Sounds like you made out pretty good.
Toss a 5 or 10 round mag in that (whatever's legal) and that'd make a pretty handy hunting rifle. If you can get it to swallow 77 grain pills without keyholing, you'd be in great shape. I'd almost be willing to put money down, that rifle would do better and be more precise with 69's.
Have you determined where the lands are yet? Load a dummy round "way too long" (making sure you've still got enough in the neck for positive retention), mark it with a marker or similar coloring, CRIMP it, chamber it. I say crimp it because if it engages the rifling enough, sometimes you can extract an empty casing and leave the bullet in the lands, which you then have to tap out, and start all over again.
Anyway, the rifling will leave marks and scrape away your coloring of choice.
Now measure the base of the case to the start of those marks. That's your reference point on how far forward you can get the bearing surface of loaded projectiles out there.
I know you want to feed from the magazine, but it certainly wouldn't hurt to know where your lands are, so you can have an idea of what's happening when the powder starts to burn.
You can probably squeeze a
little extra length out of rounds and still have them fit in the magazine and feed OK.
You want to get as much length as you can, to get the bearing surface close to those lands. With some rare exceptions, the less freebore the bullet travels, the better those longer, heavier bullets are going to shoot.
But there's no telling how your rifle will behave until you try.
