I'm working on a Revell (DML rebox) Pz IIIJ kit. Well, I messed up the L/60 barrel in the kit, so I bit the bullet and bought my first Jordi Rubio barrel. My measurements were made with a ruler, and comparison to the 1/35 scale drawings in the Schiffer Pz III and its Variants book. I'm not sure how accurate these drawings are. They date from the 70s and may be superceded by something more recent (in a book I don't own yet!). The gun barrel in the DML/Revell kit is too short, as detailed in many reviews. The kit barrel is about 7mm shorter than in the diagrams according to my measurements. So it needs replacement to be accurate. Unfortunately, the Rubio barrel is about 4mm too long!! The diameter of the barrel matches the drawings, but not the length from muzzle to recuperator housing!
I guess this makes it less bad than the kit version...To use this barrel with the DML kit requires a small amount of surgery. The kit supplied barrel is just the gun tube visible outside the vehicle and is made to be glued onto the 'recoil cylinder'*. The latter is molded to the front of the recuperator housing which is glued to the external mantlet. It's pretty easy to hack off the ‘recoil cylinder’, and this leaves a hole in the recuperator housing. The barrel you get is well machined, with a nice looking taper as the barrel meets the 'recoil cylinder thingy'. There is a smaller diameter peg at the breech end of the JR barrel. This peg fits perfectly into the hole left after surgery to the plastic parts. I superglued the barrel in place.
It certainly looks good, but maybe too long! Much longer than the kit part, and when I glued the parts together my wife exclaimed that "it looks a little big for that little thing!". She meant that the turret seemed too small for that long a gun barrel. Test fitting the turret to the kit reduces that impression. I can see why these were called Mark III 'Specials", given the length of the gun barrel, and perhaps JR have supplied me with a ‘super-Special’.
All in all, I think this part is an improvement on the kit part. That's good. The bad part is that it appears too long. Sigh... I matched up other parts in both the Tamiya Pz IIIL and DML Pz IIIJ to the drawings in the Spielberger book. The parts from both kits are very close in size to those in the diagrams. So either the barrel is too long, or the barrel in the diagram is wrong. I think this barrel would be a real bear to use with the Tamiya kit, given the way you get a complete gun tube in that kit to insert through the recuperator housing and recoil cylinder. I'm not sure what surgery would be required, and I have not assembled the Tamiya kit to do the measurements needed to see if the JR barrel is any improvement on the kit part.
In sum, you get a nicely machined barrel in the JR package that does not fit the main Pz III kits available. The barrel is also too long. Why does it get 3 stars then? Because it looks good, and is nicer than the DML kit part. For my next DML Pz III kit I'll try some other company's offering.
*recoil cylinder - my name for the cylindrical metal piece that is fixed to the recuperator housing on the mantlet. The gun tube/barrel itself is free to move within that cylinder in real life. I'd love to know what this thing is supposed to be called!