I had a similar thought because some of the guys (including me) had stated that especially the pipe machinegun is OP (easy and early to craft).
And with ammo being so regularly found, that thing is a just too reliable DPS monster.
To counter that:
What about all pipe guns have a chance to jam and you have to reload to make em work again.
Chance to jam could be for example 10% for low/grey quality, decreasing to 2% for high/purple quality.
If you ask me they even should have a very low chance (0.5%?) to explode and brake completely (maybe also hurting you) when fired.
So there would be a constant need/interest to develop further/buy a better one/invest points or whatever.
And - well I know the word realism isn't the thing to bring up, but - guns made of just pipe pieces, glue and wood shouldn't be reliable at all.
...says the guy who is able to construct those, but can't figure out how to make coffee and bacon&eggs without a recipe