The only vertically split rings for Weaver bases that I have had any experience with were abominations!
In the mid-90's when we had the gunstore, the Savage 110 package guns would come with a Simmons scope, rings(split like you describe), swivels, sling, trigger lock and target, as a package deal. They were promotional guns, and were a good buy at the prices then.
Now, having given half a life history here, let me say that I have no idea who made those rings.. they simply came with the rifle. But when someone wanted to upgrade a scope, those rings and I always had a fight! Often times I would throw in a set of inexpensive tasco 1" Weaver style rings with the deal, just to keep from having to use those vertically split rings that came with the Savage package guns.
Now that my bias is all out in the open, I must be honest, that I sold MANY of those package guns in everything from .223 to .30-06, and I never had a complaint from a customer of impact shift, scope slippage or other mount related ailments. I'm sure they work just fine... I just don't want to be the one installing them!
I have no idea who made them, perhaps the ones you have would be less of a pain to mount.
I use almost nothing but Warne Rings, Premier and Maxima. They are all verticle split rings and I have never had a problem with any of them. Like any ring I guess, use a good quality ring and there won't be any trouble, but use a cheaper ring and look out. One thing I have noticed about the Warne Rings is that the tighening process does not torque the scope out of alignment. If you have ever used Weaver rings you know how frustrating that can be.
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