I just bought a new Springfield Armory GI-45 in it's basic WW-2 configuration.

Shoots Great, but it's got Springfields' "ILS" Mainspring lockout system to disable the gun.

I don't want to deal with it possibly malfunctioning so I replaced the  mainspring, mainspring housing, mainspring cap and related pins with Colt Mil-Spec Parts.

But when I got the Colt Mainspring and compared it to the Springfield, I found it was about 1-1/2 inches longer. It would have had to be greatly compressed to get inside the housing and it would have been MUCH STIFFER than the original Springfield was factory tuned at.

Figuring the Gactory knew what was best for it's pistols, and realing it only had about 200 rounds on it, I re-used the Springdiled Mainspring in the new housing, and it seems to work just fine. The trigger pull is exactly like it was out of the box...which for me...feels great for a factory set-up.    

My question is: Did I do the right thing by sticking with the Springfield factory spring that was tuned an shiooed with my gun, or should I have jammed the new Colt Mainspring into the housing even if it added much more weight to the hammer?

FWIW: The Springfield GI handled 230 Grain factory RN and 200 gr semi-wadcutters equally well. Should I add on a Wilson Full Length guide rod..or leave it alone with gthe mikl spec shorty spring guide?

www.ar15.com/forums/topic.html?b=5&f=34&t=20498

As far as the guide rod.......that is one of those holy ground arguements around here.  I suggest if it shoots fine with what you have, leave it be.   There are a couple of current topics going on about that exact arguement.  I can't say I see a clear winner.

I did the same thing with the ILS on my SA wwII. I liked the feel of the trigger pull too so I left the spring in like you did. A few thousand rounds later and its working fine.

Full length guide rods are a personal preference. Theres no set in stone data on whether they are good or bad in a 1911. I would leave it be, spend the money on an extra quality magazine(s)...

The trigger pull on the  GI .45 feels exactly like it did with all the ILS Internals.
Even with changing out the mainspring cap and mainspring retaining pin, the length of the original Springfield Spring is almost exactly the same  as when it contained the ILS parts.

The Colt Mainspring was about an inch longer, and would not easily compress into the housing. I felt if I jammed it in, it would be much stiffer than the original.

I'll test it out over the weekend.

I am sticking with the orginal Mik Spec shorty guide rod, and have even removed the Wilson Shock Buf I had installed to run it as original as possible......since the shock buff did "bind" slightly.

Out of the box, it handled ball and SWC fine. The only problem was a very occasional "Stovepipe" where the spent round wouln't eject...seems to have gotten hung on the extractor and jammed the slide open. I've had about 400 rounds through it...mixed ball and reloads, and suspect I need to break it in more rather than start tinkering with ejectors-extractors.

So far, it seems like a great product. But I'm replacing the "U-S" grips with a pair of Hogue Repros...should look a little kmore original !

You've got to replace all the MSH internals, along with the MSH.  If you're using the spring from the ILS in the GI mainspring, you must also be using the ILS cap.  Otherwise the spring would be too long.  Get the GI cap and retaining pin and the spring will fit and function just fine.