gamo g-magnum 1250 IGT MACH 1 transfer port size
- Thread starter wildscorpion
- Start date
Hi. Old post but still relevant today. Have you sorted your problem? I got reduced rifle myself. I have measured ~21 Joules average. I have drilled the port to 3.8mm and got increase in power to 31 joules. I think i need to drill further but it will probably max out at 36J. I read somewhere that G-magnum .144 is 45J and .22 is 36J. Could you give us update on your experience?
Thanks
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Hi,
I do have the original G-Magnum Mach 1 1250 IGT air rifle that i did order from Spain during Covid (ordered from Belgium), it is limited to 24J (it is written on the barrel).
The original port size is less than 2mm because a drill bit of 2mm can't get in.
I did drill the hole to 3,5 mm.
Here is the results m/s before and after (3 shots tests) :
Before (less than 2mm air port) :
Gamo magnum energy 0,49 grams : 270, 277, 272 m/s (about 17,8 J)
H&N Baracuda match 0,69 grams : 237, 238 m/s (one missing). (about 19,3 J)
Solognac 500H 0,75 grams : 220, 219, 218 m/s (about 18 J)
After (drilled 3,5 mm air port) :
Gamo magnum energy 0,49 grams : 337, 345, 345 m/s (about 27 - 29,3 J)
H&N Baracuda match 0,69 grams : 269, 271, 268 m/s (about 25J)
Solognac 500H 0,75 grams : 262, 257, 259 m/s (about 25,8J)
I did not dismantle the gun completely to see the piston ref number.
I do have the original G-Magnum Mach 1 1250 IGT air rifle that i did order from Spain during Covid (ordered from Belgium), it is limited to 24J (it is written on the barrel).
The original port size is less than 2mm because a drill bit of 2mm can't get in.
I did drill the hole to 3,5 mm.
Here is the results m/s before and after (3 shots tests) :
Before (less than 2mm air port) :
Gamo magnum energy 0,49 grams : 270, 277, 272 m/s (about 17,8 J)
H&N Baracuda match 0,69 grams : 237, 238 m/s (one missing). (about 19,3 J)
Solognac 500H 0,75 grams : 220, 219, 218 m/s (about 18 J)
After (drilled 3,5 mm air port) :
Gamo magnum energy 0,49 grams : 337, 345, 345 m/s (about 27 - 29,3 J)
H&N Baracuda match 0,69 grams : 269, 271, 268 m/s (about 25J)
Solognac 500H 0,75 grams : 262, 257, 259 m/s (about 25,8J)
I did not dismantle the gun completely to see the piston ref number.
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I update information during my tests and the maximum power is achieved in the Magnum models with 40460 spring and with IGT 80Kg/160 atm:
Gamo Jungle cal 5.5 with spring Ref. 40460: Drill Port Size 3,2 mm. Max power 33,8 to 36 Joules. - 260 - 268 m/s Pellet 1g. (15,43 grains) occasionally I have reached speed 272 m/s - 37 Joules
Gamo Socom 1250 Mach1 cal 5.5 with IGT 80kg/160 Atm Ref 36040: Drill Port Size 3 mm. Max power 28 to 29,5 Joules - 240 - 245 m/s. Pellet 1g. (15,43 grains) occasionally I have reached 251 m/s - 31,5 Joules
This is the optimal size port transfer for these configurations to find optimal balance. It is about achieving the optimal flight speed of the cal 5.5 - 1g (15,43 grains) pellet between ideal range min. 230 m/s - 26,5 joules - max. 280 m/s - 39 joules, for good precision and shooting tension straight path.
If we put the IGT Ref. 40450 FAC only for models SuperMagnum we can open the transfer port up max drill to 3.7 mm for cal 5.5 to have an optimal balance at high power and achieve 45 Joules. My recommendation for maximum power IGT 40450 and having a minimum of balance is to drill open the transfer port max 3.5mm and opt for max 40 joules to minimize piston gas shock stopped. The Supermarnum IGT 40450 configuration cal. 4.5 optimal open transfer port is 3.2mm for 45 Joules, transfer port 3,5mm in cal 5.5 for 45 Joules and cal. 6.35 transfer port 3.8 to 45 Joules.
