NOTICE, THIS IS NOT MY WORK, I found it on a website that no longer exists. I have attempted to contact the originator of this piece but to no avail, if it is YOU, please contact me so that I can credit you with the work, thanks
NOTICE, THIS IS NOT MY WORK, I found it on a website that no longer exists. I have attempted to contact the originator of this piece but to no avail, if it is YOU, please contact me so that I can credit you with the work, thanks
GAMO Compact & PR45 Power Mod
Disclaimer! This page contains instructions that are for information only! If you decide to try this yourself, you are completely responsible for the results. If you do not agree with the above statement, please leave my page!
I am on my 2nd GAMO PR45. This pistol is the field version of the Compact, and lacks the adjustable trigger, and target grips. As far as I know, everything else on these pistols are the same. The first one I had had a plastic compression chamber. It was very accurate, but the power left something to be desired. I sent it into to GAMO after shooting it for nearly 10 years, and was sent a new PR45 with a steel chamber! Needless to say I was very pleased with the swap. The new gun shot every bit as accurately as my old one, but still had the long trigger, and low power. I was getting around 300fps from cheap Crosman wadcutters… hardly acceptable. I got the idea for this mod while trying to figure a way to increase the compression inside the chamber.
I call this the Hot Glue Power Mod!
Step 1: Acquire materials
- Gamo PR45 (duh!) or Gamo Compact (same power system).
- Hot glue gun
- Fine (400) grit sandpaper
- Degreaser
- Small torch
- X-Acto or other sharp knife
- Airgun oil or grease ( I use dow33)
- 4” or 6” adjustable wrench
- Phillips screwdriver
I work on a old bath towel to keep everything clean.
The Victim:
Gamo PR45, factory rated at 400 fps (mine must have come from a different factory!) .177 calibre single stroke pneumatic, Sights adjustable for windage and elevation, with width-adjustable rear notch.
Step 2. Disassemble
Remove right grip panel screws, and rear pivot pin. Remove hammer spring, hammer pivot pin, and hammer.
Step 3 Pivot compression tube upwards, drive out pin holding in back block, and slide back block out. Thoroughly clean face of block with plastic-safe degreaser, and clean off any residue with alcohol. Lightly sand the face, and re-clean with alcohol.
Step 4 Glue time! Apply hot glue to the face of the back block, building up to just under 1/8”, leaving a horseshoe shaped area around the valve intake hole.
Step 5 Allow the glue to dry a couple of minutes, until it is no longer tacky, but still a little warm. Lightly oil or grease the inside of the compression chamber, and the face of the piston to keep it from sticking to the glue. Re-assemble the back block, and replace the rear pivot pin. Cock the gun down to seat the piston against the glue (you can hold the valve open to make this easier, let it set for a minute so the glue can take the shape of the piston face, and then disassemble everything again. You will notice the imprint of the piston in the glue, and some excess may have squeezed out towards the air hole.
Step 6: Trim off the excess, retaining the horseshoe shape, and re-heat the trimmed area with a small torch until it is smoothly shaped & melted back into place on the back block.
Step 7: Repeat step 5 and 6 until you are satisfied that the piston is just seating against the glue without binding when the gun is cocked. I also took a large drill bit and , turning it by hand, cut a chamfer into the intake port of the valve to help the flow a bit. Your final product should look similar to this:
Step 8: Reassemble! Don’t forget to make sure everything inside is completely clean, and re-lube the chamber and pivots. You will find the pistol a little harder to cock, but still very manageable. I have around 500 shots through mine since the mod, and have found no ill effects. The power is the same as before, and very consistent.
Results may vary (I have only done my personal gun), but I was very happy to see an increase in velocity of over 100fps. The gun is still deadly accurate. After taking a little off the trigger and sear, buffing and lubing the trigger mechanism, this little pistol has made a very nice target-field plinker. I have not had a chance to shoot any of the GAMO match pellets through it (I’m out!), but I hope to see even better results, as the GAMO match seems to be the pellet of choice for my pistol.
Have fun! And above all, shoot responsible and safely.
