I've got a 1987 .177 RWS 48 that I've been working with. The best accuracy i was able to get out of the gun was 2 1/2" 10 shot groups at 50 yards.
I lapped the barrel and cleaned up the crown. Although there were no burrs on the crown I did even it out and install a bevel from the top of the land to the bottom of the groove for about 45 deg.
I just put 15 rounds into a 1 1/2" circle at 50 yards thus afternoon. I did this with both the 8.4 gr JSB's and the new JSB heavies. It was gusty this afternoon also, so I'm pretty happy with the results.
I was using the Leapers 16X56 side focus on a one piece adjustable B-Square mount.
Oh by the way, I haven't touched the trigger yet. It's still around 10 pounds of pull.