As was mentioned, you can get a conversion for your present 1911 and it will not result in any damage or modification to your Grandfather's old war horse. You just strip it like you are going to clean it. Instead of putting the original top end on your frame, you just put the conversion top end on it (top end meaning slide, and barrel). When you want to shoot .45s, you just pull back the slide, remove the slide stop and put your .45 top end on the gun.
"BTW do NOT get a ceiner(sp?) those things are garbage!! (built like a toy, the marvels ont eh other hand are, as i understand it, built to aproximately the same specs as the old colt ACE style slide/barrel assemblies. ie built like a REAL and serious use pistol)."
I have a Ciener 1911 conversion. I would not say it is garbage. It is very accurate. The slide is made from alluminum, but this doesn't make it a toy. I wouldn't call an AR15 a toy even though it is made from alluminum. The one drawback of my Ciener is that it is very finicky about ammo. I found that it runs flawlessly with CCI Mini-Mags and bought a case of 5000 rounds. Mine will NOT run on Wal-Mart bulk packs (which run fine in all my other .22s).
I love the idea of the .22 1911 conversion. The 1911 is my primary defense and competition gun. I can use my same frame, my same holsters etc for practice. I have the Officer's Model Ciener conversion. The Officer's Model is my carry gun. I can practice draws from cover until my heart is content.
I owned a Colt Ace once upon a time. I considered it a piece of crap. It had an extractor that was made from really thin alluminum or tin. When you stripped the pistol for cleaning, you couldn't help but to bend it. Then you spent the first couple minutes of every shooting session adjusting it by bending it in your fingers. I wish I had kept it, but then I say that about every gun I ever sold.