To clarify for the OP, these don’t generally scale down the whole gun. Caliber conversions can be as simple as swapping the bolt.
You can also sometimes swap to a larger caliber. They make ‘conversion kits’ for the AR-15 that are functionally just most of a new gun. You can get those for a variety of calibers from 7.62x39 to .50 Beowulf.
shalafi@lemmy.world 5 weeks ago
I have an easily swapable bolt that let’s my AR-15 shoot .22LR. Pretty nifty, though not quite as accurate since the bullet is .003 thinner.