Hello I have two cz 550 300 win mag model magnum and 7mm magnum model lux with which the two will be better to make a custom 375 H & H mag pieces that need a barrel

greetings.

you will spend far less by selling one of those abd buying the 375hh on a cz 550 magnum ., your rifles are mediums and are 3.35 or 3.4" mag boxes

375 Ruger

perhaps I wasn't clear here.
there was SOME cz 550 magnum's made in 300 something mag.. i forgot which..

BUT, most 300 winmags and 7remmags were made on the cz 550 medium, which is an entirely different action.. is VERY much smaller.

converting either to 375 HH will incur barrel, sights, bluing, and custom feeding, or at least 800 bucks, if done CHEAP ..

the whole 375 HH from CZ is like 900 bucks brand new.

And, if you are set on making either into a 375, what will said is correct, just rebarrel, for the same 800, to 375 ruger.

oh, I'll sell you a cz take off barrel, for the 550 magnum, for $150 with sights.. but no guaranty that it will fit

jeffe