I bought my P15 last week and I am having problems getting consistent groups, even at sub-20 yards. Could it be gunk in the barrel (I have cleaned it, I think) or pellet incompatibility?
On another point. The cups in the shroud can be replaced with: 25mm m6 washer- spacer-washer-spacer-end cap to make it quieter. I used some 25mm springs as the spacers. Much less 'sharp' report.
I think that the magazines will be the Achilles heel on these.
I have one also, bought from Rashaadk ( [NEWSFLASH] SPA / ARTEMIS P15 PCP Bullpup ~ Air Rifle SA Forums ), my is laser accurate with JSB's 15.89 @ 25m, muzzle repost is on the loud side but playing with the baffles as Carnavore said it will quiet it down a lots.
The mags it's a bit funny, some slots are a bit smaller in diameter than others, so watch when ;loading the pellets, some won't sit properly and when rotating the lid can damage the skirts, just pay attention to that, also when you probe the pellets to the barrel, you will feel "stiff", just push all the way, if you re-cock it, will double load. I think with time it will worn off and be much more smoother. Awesome little rifle!!
Edit: that if it is a 5.5mm
If it is a 4.5mm a 6mm center hole is enough but use 25.9mm OD washers
I see that the centering cone inside the shroud is moveable so it would be possible to move the shroud forward giving more space ahead of the cone for silencing materials. Of course, that would be at the expense of the vented rear section and would give a little extra length. If dampening the report is a problem you could just fit a 1/2inch UNF silencer. Not a perfect thread fit but good enough.
Shot mine a few times today, couldnt do much more, its raining in the Cape. Very happy so far. I agree that the mags are perhaps the weak point, but i found that by using something to seat the pellets deeper in the mag, it improves a lot. I didnt find it very loud but i will play arround with the baffles at some stage.