Why not a repeating crossbow?
With modern materials and design, you could have a cylindrical magazine in the body and a pump or lever action with modern gearing. You could set the skeleton framework up with templates and basic implements for transforming appropriate local materials into bolts, even. Using modern materials for springs and the bowstring(s) you could have a very powerful weapon, collapsible for storage, with a good range and with the ability to make its own ammunition in many environments.
For example, from "Audace ad Gloriam" (my pseudo Traveller supplement for Exploration and Survival gear) ...
This is simply a 1½ kilo block of mixed ePolymer and Smart Metal which can transform, on command, into a standard Crossbow.
The main benefit is in storage, as the unit packs down to a 1 liter volume shape to fit most conveniently and with perfect efficiency into any space available in a pack or emergency supply capsule.
The transformation takes 15 Combat Rounds from, or 30 Combat Rounds to reformat back into block form.
The basic package includes a ½ kilo block of ePolymer and Smart Metal which, when triggered, forms into five Bolts for the FlatBow in 5 Combat Rounds.
These two components are often found as a combined 2 kilo, 1 ½ liter volume, block for storage purposes.
Bolts can be reformed in the same way that the FlatBow itself can be, though this is most often done to repair broken Bolts – as long as all the parts have been gathered together, they can be reformatted into a whole Bolt (or Bolts).
The body of the FlatBow has integral templates allowing the measurement of replacement Bolts, if forming them from local materials.
Mass: 1½ kg. Cost: 50 Cr. Power: 1 x A Battery (15 PP to format/reformat). Accessories: 5 round BoltBlok (½ kilo), 5 Cr (AAAA Battery, 5 PP to format/reformat). Law Level: 8 (General Use), 9 (Survival Kit).
A FlatBow is tricked out to mount standard Scopesights, but does not come with them as part of the package.
FlatBows are Law Level 8 if a character wants to possess one for their own personal use and keep it in their own home, but Law Level 9 for inclusion in a Survival Kit kept for offplanet use and stored appropriately (or if owned privately but stored and used only on the premises of a registered sporting club).
Range: Assault Weapon. Damage: 2d6+1. Recoil: 1.
A FlatBow takes three (3) Minor Actions to recock and reload. They can take any type of Bolt used by any of the Crossbows or Flatbows in the game.