The .177 HW45 could produce sublime accuracy provided all trace of grease is removed from the gun. The 45 hits almost ideal parameters (I have run the numbers) for combustion if anything near flash point finds its way into the gun. I might agree that the .177 compression ratio will have an even greater effect in this regard and will agree that the .22 is the better shooter. However, cleaned out, with a hint of high flashpoint grease for the spring (if you must use it) and the .177 45 can produce very good accuracy if using RWS flat heads.
However, the Magnum can not unfortunately.
There are key reasons as to why this is the case but once sorted it out it can achieve quite good accuracy which can mount a challenge to a Tempest....reasonable accuracy with consistency issues if not maintained.
Key problem areas is a barrel which is far too short for the compression ratio, particularly in .177 (controlled tests conducted by TR Robb proved it) Hit and miss fits of the Lexan guide rod.
Lexan being an easily moulded plastic but awful quality in comparison with say Delrin. Would much prefer to have seen Delrin which was machined properly. The consequence of which is moulding flash, and slightly warped guides. Try one in a lathe to see what I am saying.
Breech seal reliability seems to be something of a hit and miss affair after reading these posts but the pair we had were very poor in this respect after about a 1000 shots.
Trigger is better than the Tempest but no way can anyone say its as good as the 2 stage unit in the 45. If one did, we would know instantly they were telling porky pies. Tweaked right, the 45 can achieve near match quality barely behind that of the 75 which is match quality.
Having said all this, I hate the look of the 45. Just seems too top heavy and slab sided for my taste.
I much prefer something like the LP53 personally