The newer 50 caliber sniper rifles, exemplified by the Barrett light 50 is likely the best choice. Since its introduction in 1982 several competitors have made similar models. The light 50 would allow Jeramie Powers to first engage the T. Rex at about 2000 meters.
Link to the column: The Straight Dope: Could I take down a T. rex. with my Beretta 9mm pistol?
On this board we’ve discussed the question of T.Rex shooting several times. To give just one link (which in turn links to still earlier discussions of the topic): You, a single-shot 50cal rifle, and an angry T-Rex. Hope? - In My Humble Opinion - Straight Dope Message Board
The .50 Barrett is certainly powerful but has the perhaps literally fatal drawback of not being designed to be freely wielded; it has to be deployed and fired from a prone position like a light machine gun or small artillary. Heavy game rifles or classic bwana elephant guns would be better.
Perhaps a 12 gauge pistol?
Or not.
That’s cool and funny.
There’s actually a round made for this, the .577 Tyrannosaur made by A-square in the Dakotas. A lot of people have seen the videos of people shooting the 577 Trex, where they drop the rifle. Those people are not dropping it because of recoil, at least not primarily. They are dropping it because the inertia of the bullet tries to keep it going in a straight line, while the rifling tries to impart a spin. The gun is literally wrenched from your hand. Personal experience speaks.
A large double like a Holland and Holland in 500 or 577 Nitro has a lot of recoil, but the big doubles have a lot of weight to help counteract the recoil.
Having hunted cape buffalo with big bore rifles, I can tell you, there is never too much gun. Where more dangerous game is concerned, there is no such thing as too much practice.
At the end of the day, though, WDM Bell killed more than a thousand elephants with a 275 Rigby. Humongous balls can apparently fill in for humonghous rifles. Of course elephant skulls are soft and in places thin compared to T-rex skulls.
According to Templar’s T. Rx. calculation, the .577 Tyrannosaur scores between a 148 to 165, depending on the load.
I’m thinking the effective range on that thing is way shorter than the closest I’d want to get to a rampaging T-Rex.
You get one shot. Don’t miss.
I’m disappointed with the quality of the article. There is no reference to supporting evidence, such as a comparison of T. rex physiology to large mammals for which we do have some notion of what it takes to kill. There is no discussion of current paleontological thought on things like the speed of a T. rex (assuming that it is fast because that’s what sci fi movies and tv shows assume to make it look horribly dangerous doesn’t seem like very helpful analysis). Usually, Uncle Cecil and his helpful minions are much more analytical.
This is the second column in a row with that style of writing. Hope it’s not going to be this style going forward.
After all the cutesy filler the column actually says very little.
No you can’t take down a T-Rex with a Baretta 9mm. There aren’t any T-Rex’s around to shoot unless you shoot at the right rocks. Maybe it’s make a piece of the fossil fall down.
The column answers the question: “Could you kill a T. rex with a Beretta 9mm or a 12-gauge shotgun”, and the answer is “no.” The column by definition is speculative due to the fact that there are no living T. rex’s to use, and there is a lot which is not well understood about their anatomy and physiology, despite people trying to do things like make 3D models of thei heads and simulate tensile and compressive stresses. For example, researchers are uncertain about the purpose of the gastralia, which are bony rib-like structures which seem to protect the abdomen on the front side. They are not found in all specimens, and are often missing from mounted skeletons in museums (Sue has them, but not mounted). They may be related to similar structures found in terrapins, or may have been something completely unrelated.
Quite a lot of research was done on the known and speculative anatomy of the head and vital organ areas of the T. rex, and again it was found that in some cases there is a lot of speculation. We have this image that we know a lot about dinosaurs because of their frequent use as a plot device in fiction and because of their frequent appearance in science programs, but the truth is a lot is unknown about them.
There was an idea about going into the fine details of ballistics and firearms for this column. Cecil, Ed, and I felt like that was the wrong direction to go to address the question for the average column reader. We did this in mind that it would not satisfy some readers, but there you go.
If someone had a 9mm and a 12 guage shotgun and could be teleported back in time they could demonstrate their magical powers by killing a few random things in front of witnesses. Word would spread and they would quickly become a warlord emperor, feared and awed by all. Then they could recruit a few hundred local cave dwellers to attack the T Rex with pointed sticks, or face the wrath of the thunder maker warlord emperor who would not be pleased if they refused. They would eventually kill the T Rex. The 9mm wins.
Anyone else suspect the question came because of the t.v. series Terra Nova? 
I was late to the viewing party, just having watched the first episode last night, so I read the column first. This had me checking out all the guns they were using, and determining that the technology is apparantly going to improve quite a bit in the next 30 or so years!
So perhaps the answer should have been “Not yet”.
http://www.google.com/search?q=t+rex+size&hl=en&rlz=1C1CHFX_enUS443US443&nord=1&biw=1600&bih=799&site=webhp&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=z8WITpq7OrDjsQK0wc2rCQ&sqi=2&ved=0CEcQsAQ
T Rexes are huge. i suppose they could take a lot of damage before you could kill one. They were 40 feet long and could look in a window third story of a building.
I think at a minimum you’d want One of these
firing These.
I don’t know if I have the exact weapon, and IMDB is down right now, but I think Michael Gross’ character is firing an 8-gauge shotgun with slugs (T. Rx. value of 98 at best, which would not be sufficient for an adult T. rex, according to Templar). However, I’ve also seen sources claim it was supposed to be a 4-bore, which definitely is T. rex capable, also according to Templar (T. Rx. value of 116 to 342, depending on loading).
Looks like the revolver from Roger Rabbit.
I’ll see your 12 gauge pistol and raise you a three shot pistol.
How about a belt-fed 1911?