Key holing is caused by undersized bullets, oversized barrels and sometimes excessively low velocity. Using the word 'random' suggests an ammo quality thing. Rimfire ammo can just be like that. Changing ammo is the way to go.
However, according to Midway's site, your biggest problem fixing this is the relatively crappy availability of different brands of .17 HMR ammo(stuff's as expensive as .22 Magnum ammo too). Your options are the Federal(Using a 17 grain V-Max), the CCI(also with the same bullet), a Hornady with a 17 grain V-Max and a 16 grain Speer TNT HP bullet from CCI(one grain isn't going to change much). Everything else is either not available at all or 'mixed' availability(Federal V-Shok using the same 17 grain V-Max anyway.).
Graf's is showing Winchester in stock, but it's still with a 17 grain V-Max.
However, according to Midway's site, your biggest problem fixing this is the relatively crappy availability of different brands of .17 HMR ammo(stuff's as expensive as .22 Magnum ammo too). Your options are the Federal(Using a 17 grain V-Max), the CCI(also with the same bullet), a Hornady with a 17 grain V-Max and a 16 grain Speer TNT HP bullet from CCI(one grain isn't going to change much). Everything else is either not available at all or 'mixed' availability(Federal V-Shok using the same 17 grain V-Max anyway.).
Graf's is showing Winchester in stock, but it's still with a 17 grain V-Max.