Trigger mods for a Gamo Compact
1. IntroductionThe Gamo Compact is one of the most affordable target pistols around to start you off in the world of precision target shooting with a pneumatic pistol. At the time of writing (December 2005) the Compact can be bought in most gun shops for between 160 and 180 euros. It is a product that has a good balance of quality and price. Of simple but effective construction, it has all the characteristics of a competition pistol. Precision barrel, wooden anatomical grips, recoil free with adjustable sights and a soft trigger (this last bit is debatable).
People say it has numerous defects, the grips cannot be adjusted, the trigger can not be regulated in weight or in distance to the finger, the sights are too simple, small and fragile (they are made of plastic) and even its low weight can be seen as a defect. I don't really consider that these are defects; it’s just that for the low price of the gun, improvements can easily be done by you yourself.
2. Problems with the trigger
According to the maker, the pressure of the trigger is originally 750g and is fixed, it cannot be adjusted. The adjustment screw that it incorporates is really to modify the length of the second stage, not the pressure. The reality is that I have measured in mine a pressure of 1050g and that the adjustment mechanism doesn't work.
This adjustment mechanism problem can be solved easily and it is possible to modify the internal mechanism of the trigger to not only make it lighter, but also be adjustable in pressure. The first thing that it is necessary is to disassemble the gun to see how it works. The whole trigger mechanism is located in the hilt of the weapon, under the wooden grips. Therefore the first thing to do is remove the grips. Be careful with the nuts as they are difficult to replace if lost.
In the right side of the hilt, there is a semi-transparent plastic cover that protects the whole trigger mechanism. Remove the screws (Red arrows)
The following pictures show the gun un-cocked and cocked.
3. Modifying the travel adjustment of the trigger
As shown in the picture, the operation of the trigger is simple: when pressing the trigger, it pushes back the piece A, which then forces B to rotate on its axis. This then unhooks the sear C, which then drops down with D, which then opens the valve allowing the compressed air to escape.
The adjustment screw for the trigger is supposed to press into the angle that is formed between the pieces A and B. By doing this, it limits how far B can move on its axis and also determines at what depth the two sears B and C are ‘hooked’.
The problem with the adjustment system is that the screw is too short and therefore the screw never even touches the sear B. This is difficult to see in the photo, but it is clear in the following outline (The outline is clearer than the actual photo)
This same problem is also found with Gamo rifles, the adjustment screw for the trigger length of travel is too short.
The solution to this problem is simple. Substitute this screw for another 2 or 3 m longer, but to find one of the same thread size with a pointed end will be difficult.
The head of the adjustment screw doesn't stand out of the plastic frame of the gun, but rather it fits in a hole. The trick is to make this hole 2 or 3 millimeters deeper, this way the screw will be able to more make a better contact with the pieces A and B. See diagram.
I recommend that to enlarge the hole, use the appropriate drill, but by hand, without using the electric drill. Since the material is plastic, with a very sharp drill this won't be problem and it allows much finer work.
4. Modification of the trigger pressure
As we have already seen in the previous picture, pressing the trigger moves the piece A that in turn moves the piece B. But this piece B is tethered by a spring, Mb, it is this spring which dictates the pressure on the trigger. Therefore, changing or modifying this spring will alter the necessary pressure to shoot. But this spring pressure cannot be altered to much either way otherwise it will affect the workings of the other components.
To substitute the spring for other softer one is a solution, but it can be difficult to find one of the appropriate characteristics: longitude, diameter, strength, etc. I have read that people have even tried rubber bands to various degrees of success, but the problem with rubber is that it rots, quickly.
The spring is connected at one end to a hole in the sear C and at the other, it is simply wrapped around a plastic post, hence, there is no room for adjustment.
If it were possible to move the plastic post by only a few millimeters, this would allow for adjustment, but it isn’t. The method used here to make an adjustable post is non-reversible so be warned!!
To begin it is necessary to remove the plastic post, and then to drill the frame to insert the new adjustment screw. Then it is necessary to build the new adjustable post where it will hook on to the spring. I have manufactured it from a bar of aluminum of 4x4 mm and rounded off using a file. This piece could also be made from plastic or even steel. The screw used is a 3mm one and the thread in the piece should be the same, although the screw could simply be held by a nut on the inside of the frame, it should look something like this;
A detail. The new adjustment screw should not actually screw into the frame as this will affect the operation of the adjustable post. Make sure the hole through the frame is enough for the screw to slide in nicely.
The whole assembly will be similar to the following picture:
This new system works very well and fine adjustments are easily done.
The only inconvenience is that when modifying the pressure of the trigger, it is necessary to disassemble the wooden grips, since the screw is hidden by them. The grips could be drilled to allow for the head of the screw, but I don't like to make a modification so extreme, it makes it uncomfortable to hold the gun. It is easier to make the indents as seen below.
5. Modification to the weight of the weapon
The Compact is a very light gun. The example used to carry out the modifications weighed 935 g. Other manufacturers models, of high competition standard and of more than 5 times their price, weighed between 75 and 100 g more than the Compact. Therefore, some extra weight won't present any problem and it will improve the behavior of the weapon. The gun will be more stable, better balanced and will improve accuracy.
It seems clear that any problem is due to the fact that no extra weight can be added to the front of the Compact unlike all other target pistols, but there is a way of doing this;
In that rectangular hole it is possible to insert a lead ingot molded to the size and shape as required. I have fused ingots of 10g, 25g, and 50g. Combining them and doing tests, you can arrive at the best weight for you.
To melt lead doesn't have too many problems. A simple iron or aluminium saucepan and the house kitchen are enough. The mold for the ingots can be made using foil. For the lead weight, why not utilize used pellets?, This way I have not had to weigh the lead. A pellet of the caliber .177 weighs 0,5g more or less. This way, 10g = 20 used pellets; IMPORTANT, lead vapours are TOXIC so do this in a well ventilated area.
The lead ingot can be fixed it in the hole with 2 sided tape, or with a little more work, can be screwed in.
6. Conclusions
If all the modifications shown here are carried out, the Compact will improve its behaviour substantially, but it will still be a modestly priced gun, don’t deceive yourself into thinking you now have a top end pistol. What you will have is a gun that is light, easy to use, accurate and most of all, consistent, and well worth the effort spent in modifying it!!
