The 300 RUM is capable of great accuracy and energy at Long distances.
They are at there best with 180 gr to 200 gr class bullets.
The 300 should whistle the 150 Swift if you want flat, But the lightest bullet I would
recomend for it is the 165s .
There are a lot of 30 calibers that would be better with lighter bullets (Smaller case capacity)
If that is as big a bullet you wanted to shoot.
J E CUSTOM
except the lightest bullets I would recommend for the 300 ultra would be 180's and higher. That's what it was made for. There are a lot of advantages to going with the larger bullets in the RUM. I zero mine @ 300 yds with the 180's @ 3400 fps. If you compare the trajectory of the 180's vs the 150's at lets say 3600 fps, zerod at 200 yds, the difference in drop @ 300 yds is only .3", 4.6" vs 4.3"
Would also recommend the 300 yd zero for a farther/flatter point blank range.
On your Warbird... some good inputs already...
Clean well... on cleaning, a lot of guys think they have a clean bore that is actually loaded with copper. Just because you get a clean patch doesn't mean the copper is out. Most solvents are medicore to poor at removing copper. The two best that I've used are Wipeout and Bore Tech Eliminator. With Bore Tech, the best way I've found to use it is to wet patch trhough, waiting a couple of minutes between passes until blue starts fading. Then soak and scrub with a nylon brush and wait for about 20 min. The blue will get heavy again. Do this until blue disappears. With Wipeout, spray it in and let soak for about 8 hours and dry patch out. do this until patches come out clean. Either of these methods WILL remove ALL copper.
After a good cleaning, make sure your bedding is clean and dry of solvents and other material. This WILL affect accuracy. I have proved it.
Make sure you recoil lug has good solid contact with stock bed.
Make sure action screws are not touching any part of the stock and the receiver has good contact with the bed. Use a torque wrench to tighten action screws to recommended torque.
Hopefully you have pillar or full aliminum bedded stock. If not, get that done. Stocks will compress over time and cause problems. Been there, done that.
Check scope bases and rings. Use torque wrench again.
If these dont work...
Swap out scope with known good scope to rule out the possibility of a bad scope.
Have the barrel crown checked and the bore scoped. The bore/throat may be fried, especially if many rounds have been fired through without cooling periods between shots.