Here's an article from 60 years ago . . .
With the advent of Steve Reeves a new type of pectoral development was evolved. Note the high, square, flaring pectorals of this great champion.
Every great physique star credits the Bench Press for most of his outstanding pectoral development, yet no matter how much it is praised there are some bodybuilders who get little from it simply because they perform it incorrectly.
Although it is not an intricate exercise, its performance -- together with the variation most suitable for your particular chest structure -- is indispensable for maximum upper body development. The pectorals, like any other muscle or muscle group, must be exercises from a state of extreme extension to one of complete contraction to attain the greatest possible muscle stimulation. This can be done only when an exercise is performed correctly and the muscles worked throughout their entire range.
There are two factors which can prevent full range movement on the bench press:
1) a too-wide exercising bench, and
2) the wrong choice of hand spacing.
The only bench permitting full play of the pectorals is one measuring out more than 14 inches in width. The Weider Adjustable Dual Purpose yada yada . . .
You have a choice of doing the exercise with either barbell or dumbbells. if you seek bulk and exceptional strength the barbell is preferable. If you choose to work for muscle sculpture, contour and chiseled definition of the pectorals, the dumbbells are what you need.
There are various hand spacings which determine just how effectively the bench press will work for you -- and since all of us are structurally different it will pay you to experiment with all of them until you find the one grip that serves you best.
To help in that respect here are some examples of how the stars do the bench press -- which gives them the desired results.
Steve Reeves practices the Dumbbell Bench Press -- in both flat and inclined positions -- solely with one type of hand spacing. He holds the dumbbells very wide apart, made wider still by pulling his elbows well back toward his head until they are at right angles to his body. Bench pressing in this way has helped him develop "square", well defined pectorals which sweep out magnificently from the deltoids at the top to the topmost ridge of his serratus underneath the pectorals. Performed in this manner all the weight and tension is focused on Steve's pectorals and not on the triceps and deltoids.
The same movement can be performed with the barbell, using a collar-to-collar grip but this works best on the type of chest that is very wide and not highly crested, such as the so-called barrel chest. Very heavy weight can be handled in this variation with ease and it builds the "Eiferman" style of pectoral, so named for the popular Mr. America winner, George Eiferman.
If, however, your chest is quite deep and not especially wide, the Reeves variation with dumbbells is what you need. What works for George doesn't work for Steve, and therefore may not work for you.
Heavy dumbbells are difficult to balance at first, but practice will assure you of a correct technique which permits you to handle the heaviest weights with ease. Many physique stars use 130-pound dumbbells in this exercise! i am sure you understand that you MUST use continually heavier weights to further your development. For the most muscular gains I strongly recommend that you do at least 5 sets of 8 repetitions with all the weight you can handle in this exercise.
Leroy Colbert has an incomparable deltoid and arm development -- perhaps the world's finest (his arms measure an astounding 20.5 inches!) -- but for a long time he couldn't get a proportionate pectoral development from practice of the bench press as it is customarily done.
Leroy was confused for a while because every time he did the bench press his frontal deltoids would blow up like melons while his pectorals received little stimulation. At that time Leroy used only the medium grip variation of this exercise. Then one day while coaching some of his young friends at a neighborhood YMCA he was called on to demonstrate the bench press. The only available barbell had a very long bar which was damaged in the area Leroy would normally space his hands. This forced him to grip the bar at a much greater width than he had done before and he was surprised to discover that even in using a lighter weight than he had been handling his pectorals were thoroughly stimulated for the first time.
He had been using a grip too narrow for his type of chest structure which had given him big deltoids and powerful triceps but which had also taken the tension off his pectorals where it should have been. Once he discovered the grip that was more suited to him his pectorals soon grew to the proportions and contour he desired.
So, for maximum pectoral development experiment with various hand spacings and try especially those variations described here. If you feel no pectoral stimulation from a particular hand spacing then give it up and try another. You'll certainly discover the one which gives you good results.
Enjoy Your Lifting!