So claims the title of this video, showcasing JD Jones' very large .950 JDJ rifle.
I've seen this video swimming around on the Interwebs a few times, usually with that claim either in the title or description.
Is the .950 JDJ rifle the largest centerfire rifle ever made?
The answer is "it's complicated" and also "no".
The qualification of "centerfire" begs the question: Does electrical priming count? It's normally located in the center of the cartridge, and it is a priming method, so is it "centerfire" or not? If it doesn't count, does that mean that the .950 JDJ is the largest bore cartridge that primes via standard Large Rifle Primers? If so, why is that significant?
Beyond that, we can then argue whether "rifle" refers to a firearm that is shoulder-fired and rifled, or just rifled, because neglecting the shoulder-fired requirement, there are of course a whole host of larger-caliber weapons than the .950 JDJ. For the purposes of this article, I'll assume that "rifle" refers to any firearm that is shoulder-fired and rifled, because that makes the competition much more interesting.
In fact, a number of centerfire rifles out-bore the .950 JDJ. The XM109, a 25mm anti-materiel rifle, has a bore of around .973". There are numerous 4-bore rifles in the world, and, though the exact diameter of a "4-bore" varies from maker to maker, a number of them measure over 1" in diameter. The video I just linked even proves that the .950 JDJ isn't even the largest bore centerfire rifle to become an Internet sensation!
Moving on, every grenadier who served from Vietnam until now should raise an eyebrow at the title of this video, as they used rifles of much greater diameter during their service.
Going even bigger, we have the various recoilless rifles of the world. While perhaps the most famous, the 84mm Carl Gustav does not actually qualify for the purposes of this article, because it is side-priming. However, numerous centerfire recoilless rifles exist. Among those that are also shoulder-fired, we have the M18 57mm (2.24") rifle, which has almost 2 and a half times the bore diameter of the JDJ (more here, and here); and the M67 90mm (3.54") recoilless rifle, with a bore nearly four times as wide as the JDJ.
At the risk of going a bit smaller, there's also the very interesting 76mm High Impulse Weapon System, which is notable in that it does not redirect any of the energy of the cartridge to help mitigate recoil.
This isn't intended to be a slam post against JD Jones; they make some really interesting stuff. I bet that .950 is a hoot to shoot (though maybe the one guy with a cracked rib didn't think so), but just remember, the next time somebody claims to have made the "largest", "biggest" or "most powerful"... They've probably been outdone before they even started.