HK Mr556 + Geissele SSA = fail?

[AlphaKoncepts]

Recently swapped out a trigger & hammer on a HK MR556 build. Actually the lower is not HK, but the upper is a factory HK MR556 upper. The customer purchased a Geissele SSA trigger & hammer and had me install. I informed the customer upfront that it may not work due to HK's disclaimer about requiring a mil spec hammer, and the fact that Geissele makes a MR556 specific trigger & hammer. The rifle is experiencing a failure to fire. I told him it's probably the hammer, but his trainer is telling him the firing pin is too short. For some reason he is convinced his trainer is correct.

WTF? Firing pin too short? Everything worked fine with the mil spec FCG, FCG is changed, now it doesn't work. Seems cut and dry to me. I told him to try it on another lower, he says same FTF. I have no idea what FCG was in that other lower as he was calling me to trouble shoot by phone.

I'm 99% sure it's the hammer, but haven't had a chance to trouble shoot myself. I'll probably take to the range and mount on a mil spec lower next week. But before I do that, is there anything else I should be looking at with this particular setup? Any way to remedy other than the obvious, swap the FCG back to the previous or buy the Geissele MR556 SSA? I'll also measure the firing pin but don't know if HK uses the mil spec length so nave nothing to verify against.

[chococat]

HK MR556 has a hammer actuated firing pin safety in the bolt carrier. The SSA hammer is too short to move the firing pin safety out of the way. Thus the requirement for Mil-spec height hammer.

There is a list of HK compatible fire control groups on HK Pro.
Hope this helps,
Al

[GTF425]

When I had my 416 upper, I had a purpose built Geissele SSA. A standard Geissele would not drop-in due to the firing pin safety.

He either needs a hammer without the "notch" on the surface that strikes the firing pin, or he'll have to punch the firing pin safety out of the BCG and then he can run any standard AR trigger.

With a standard FCG, he needs a hammer like the "M16" in the diagram below.

http://img.tapatalk.com/d/13/09/02/adesu9ej.jpg

His trainer is retarded and has no idea how a 416 works.

[Iraqgunz]

This is an easy fix. Put it back the way it was and tell him to go elsewhere. If he is going to listen to some retard trainer and not you, then you are pissing in the wind.

[AlphaKoncepts]

This is an easy fix. Put it back the way it was and tell him to go elsewhere. If he is going to listen to some retard trainer and not you, then you are pissing in the wind. LOL perfect way to put it.

Thanks for confirming my suspicions guys.

[TMS951]

http://geissele.com/hkmr556trigger-2.aspx

Requires Specific trigger group, Geissele makes one

[Hookuleez]

Recently swapped out a trigger & hammer on a HK MR556 build. Actually the lower is not HK, but the upper is a factory HK MR556 upper. The customer purchased a Geissele SSA trigger & hammer and had me install. I informed the customer upfront that it may not work due to HK's disclaimer about requiring a mil spec hammer, and the fact that Geissele makes a MR556 specific trigger & hammer. The rifle is experiencing a failure to fire. I told him it's probably the hammer, but his trainer is telling him the firing pin is too short. For some reason he is convinced his trainer is correct.

WTF? Firing pin too short? Everything worked fine with the mil spec FCG, FCG is changed, now it doesn't work. Seems cut and dry to me. I told him to try it on another lower, he says same FTF. I have no idea what FCG was in that other lower as he was calling me to trouble shoot by phone.

I'm 99% sure it's the hammer, but haven't had a chance to trouble shoot myself. I'll probably take to the range and mount on a mil spec lower next week. But before I do that, is there anything else I should be looking at with this particular setup? Any way to remedy other than the obvious, swap the FCG back to the previous or buy the Geissele MR556 SSA? I'll also measure the firing pin but don't know if HK uses the mil spec length so nave nothing to verify against.

Is there any way to make the gun work with a trigger that is not designed for it?

That is not very smart.

Geissele makes a trigger specifically for the MR556 because their standard trigger will NOT work for that gun.

You should not be installing parts that you know won't work properly into other people's guns. You are playing with fire.

[Larry Vickers]

I agree with Iraqgunz on this one - I couldn't have said it better myself