Ok, guys, I sighted in a .300 WSM today (a Winchester Model 70 Classic Fwt.). I knew the last time I shot the rifle (2 weeks ago), I sighted it in while it was a clean bore, had it shooting about an inch high at 100 yards. I went home, cleaned the rifle, and put it in the safe. Went to the range today, shot a few from the bench, it was still an inch high at 100. I thought, great, don't need to change anything, like I anticipated. Then I shot a little from standing and sitting, without the rest. It was a quick range session, only shot around 10 rounds here. For whatever reason, I wanted to shoot a one more group from the bench. I got the normally really tight group with it, but it was around 2-2.5" to the right of where I had it shooting before! So, I adjusted the scope, and got a nice group 1" high right over the bull again. I thought it was because the barrel got dirty. Dropped the rifle off at home (didn't clean the barrel because I didn't want to have to foul it the next time I take it out, which will probably be the first day of deer season), and drove back to school. Anyway, my dad asked me if I checked the mounts, which never even crossed my mind. What do you think it could be? I wish I could pick the rifle up now and look at the bases, but I'm a few hours away from it. Do you think it would hold zero for a few shots and then move if the scope bases were loose? I really didn't think so, because the rifle was shooting around .5" groups today, but now I'm kind of worried. I'll probably get so worried about it I'll shoot it again before the 1st day (might have 1 oppurtunity to do that), but I'd rather save the cash (using factory ammo). So do you guys think it could be loose scope bases or just a dirty barrel? If it makes a difference, ALL the groups from the bench were 180-grain Ballistic Silvertips, the offhand shooting was done with some 180-grain Power Points I had left over (which usually shoot very close to where the Silvertips shoot, I was just burning up some extras I had left over from a while back). Like I said, though, all the groups that I based sighting in the rifle were on the Silvertips, so that's not the issue. The offhand groups were more or less centered, as well, but, obviously, they were much bigger, standing was probably 6" and sitting around 4".

Since both groups were tight, I highly doubt the problem is loose scope mounts. I believe the difference in impact points was probably related to barrel heating.

I would check for such things as a loose stock or something from the stock pressing on the barrel where it shouldn't be pressing. A barrel that hasn't been properly stress relieved could also do this but that would be uncommon.

That was a lot of movement for barrel heating but it could have been. What scope do you have mounted on your rifle?

beartooth,

It's a Leopald VarXI 4-12x. Haven't had any problems with it in the few years I've had it on this rifle.

If it is a relatively new rifle, or if the barreled action has been out of the stock recently, it may just be becoming seated in the stock.

Back when the M1 was being used in the National matches, it was claimed that it took around 20 rounds to reseat the thing if it had been stripped for cleaning......

LOTS of things can be wrong, you have to use a method of investigation, catch and release! a process of ilimination

Iliminate the problems one at a time. It could be a new barrel not broken in, barrel that is prone to be rough, clean or dirty, stock problems, scope bases, scope problems..Some guns are tempermental as hell, others are not, always own the ones that arn't.

Changing ammo brands, bullet weights, any component is a recipe for disaster.

I know its damn easy to knock a big belled scope off a little as too much is exposed forward, that is why I use smaller scopes on big game rifles. I see this problem every year. Sight it in, give it a hard bump and then shoot another group, you will see what I mean..hunting rifles take some good bumps. I use a 2.5x5 Leupold or a 1x4 or a fixed 3 or 4 on big game rifles, and a 2x7x33 seems to work well.

Sorry it took so long for me to get back here, guys. I did end up taking it to the range one more time before the season. When I shot the 1st group, it was about 2" to the left. So, I thought about it, had to have been a hot barrel the last time, so I moved the scope and gave it a lot of time to cool between shots. After that every shot was pretty much where I wanted it (except the one where an AR threw a piece of brass onto my ear muffs, but I didn't blame my rifle for that one!). Got a shot at a doe at about 90 yards the first day, bullet took the heart and one lung....good enough! Thanks for all of your help.