Reloading Gun problem ?

I would like to help me to figure out what’s going with my animation when I try to export into unity.

Let me introduce to this , I need to start a good workflow for using blender and unity for FPS animation , I decided to start with a simple character ( 2 hands and a Rifle for now ) , then when I feel confortable with , I like to incorporate a complete 3D character (biped and full body ) .

this is my “gyazo” gif where you can see the main problem (see below this first link to gyazo).

Link for my Gyazo gif…(click below, let begin the animation’s gif a few seconds)

as you can see there is not “mag” (magazine) . So I atribute that to the “mask modifier” ? ( I ve used this modifier to hide the magazine and pick up a new one) as you can see, the player drops the magazine and pick up a new one from one of his pocket )

1 - Here’s in the first image I use “mask modifier” to hide it in the next keyframe “50” , the image is showing you keyframe number “49” (49/132). to create the ilution of take another one from his pocket for example .

2 - here in this keyframe I put “I” and press in the eye button to hide the respective magazine.

3 - I have IK constraints in Left and Righ hand to move the character , and I have some “contraints” too. How can I resolve this problem. Here’s is the image of the “contraint” tab and this relation between bones.

4 - Now it is time to export this model in “fbx” format to check a test for animation and deformation in unity , I did NOT bake the animation …could be another reason ? well let me show my export parameters setting for this exporting process. (check this link for step “4”).

5 - the another options “armature” and animaton" , I ve chosen these. (chek this link for step “5”).

6 - If I apply “all the modifier” in the exportion process I lost my work for hiding the “magazine” I do not how to appear or disappear bones in animation. and could not find for bones, just for default’s objects. I realised then , if I Do not apply the modifier I lost another things too.

7 - With that setting I entered to unity in “rig” configuration I put “legacy” and Apply root. THen go for “animation” tab (in unity) chose the “reloading” animation and hit play button , but the mag…never appears to the Unity’s project… what’s I am ignoring or doing wrong? (Check this last link for this weapon in unity).

as you can see in the final image, there is not mag ( mag is not another objects , is part of m4a1) I think Unity do not supports Constraint or perphaps was a really bad Idea to create an animation with “masking modifier” just to hide the magazine. I do not how to hide “bones” for animation? If I apply “masking modifier” the mag dissapears too because masking modifier is useful when is “active” ? .
9 - Please help me , If you want to understood too or just helping me , I upload the file . Here is the link I ve search for masking modifier. (Link for he masking modifier) … I think this modifier is good but not for exporting (cause You may apply the modifier in the exporting process, so that is the way …it dissapears)

the blend file in pasteall
check the pasteall link if you wanna help me .