There is a habit in RPGs to heavily equip characters with weapons for every possible fight. From the lowly dagger through high powered rifles, modern and post-apocalyptic characters carry a bunch of weapons for a bunch of purposes. One of these purposes is what we’ll call Melee Fighting. hand-to-hand combat with weapons. Effective melee weapons are often 2-5’long, with polearms being even longer then that, sometimes over 12 feet. While it is wicked Cyberpunk to carry a couple of Katana on your back, and street as fuck to bring a 3’ segment of pipe or a crowbar, carrying all this stuff gets kinda ridiculous.
Modern longarms have abandoned the ancient carryover of being a pole arm as well as a missile thrower. Old long rifles were that bag because after you fire the 1-5 shots, you were expected to fight as pikemen. Current trends in shoulder-fired weapons is to be as short as possible to be handy in close spaces. Personally this is what I want in a fighting long gun, an overall length of less then 36” and as light as possible.
But our RPG characters might not want that. In hypermodern, post-apocalyptic and space fantasy settings, we may build a lone wanderer who needs to fight with lethal and less lethal force in close range and carry a shoulder fired weapon. To minimize weight and bulk, why not revisit the combination weapon? The new series The Mandolorian does, and Promo imagery from that series sparked this idea. Other media has shown fictional protagonists engage in melee combat with their long gun, most notably Quigley down under.
Real World Options:
I’ve long held that the Mosin Nagant carbine with the integrated bayonet might the best zombie apocalypse rifle as it functions as a club, a pike and a gun. at about 40 inches long with 12 more of intregral folding bayonet, it's small enough to easily carry and big enough to functionas a 2 handed melee weapon effectively.
The M1 Garand is another idealized bayonet fighting rifle. A little heavier the the Mosin, but semiauto and holding 8 rounds easily loaded at once. At about 44" long and with a detachable 10-16" bayonet it's a bit longer then the Mosin as well while not yet being unwieldily.
Science Fantasy Options:
The Mandelorian's disentrigation rifle is near idea, and I've sketched out a family of similarly styled models using modern ammunition.