Fellas,
I have a Savage 112 Stainless in 7MM STW. It will shoot groups at 200 yds of about 3/4" to about 1 1/2" with bullet weights ranging from 140 to 162 grs.(Hornady btsp.) Good enough for Critters. The one bullet I'm having trouble with is the Hornady 162 gr. A-Max. Can't make the damned thing shoot for Sour Owl Crap!! I've tried different powders, Primers, and a whole range of different bullet seating depths, clean out to touching the lands. (Have to shoot these single-shot). It will group about a 2 1/2" group at 200 yds with nearly any of the different load combinations - WHEN THE BULLET GETS THERE! Some groups are better than others but for example, the last 5-shot group I fired was with a bullet seated out to the lands, (the 162 gr. Hornady A-max) loaded with 83 grs of RL-25 @ 3340 fps. Two bullets grouped about an inch apart, one hit the ground in front of the target at about 85 yds, another hit the ground in front of the target at about 138 yds. and I don't know where the hell the 5th bullet went. Obviously this STW don't like A-Max's and I'm accepting that but if anybody got any ideas as to what's going on I'd like to hear them. The barrel has a 1-9.5 twist and maybe at the faster speeds, it's over-stabalizing but whether I shoot bullets slow or fast, I can't get them all on the paper. I haven't seen any bullet holes on the target that were sideways on the paper, so maybe they ain't yawing. Godsdog.

I would start by cleaning the barrel good. make sure there was no copper fouling.
Then if I were loading for that rifle and bullet powder combo, i would start low and load a ladder from min to max at 1/2grain intervals.
Number each load and shoot them starting with the min at 200yds. across a chronograph. Watch for pressure and velocity spike or drops.
Thats a pretty slow powder do you crimp or have you considered that in order to get a good consitent burn?

Some guns/barrels do not like particular bullets. I have a 300 WSM that loves every 180 grain bullet I've tried in it except the Grand Slam.

I solved that problem pretty easily, I don't shoot the Grand Slam bullet.

purely a guess....the A-Max bullets are quite thinnly jacketed. Your speed and twist may be causing them to come apart in mid air.

What Fjold said, some bbls. just don't like some bullets. My .338-06 just won't shoot any 225gr bullet worth a crap. It's a amoa rifle w/ the 210grNP & almost any 250gr bullet, but 2MOA avg. for the 225gr. No worries, just don't use that bullet, plenty of other choices.
BTW, I have about 60 Hornady 154grIB left, they won't shoot worth a crap in either of my 7s.

Fjod:
I have the same exact problem except mine loves the Speers and pukes everything else. Maybe we should work out a trade.
Its just crazy--and some barrels are like a hungry hound dog, they will eat anything and be happy, like it, and be thankful.

I may not be correct, but I think Hornady recommends a 1-8" twist for the 162 gr AMAX.


SBB

Do what the "Hee-Haw" doc would tell you.

Don't do that!