The main problems with the hammer extensions are the steel ones with extra weight compared to the aluminum ones. The extra weight has contributed to a number of breakages in my shop so I install aluminum or delrin/hd plastic extensions. The more weight you add to the hammer the slower the locktime. Besides that, they may induce light primer strikes and may not be able to overcome excess headspace. Putting a heavier hammer spring in addition to the hammer extension helps both cases. Also I recommend better hinge pins like the accuracy locker by eabco to prevent point of impact shift and less movement overall. Sorry about the long post but to prevent breakages do not use steel!!!