It's been a while since I have played Fallout 4. I played after Automatron came out, but it broke so many of my mods that I decided I wasn't gonna bother playing again until all the DLC was out so that I didn't have to constantly fix mods. I'm waiting until Nuka world comes out, then for all my favorite mods to get updated, THEN I am going to do another play through. So it has been a while, and I might have forgotten a few things. To start, everything on your list is 100% correct in terms of real world physics. Next up, all of the sniper rifles in the game are left handed, when in real life the vast, VAST majority of bolt action rifles are for right handed shooters. Creating a repeating firearm, let alone a semi or full auto like the pipe weapons can be, out of salvaged parts, is basically impossible without advanced machining tools like a lathe and milling machine. The most rudimentary pipe weapons that are the easiest to create would be slam fire shotguns. Something like this could actually be made with just some right size bits of pipe and a pocket knife to whittle out the stock. I haven't played any DLC since automatron, so I don't know if this is still true, but at that point in the game, there wasn't any kind of real "assault rifle" in the game, despite them being the standard military rifle in all the previous fallout games. Like you said, the Fallout 4 "Assault Rifle" is closer to a water cooled machine gun (Why are they still using water cooled guns when the game already includes examples of air cooled guns?), and the combat rifle is closer to an old school battle rifle. .45 ACP ammo would not work in a revolver like the pipe revolver without moon clips. .38 ammo is stupid and should have just been replaced with 9mm ammo. Laser weapons should not have recoil because light does not have mass. Increasing the barrel length of any ballistic firearm should increase velocity, thereby improving damage slightly. Converting a firearm to accept a different, larger caliber will almost always require changing the external dimensions of the receiver/ barrel. The combat rifle's magazine well is like 3 times wider than it needs to be to accept the single stack magazine it takes. If ammunition has weight, the magazine that hold that ammunition should also have weight. Power armor now requires fusion cells, even though there is nothing in the lore to support this. 5mm ammo is stupid and shouldn't exist. 5.56mm ammo should just be a lot more common, and the minguns should just take 5.56. Options to convert the minigun to fire 7.62 and .50 ammo do make sense, but would require bulking up the weapon. Heavy weapons like the minigun and gatling laser should only be usable with power armor. Using normal small arms like assault rifles and pistols while in power armor would be nearly impossible because of the added bulk in the hands. 10mm is a vastly more powerful round than .38/9mm and should be reflected in the damage numbers. Cartridge reloading should be a thing. Fallout New Vegas did it perfectly, and I have no idea why they dropped it. I don't know if there are mods to recreate that yet. Guns need to be cleaned every few thousand rounds to keep them functioning. It could be argued that not cleaning guns is just artistic liberty, but given the fact Fallout 3 and NV had degrading guns, I'd like to see a mechanism for guns getting more dirty and jamming as you use them, although outright breaking like in 3 and NV is a bit excessive. A gun breaking should be a very rare event. Carrying more than 1 or 2 long guns plus a sidearm would be very difficult just because of the bulk involved, let alone the weight. This is less of a gun thing, more of a realism thing, players are capable of carrying way too much weight in the vanilla game. An average combat load for the military weighs roughly 60 pounds, double that for long patrols. An average guy carrying around 300 pounds all day is ridiculous. In fitting with the lore, power armor would allow you to carry much more gear. Going hand in hand with the reloading thing, every caliber has different loadings. 55 grain 5.56mm vs 62 grain. 150 grain 7.62 vs 175 grain. Buckshot vs slugs. Again, Fallout NV did this perfectly. That's pretty much everything I can think of off the top of my head. Like I said, it's actually been a while since I played, so there is probably more stuff I am forgetting.