Accuracy decrease with supressor on

I just had a similar experience with a 6.5 PRC this past weekend when I added a can to try it out. The results were all over the place. The gun shoots 1/2" to 5/8 consistently. Put the can on it and the group was 2-3" every three shot string.
Was that a 7.62 caliber can? That's exactly what happened when I put my 7.62 can on my 6.5 CM. Went from 0.6" to 2.5".
 
Bought a cheapo Ruger in 6mm years back that I always forget to shoot suppressed only or it looks like the scope lost zero. Shoots excellent but as far as our range goes is 600
 
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