I have a M1911a1 Colt series 70 in 45 ACp. After the last round is fired the slide does not catch or remain in the rear.

I have tried different ammo; and diffent magazines. With an empty magazine inserted when I rack the slide to the rear it catches.

Does this sound like a problem with the spring? Should I buy a lighter spring.

Thank you for your help.

Jim

Does it lock when you slowly draw the slide to the rear or just when you rack it. Did you buy the gun new or used.

Recoil spring I would think. When you say "different ammo" do you mean some "white box" and some self defense ammo? If you handload, load up some max 230 gr. hardball ammo.
Peter.

The slide locks to the rear when I pull it hard to the rear. Does not lock when i pull it slowly.

The second type of ammo was pmc 230 gr FMJ.

Jim

Is this a new problem or a new gun?

It could be one of three things, to strong of a recoil spring (I'll include a buffer impeeding magazine travel here), magazine not lifting the follower high enough or fast enough, or weak ammo.

You have tried factory ammo with the same problem so that fairly well eliminates ammo.

If you have been shooting the gun for a while I don't think the spring has been getting stronger.

Have you tried more than one magazine? Check followers or for dents in the mag body.

I just had another thought, so make it four, what does the profile on the slide and slide stop look like? Any thing wearing down there?

New problem with a gun that i have had about 30 years. I have tried different magazines and magazines manufactured by different firms.

Move your thumb out of the way.

Rich

Strip it down and clean it very well look for burrs on all parts involved.

Look at slide stop and make sure it hasn't been bent or has some other trouble spring out of place broken ect.

Look for cracks in frame ,slide and other parts.

Look for pins that might have walked out of place

Look at the frame rails to make sure they haven't been damaged.

I am going to order a new slide stop and see if that works.

Polish the old slide stop pin and make sure the notch is clear of debris. See if that helps.

I bought a new slide stop and that did not work so on a buddy's advice I bought some Wilson 47D magazines and it now works like a charm.

Jim

Gald you got it working right.

I've been using SS mags I pickup at a gunshow that have checkmate(?) followers. The mags are up to $12 now and they are great.