Lockup on 61 ASM

[Dusty Morningwood]

Shot the 61 ASM today.  Light load (only 16 gr 2F).  Several times on just one cylinder, it failed to cycle.  No jammed caps.  Seemed that blowback caused the pistol to partially go to half cock.  Is this because of the too large nipple flash holes?  Very annoying.  Treso nipples are hard to find now.  Any other suggestions?

[Dusty Morningwood]

Hello?  Is this thing on? 

[Halfway Creek Charlie]

Nipple hole my be too big, or the mainspring to light, but it sounds like one nipple, at least, may be shot out or out of spec.