Doubletap is one of a number of small specialty ammo houses that do their best to max out a caliber's potential.
My carry gun is a 357 six-shooter. The first two rounds are good 38+Ps, usually the Speer Gold Dot 135+P. Out of a 4.68" Ruger barrel, figure they'll pull about 250ft/lbs energy.
The next four in my gun right this second are Doubletap 125gr "full house" 357s. They'll net around 800ft/lbs energy. In contrast, typical police 40S&W ammo runs about 500-550ft/lbs energy at most.
I had a chance to shoot one of those DT125s at a bowling ball 20 yards out. Managed to hit it square on, split it clean in half, sent pieces of the concrete core back past me. The guy I was shooting with (who owned the ball and range) said he'd never seen handgun ammo do that, period. We were both shocked.
My gun weighs over 2lbs. To be able to comfortably control those monsters, I softened most of grip checkering.
Doubletap and a few other small ammo houses compete to produce the most "thermonuclear" (yet safe) ammo possible. Doubletap and Buffalo Bore are tied in high-end 357 defense loads; Buffalo Bore holds the title of "world's hottest 38+P" right now
. Also in the running are Grizzly Ammo and Garrett, although they specialize mostly in hardcast slugs for critter defense and hunting whereas DT and BB do jacketed hollowpoints for defense as well as hardcast.
Part of what these guys are doing is using large amounts of slow-burn powder. They're trying to spread the pressure (the "push") across a broader period of time, rather than letting pressure "spike".
See, any caliber has an upper limit to how much pressure it's specified for. 357 is capped at 35,000psi by industry standards - and these small ammo houses are NOT exceeding that, or we'd be getting reports of blown-up guns.
What they're doing is trying to get the pressure up near the max and keep it there for a longer time period than normal. This is difficult to engineer and requires more powder bulk, but when achieved (and I think both DT and BB are succeeding, BIGTIME) you get genuine advantages. Bullet speed goes up without wrecking the gun, for starters.
Now. If your gun is "strength marginal", you may not want to play with this stuff. I own a 38 snubbie that's good quality but a bit delicate (1970s vintage Charter Arms Undercover). I won't shoot BB or DT 38+P in it. My Ruger 357 on the other hand is a tank and eats this stuff up no problemo. There are some "357" guns that just shouldn't be fed these very high end ammo houses' 357s: any toggle-link levergun, the EAA Windicator, any Charter/Charter Arms 357, a few other dodgy critters. A vintage S&W K-frame 357 can take light diets of this stuff. Etcetera. You need to learn your gun's history and what it's capabilities are...