The CAV-15 MKII receiver, while being very similar to an AR15 receiver has some differences that allow some match triggers to work, and others to not work well at all.
What Won’t Work
Rock River Arms 2 Stage Triggers. Over the years I have tried 4 different RRA 2 stage triggers in CAV-15 MKIIs with varying results.
One didn’t work at all, one immediately started doubling, one worked for about 500 rounds then wouldn’t reset anymore, and the last worked for a few hundred rounds then starting doubling.
The Timney trigger tensions against the bottom of the lower. This works in a normal aluminum receiver. In the CAV-15 MKII it just makes the lower flex, and the trigger will not reset correctly.
ALG Combat Trigger
The ALG is a good option for people wanting Mil-Spec style trigger, but cleaned up to be as crisp as possible and the minimum mil-spec weight. This unit installs just like a GI trigger and requires no modification to the CAV-15 MKII lower
Spike’s Battle Trigger
This is a mil-spec trigger with nickel boron coating. It features standard installation, and a trigger pull of 5-9 pounds depending on individual spring variances. No modifications are necessary for installation in the CAV-15 MKII.
Modular cassette type triggers like the McCormick AKA CMC.
I feel these are of particular benefit in the CAV-15 MKII because they are not effected by the flex of the plastic. While USGI style triggers have no issues in the CAV-15 MKII due to their generous engagement surfaces; match triggers that function in the normal manner may not have enough engagement surface to accommodate for the flex the plastic may experience through function. Modular triggers are self contained and immune to this issue.
Modular triggers also do not require any adjustment to the trigger on the part of the user. Triggers that require set screw adjustments to work are best installed by gunsmiths, and sometimes require readjusting. I also recommend the CMC for use in aluminum receivers for this reason; I have over 40,000 rounds between my several CMC triggers and they’re still working without issues. The Wilson Combat trigger is a similar modular cassette type unit and will likely work the same way.
Modifications are required for use in the CAV-15 MKII.
The front of the fire control area of the CAV-15 MKII has a radius that will prevent the modular unit from sitting all the way in. This is easily remedied with a dremel tool in a few minutes.
The hammer pin area on the CAV-15 MKII receiver is wider than an Aluminum receiver. Standard USGI triggers and the ALG use a J-pin in the hammer to hold the hammer pin in place and thus a longer pin is not needed with those triggers. Modular triggers do not use a J-Pin to capture a standard fire control pin like USGI triggers or the ALG; they generally use pins with small screws or C-clips to be held in place.
There are several Options for the modular trigger user with the CAV-15 MKII to deal with this issue
1) Use the Cavalry Manufacturing Big Pin for the CAV-15 MKII receiver. This pin is sized to correctly fit through the CAV-15 MKII receiver for use with modular triggers and is retained with E-Clips. These have been out of production for a few years, but Cavalry Manufacturing will be resuming producing them now that GWACS Armory is producing CAV-15 MKII receivers again.
2) Use a long machine screw and nut through the hammer pin area. While it won’t look pretty it will work.
3) Have a machinist mill down the outside areas of the receiver to be flush like an AR15 lower. I saw a few examples of this working at Cavalry Arms, but there was no long term testing conducted with regards to structural integrity issues. This will also probably void your warranty
4) The modular trigger may fit tightly enough that the longer hammer pin is not required at all and the trigger pin alone is sufficient to hold it in place. If you choose this method, test it thoroughly for reliability.