Early 7x57s #1s had very long throats. I think it was designed around the 175 round nose. I can get 160s to shoot fairly well but it's the least accurate of the 53 #1s I own, about 2"+ at 100. That is with 160s. The lighter the bullet the worse the groups.
120s shoot patterns instead of groups!!!
You are absolutely correct in that it's about length of the bullet and the OAL and how much "Jump" it takes to get to the lands rather than weight.
Mine was made the first year the chambered the 7x57 "A" , 1977. A 140 grain bullet falls out of the case before it touches the lands. I also have a "B" in 7x57 that was made in 12975 and also has a very long throat.
Not an ideal situation for accuracy.
Later on they shortened up the throat but I can't give you a specific date.
You want the FL size the first time for your #1. After they have been fired you should be fine with neck sizing only. As long as you keep your ammo seperate from the Model 70 and the #1. If you are going to want to mix and match ammo from gun to gun you may well need to FL resizer everything each time.
I have many duplicate in cartridges among my #1s. Even if marginally identical, say 5 #1s in 257 Roberts, I keep ammo separate and loaded for each ring for best accuracy. After all that's why I reload, to tailor the ammo to the rifle.
There are a few exception, the brothers, cousins, son and I all took our #1s in 7mm STW to the smith and had them all throated identically and cleaned out the chambers to the largest of the 9 rifles, so that the ammo would interchange and we didn't need to worry about keeping stuff separate.
It's a real bummer to get to the mountains with ammo that is too long to chamber!!
Ross
