View Full Version : new 9mm AR help/questions nmew

06-08-2012, 3:09 PM
I have a plum crazy lower

and this upper
16" BD 9MM SS Barrel, Flat top upper A2 Flash Hider, complete with ramped CMMG 9MM bolt assembly and charging handle.

1- Do i need to buy a 9mm hammer?

2- new question if i add a 9mm hammer will it work with a 223/556 upper also?

3- Do I need to buy a 9mm buffer?

4- Should/Do I need any other parts to be switched out?

i have a mag block already thanks

I am very new to ARs

06-08-2012, 3:26 PM
If you have a ramped bolt you should be fine with a standard (un-notched hammer). Operation with the plastic fire control parts of the plum crazy are an unknown to me. Also, the force at which the 9mm bolt slams into the plastic bolt catch on the plum crazy would also be a concern to me. You will need a 9mm buffer and I would also suggest you add a 9mm stock spacer as well.

06-08-2012, 5:09 PM
You need the mag block and 9mm buffer.Use Metalform , converted Uzi mags or c/p mags.If you use hot police loads,a new stronger buffer

Reverend Clint
06-08-2012, 5:12 PM
plum crazy offered a special hammer for 9mm ar's

06-09-2012, 11:07 AM
bump with new question

06-09-2012, 7:00 PM
1. For a CMMG ramped bolts use a round head/no notch hammer.
2. Though no need... No, the 9mm hammer won't work for a 556 upper well...
3. 9mm buffer is suggested depending on the loads you are using. The 9mm buffers are longer than the 223/556 buffer. This is so the buffer doesn't unnecessarily go too far back and bring too much energy forward. Too much force tends to put a lot of stress on the hammer pin so a lot of people tend to upgrade to the kns pins on the 9mm ar.
4. Dedicated 9mm buffer and possibly kns pins are the only thing I can think of...

06-09-2012, 7:04 PM
update i just got my upper in the mail and my hammee on the plum crazy does not fire when the upper is attached it seems like its getting stuck and does not fit

Dutch Henry
06-09-2012, 7:30 PM
You may need to use a blowback style hammer. New Frontier Armory has them for their polymer lowers and they say that they'll work in the Plum Crazy lower as well.


06-10-2012, 5:30 PM
The hammer on the plum crazy lowers is CRAZY out of spec. Don't use it. Replace the FCG with a standard FCG.

Better yet, replace the lower with a real lower.