Picky about ammo

[Neal Bloom]

I have a Ruger #1 in 30-06 that according to the Ruger web site was manufactured in 1978. Picked up awhile ago and just recently had the chance to shoot it. The rifle seems to be very picky about ammo. When I shoot 150 gr. they are all over the place with some very high flyers. With 180 grain sp I can get some decent groups. All the bullets are reloads and work fine in other rifles. My dealer told me that the rifling twist may only like the 180 grains bullets. As anyone else experienced this with a #1? Also what is the twist of a #1?

I do have another question about floating the barrel but I put that in the gunsmithing section.