It's all tied to the region and the time period.
I grew up in PA (born in the mid 60's) and probably the most common guns were the 30.06 and the 30-30 with the 270 not far behind. There were a lot of lever and pump guns around but the bolt guns were the only option for "serious hunters". At least that's what all the magazines said... I honestly couldn't say if there were more 06's than thutty-thutty's or not, I never kept tabs. Of course, the 308 is close up there too but I think it lags behind the 06 and the 270 in that part of the country for some reason. Another common gun (when I was a kid but not today) was the 30-40 Krag which goes back to the theory about cheap military surplus guns being popular. I remember my uncles talking about going into the hardware store (before I was born) and they'd have a barrel full of Krags stacked like cordwood for sale for about $4 to $6 each. Wish I could find a couple of them today!
In the mid-east Atlantic states up through the new England area, say from Virginia on up through Maine, I believe that the 30-30 is still a VERY popular caliber but so is the 35 Remington and the 30.06. There are a ton of them around on the used racks. I expect that most of these are guns being sold by the children of the original owners who buy into the hype about the modern magnums and think a 30-30 isn't enough gun. In the last 30 years or so, there has definitely been a big push for and promotion of various new, modern calibers. The 7mm mag, the 243, the 300 mag, heck even 338's but look at all the fancy new calibers that really (in many cases) don't do much of anything special when compared to the old standbys. Calibers like all of the short magnums, super short magnums, ultra magnums etc. See the trend? When I was a kid, the general consensus among deer hunters was that the 30-30, 32 special, 35 Remington, 30-40 family of guns were all great deer guns but somewhere along the way, it started to become commonly accepted thought that if a guy could only own one rifle, it should be powerful enough to hunt not just whitetails but also game like elk, moose, bear etc. This is where the 30.06 seemed to gain such a huge following. Being available in a surplus deal sure didn't hurt. The gun magazines were always promoting hunts for exotic western game and all the hunters from the Midwest, south and northeast of course had dreams of going on such hunts. Many of them, when the opportunity arose to buy a "deer rifle" would buy the bigger, faster, more powerful guns in the hope that "someday" they might get to use them out west.
Also, being guys, there has always been a certain amount of size envy... Mine is bigger, faster etc. The guys with the real experience, those who killed multiple deer every year, quietly and with no competitive egos continued on in many cases with their old classic calibers. It's funny that almost any gun magazine will annually run articles about deer hunting that include statistics on average shot distances. In most cases, the national average last I saw was still under 150 yards and in many parts of the country was well under 100 yards. What can a magnum do at that distance that a 30-30 can't besides blow up more meat?
I think that there is a bit of a push-back trend where a fair number of guys my age give or take a decade, say 40-60 years are returning to the guns they used as kids both for nostalgia sake and quite simply because they do in fact still work and work well. Of those, the 30-30 is probably at the very top of the list.
What's all that have to do with the original question? Well, it's just trying to show that asking about the "most popular" and "most used" deer hunting calibers is sort of a loaded question and the facts are constantly changing. I think you have to go back to the original math in the front of this thread showing that about ten million or more 30-30's were made in this country. Those guns are almost all still out there either being used or sitting in someone's collection. They have been around for a LOOONG time and will still be around for a lot longer time. Todays young hunters probably don't even think they are fit to use but I suspect that in time many will get curious and give them a try. Most will be pleasantly surprised but as long as there gun rags, the internet and hunting videos that are blatant shills for the modern gun companies, the 30-30 and similar classic calibers will probably continue to loose ground. At this time though, I think it and the 06 are probably about tied for most deer killed in the last 100 years.
What do you want to bet that in another 20 or 30 years most people will think that the 223 in an AR platform will have taken more deer than any other gun? Heck by then the young guys might not remember how good the 30.06 is, let alone the 30-30. By then the 30 -30 will be like the old hyphenated calibers are today. You know, ones like the 38-55, 30-40, 32-20, 44-40 etc. Provided of course there is still legal gun ownership in this country.
