→Mechanicum Understanding of Science
There's the common misconception that the AdMech don't really understand science and approach all tech with ritual and superstition. That's arguably wrong. In the "Mechanicum" novel they demonstrate theoretical knowledge of physics. Yes, it's set in the 31st millennium, but it's quite clear that even in the 41st they know "normal" sciences like mechanics, thermodynamics, biology, optics, quantum physics, etc. The AdMech definitely has as much scientific knowledge as we have today, and probably more. And they are quite happy to play with it. What they don't really understand, and don't like to play with (unless absolutely forced to), is the hyper-advanced tech from the Dark Age of Technology. Basically, if it isn't so advanced that it's literal techno-sorcery, then they don't mind messing with it. Which is why we get goodies like Power Armor and Terminator Armor from back before such things started to decline; even volkite weaponry before that went out of style. But, they're not going to meddle with ridiculously advanced technology because they might create an abomination like something from the Long Night. In fact, it's entirely possible that's how horrifying techno monstrosities like those in the Age of Strife came into existence. Especially given the fluff (especially-especially obscure pieces of fluff) involving people do-it-yourselfing technology or an adept putting something together wrong.
You may think this means the lego-tech of the Imperium (and every other faction) should be exempt from this since it's so simple and basic in design if not actual power. You would be wrong. Look at it this way, one man loads
a Basilisk with a shell nearly as big as he is and it hits like a Nazi railgun (on a railroad, that gun) but over only fifteen kilometers. The mass, force, and energy ''do not add up.'' So, just imagine what kind of stupidly advanced bullshit actually goes into making the damn thing and just what is ''really'' going on with it at a quantum or perhaps ''spiritual'' level. Do you really want to screw around with that?
Take the Lasgun for example. There are almost infinite patterns of lasguns, many developed ''after'' the great crusade as the lasgun wasn't all that common back then. The AdMech understand materials and mechanics well enough to create different stocks and triggers. They understand optics to a decent degree as they can focus the las beam with different barrel lengths. What they don't understand is the power pack, because the power pack is a scary super advanced piece of technology that will not only hold enough energy for a hundred shots powerful enough to kill an armored man, but it can be easily recharged thousands upon thousands of times. And they don't have the slightest clue as to how it works.