Miroku 73 carbine mag spring/capacity

[Malamute]

 I was wondering why the capacity of the current Miroku 73 carbines was 10 rds, the originals showed 12 rds of 44 WCF capacity. Lining up 10 rds of 357 showed a fair bit of apparently unused space in the tube, much more so than other Winchesters I have. I thought there may be a plug of some sort to comply with import or certain states laws. No plug, just a LOT of spring. Stacked solid, it took up quite a bit of space, much more so than is normal for Winchesters. Trying a 94 carbine spring, it would accept 12 rds, but just barely, and wouldnt raise the first round. Hmm,....clipping 7 coils, it loads easily and cycles fine. Is there any downside to this change? Is the 73 sensitive to having any more mag spring tension than the very soft factory spring? Did they just use a rifle length spring and call it good?

Mine is more of a working gun, match rules arent part of my priorities (havent shot a match in a decade or more), having the gun able to use the full practical capacity is attractive to me. The 357 makes a fair walk around gun for my place since injuring my shoulder and back.

Thanks for any insights on the operation of the 73 action, its new to me.