Ways to attack the problem,

You can lower the top edge of the firing pin contact pad.  You don't need to make the entire L cut, just draw a line from point A to point B of the outer edges of the L and take down the material.

It may be just as simple as the tail of the hammer being too long, and removing material off of the tail will allow the hammer to be lowered down without binding between the carrier bottom and the back of the disconnector.

Or it could be that the bottom of the carrier is not ramped wide enough and the hammer is catching on the milled sides of the carrier ramp.

When all else fails, use a maker and smoke the bottom of the carrier (ramp section), and the tail/top edge of the hammer to see just where it is binding to figure which of the above is the problem, and needs to be resolved.

P.S. The hammer is heat treated so you will need to use a grinder to remove metal on it.

If you are going to speed hammer it, you just need to take off the tail, then make a small 45* cut on the top of the firing pin collar instead of the full L edge to edge cut.  Really, you are just making a top edge beveled that is allow the FP collar to glide over/make contact lower on the firing pin contact pad, instead of the FP collar contacting the top edges as the carrier moves back forward over it.

P.S. With the new speed hammer, do confirm that you have .032 to .037 FP protrusion, or the mod may lead to light primer strikes with a lightened hammer spring.

The problem with some hammers having problems is not always directly related to the hammer it's self/alone, but also to the geometry of the hammer as well (distance from the center line of the pin hole to the front edge of the sear).

To keep is short, the FCG must spec as a unit to work in any given rifle, and when installing either a new part or a full FCG, there are times that you will need to re-time or mod a part of the FCG to get the complete working FCG into working specifications.

Since this disclaimer is always present with every single part that you buy,
"Should be installed by a competent gunsmith",
Some fitting/tuning may be expected from even the best of suppliers, especially when the complete rifle may be made up of sourced parts by many different manufactures.  

On the bright side, this is more than a handful of members here that can walk anyone threw the simplest of needed modifications if problems present themselves when a part/combo of parts need to be fitted to bring the parts as a whole into working order.

Note: It’s either fit the parts, or you better have bins of them to start swapping until you find the combo’s that will work in the rifle.

The non-L cut hammer is just a M-16 hammer with the auto sear tab ground off.
The L cut hammer is a Colt type designed ar-15 (read SP-1) hammer that worked as a safety device with an un-shrouded carrier to prevent hammer follow threw if the disconnector ever failed.

Since a Modified m-16 hammer leaves the hammers firing pin pad full height, it all boils down to the receivers FCG pin placement, and FCG total geometry if the hammer will work as a drop in unit, or if the hammer is going to catch the FP collar or the hammer tail to bind on the disconnector when lowered by the carrier.

To add as a tidbit: To see if the modified hammer started it’s life an a-1 or a-2 unit, look at the disconnector sear on the hammer. If the disco sear is wide (overhangs) on the ejection side, then it started its life as a M-16 A-2 hammer.

Quoted: DPMS hammers are used with 9mm Colt uppers with non ramped bolts I think as well per the 9mm thread. I"ve bene studying up because I'd like a pistol caliber AR soon as well. Randall

www.biggerhammer.net/ar15/hammers/