9.3x62 Bullet Swap Question

[geoff rath]

Glad you resurrected this as I have since found an issue with the numbers I reported.
The 270gr bullets came with my 9.3x74R Chapuis, in bags marked as PPU (not factory bags). They look and measure identically to the box of Speer 270gr SP that I have. Would not surprise me if they are actually Speers.
What I have determined after making this report, is that my old Chrony is no longer giving me accurate readings. So I re-shot some of this experiment after buying a new ProChrono DLX. The new numbers are more in line with what I had expected, and closer to what others had experienced.
The factory Nosler 286gr Solids averaged 2394fps, which is very close to the 2400fps listed on the box, and 1.3" group for the 5 rounds. The Woodleigh 286gr PP/SN averaged 2379fps and without the called flyer, put 4 rounds in 1.25"; the flyer pushed it to 1.76".
With the results gathered with this rifle/loads and a couple others shot since, the old Chrony was giving me readings about 150-160fps high that day. Running it in tandem with the new ProChrono has shown the Chrony to be inconsistently high. Lots of digging into old records, and shooting some old loads across the tandem setup, has shown that the Chrony started lying to me late last summer. Quite frustrating. But fortunately, it allowed me to confirm a number of other loads that had been developed prior to August last year. After 30+ years of good service, the Chrony has been officially retired.
Just a side note that might save some of you some headache, there is no way to recalibrate any of the chronographs out there. The really expensive ones might be worth the effort to adjust the sensor spacing (and that would be a LOT of effort), but realistically, when one of them is determined to be out of spec, the solution is to buy a new one. Even with a new one, it is suggested to run some control loads over it, either a previously measured load or a factory load of some sort that tends to be consistent (like 22LR Match ammo), to see how the new chrono registers. And not a bad idea to start every session with 5 rounds to "calibrate" for that day's efforts.
Consistency in lighting seems to be the most critical factor in getting consistent readings from any of these chronographs. That was something I had figured out years ago and after multiple attempts, finally came up with a simple oversize diffuser that seems to work well, and works with any of the remote chronographs. Since I don't have, and haven't ever used one of the barrel mounted systems like LabRadar, I can't speak to those.

Great research; thank you on my, and others' behalf

 

[MS 9x56]

Well, the river receded, the skies cleared, and the wind is but a gentle breeze today. Had everything out and setup to start running these loads over the Chrony. But when I walked out to the backstop to hang targets, I saw fresh tracks in the mud, then saw a doe just over the edge of the sandcreek beyond the backstop. She was just staring at me, but not moving away. About 40-50yds from me.
Figured I would "encourage" her to move away, so I walked up and crossed the fence. That finally got her to trot off and head north. About that time, I saw what I initially thought was one of our rather large jackrabbits lying in the grass, then realized it was too dark, and had spots! This little guy was less than 12 hours old, probably closer to 6 or 8, when I found it.
So much for shooting today; have to find something else to do this afternoon....
View attachment 540178

You are a good man and good steward of our game.