The weather being quite lovely today, I took a few more shots comparing details of the three full-stock 27's. In these photos the 1930's DRP gun has the pale walnut finger-groove stock, the 1950's gun the dark beech finger-groove wood, and the 1981 RWS 27 the dark stock with plain fore end.
The shot above illustrates the overall major parts of each gun. Again, it appears the receiver tube is actually identical on the DRP and 50's rifles, but significantly revised on the newest example. I think this re-design was part of the overall simplification of the Diana line that seems to have happened around 1964.
This view also shows one of my favorite details of the 27--the artful design of the breech area. Viewed from the front, the top and bottom of the breech block are curved--visually a flat-sided extension of the receiver tube. When viewed from the side, the breech block and cocking link blend into a single elegant curve that mirrors the front of the fore end wood. (People often ooh and ahh over the older Weihrauchs with the stock extended to cover the breech block...I say Diana had a better idea: don't make the breech ugly to begin with!)
Above is a close-up of the breech area. Note the elegant little cut-away on top of the breech jaws on the DRP and 50's guns--missing on the RWS. Also note that the main pivot bolt and its keeper screw are identical on the two older guns, ditto the cocking link pivot screw and keeper. All are significantly revised on the RWS. The stamped cocking link itself, however, is identical between the two newer rifles, replacing the heavy pre-war milled piece. The breech block is somewhat longer and differently shaped on the newer guns than on the DRP example.
A shot of the open breeches. Once again the 1950's rifle is more like the pre-war example than the newer one, with a leather breech seal and wedge detent. The late RWS gun has a greatly revised rubber O-ring seal and ball-bearing detent.
Above is a most interesting shot. Note carefully the position of the pin through the rear receiver--visible just above the wood, in front of the rear cap. It's identical on all three guns! This is interesting because the DRP gun has a totally different trigger design (note the blade is much further forward and lower than the postwar rifles). The bulge is the rear cap is an indicator of the postwar ball-sear trigger. (The trigger in the DRP gun is fantastic by the way. Like many current match guns, it can be set and dry-fired without cocking the gun, perfectly duplicating the pull when actually firing.)
Diana may have started production of their revised post-war guns with a large stock of pre-war parts; the new 27's ball-sear trigger was obviously engineered to use the pre-war crosspin location. This goes a long way toward explaining the trigger blade position of the modern 27, which, as often noted, is oddly close to the grip.
Another detail of the triggers. The blade on the DRP rifle is case-hardened steel--note the tiny adjuster screws, one of them in the front shoulder of the blade, which require removing the stock to access. The 50's gun has a very nicely-finished solid aluminum blade with a ribbed face, with two adjuster screws accessible through the trigger guard. The modern 27 has the same arrangement, but with a re-shaped stamped steel blade and smaller protruding adjuster screws.
Finally a shot of the butts. The DRP rifle has a rather odd "upside down" shape, wider at the bottom than the top. The 50's gun duplicates this look fairly closely, albeit in a parallel, flat-sided (no doubt machine-cut) stock. The modern rifle is a rather more graceful shape with the distinctive red rubber non-slip button.
I have to say the recent acquistion of the 1950's gun has really been quite educational. This gun has a much closer affinity to the pre-war model 27 than I had ever realized, and the mid-60's re-work of the 27 was also more wide-reaching than I had thought.