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    If your friends threaten to throw you in the pond because your guns spurt, or laugh at you for coming off the water because your guns jam and then don't fire, this article may help. This article is my method for dialing in the piston in the spring and piston type of interrupter mechanism. The article assumes that you are starting with a new piston that is overly long. Adjustments with an already trimmed piston may not be possible, due to there being insufficient material left. If this is the case try swapping parts between guns as suggested later in the write-up.

    First you need to be able to test fire the gun and then disassemble it to make adjustments. If your final gun arrangement allows the interrupter "T" fitting to be entirely removed from the rest, then go ahead and build the other pieces. If you solder either the magazine or the breach to the interrupter make temporary removable pieces to substitute for them and don't assemble the permanent pieces yet. These temporary pieces are a good thing to have around to test interrupters before assembling the final guns anyway. Once you know that there are no problems with these pieces or the interrupters, any nonfiring problems can be isolated to kinks, misalignment of joints, solder inside the joints, etc. in the final gun assembly.

The requirements for a properly operating interrupter mechanism are:

1. The piston must sit even with or just below the bottom of the "FEED" inlet when at rest.

2. The piston must extend into the "FEED" opening at least 1/2 and preferably 3/4 of the way when pushed from the bottom, with the spring installed.

3. The piston and the inside of the interrupter "T" must not have any burrs or groves that the piston can catch on.

4. The spring must not be so strong that it prevents the piston from moving fully when under pressure, or so weak that it can not return the piston to the retracted position.

5. The spring must exert pressure on the piston for its entire range of movement.

1. If the piston is too long when retracted it can block the feeding of BBs entirely, or you may have to shake the gun to get it to work.

2. If the piston does not have enough throw to reach far enough into the "FEED" area you will get spurts with varying degrees of frequency.

3. If burrs exist, the piston can hang up when either extending or retracting.

4. If the spring is the wrong strength you will get symptoms similar to 1 & 2.

5. If the spring does not exert pressure on the piston for its entire throw the piston may not always retract entirely, creating symptoms similar to 1.

    You need to start with a bored out interrupter brass "T" fitting, the proper spring, a bottom piece to retain the piston, and a "T" shaped piston that is longer than needed. If you do not have or know how to make or assemble these pieces contact another member of the club for help.

    The spring I recommend is a stainless steel spring (no rust problems) part # CC-14 from CENTURY SPRING CO. INC. 1-800-237-5225 (outside CA) or (213) 749-1466 (inside CA). The minimum order from this company is $25, so you may want to order with some friends. This spring is too long as it comes, but will make two springs when modified.

    To modify the spring cut off an a piece 4 (four) coils from the end, counting the end coil which comes back and touches the next coil (see Figure #1). Do the same for the other end. These two ends are the two springs you will use, one for each interrupter you make. Discard the center section. You could make more springs from the center section but the performance of these has been spotty in use.

    Next take the last coil, where you just cut, and bend it out so that it is bigger around than the rest (see Figure #2). This will keep it from getting caught between the piston and the brass "T" during movement. Now stretch the whole spring just a little to increase its (at rest) length. This allows it to exert pressure on the piston at all times.

    Place the spring on your piston with the newly bent end away from the piston base (the original "flat" end on toward the top of the "T" formed by the piston base). Insert the piston into the interrupter and install the base piece. The piston should now be fully retracted and not move any further into the Feed opening when the interrupter is turned upside down (base piece on top). If it does stretch the spring a little more.

    Now mark the piston were it meets the bottom of the Feed opening. If you can not push on the piston to move the piston further into the opening with the base on then remove it. Push on the piston, with the spring in and make sure that the mark moves so that it is past 1/2 or 3/4 mark (I recommend at least 3/4) in the opening. If the piston does not move at least this much the parts are not properly made.

    There are four things that will reduce the throw of the piston, correcting any or all of these will fix the problem.

