I remember them talking about “Sniper on the Eastern Front” during the explosive ammunition tests. Is that it?
Hold Up Displays - Horizontal Gun Rack Storage and Shotgun Hooks Store Any Rifle Shotgun and Bow - Heavy Duty Steel - Made in USA https://www.amazon.com/dp/B00AB2GJ48/ref=cm_sw_r_apan_glt_i_7BRDP1TWKWZ5FFA78M3X
Get a spark plug gap tool, the metal should be thin enough to get between the buffer and detent. If it is too wide, use a dremel to narrow down blade width.
I'd consider trying to use bailing wire which is thin and dense, bend it to a hook, see if you can push the detent down with it.
Good luck!
Like this...
https://www.amazon.com/Hotop-Blades-Feeler-Imperial-Measuring/dp/B06XHXJG31/ref=sr_1_36
https://smile.amazon.com/dp/B097JJCZFX/
I bought three different variants of this case from various manufacturers and this was the nicest. Depending on the price it may also be the cheapest and if it's not I assure you it's close enough for the added features. Admittedly it's a bit long for a 16" barrelled KP-15 with an A2 (would hold 18" with most muzzle devices or even 20" if you went diagonal), but most dual rifle cases on the market seem to be this size. Also it has a spot for your WWSD patch.
Probably not the best quality, but something along these lines.
JIALITTE Quick Detach 1 Inch Sling Mount QD Loop Adapter Kit with 4 Screws + 1 nut + 1 Wrench https://www.amazon.com/dp/B07WDR3PYV/ref=cm_sw_r_cp_api_glc_fabc_-Wt4FbRTEVGSD
With this guy on the MLOK foregrip
JIALITTE M-lok S-ling Swivel 1 Inch QD S-ling Mount Adapter Attachment for M lok Rail https://www.amazon.com/dp/B07L4LGJ9R/ref=cm_sw_r_cp_api_glc_fabc_RXt4FbC3YV844?_encoding=UTF8&psc=1