Resealing a Diana Model 14 clone

 

A no-name clone of the pre-WWII Diana Model 14

The airgun above is a clone of the Diana Model 14, which was made from 1913 until 1940.  I call it a "clone" since there is no maker's name stamped anywhere on the gun, nor is there a serial number or date stamp.  Diana 14's have a barrel made from bar stock; this 14-copy has a built-up barrel consisting of a brass tube within a six-sided nickel plated housing.  The two parts appear to be joined with lead at the muzzle, but I will in no way try to find out and damage the gun.

I was also surprised to discover that this gun is 4.4mm (.173 cal) instead of 4.5mm (.177 caliber).  I assume it was intended to fire darts instead of pellets; darts were available in many sizes from 4mm to at least 8mm in the early 20th century.

While my gun was complete, the seals were shot; the breech seal was falling apart and the piston seal was severely undersized and had been damaged by some former, idiot owner shooting brads instead of proper ammo.

Yes, that's a small nail stuck in the piston's leather seal.

Making a new seal
The damaged seal was removed from the piston, and everything cleaned up.  The seal was 19mm in diameter and about 6mm high.  A 1.25-inch square piece of 1.5mm thick leather was cut to form the piston seal.   A small disc the same size as the metal piston washer was also cut to provide enough thickness below the washer.  After a day's soaking in denatured alcohol a hole was punched in each piece.

New seal parts after soaking in denatured alcohol.


Attached to the piston.


A hose clamp was used to force the leather into a round shape.


Rough-formed seal after a day of drying.  It is currently 
too large in diameter.


Trimmed to length.  Sizing is the next step.

Sizing the seal
The new seal is too large by about 2mm and must be sized to be usable.  A sanding drum was locked into a Dremel tool and the lowest speed was selected.  The piston was held on a ratchet handle to allow it to spin freely.  Holding the piston loosely, but still firmly enough for the sandpaper to do its work, it is possible to evenly reduce the seal's outer diameter.  The goal is to get the seal down to the size where it will slide in the compression chamber with just a couple of ounces of force.  It may seem a little loose at that point but the seal must still be oiled which will cause it to swell slightly.


Sanded to size and ready for a soaking in silicone oil.



Top view of the receiver.  In the corner of the shadow inside the tube you can see the countersunk
hole for a short screw to prevent the receiver from moving within the stock.


All of the parts that go into the receiver; the 14-clone is a very simple airgun.


Finally testing!
Since the bore is 4.4mm instead of 4.5mm/.177 caliber I took about 25 shots with some H&N copper plated lead balls.  The muzzle velocity eventually settled around 350FPS / 106MPS ranging from 345FPS to 355FPS.  Muzzle energy is 2.0 FtLbs or 2.7 J.  Not bad considering the small, 19mm bore and the 65mm stroke.

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