Still puzzling over the higher than expected velocity, I checked the diameter of these SPS partitions. It seems fine at .2568". I tried slipping one into a fired case mouth and it took a pretty good bit of force. So I checked the diameter of the Barnes 100 TSXs that I've been using since I first got this rifle 15-20 years ago, and they are .2565" - not really enough to matter I'm thinking, but I could be wrong. From checking case mouth variance, I already knew my case mouth walls run .014-.015", which is a little on the thick side, so I think I will give them a light turning and see if that gives a little smoother slip fit of a bullet into the fired case after the next rip to the range. Perhaps the neck is being pinched a bit in the chamber.
BTW, I deprimed with a Lee universal deprime die, sized the cases using an RCBS FL die with the decapping/expanding rod removed, then expanded the necks with a Sinclair expander mandrel, which put them only .002-.003" under bullet diameter prior to seating the bullet, if that makes any difference.
Happy shooting,
Rex
Hello all.
I neck-turned a thousandth off of nine cases and loaded up the same 51/Magnum, CCI 250 load I posted earlier, and it did not improve accuracy nor reduce velocity. It turns out there was nothing wrong with my cases with the thicker neck walls of .014-.015". After the fact, I discovered that as I withdraw the bolt slowly on the Rem 722 Roberts, intending to catch the case before it is fully ejected, the ejector plunger spring has so much force behind it that when the case mouth clears the rear of the barrel, and snaps right until it hits the inside of the receiver, that puts a tiny little barely noticeable dent in the case mouth. This was the source of the "tight" case mouths I found earlier on my untuned brass. I took a loose one of the .525 ogive partitions to the range with me, and indeed, it did slip easily into the turned case mouths (once I pushed that little dent out of the way), but now knowing the dent was there, it fit the once fired mouth of the unturned brass even better, once I smoothed out the tiny dent.
velocity averaged around 3040 with 51/Magnum in the turned cases and groups averaged 1.24".
The next week I went back with the unturned cases with the thicker walls, loaded with 50.2, 50.5, and 50.8 grains of Magnum. Same CCI 250, and same OAL of 2.81" which puts the partition .025" off the lands. Results:
50.2gr - 2990', 0.88" group, SD 29
50.5gr - 3023', 1.04" group, SD 31
50.8gr - 3020', 0.79" group, SD 22
I'm puzzled by the big velocity spreads, and am wondering if I am getting some squirrely readings off the 35P. I'll change the battery before the next range session and see if that makes a difference.
But overall it looks like that 50.8 grain charge may be a sweet spot. I might try a couple different primers and maybe seating a little forward or back, but that is a pretty darn good load there for a rifle that turned 70 years-old this month.
Anybody else had a chance to work with these and have more to share?
Cheers,
Rex
