So I have an ATI M1911.  It is WWII clone meaning arched main spring housing.  I hate those because I have small hands (short fingers/wide hand).  I got a WWI flat mainspring housing for it.  over an hour of dremel time to get this thing to fit (hole was not lined up and too tight to go all the way in.  Not it is cooking after some touchup on the finish.  If this is how all the parts go I think my ground up build may take a minute or 2, challenge accepted.

Pray tell, tell what were you Dremelling on?, you did have the hammer in the cocked position during this struggle, correct?
Any pics handy?

Well no matter what I do I could not get the pin to go in, it would go crooked.  My best guess is the thing was out of spec, or drilled wrong.  It got to the point I chewed up up just trying to force it on out of spite.  I said piss on it and installed the original, it popped right into place with only a minimal amount of effort.  It was a 16 dollar part but I wanted to make it work.

$16.00 MSH = junk

Yes, I see that now, it was just a nice looped WWI replica so I figured why not.  I may have made it work but holy hell it wasnt easy.  An this boys and girls is why I am getting a bunch of wilson parts when I do my other build.  Still not sure on my frame, down to the RIA and the Double star Rail I think

Put the Dremel away next time.

There are a few very limited tasks which are suited to a Dremel.  The rest needs to be done with little files and emery cloth.

And don't polish the feedramp.  Ever.

I started with the file, then I realized just how far out of spec the part was and I decided to "make" it work.  Next go around I will start with higher end stuff so it will be much less of an issue.

You can buy the most expensive MSH, trigger, grip safety, etc, etc, etc, and they will not fit any better or worse than the cheap-o one.

Point is that in 1911-land, most guns and most parts require hand-fitting.   Sometimes you get lucky and things essentially "drop-in", but that doesn't mean that they are fitted.  It just means that they dimensionally work.

One thing you hadn't considered in this thread is that it is possible that the gun is out of spec as well?  ATI is Turkish and are known for taking more liberties with dimensions and materials than say, the Phillipinos, who manage to stay fairly true.  That being said, I'm not saying it's a bad gun.  I happen to favor the simpler, more unadorned 1911's of the world.  True GI style and spec is what the 1911 was for the first 50 years of it's life, and only in the past 20 years have the custom shops, have they gone from being a cottage industry to a full blown art form.  Wilsons are nice and all, but the basic import gun is more true to the original.  Rattles and all.

Oh yeah, put the dremmel down.  Files, stones, etc are what you should be using (if anything).  Watch some gunsmithing videos first too.  Learn how to do function and safety checks after you make any modifications, etc.

Have fun, and stay safe!

The ATI is made in the Philippians.  If the description is correct on palmetto it is part of shooters arms.  The GFX seems pretty nice.  The pistol actually seems very well built.  I was impressed for the cost.  Obviously I still have my original MSH which is fitted much better.   I took a piece way off and made a go of it, figured it was no good as it sat so no harm no foul to see if I could get it.  i was out $16 at the most.  I may get a different flat MSH not I know I like it on this gun and fit it a little better.  Or just say piss on it, leave it as is (looks good unless you look close) and focus on my educational build.  I am hoping not to encounter such a drastic deviation on the build but you never know.

Ok, I thought the ATI were Turkish.  Maybe they used to be.

The Phillipene guns seem to all be very good for the $$

Yup.  Projects are good.

I fitted a ATI Compact for a mag-well for a customer and it was a BIOTCH getting it lined up, pilot holes in the frame were
off "by THIS much".... destroyed a new file and hand cramps for the rest of the day..

A ground up build is not something that can be done properly with a dremel...in fact, if using a dremel,  as others mentioned, you're doing it wrong.

Most of the amateur builds I've seen have all the style and grace of an old, beat up, worn out GI gun, only with misc sanding wheel marks under the attempted felt wheel polish.

I have an ATI Military model 1911A1 and changed the arched for strait as well, I like the ww1 1911 look and feel better too.

I fitted my ebay "$20 delivered" flat mainspring housing with loop with a file, worked fine.  

I ended up getting another housing, without that damn loop.  This one was much closer, a little love with the file and it worked.  I tried my Wilson housing and it went with no adjusting.  I have a nice box of parts to start my ground up build.  Saving it for winter.