The accuracy thing is on a rifle by rifle, barrel by barrel basis. Some are great, some are good, some are so-so. My experience having owned 6 matadors is they've all been in the great to good category, most in the "good" category. I've had 6 Matadors over the years (.22 R2.5, .22 R3, .25 R3, .22 R3M, .25 R3M, .25 R5M) and all have been accurate-- but some more so than others. My .22 R3 was the most accurate of all of them followed closely by the .25 R3M. That being said, each rifle required tuning for regulator pressure and velocity to find where they were the most accurate with a given pellet.
You say you have a .25... what's the regulator pressure set at, and what's the velocity plateau if you increase the hammer spring tension? Both my .25 R3, .25 R3M, and .25 R5M were most accurate with 25.4gr JSBs at about 870-890 fps with the hammer spring set about 15fps under the velocity peak for a given regulator pressure.
With the .25 R5M I'm running 34gr pellets. With Ed's stock plenum this required too much regulator pressure and too much hammer spring tension in my opinion which resulted in a very stiff cocking action and fewer shots per fill. Running the 34s in my opinion really requires the larger huma power plenum and regulator; with the 34gr JSBs the Huma plenum and regulator allows you to achieve the same velocity as the stock regulator and plenum with about 25 bar less regulator pressure, which means you can also decrease the hammer spring tension and the decreased hammer spring tension reduces the cocking effort.
I will agree the cocking effort on the R5M is a bit on the hard side and can be clunky. Unfortunately it will never be fingertip light or totally with, this is a drawback of the mechanical magazine indexing combined with the straight pull action which doesn't give you any mechanical advantage unlike a sidelever action which uses the mechanical advantage of the levers to decrease the cocking effort.
As far as magazine indexing, on the first batch of R3M's Ed used the same magazine indexing lever for the .22 and .25 which was a problem, because the .22 uses a 10 shot magazine where the .25 is a 9 shot magazine, so the early .25 R3Ms would not index the magazine fully with the .22 indexing lever installed. I had to TIG weld up the indexing lever on my .25 R3M and rework it so it would index properly. This issue was fixed on later production batches of the R3M and is also fixed on the R5M. My .25 R5M indexes properly. Maybe your .25 R5M accidentally had a .22 or .177 indexing lever installed which would mean the 9 shot .25 magazine will not index fully every time you cock the rifle.
The R5M does need a firm and deliberate hand when cocking, the handles need to be pulled firmly all the way to the rear to fully index the magazine. If you don't pull the lever firmly all the way until it stops, the magazine will not fully rotate and it will either stop the bolt when pushing the cocking lever back forward or the probe will "bump" the magazine into alignment when pushing the bolt forward and shave the pellet skirt as it enters the breech which hurts accuracy.
