Today's goal was to sample different bullets and different powders in the Talldog. Unlike last week's "leftover" bullets, today's bullets were nose-sized to fit the TallDog's throat. The jam points were measured and bullets were seated to give 0.010" - 0.015" jam.
Here are the bullets we shot today.
I started out with WC845 (the 10.5" pattern on the lower left), then switched to Varget and continued with Varget for the rest of the day. I know from experience with the BR's that WC845 is very fussy while Varget is "decent," so I felt that Varget was a safe choice. I had planned to try more powders if any bullet showed potential, but no bullets showed potential.
As you can see all of the cast bullet loads were unacceptable. So then I did something that I rarely do -- I shot some jacketed bullets -- just to verify that there was nothing mechanically wrong with the scope or the rifle. The little Vmax bullets could not reach the rifling, and they rattled around in the .246" throat, yielding a 1.9" group. Not great, but still much better than the wild patterns produced by the cast bullets.Observations and Conclusions
-- the 89 gr. bullet has a Miller Stability factor of 1.24 at my elevation -- only borderline stable -- but all of the bullet holes were round, so it did appear to stabilize just as the Miller formula predicted.
-- no errant gas checks hit the chronograph.
-- the Talldog's generous throat appears to eliminate the 6BR's errant gas check problem. That seems to confirm the hypothesis that gas checks were "catching" at the entrance to the 6BR's throat.
-- but the generous throat kills accuracy with cast bullets, even when the bullets are sized to be a good fit in the throat.
-- I'm going to assume that the throat is the problem with the Talldog. The rest of the chamber is smooth and snug. The Talldog's capacity of 33.5 gr. H20 is nearly identical to the proven PPC (32 gr.) and close to the 6x45 (30.5 gr.) so I think the cartridge itself is fine.
-- while the 3-groove Pacnor is smooth enough, and does not foul significantly, I'm skeptical that 3 grooves are optimal for cast bullets. This 3-groove barrel seems much fussier than my other barrels.Where Do We Go From Here?
-- while there are always more load tweaks that could be tried, it's obvious that this chamber does not want to shoot cast bullets.
-- I may set the barrel back a thread or two, enough to replace the long, sloppy throat with a short, snug throat as per conventional benchrest practice. The barrel is useless in its current state so i have nothing to lose by setting it back.
-- but will a short, snug throat "catch" gas checks?
-- also, I happen to have a 14" twist, 6 groove Shilen barrel blank on hand. If time allows I may chamber it for 6mm Talldog with a short, snug throat. It'll be interesting to see if the 6-groove barrel "catches" gas checks. I bet it won't.
-- ditto for the 10" twist, 6-groove Shilen left over from the 6x45 project.
This Talldog project has disappointed me, but I suspect the fault is with the throat and perhaps with the 3-groove barrel, not with the cartridge itself.