Is the Handi rifle in 44 mag strong enough for max. handgun
loads? 23 grains of 2400 with 200 grain jacketed bullets which
are shot in Ruger super blackhawk.

...lots of Handi Rifles out there in 45-70...and I saw one of those that was reamed out to 450 Nitro Express...

...so I'd say...yes...

__________________
A Country Boy Can Survive

...actually...here's the definitive answer...from the Buffalo Bore website...the load below is the heaviest 44 Magnum load anybody puts out...the Handi Rifle is specifically mentioned under approved firearms...

Heavy .44 Magnum +P+ Ammo - 340 gr. Hard Cast, L.F.N. - G.C.
(1,425 fps/M.E. 1,533 ft. lbs.)
20 Round Box
ITEM 4D

NEW HEAVY 44 MAGNUM +P+

APPROVED FIREARMS

This new load is designed ONLY for certain firearms. They are as follows; Ruger Red Hawk, Ruger Super Red Hawk (the Ruger Alaskan is a short barrel Super Redhawk), Ruger Super Blackhawk or Vaquero, Freedom Arms Model 83, Taurus Raging Bull, Colt Anaconda, Magnum Research BFR and Dan Wesson Revolvers. Suitable rifles include T/C Encore, CVA Hunter, Handi Rifle and any rifle with a falling block action.

__________________
A Country Boy Can Survive

The pistol caliber Handi-Rifles are built on different receivers than the actual rifle caliber guns. That said, they should be OK with factory pressure .44 Magnums.

I know of at least one example that opens itself when fed loads that exceed factory pressures. That may be an example that needs a different locking bolt spring, but I'd stick to SAAMI spec loads if I or family members were going to shoot it.

FWIW, Henry firearms is also making a single shot rifle at a similar price point to the H&R. Don't know if they're using the same receiver for all of them.

On an SB-2 frame yes. Older cast iron frames questionable. Older frames were designed for shotgun and low pressure rounds like the 30-30. I am sure factory 44 mags are fine. I question the wisdom of those hotrodding the 44 mag in an old cast iron frame. The last frame made before they closed was the SB-2 for the old single shots and it could safely handle the 500S&W and 45/70 2nd tier handloads. It would take anything up to Ruger #1 level loads. Just make sure it is a handi Rifle on an SB-2 frame. BTW "self opening or also known as "pop opens" have nothignt o do with safety features. They pop open for one of 2 reasons. 1. Thee mating surfaces of the action have a spec of dirt or even a film of oil. They are milled to very close tolerances and lock solid a s a vault when cleaned and maintained. 2. You have over pressure loads and have exceeded the safety design of the action. Make sure you know which is going on. Breech face and mating surface should be CLEAN AND DRY. Even left over cleaning solvent will allow it to pop open on higher end loads such as Hornandy leverlution ammo.