The chamber on your M629 will take the Keith bullet just fine IF it is in brass that isn't too long and you crimp in the crimp groove. Now, they won't fit in a Ruger M77/44 magazine, effectively making your bolt action rifle a single shot but they will chamber.

I, and a whole lot of other folks, have used this bullet for a few years in all of their M29/M629s with no problems at all.

Here is a picture of my Keith style bullet, it is an H&G #503 and not the Lyman, but the same bullet nonetheless.



Here is my new bullet for it though. Nothing to do with this topic, just sayin'!