Hello. Yes, I have shot one and yes, recoil is definitely there. The rifle belongs to a friend of mine who has used it in Africa on lion and other critters. Part of the problems being had by some shooting the 577 T-Rex is that they really were not expecting as much recoil as was delivered and were not really ready for it. That is not to say that it doesn't kick like the devil but believe it or not, I've seen an A-Square rifle in this caliber fired as rapidly as the bolt could be operated and the crosshairs centered on bowling pins at 50 yards and in to simulate shooting at dangerous game closing the gap. The fellow doing it had no problems but admitted that "it was plenty."
In my opinion, this cartridge is probably too big for most of us and certainly more than is needed. I honestly think that it might be getting a bit large to be practical in a hand-held rifle w/o a muzzle brake.
The cartridge is/was a proprietary round from A-Square intended for use in their big game rifles.
From A-Square's loading manual:
Cartridge LOA: 3.710"
Average Velocity using a 750-gr. bullet from a 26" bbl: 2470 ft/sec