Look at the wood on that Ruger...
GCF...A question or two or comments if you do not mind.
Looking at your targets my attention was drawn to COL. Target #1 shows COL 2.985" with Sierra 140gr SP which is just shy of Sierras suggested COL of 3.000" Target #2 shows COL 3.070" with Nosler 140gr BT.
Are you seating out the bullets just shy of the lands or are you backing away to a specific sweet spot?
My M77 magazine length is 3.390" so I seat bullet to obtain COL less than that...for example 140gr Sierra SP COL is 3.120" and 154gr Hornady SP Interlock COL is 3.280".
My M77 TS 7x57 is a pre-1985 with a 1:9 1/2" ROT and has a propensity for 140gr and lighter bullets. A couple of amigos in the gun club have post-1985 M77 7x57s with 1:8 3/4" ROTs and they tend to shoot the 150 - 160gr bullets well although my pre-1985 does a respectable job.
RoundOak -
Thanks for your interest. W/ regards to COL, trying to nitpick distance off lands tends to give me a headache, so w/ a bullet short enough (140 grain SP),I've taken to a somewhat simplified / un-scientific approach: I simply seat the bottom of the bullet bearing surface, to the base of the sized case neck. The longer, heavier HRDY 154SP needs to seat a bit deeper to chamber.
The beveled base of the 140 Ballistic Tip, hangs down below the neck, just a tad.
As long as the neck is true, I get minimal runout. Also get maximum bullet "pull" from the case - if that matters.
I'm not sure this approach would work w/ an older, long throated 7x57, but from what I've seen, the newer No.1's are throated much more reasonably. Well, unless a guy has a hankering to shoot 175 grn ball, anyways...
I've not shot anything lighter then Hrdy 139's, or heavier then Hrdy 154's. Shot more 140's to date, then anything else. Pretty sure this barrel is a 1:8.75", & feel that it would probably shoot a 160SP well.
Interestingly, this little gem seems to shoot inexpensive, flat base, cup & core bullets, w/ very little drama - or trauma. The Sierra 140SP "ProHunter" has been a pleasure to work with.
Gary
