The 30-30 round itself would be perfectly adequate as a combat round. Set aside for a moment the shortcomings of its normal platform, the lever action, and look only at it's terminal ballistics. I am sure that if a modern action with the requisite removable box magazine were designed for it, it would be a useful battlefield implement. There are of course many other cartridges that surpass it and the amount of work going into creating a suitable semi-auto rifle that would take into account the physical dimensions and issues caused thereof would be daunting. Therefore, we will never see the venerable .30 WCF as a combat munition ever again (the Russians did use it in some numbers if I recall, as well as the US Army in very small numbers to guard spruce timber reserves).
I think perhaps the more telling question would be "if I were armed with a lever action in 30-30, would I be effective on the battlefield in modern combat?"
The answer there of course is no. Modern combat requires a long logistical train, large numbers of well trained troops equipped with what will give them the greatest tactical flexibility. The small arm they carry is practically the least of these. Simply compare the weight of the individual weapon as a percentage of the total combat load and how it has changed over time to see what I mean. However, in spite of that, the issued small arm must conform to the principle of giving the greatest tactical flexibility, hence the common run of modern small caliber, small dimension, combat rifles.
Another relevant question might be "if I am armed with a 30-30 lever action rifle, could I be an effective guerrilla fighter against those typically equipped for modern combat?"
For me, the answer is of course I can. But that is perhaps more of a reflection of my training than of the efficacy of the weapon itself. What answer would be correct for you, who can say if you cannot?