    The first is that the base fitting pushes the piston to far into the "T", limiting its total throw. There are two ways to fix this: Back off the base piece or grind away the ridge inside the base piece if it is of that type. I prefer to modify the base piece rather than back it off. If the base piece can be screwed down all the way you do not have to disassemble the gun to readjust the pistons retracted position if you need to remove the base for any maintenance. This is really important if you will be soldering the final magazine to the breach.

    The second cause is that the base of the piston is too thick. This can be corrected by thinning the base with sand paper or a file. Do not thin the base down so much that it is overly weakened!

    The third cause could be that the "T" fitting was not bored deep enough. If you decide that this is the case do not deepen it so much that the hole punches through the side of the fitting.

    The fourth cause is of course that the piston is already too short.

    Unless any of the fittings look to be badly out of tolerance and you have more that one gun's worth of pieces, try mixing and matching until you get a good combination for all. If you can not fix them this way, only then will you have to make a few new pieces. It is generally a good idea to have enough pieces for at least one extra gun in case of a really bad piece or a mistake on your part, in any case.

    Before continuing check the inside bore of the "T" fitting. Some times the fitting will shift during manufacturing scoring the walls. Brass has a tendency to "grab" when being worked. This scoring of the inside is fine as far as the manufacturer is concerned as the "T" is designed for transporting fluids and the scoring does not effect this. For our purposes it has a major effect. The only cure for this is to try to smooth the scoring. Failing this solution you have to replace the "T". I recommend you buy several more "T"s than needed before you bore them out. This will allow you to prescreen the parts and make a few extra for future use. The "T"s are fairly cheap and this will prevent many frustrating problems later.

    Now that you have a good set of pieces you can start the tweaking process. Reassemble the interrupter without the spring. Check your previous mark (for the piston Feed opening point) and remark if necessary. Remove the piston and cut at the mark, being sure not to cut too much off. Reassemble and check to see if the piston top is at or below the opening (hopefully it is at or just above). Remove the piston and file or sand the top a little if the piston was too long. Repeat as needed.

    Next remove any burrs caused by the trimming and reassemble the interrupter with the spring installed. Push on the piston base to force the piston into the opening and check that it blocks the opening at least the amount recommended earlier.

    Push the piston in and out repeatedly, checking that it moves smoothly without catching at any point in its travel. If it does check the piston for burrs and the "T" fitting for scouring or ridges.

    Holding the interrupter level push a BB into the feed opening and then tilt the interrupter just enough to start the BB rolling toward the piston. If the BB rolls onto the piston smoothly without hanging up the piston is sitting properly. If not shorten the piston a little more. Also check for lack of scoring in this area of the "T".

    Next is the "acid test". Install your magazine and breach assemblies (no O-ring in the breach). Now test fire the gun. It should give good consistent results. Fire 10 or 12 full loads through the gun to be sure.  If the gun spurts, either the piston is too short, there is a burr, or the spring was stretched out too long. Try a new spring, if this works throw out the old one. If it doesn't the piston is too short or there is a burr. Also make sure the spring is not caught between the piston and the "T". If it is bend it out some more.  If the gun does not feed properly, first try tipping it a bit more to help the BBs roll into the interrupter. If this fails, carefully disassemble the magazine from the interrupter and check to see if the piston is retracted. Turn the interrupter upside down and test fire the gun (without the magazine installed) a few times observing the piston through the feed inlet. It should retract every time. If it fails these tests, either the spring is to short, or there are burrs.

    A no feed condition can also be caused by a kink in the magazine or restrictor feed tube assemblies, so check these. Another possible cause is a misalignment between the magazine and the "T" fitting. The ¼" copper tubing is a somewhat loose fit in the "T". This can allow the end of the magazine to fall below the edge of the internal passageway of the fitting, causing an internal lip to be formed. This lip can then catch the BB preventing it from entering the fitting. To stop this from occurring drill out the magazine feed port of the "T" fitting with the next larger (1/64th) size drill. This should be done before any of the above steps.

    Once your interrupter is working well it should continue to do so for a long time. Good luck, and good hunting!!

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