Hi Ped
The first Crosman I bought was a new 1377 in January 1979 which came with a steel breech and I remember that they changed to a plastic breech the next month --- this pistol cost £20 new complete with shoulder stock and peep sight plate.
I'll have to dig my 13xxs out and have a look at them, I have quite a few ranging from 1978 up to @ 2008, my favourite being a 1322 from 1978 having steel rear sight, steel piston and steel breech.
I'll see if I can find the Crosman article I wrote for Jim, unfortunately after my first RAS article was published the magazine only ran for a couple more months before folding.
Hopefully the Crosman article got transferred onto my new computer off the old one so I'll see if I can find it over the weekend.
All the best Mick