296 should be a good choice for building fire breathing loads.
A word of caution, Follow your load data! 296 (& H110) have some specific requirements that can't be ignored. The problem with pushing limits is that you can exceed them easily with disastrous consequences. Working at or near maximum loads requires lots of attention to detail. Take your time and work up carefully. Watch for pressure signs.
A powder that's not quite as slow is Alliant 2400, I like it a lot in .357. I've not used it for .44 mag, but i suspect that it will perform quite nicely for your needs. It's more tolerant of lower power loads than 296 (H110.) I've not used them but I recall that Hodgden & IMR 4227 are another option for playing at the high end. Near is I can tell the VV N110 should perform in a similar manner to 2400. All of these will provide a very nice fireball

VV N110 does not produce the huge fireball seen with 2400. I prefer it for hot .357 loads because of that factor. If pushing the limit go slowly, Inspect the primers at each step, use a chrono so you know what is realy happening and pay attention to the manufacturers data.

Also: Stand off to the side when shooting so others aren't injured when you find the true limit.

As Overkill said,pay attention with 296 and don't play around with the data.296 has a narrow operating window so seating depth,bullet shape,anything that varies case volume or powder compression can really throw the pressure curve off.Don't go below the starting load,there isn't a fudge factor like some other powders.I can't recall the term,but I'll say detonation although it isn't correct.Too light a load can cause an insane pressure spike that can be worse than a double charge.The worst blown revolver I saw was from this under charge,the cylender was gone from the pin up,the topstrap was peelsd back over the hammer,and the barrel was pointing about 30 degrees down,nothing I would want to experience.

Alot of heavy loads are going to be hard on a Smith,so keep that in mind.If you plan on doing alot of shooting with these loads,a Ruger will hold up longer.Cylender slop can easily be repaired,but gas cutting and stretch in the topstrap can't be fixed.

thank you all for your suggestions and warnings!
i'll pay even more attention while reloading, now that you made me think about how easily i could exceed the limits of my gun.
do you have any "near the limit" load that you have personally tried to suggest?

What is your intended target that you want/need to push the limit?
I always found normal 44Mag loads to be sufficient for any paper and most animal targets in the lower 48.

Originally Posted by TOF

What is your intended target that you want/need to push the limit?
I always found normal 44Mag loads to be sufficient for any paper and most animal targets in the lower 48.

given my living in italy paper is my only available target..nevertheless i'd like to see how far my 629 can go.
my intention is not to put my gun on a test but just to have fun..that's why i asked for suggested loads.
i'd love to have a XVR 460 so that i could have all the big boom that i want but i can't afford it at the moment; also, shooting an XVR in itlay is NOT the same thing as shooting it in the US..it would be like driving a Ferrari only to go from home to the mall..