First....thank you for your service to our country.
After working with reenactors.....and making "Blanks" for over 20-years (after 20+ years in the US Army/Retired).........I would suggest that you do a couple of things first.
1: Review the "designs" used in the "BFONG's" (Chuck's original guns).......and with Indiana-Ordnance-Works (?) Blank-Firing-Guns/Models.......
What one Company did was to design a Blank-Firing-Only gun that would only load and fire towards the rear............the second Company made their Blank-Firing-Only gun where it had "proprietary-parts" (by design and "size") so that they would only work in their guns ("supposably").
2: Come up with a couple of ideas........and then meet me first at:Blanksguy2001@outlook.com
I would like to be able to give you a more in-depth idea of what is required (by BATF and/or "locally" to you for this to be legal.).......and then help to guide you through design and making it so that with your initial posting to the Blank-Adapting-Thread.....more of our MG42-Board readers will be able to benefit from our discussion.
After review, and maybe a couple quick questions, I can direct you how/where to post your initial questions into the "Blank-Adapting the MG42/SA42/M53" Thread in the MG42 General-Section.
If that sounds acceptable.......I will await your e-mail.
US Army, RetiredBlanksguy2001@outlook.com