All were steel. They pretty well had the kinks worked out of the autos by the 7400's and they are excellent rifles.

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The 740, 742, and 760 were aluminium receivers.
740 and 742 were Semi auto, and the 760's were pumps.

The 7400's were steel semi autos.
The 7600's were steel pumps.

The 740's, and 742's were badly over-gassed, and when chambered in 30.06, or.270 they wear out eventually - look for bolt chatter marks in the top guide rail of the receiver - you can shine a light in through the slot for the operating handle and inspect it. I've never seen one wear out in .308.

760's were pumps, and I've never seen one wear out in any caliber.

The 7400's, and 7600's are good modern guns, and don't ever seem to cross my bench worn out in any calibers.