What is Happening here??!!

[Miseryguts]

Ok, so nice day, took my BA 22Lr rifle out to the range to get the cobwebs out of the barrel

Rifle is Ruger Precision in 22LR with 15 shot magazine, and fitted with a One Less Charlie moderator

Ammo is RWS Special Match

POA on each  7.9 inch target is centre of target spot, and there are target spots at centre, 3, 6, 9, and 12 o'clock

First 5 shots are centre of Target 1 -  high shot is 1st shot which was definitely supersonic. Next 4 shots were definitely sub sonic (as RWS special Match is) After shooting rest of magazine, put gun down, had a cup of coffee - 10 minutes?? 

2nd Mag, first 6 shots are 3 o'clock on Target 1 - High shot as before, the other 5 subsonic and where I aimed(well nearly). Rest of mag as above, left for probably 10 minutes

3rd mag, 15 shots to target 9 o'clock on Target 2 - first 2 shots are high shots, first supersonic.  Rest of mag (13 shots) more or less at POA. Again left to rest for a few minutes

4th Mag, 10 shots to target at centre on Target 2 - result as above, 2 high shots, first supersonic, 8 close to POA

Any one any ideas??

M scratchin' 'is 'ead in sunny Monmouthshire

PS: range is 50metres, and the sghts were adjusted slightly after the first mag - no comments about markmanship please, I know I am not very good