Hey mate, i have a 788 too in 22 250AI. the problem is they are single feed (the magazine presents the round in the sample place every time) whereas most top load rifles are double feed (the round gets presented alternating sides for feeding) so i dont think it will feed without some modification to the feed ramp, but also i dont think the action has enough space inside for a double stack magazine unless you mill it out. but at all that cost you might just as well buy a rem 700.
FYI, i measured mine up and it looks as if a Howa mini magazine and bottom metal might work on mine (with some modification) as the 22 250 as about same length as a 6.5 Grendel if I stick to light bullets. the aftermarket howa magazines (legacy sports) are single feed even though the internals are double feed. so maybe you can get a legacy sports howa 308 magazine and bottom metal (plastic) to work but then you will still have a detachable mag and not internal
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