To be fair, the 577-450 is rather overbore - and combined with the oversize military chamber and generous throat, they can be a bit cranky to get to shoot accurately.
However, nothing to do with the action (IMO a Martini is superior by far to a TD - I might be prejudiced - I am not, of course, but...).
It really takes handloading to get the accuracy potential out of a Martini - and the case being a BN, requires different techniques than the ordinary straight case.
However, I still have the intention to prove that a standard military Martini can be accurate by at least making a good score in either the Imperial or the Trafalgar meet at Bisley. I did win the Trafagar 500 yds 2004 vintage military rifle match with a Martini in 500/450 #2, so the next one in line is the 577/450. Much more of a challenge, of course, but we'll see...
As to the really long range, I only once shot the 500/450 #2 at 900 and 1,000, and it performed admirably - 1st time out I was able to keep my shots on target without any problems. This is a standard military rifle with open barrel sights, BTW.
Recoil was another matter, unfortunately! Never tried the 577-450 though, I would need a cheekpad for sure
A couple of things to respect when loading/shooting 577-450: DON'T use a sling - you ll be spraying your shots around. Shoot at least the LoC charge (85grs) - anything less will cause fliers.
And beware of fillers - this is a BN case, so...