The current Winchester 1873 carbines in 357 hold 10 rds as issued. That seemed odd since the originals held 12 rds of 44-40. Observation of the magazine spring showed it stacked solid at 10 rds, but had far more spring stack than a 94 carbine. Swapping the spring to the 94 carbine version, it held 11 1/2. 12 would actually fit, but the lifter was jammed tight. Clipping 7 coils, it then easily accepted and cycled with 12 rds of 357.
The 30-30 is a bit above 7.62x39 ballistics but doesnt hold up as well at distance due to bullet shape. 125 gr 30-30 handloads show around 2650 fps in the manuals if I recall correctly. 150s seem to be in the 125 gr 7.62x39 velocity range. Good, widely available reliably expanding loads for the 30-30 is a point in its favor ammo wise. Ive tended towards the 150 gr loads recently, partly for any reduction of recoil possible with a bum shoulder and partly because they tend to run a couple hundred feet faster than the 170s and should give best possible expansion on game etc up to large deer size. I always used 170s, the common comments seemed to be along the lines of "the 150s usually penetrate all the way through deer and seem to put deer down faster, but use the 170s because of some vague unstated reason related to just in case" (probably in reference to oddly angled shots, but its never been clearly stated that I recall). If the 150s expand faster and more reliably, whats the advantage of the 170s in the game size range of deer? Ive had a couple WTF moments shooting deer with Speer 170s. They didnt show much damage on after action investigation and took several decent hits to get a doe deer to stay down. Same general hits with a 30-06 was more like what one expects. Will have to see how the 150s seem to work if/when I get to hunt again. The 130 gr Speers have a good reputation in deer also.