Just a suggestion you might want to consider. Before you start altering your rifle sights. By (filing.) There are a couple easy to do things first. To see if your can change this rifles point of impact at different distances.
After a return trip to your earlier thread chickenmcnasty. I took a look at your Pix Links. I thought I could see on one link what appeared to be a non-adjustable rear sight on your rifle. Having that type of sight kind of limits to some degree your rifles ability to shoot different bullet weights accurately. Many times usage of a non-adjustable rear sight requires the shooter to compensate for height, drop, left, right, at a known distances. If your willing to try different bullet weights and again changing your powder charges up or down some as needed. You still should be able to get this rifle shooting pretty close to acceptable with a little experimentation on your part.
First off. As anyone would say here. A 350 gr anything is allot of lead to push down that barrel. Unless your into elk, moose, or BIG bears. I think you could afford to drop down some on bullet weight. Someplace around 250-275 should be a sufficient bullet weight in your 50 cal 1-48 twist. Consider trying a Sabot Bullet or perhaps a Power Belt Bullet. In that weight range of (250-275) they should offer you a little better accuracy out to the 25 yard mark (first) and then out to the 100 yard mark for comparison.
Next item on the agenda. Powder. I never said you couldn't use Triple 777 chickenmcnasty. What I said is: I don't use it. Nor do I know of any shortcomings that may exist when 777 is used in a Traditional application. (So we have that settled for that other guy who purposely critiques others.) Back to the powder issue:
Consider dropping your charge rate or perhaps increasing your charge rate 5-Grs at a time. (But stay within the manufactures limits set for that rifle) Keeping in mind the reduction factor of 15% and trying not to bare down hard on your bullet or Sabo as to pack the 777 powder charge excessively. But keep in mind it does still require some compression. Just lightly done compression is all that's required. (777 apparently does have its quirks.) Now back to the sight filing advise. Under certain circumstances that indeed pays off. But keep in mind once its done. You cant undue. (other than buying a new sight)
If you just hang in there and do what I've suggested here. Keep in mind you might have a long string of changes in powder charges. And perhaps different projectiles. But most rifles do indeed have a Sweet Spot. No doubt it won't be easy to find that sweet spot. But it is there. In the end you'll gain some valuable knowledge and come to understand your rifles workings. And more than likely a fine shooting weapon will develop out of all that experimenting.
Another suggestion: When changing powder charges or bullet weights. Always keep notes of your findings and actions preformed. Write it all down on a scratch pad. Doing that will save you time and effort. Also.
Were all here for yaw. Just a little update every now and then would be appreciated.