What logic to choose calibers?
This is an age-old question, and there are several paths to follow.
For example...
Some will get a caliber that has captured their imagination
This was my case with the .340 Wby after the iconic article
Leader of the Pack by Ross Seyfried in the September 1989 edition of
Guns & Ammo, that I posted there before for AH members' pleasure:
As a fan of big .338s, I really want a new rifle in .338 RUM but it seems that no one is making it in this cartridge anymore. If the RUM is dead, I might as well just get a .338 Lapua, as everyone seems to be chambering it now. Thoughts on the life of the RUM?
www.africahunting.com
Is this a valid criteria? Heck yes! Nothing beats getting what you desire...
Is it always a great rational choice? Not necessarily. In my case, the .340 Wby IS everything Ross Seyfried says it is, and one can veritably hunt anything anywhere with it, from gophers in the US to Elephant in Africa, through Argali sheep in Asia, but there is a downside: recoil is substantial...
Some will only get metric calibers
And why not if this is what tickles your fancy...
From 5.6 mm through 6mm, 6.5mm, 7mm, 8mm, 9.3mm, 11.2mm, to 12.7 mm, and everything in between, you can get whatever you want.
I share
dchamp's love for the 8x68S, and one could think of a lot worse battery than 6.5x68; 8x68; 9.3x64 (OK 9.3x62 wins!); 12.7×70.
Note: the 9.3x64 more than makes up for the 9.3x62 limited reach/power, and is considered by folks in the know as the only mid-bore actually better than the .375 H&H, but it has sadly all but disappeared from the market. As to the 12.7×70mm Schuler, re-baptized .500 Jeffery by the Brits, it needs no introduction as a "stopper" cartridge.
Some will only get "classic" calibers
The 9.3x62 fully qualifies, although some may have a more limited definition of "classic" as "British".
In this vein, the .275 Rigby - which is nothing but the re-baptized 7x57, a legend in its own right - would go very well with the 9.3x62 on one side, and the .404 Jeffery on the other side. Aficionados are also familiar with its other designation: the 10.75x73, and whether Jeffery or Mauser designed the cartridge remains a little unclear...
And some only want American cartridge; and some only want belted cartridges, and some only want beltless cartridges, etc. etc.
A rational approach?
It seems to me that all the above considerations duly acknowledged, there can be a rational and easy way to consider calibers selection. My own rationale has evolved to consider diameter as a prime criterion, assuming that all other factors remain equal (e.g. not mixing black powder with smokeless powder, lead bullets with modern bullets; etc. etc.
I have come to believe that a progression of ~0.05" or ~1mm makes sense and that a battery articulated on this make eminent sense, For example, .25" to .30" to .35" (OK, .375" wins!) to .40" to .45" to .50" is a strong rationale. And 6mm (OK, 6.5 wins!) to 7mm to 8mm to 9mm to 10mm (or 11mm) to 12.7mm is essentially similar.
So, where to go after 9.3x62?
Why 9.3x62 to begin with? If this was just an opportunity purchase, the next step can go in almost any direction.
But if this was a conscious choice for a reduced recoil mid-bore (and this is a very strong rationale, namely the reason why my wife shoots the 9.3x62 rather than the .375 H&H), then the rationale can be further embodied.
Going down with low recoil in mind... In this case, the .30/06 makes a lot more sense than the .300,
Later on, a .25/06 would be almost ideal if Blaser offered it. Sadly they do not, which is a shame if you ask me because it is a
great caliber. But one can still find happiness in one of the six 6.5 that Blaser offers, including of course the 6.5x55, which, excuse my blasphemy, is every bit as practical
for hunting purposes as the currently fashionable Creedmoor that really shines for long-range paper punching.
Therefore
Shako Badhan, your thinking, either purely coincidentally, or based on the same low recoil rationale, and mine are in complete agreement, and to your question .30/06 or 6.5x55? I would answer: in time, both!
As to the .308, I see its value in military applications, but I entirely fail to see why someone would select it for hunting applications over the .30-06 that can carry a much bigger payload. The .308 will not do well with a 200 gr slug...
Going up with low recoil in mind... There are not too many options, because the concept of low recoil quickly fade above 9mm in a cartridge assumedly tasked with killing, and preferably "stopping" dangerous game. Stopping is a misnomer, because kinetically it would take something along the line of a howitzer to actually stop in its track a charging buffalo or elephant with anything else than a brain shot, but "stopper" is an accepted term for calibers designed to deal with charging DG...
Going up with relative low recoil in mind would lead logically to the .404, but Blaser does not offer it. I wonder why by the way, because I would expect sales to be brisk in the British and U.S. markets. But there is an interesting alternative: the new RWS 10.3x68. For lack of either. I guess that the .46 Rem or .458 Win are the default choice, and the Blaser .458 Lott will do as it can fire the .458 Win. But in truth either .416 Rem or .458 Win are substantially above what I would characterize as mild recoil.
After market barrels?
To each their own, by my own experience, and that of many others, trying to deal with J. Sip & Sons and Pale Horse has frozen my enthusiasm. And quality appears, well, let's say, uneven compared to Blaser.
To each their own, but right, wrong, or indifferent, only Blaser factory barrels find their way on my R8...