Interesting read this as i'm having problems in the last few weeks. It's my HFT Steyr that is over 10 years old and it's a bit of a story so here goes....
The rifle has been spot on and won the gathering last Nov...however i have had a niggly doubt for quite a while. Grouping seemed good and then i tried the new JSB premiums through it to see what they were like. After about 150 of the premiums i shot a few felts through the barrel and switched back to my batch 22 JSB's to find the group was 1" left at 35 yards. I pulled the barrel though and carried on shooting the batch 22's and all seemed fine as the zero returned to normal. After approx 300 pellets i noticed that the zero had once again shifted left so i pulled through again. another few hundred pellets and the zero again shifted so i decided to re-zero onto the new aim point and leave it alone. All was good for another few hundred pellets and then the groups opened up with the odd flyer in the 12 o clock position...the groups continued to get worse so i shot a few felts through and now the POI moved 1" to the right...Aaargh!!
With only 2 weeks to go to the HFT worlds i was a bit ****** off but do have 2 other Steyrs that are good...one is my FT rig that i don't really want to disturb and another one in a GinB FT stock . The last thing i did at the weekend was to VFG the buggery out of the barrel and will see whether that helps on Sat...if push come to shove i can swap a barrel over and just order a new barrel from Steyr.
The only problem is the doubt that the VFG'd barrel might be sound at first but could just change POI on me as it leads up. Not good if i score well on day 1 for it to go tits up for day 2.