I am installing 1/2" thick 5" wide shaw engineered wood flooring. I am using Bostitch 2", 1/2" crown staples that are 15.5 gauge. Everything looks great until you look at the floor in the right light and right angle and see lumps over where the staples are seated over the tongue. The prefinished part of the board is slightly raising, but you cannot tell by touch, only in certain light and the right angle. Wondering is there anything I can do different to keep this from happening?

I read somewhere that a different gauge of staple may be used, but I could only find 16 gauge. would that make much of a difference? Please help!

If you lower the presure of your compresor , so that the staple does not go to far into the wood , it may prevent this problem . however not to low otherwise the staple will prevent the next board to fit corectly .
Also , did you make sure that this flooring is supposed to be stapled ?

yes, it states it can be stapled. I found out that I need to use an 18 gauge stapler with 1/4" crown and 1 1/2" leg. The 15.5 gauge 2" staples are to thick and is thus causing the finish to rise once set into tongue. You can only notice it if you are carefully looking for it. I am only 7 rows in, do you think it may cause a problem later on? If not, then I will leave it and continue on with the other ones.

The staples are too long for one. 1&1/2" max. Also, that Bostitch stapler, the M111 FS, has a foot/shoe for 1/2" flooring. Are you sure you are using the correct 1/2" shoe? I've stapled down 1/2" with my Bostitch and the 1/2" shoe no problem. You're most likely using too much air pressure, too long of staples and the wrong shoe.

Take a small block of flooring, and place it over the pimple, and smack it with a framing hammer. Then switch to the 18 or 20 gauge staples.

Staple spacing is every 4-6 inches on most engineered.

I laid a whole house of customer supplied 1/2 engineered prefinished from LL.
They recommended the M111 FS as one of the staplers to use. I used the 1/2" shoe and 1&1/2" staples and stapled every 6" or so. It worked very well and secured the flooring great. ZERO damage from the stapler or staples. No squeaks or noises either. It was easy money.