These pictures were taken over the course of 2 weeks and during different phases of fabrication and assemblage, using two different Super Streak air rifles, both of which were in .22 caliber. Once I had the guns apart, I deburred the receiver tube and thoroughly cleaned it out. Then it was to the shop to get the internal parts modified and a new one made. I ordered J. Maccari seals before I did anything and once they arrived, the fun began. At the shop,
the spring guide rod needed to come out from inside of the Piston Assembly, all the way flush to the backside of the top hat, so that the inner spring guide sleeve could be reused.
Here is the piston assembly minus the internal spring guide rod and before a new seal went on.
Then the back spring guide was cut where the flat part ends and the round part begins. There are two variations of this back spring guide - one has two flat surfaces on opposite sides with one flat surface closer to the stock link pin threaded hole than the other. This flat surface closest to the threaded hole is where you want to cut. When you cut this part, it will expose a hole where the ram rod will go through and where you will seat the new rear ram rod guide. Since there was no longer a spring, this part merely served to attach the stock link pin. A new rear ram rod guide was needed, so I made one:
Using a 1/2" diameter x 2-1/2" long hex bolt, I put it into a heavy duty drill press and turned down the hex head with a file until it fit into the receiver tube end cap,
and then a recess was drilled out the center about 1/16" deep to receive the gas ram's ram rod end.
Here, the modified back spring guide, which I will now call the "stock link pin block" has the rear ram rod guide inserted into it. Notice that I cut the hex bolt to the exact length where it wouldn't interfere with the stock link pin when it is screwed in to hold down the trigger assembly.
Here is the assembled nitro piston with masking tape shimming around the body to fit snugly inside the inner guide sleeve (that used to keep the spring straight when it was compressed). A 3/4" dia. brass washer was also turned down to 47/64" and was installed between the nitro piston body's end and the inner guide sleeve for uniform pressure to the top hat.
Here is the rear ram rod guide sitting perfectly inside the receiver tube's screw-on end cap,
The assembled powerplant with a new Tesla seal, a nitro piston inside the inner sleeve inside the piston assembly, with the ram rod through the stock link pin block and the rear ram rod guide sitting inside the receiver tube rear end cap. Assembly was straightforward: carefully insert the piston assembly without damaging the piston seal; push entire assembly into the receiver tube completely; insert stock link pin block (with the cut side towards the inside) and install the trigger & stock link pin using some blue loctite; then install the rear ram rod guide and receiver tube end cap carefully and tighten it down. Make sure the bear trap lever is properly reinstalled and then reinstall the stock, using blue loctite on the 3 stock screws.
Oh, and if you hadn't already done so, get yourself a GTX trigger from Airguns of Arizona (http://www.airgunsofarizona.com/GTX.htm) and replace the crappy stock trigger before you reinstall the stock.
After all was said and done, the gun was shot through the chronograph. With 14.3 grain pellets, it was averaging 905 fps, and accuracy to 35 yards was much improved with pellets dancing all around a nickel-sized bullseye. All the movements associated with a spring were gone and all you felt and heard was the solid thump of the nitro piston. And as the guns were being shot, points of impact were going up, as I suspect the pellets were shooting faster due to the parts meshing together better.
Needless to say, both of my friends were ecstatic with their much-improved Super Streak rifles, which they used to call The Beast, because of the way it used to shoot. The beasts have now been tamed. Let's see now if they can pick off starlings at 40 yards with their Nitro Piston Super Streaks, like I was doing with my Theoben-upgraded .22 cal. Gamo CFX.
So, there you have it. A complete conversion of a Benjamin Sheridan Super Streak to a Nitro Piston air rifle. I have to give a lot of credit to David Slade of Airgunwerks.com, Tom Gore of VortekProducts.com, James Maccari of AirRifleHeadquarters.com and Steve Woodward, inventor of the GTX trigger, without whom, none of this conversion would have been possible. Thanks, guys.
Disclaimer: I take no responsibility for any injury or death, to anyone who attempts to do what I have done in this conversion or any future conversion that I may post. Anyone following my instructions do so at his/her own risk. Modifying your air gun most likely will void the warranty and the user assumes the risks inherent in any modifications to his/her air gun.