I would like to thank both of you on your input I will try the method described . I have another qiuck question. I have had problems with the rifle holding good groups with 180 grain bullets . I changed to 165 grain and it closed the group up well . A feller told me at the range that I should research the rate of twist for the rifle . He said that 180 grain bullets would shoot better out of a 1-12 or 1-14 twist . He also said that my rifle was probably a 1-10 because the groups tightened up with the smaller bullets . He also said that if I went to 150 grains it may even get better . The big question for me is , can anyone give me a second opinion on this . I am no expert on the subject . I am hunting deer with the rifle and shooting factory loads . Is there any truth in what I was told at the range ??
Usually a faster twist is better for heavy bullets. For example a .223 with a 1:12 twist will stabilize a 45gr bullet, but won't stabilize a 75 gr bullet well, a 1:8 twist will stabilize a 75gr bullet, but may be too fast for a 45gr bullet.
Have you tried different brands/types of 180 gr bullets or different powders? What loads have you tried so far?
Your advice I am afraid is about the exact opposite of what is the actual case. If your rifle will not shoot the 180's because of improper bullet stability, then I would say you have a 1-12 twist.
May just be a case that your rifle does not like the 180 gr bullet you tested.
The generaly rule here is that lighter bullets will shoot accurately with a slower twist.
For example, a 150 gr .308 bullet will generally shoot very accurately out of a 1-14 twist.
The 165 gr bullets will need a 1-12 to shoot well on averge.
The 180 to 200 will generally need a 1-11.
The 200 to 220 gr pills will need around a 1-10.
The big 240 to 250 gr bullets will need a 1-8 to 1-9 twist.
This is all dependent on velocity as this effects bullet RPM dramatically. It is really RPM that stabilizes bullets so velocity can help you get by with slightly slower twists but it is smart on average to get a little more spin the is required, especially if you will be hunting in colder weather where velocities may drop off a little.
jarhead, perked my curiosity, so I ran out to my shop and pulled a manual off the shelf, Speer #11. On page 472, under the heading 30'06, it lists a bunch of manufacturers that use barrels with a 1 in 10" twist, including the Ruger #1 and Model 77. In fact, only Husqvarna and the Browning Model 78 use a 1 in 12" twist. Of course, that was in 1986, some things may have changed, since then....but not your Model 77 built in 1978.
Additionally, these gentlemen are correct about requiring a slightly faster twist, with heavier bullets, or as mentioned, increasing the velocity also increases the RPM and the stability for those bullets running on the ragged edge, accuracy wise.
Also, and I'm sure the previous respondents are aware, although you may not be, that the actual problem is the length of the bullet, rather than the weight. Since most jacketed bullets have a lead core, it amounts to the same thing, excepting solid copper bullets and design features like a boat tail or the VLD ogives. Those bullets may weigh the same as a shorter bullet, however, they require a faster twist, again, for different reasons like a shorter bearing surface relative to the rifling.
Basically, your rifle should shoot Factory 180 grain bullets every bit as accurately as the 165s. If you are happy with the 165 weight, look no further, but there is probably something else going on, as to why your groups were worse, with the 180s. Because you do not handload, you can't try different seating deapths, which is the first thing I'd do? You might check the pressure on the forearm, there is a remote possibility that the harmonics are screwed up when you are shooting the heavier bullets? Next best solution is to try different brands, or get into handloading; which is the smart thing to do, regardless.
Again gentelmen, thankyou for your advise. I really appreciate your time to help me out . I am really a small fish in this shooting world . I am really impressed with the amount of knowledge you all have shared with me . I plan to try some different brands of ammunition . I will also research this harmonics idea. Thanks again fellers.