Not always the easiest problem to over come as there can be a number of factors to consider , had the gun come to me these would be my first thoughts and what I would check :
1,Are the rim depths to deep ?
2, Have the trigger pulls been altered at some point , thus the sears may have been shortened to much so there is not sufficient throw/drop on the hammers .
3, Does it have loose strikers or are they integral to the hammer , which is most common . If loose are the floating freely with enough free play ?
4, There could be an outside chance of something along the cocking train that is preventing the hammers from falling fully . This can only really be investigated by stripping down a checking .
