The model 50 was made by Diana from the mid-1950's to about 1983. Its basic layout is similar to a gun the Diana made before WW2, the model 30 military trainer, but is larger and different in detail. It was the top model of the new line that Diana introduced after the war, and remained so for many years.
The model 50 used the same powerplant and trigger assembly as the well-known model 35 barrel-cocking rifle, with the exception of the very last variant. The model 50 T01 was a somewhat longer and more powerful gun based on the original model 45 barrel-cocker.
The 50 went through, in my opinion, two major revisions. The earliest guns had solid forged cocking arms, a solid aluminum trigger blade, and were made in several variants, including one with a full match stock. In the early 60's the model 50 was slightly simplified into a single sporter variant with a Monte Carlo stock and more stamped parts. Finally was the T01 variant as mentioned above.
I really like the model 50, and IMHO it is rather under-rated as a collector's item in the US. They definitely seem to be more highly valued in Europe. It's not a particularly efficient or powerful gun (mid 600's is typical power in .177), but is beautifully made, fun to use, and pretty accurate. Always reminds me of handling an old military bolt-action.
Here is a pair of model 50's dating from the early 1950's. These had upgraded sights and were known as the model 50/a (open sight) and 50/b (receiver sight).
