No pictures because I don't think this post needs any.

So being a "pseudo-realistic" builder, I wanted to add a bit of realism to my builds. One of these being a custom rocket for an upcoming tracked MLRS(multi launch rocket system).
Now I know what you're thinking and what I thought as well:

Why not use the stock rocket?

And yes, I want to, but- If I'm not mistaken(most of the time, I am, rockets fall down, they have a trajectory, and if I'm not mistaken again, the in game rockets have an unlimited range- or maybe they don't(not sure if they run out of fuel and fall).

What I'm trying to get on is I wanted to make a rocket that you can visibly see fall down a few miles away and not disappear miles away and fall down into the ocean.

So I started to design the rocket and named it boringly, the Mk.1 Rocket.

I designed Mk.1 the same way custom missiles are built, with a detacher, fuselage piece, and the rocket for propulsion. Everything seemed to go fine until the rocket suddenly exploded in midair.

After said first test, I couldn't seem to find the problem.

After a few seconds or a specific range, the rocket would blow up.

I tried everything from disabling aircraft collisions, mass and drag scales, and all either made the rocket too heavy to fly away or fly up and explode again.

I did put bombs in the tip for the main warhead and both versions, with or without the bomb, exploded.

tl;dr

My custom rockets won't work for some reason, any way to make custom rockets using the rocket part or should I forget about making a "realistic rocket" and use the stock ones?

-UC

PS. when I said MLRS vehicle, I meant the fourth variant of the Thunderbolt