New load testing - didn't quite expect this to happen

[Tangle Eye]

Went to the range Friday I think it was to begin testing and developing a new load using 1.5Fg Swiss.  I was hoping for the unthinkable - that I would find a load that shoots accurately in all 3 of my rifles - I doubt that will happen. Anyway - the big question was "how important is it that the bullet be up at the lands?". With that in mind - I seated the bullet for an overall length of 2.875 - well away from the lands on any of the rifles.  2 inches (5 shots) at 100 yards was pretty consistent for all the guns. Not shabby but not nearly what I already know the BPCR and the Sharps can do with more proper loads.  So - next I take out the OAL gauge and set the bullets close to the lands for the next go around with whatever powder compression is appropriate. So much for one load for all the guns.

Anyway - let me get to the point.  I was using the chronograph here to see what velocity differences I saw between my old 3Fg load and this new powder (about 60 fps difference between 60 gr of 3Fg and 60 gr of 1.5Fg).  I usually wipe the barrel with a dry patch after every 5th shot.  What I didn't expect to see was the 6th shot (after the wipe) jump up in velocity about 20 FPS. It was even faster than my first "record" shot after the initial fouler.  So - is this just the result of a clean barrel or what?  I also noted the second five shot group from each rifle was not as tight as the initial five shot group before the wipe. Any idea what's going on here?

[REELFOOT REGULATOR]

Tangle eye, I cant really explain that either? My best load always consisted of 60gr 1.5 fg, with .030 wad and CCI BR2 primer using blow tube between every shot for 10 rds. Usually get 1.5-2MOA at 100yrd with my pedersolli sharps.

[Tangle Eye]

That's pretty much the load I'm trying Reelfoot.  I haven't really settled on the wad yet but I think just a card is all I'm going to use. They key thing now is getting the bullet seated to the proper depth for each rifle - gotta get the OAL gauge out I guess.  I've gotten a minute of angle group with my BPCR more than once using 60gr of 3Fg Swiss. I think the 1.5Fg is much more comfortable to shoot and is a better fit for .45-70 -- practically all the long range champs use that powder so it must be the right choice.

With my lube - there's no real need to clean after 5 rounds.  I can go 10 easily.  Just wondered about that velocity jump.

[Advertising]

[Lt. Col Mark Flint]

only a theory, but the barrel heat level had risen and the barrel would slowly have expanded.  Of course expansion of a barrel means a shrinking of the bore and a lessening of blowby.  Perhaps that is the answer you seek?

Or maybe the powder settled in the can and you got a scoop of finer grade powder in that particular case?

[Lt. Col Mark Flint]

oh yeah, and perhaps your chrony isn't really accurate to trust that 20 fps difference is really 20 fps. even a 1/2% margin of error is about 7 feet per second double that for +  or _ and you are looking at an instrument that is only really accurate for trends, not individual shots