I ran into an issue with a new build and it has stirred up this question....
My issue is that the new DPMS (non-notched) hammer wore a grove on the bottom of the bolt carrier right above the firing pin. It eventually resulted in the rifle short cycling. We swapped 3 different styles of hammers, lowers, and bolt careers with a varying degree of bind. The worst of witch would hang up so bad that the bolt would hold half way open if you lowered the bolt with the charge handle instead of letting it slam shut. Unfortunately every other verifiably good AR we had around has light trigger groups with speed hammers.
Some definite things noted:
If I take out the firing pin it doesn't hang up no mater witch hammer is in there.
If I use one of the lower hammers (JP speed hammer or notched) it doesn't hang up as bad or at all depending on the rest of the setup.
There is about 1/4" difference between the height of these various hammers (about 10 in all mostly DPMS parts kits, Bushmaster takeouts and JP's)
Any ideas guys?
So you are thinking the trigger is causing the hammer to sit higher than it otherwise would (edit: in the cocked position) and therefor have more pressure on the bolt as it trys to slide by? Could be... and a un-notched or taller hammer will obviously make this that much worse...