I bought a custom target rifle in an estate sale. Ruger No. 3, 26" Lilja barrel with 10" twist, No. 1 stock, wildcat based on the 30-40 Krag. It is blown out, shoulder moved forward, and necked down to 7mm. Inside capacity is almost identical to the .280 Remington.

There were 880 Sierra 168gr target bullets with it. Seated normally, the bullets just kiss the rifling. I started with IMR4831 powder and worked up from 46gr to 51gr. The bullet was not stabilizing at the lower speeds. Possibly not at 51gr, but I could not tell for sure. Groups were getting smaller the higher I went, though. There were absolutely no signs of excessive pressure, so I went back and loaded up some more.

Went from 52gr to 55gr. The only way I could get 55gr in without crushing it was to use a drop tube. No signs of excessive pressure (no marks anywhere on the case), but from the primer, it is high as I would go anyway. But the best I have been able to do is 1-1/2" to 2" at 200 yards (5-shot groups). That is great for a hunting gun, but not good enough for a target gun.

I tried IMR4350 with the same bullet, but stopped at 52gr from primer indications. Also got some shorter bullets (145gr Speer) to try. Was able to go up to 55gr with this (drop tube again), but was not able to seat it anywhere near the rifling. Groups were about the same size as the above, but they were constant -- no larger or smaller as I worked up. They must have stabilized at lower speeds.

Any other suggestions on where to go from here?

Two things come to mind for me here And they both go against my better judgement based on past sucesses and failures.
first you might try a ball powder. You may be able to increase the volume as well as velocity and hopefully stabilize the bullet.
The other thing is you might go to a lighter bullet that is still long enough to engage the rifleing when seated out. The only why I can think of here is the barns X or one of there other all copper bullets.

I have never liked ball powders or bullets that don't have lead in them but from time to time special conditions requier special solutions. In one case with the Barns bullets in my .220 swift the Barns was the bullet that saved me. The lighter bullets were just going to fast for there constuction and I couldent get better than 2" at 100 yds and the heavier bullets were so unstable that they cartweeled out of the barrel. The 50 gr. barns was the answer.
You might start with a heavy load of 760 with the 168's then maybe try another bullet.
Sounds like a pritty cool rifle. One last thing you might check out here is the post I left about the seyfreid modification to #1's. It works well for accurizing them

Thanks for the suggestion on an all-copper bullet. I had not thought of that. It is worth a try. I have not had the forearm off the rifle yet to see what he did, but I think he did something. The rifle shoots round groups. It does not string vertically like my other No. 3's did when I first got them. I will have to think a while on ball powder. I have never used ball powder in a rifle cartridge. No bad experience with it, just no experience.

Update: I bought some 7mm Barnes 140gr Triple-Shock X bullets to try. They are just about the same length as the 168gr Sierra and were easy to seat next to the lands. I loaded up some from 47gr to 55gr of IMR4350.

The best groups were 52.0gr at 1-1/8" and 53.0gr at 1-3/16". All groups were shot at 200 yards. Haven't checked the velocity yet, but I am guessing 2,800 to 2,900fps. More than enough to stabilize the bullet. Looks like that suggestion was a winner.