Hi Cyric!
First of all, you need to understand that they only call them "Drop-in" parts for the sake of brevity.
They should actually be called
Drop-in/pull-out/mess-with/Drop-in/pull-out/mess-with/drop-in/cry-a-little/pull-out...
You get the idea.
The reason they DON'T drop in, is because of a phenomenon known as "Tolerance Stack-up"
Say you have 10 parts, each with a tolerance of +/- .003
If all 10 parts are -.003, you end up being .030 out of tolerance and this will usually translate into a gun that's so loose you need to hold a bucket under it when you shoot! (to catch the falling parts)
Obviously this is an over simplified example but suffice to say, you can run into serious trouble.
I'd really not recommend this if you're doing it with the intention of saving a little money, because your time and piece of mind may be worth more than your money by the time you finish.
On the other hand, it's a good way to learn and a GREAT way to exercise your patience and stress management skills.
LOL
There are some tools you WILL need, like a plunger tube staking jig.
*yeah, you can improvise, but unless you're REALLY talented and VERY lucky, it won't be secure*
OTOH,
I'm currently building a .45 for IDPA on a matched frame and slide from Les Baer which set me back about 850 bucks.
So it CAN be done, and it can be done well, just bear in mind that the first one is always the worst, it gets easier, and NEVER, EVER, think you can figure it out on your own.
Buy the .45 books from Jerry Kuhnhausen.
They're worth their weight in gold!
Good luck!
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Your mind is your primary weapon.
USE IT!