I have a 4506 and recently bought two additional factory magazines. The springs are installed upside down compared to the two that came with the pistol, although I may have taken the originals apart and put them back together wrong, I really don't remember.

I have the springs installed so that the smaller section with the small loop is at the top - it seems to nest into the follower best that way. The new mags came with the spring installed the other way, with the little loop at the bottom.

Which way is correct?

I have a 4506 and recently bought two additional factory magazines. The springs are installed upside down compared to the two that came with the pistol, although I may have taken the originals apart and put them back together wrong, I really don't remember.

I have the springs installed so that the smaller section with the small loop is at the top - it seems to nest into the follower best that way. The new mags came with the spring installed the other way, with the little loop at the bottom.

Which way is correct?

I have a 1006 and all of the springs are installed loop up.

Right, the loop rests on the follower.

Do all S+W mags have a 'loop' on one end and not the other? Is the loop end always installed into the follower?

I had the same thing happen to me. The two magazines that came with my 4506 had the loop under the follower. I ordered four new ones from Smith and Wesson, and the loop was at the bottom attached to the magazine butt plate catch assembly. I called Smith & Wesson, and the customer service rep told me that the loop was on the bottom to help hold the plate in place. That made no sense and certainly did not fit well, so I e-mailed a contact that I has there and he confirmed that the loop, or the narrow end as he put it, does in fact go under the follower.

The springs used in the .45 TDA/DAO metal-framed pistols should be oriented with the small loop located at the top/front of the follower.

The same spring is used in all the .45 magazines which have 6, 7 or 8 round capacity.

The magazine butt plate catch (which contains the post which snaps into the butt plate to hold it on the magazine) is generally a metal plate which has a bend through which the bottom spring coil is threaded to hold it in place, although there have been some plastic ones shipped upon occasion (which don't have a spot for the spring coil to loop through, but just fits/snaps into the bottom spring coil).

The M&P and SW1911 magazines each use different springs.

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Ret LE Firearms inst & armorer