15 shot group:
-- 2005 fps, 1.3% standard deviation (worse standard deviation compared to the Loverin)
-- 0.68" mean radius, 0.32" standard deviation, slightly larger than the Loverin but prolly not statistically significant.
-- there may have been light fouling just past the throat.
More to come .....