NEW UPDATE / VERSION 2.1 RELEASED
NEW version 2.1, check your Vault if you have purchased v2 previously.
Thanks to Damian for working out a snag with us he discovered. When replacing the SK_Mannequin mesh with some characters from the Marketplace with the same standard Epic Skeleton, weapons were not attaching properly. This was due to an extra animated bone “hand_r_wep” being used for the sockets. This has been fixed with switching from the"hand_r_wep" to the standard middle finger bone and new sockets, and redoing the animations. The animated middle finger now assists with best Rifle placement, and swapping meshes with the “Assign Skeleton” function now works perfectly with compatible stock characters. There is no other change to the Blueprints and this is very much a transparent fix with no visible change. “Assign Skeleton” simply works now, before it dropped the weapons.
v2.0 TO v2.1 CONVERSION INSTRUCTIONS - DOWNLOAD](MCO_UE4_MPTPS_Blueprints_v20_to_v21_INSTRUCTIONS.pdf - Google Drive)
We have new updated documentation about easily updating your v2 modified WIP Project with the v2.1 fix and features (link above), simple and easy. Ask Damian. 
Updated complete docs explain the new weapon sockets.
If you are not familiar with “Assign Skeleton”, it can take your custom character (or from the Marketplace) and fully replace the default UE4_SK_Mannequin in the Blueprint with a few mouse clicks. The skeleton does need to be 100% STOCK to match the UE4_SK_Mannequin skeleton, or it will fail and cause chaos. Definitely do some research and check first. A lot of great characters on the Marketplace say they are rigged to the Epic skeleton and scaled(another important thing) to the Epic skeleton, but extra bones and/or changed hierarchies make them incompatible for the AS trick.
Scale and proportions matter as well. For best fit and Rifle placement the Skeleton should have the same proportions. Hence meshes with a skeleton truly 100% matching the UE4_SK_Mannequin will transfer and match perfectly. Variations in scale and/or proportions, your mileage will vary and maybe need some adjustment.
And always backup your project FIRST! Can never say that enough before performing surgery on a project.
Of course there are others, but here’s a couple of characters we’ve tested that are 100% stock Epic skeleton and plug-n-play compatible:
Modern Soldier Camo Pack - Modern Soldier Camo Pack in Characters - UE Marketplace
Gangs Pack 01 - Gangs Pack 01 in Characters - UE Marketplace
The Soldier looks great, and the Gangs are cool looking without the bulky soldier clothes and gloves, you can see the fingers/hands fit on the weapons perfectly since they are all the 100% matching Epic skeleton. Chances are the other nice characters by these sellers are “Assign Skeleton” compatible as well, I would ask them directly.
“Assign Skeleton” is a cool feature and shortcut, if you create your own character or buy one based on the stock Epic skeleton.
Cheers
