What makes bullets keyhole

[Leon Garfield]

I have a savage model 12bvss in 22-250 that I have had trouble with bullets keyholing in. It has shot the 69gr sierra bullets the best. It will not shoot 55gr vmax or even 60gr vmax. It has burnt up some 60gr sierra's. I have sent it back to savage and they told me friday that it is on its way back and they found nothing wrong with it. So if anyone can tell me what to try next I am all ears....Thanks Leon

[Robert]

It is usually the big heavy bullets that will not stabilize with a slow twist.  I would say you have an enigma on your hands.  55's should stabilize in just about anything...except 30 caliber sabots.

[eroyd]

If it shoots the heavy/long Sierra's OK then it should be able to stabilize anything lighter. That would suggest a fast twist. The only problem you should encounter, that being the case, is bullet blow-up when pushing lighter, light jacketed bullets to the max. Odd scenario.

[Iowegan]

Key holing is a sure sign of an unstable bullet that is not spinning fast enough. Most 22-250's have a 1:14 twist. That twist rate should stabilize bullets up to 60 grains or so. To get stability, you must also maintain velocity. A minimum velocity would be about 3200 fps. Normal velocities for a 55 gr bullet factory load is 3650 fps.

Buy a box of factory 55 gr loads and see if they keyhole. Try chronographing your loads and the factory loads for a bench mark.

[gunnut69]

Just my 2 cents but something I've seen before.  Check the crown.  I've seen several rifles now with damaged crowns that had enough damage to the crown that lighter bullets would keyhole.  Recutting the crown solved the problem.  I believe the slight damage to the crown was damaging the bullet just enough that the added stress of the higher velocity/RPM's over the slower heavy bullet may be causing the jacket to partially fail.  This instability causes the keyholing..  Check the crown carefully and re-cut if needed.