From your perspective, what are the differences between these two cartridges other than ammo availability?
Thanks,

Maybe a smart chronograph can detect a very small difference but there's no hunter nor any Kudu can tell the difference.

The 300 WM will headspace on it's shoulder after the first shot and the 300 H&H will not. Thus a properly handloaded 300 WM case will last longer.

The 300 WM holds more powder but has such a short neck and magazine that care must be taken to select the right bullets.

As you know the 300 H&H requires a magnum length action.

Overall the 300 H&H has some appeal to in in it's appearance and history. The 300 WM is a funny looking case with the tiny neck.

Of the big belted magnums the 300 Weatherby may be the better of the three mentioned.

As for myself I have a 300 H&H for the fun of it and am going to sell a 300 WM one of these days. My next 300 mag would be a WSM.

Major difference is the H&H takes a long magnum action and 100fps. If you have a M70 or 700 not that big of a deal the actions are the same length just minor changes in the magazine. I never had trouble with case life with the H&H. I just resized to not move the shoulder. From my experience while only around 8 deg the shoulder is plenty to keep the case from moving forward.

In my experiance the 8 degree shoulder is not enough to hold back the case. I have made brass from 375 H&H's and carefully set the headspace on the shoulder and it still does not hold. I even used Remington brass as it has a thicker web and that did not inprove things either.

The .300 Win has slightly more case capacity than the H & H and thus can provide slightly more velocity, all things being equal (which they never are!).

Other than that, the Winchester, being somewhat shorter, can be crowded into a "standard" action with a 3.35" magazine. It is MUCH better in a long or "magnum" action with a 3.6" magazine, such as would be required by the H & H. In a long action the Winchester allows long bullets to be seated further out, an option that is limited with the H & H.

Some people claim that the long, tapered H & H case feeds more smoothly, and it may; however, I've never seen a Winchester that failed to feed properly, so I can't say that this is much of an issue.

I agree that the H & H can be neck-sized only in order to headspace on the shoulder, so no difference here.

As between the two, one will pretty much do what the other will, ballistically. I think that the Winchester is a little more versatile in the way you can load it, so is probably a little more practical choice. On the other hand, the H & H has plenty of Old World charm. Your money, your choice.

Gentleman, thanks for the insightful comments. I appreciate it and your time to post.