I'm with you on this Vangelis. The BFG article has quite a bit of work added to it, and it confirms to curious users whether or not a real weapon was the build up around the gun or not.
Even if a gun is wrapped in plastic/resin/etc., it doesn't mean it will fire a blank. Noise ordinance or other factors could lead to the gun not using blanks. Like it's been said, the BFG hasn't been confirmed to not be built around a real firearm, so simply guessing isn't acceptable. Plus, it seems easier to build up a weapon around a real gun than to start from scratch.
And while AdAstra does have a minor point (in JP3 they just added a CG muzzle flash, in Doom it was CG super flash and melted set pieces), we can't simply assume. You all know what happens we you assume.
With T2 though, the guns actually did fire blanks, but the flash was turned blue and laser bolts were added in post-production. In some cases, same with Star Wars (you can see Han Solo's DL-44 cycling sometimes).
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