Models Match1 not Supermagnum camera 33mm camera short, with installed IGT Ref. 36040 (model 29 joules) the optimal size transfer port: cal. 4,5 - 2,8 to max 3mm / cal 5,5 - 3 to max 3,2mm / cal 6,35 - 3,2 to max 3,5mm
Models Supermagnum 1250 camera 33mm but 5 cm extra long camera, with installed IGT Ref. 40450 FAC (model 45 joules) only for Supermagnum rifles, size transfer port: cal. 4.5 - 3 to max 3,2mm / cal 5.5 - 3,2 to max 3,5mm / cal 6.35 - 3,5 to max 3,8mm
Example: Gamo Black Knight and Gamo G-Magnum 1250 not indenticals, The camera is 5 cm long G-Magnum from Knight, and identical 33mm diameter camera two models, but G Magnum is 5 cm long cilinder camera.
Gamo Jungle cal 5.5 with spring Ref. 40460: Drill Port Size 3,2 mm. Max power 33,8 to 36 Joules. - 260 - 268 m/s Pellet 1g. (15,43 grains) occasionally I have reached speed 272 m/s - 37 Joules
Gamo Socom 1250 Mach1 cal 5.5 with IGT 80kg/160 Atm Ref 36040: Drill Port Size 3 mm. Max power 28 to 29,5 Joules - 240 - 245 m/s. Pellet 1g. (15,43 grains) occasionally I have reached 251 m/s - 31,5 Joules
This is the optimal size port transfer for these configurations to find optimal balance. It is about achieving the optimal flight speed of the cal 5.5 - 1g (15,43 grains) pellet between ideal range min. 230 m/s - 26,5 joules - max. 280 m/s - 39 joules, for good precision and shooting tension straight path.
If we put the IGT Ref. 40450 FAC only for models SuperMagnum we can open the transfer port up max drill to 3.7 mm for cal 5.5 to have an optimal balance at high power and achieve 45 Joules. My recommendation for maximum power IGT 40450 and having a minimum of balance is to drill open the transfer port max 3.5mm and opt for max 40 joules to minimize piston gas shock stopped. The Supermarnum IGT 40450 configuration cal. 4.5 optimal open transfer port is 3.2mm for 45 Joules, transfer port 3,5mm in cal 5.5 for 45 Joules and cal. 6.35 transfer port 3.8 to 45 Joules.
Models Match1 not Supermagnum camera 33mm camera short, with installed IGT Ref. 36040 (model 29 joules) the optimal size transfer port: cal. 4,5 - 2,8 to max 3mm / cal 5,5 - 3 to max 3,2mm / cal 6,35 - 3,2 to max 3,5mm
Models Supermagnum 1250 camera 33mm but 5 cm extra long camera, with installed IGT Ref. 40450 FAC (model 45 joules) only for Supermagnum rifles, size transfer port: cal. 4.5 - 3 to max 3,2mm / cal 5.5 - 3,2 to max 3,5mm / cal 6.35 - 3,5 to max 3,8mm
Example: Gamo Black Knight and Gamo G-Magnum 1250 not indenticals, The camera is 5 cm long G-Magnum from Knight, and identical 33mm diameter camera two models, but G Magnum is 5 cm long cilinder camera.
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Recently upgraded a 1250 IGT in 5.5mm (22 cal). Found it in America, and surprisingly had a choked port. There were no markings on the barrel anywhere that indicated it was a Spanish model, or limited in power. I gutted it out, and confirmed that it had a 40450 ram in it. Here's what I measured before and after.
Before - using a drill bit, I measured the port as being just a smidge below 2mm. I didn't have a bit small enough, but I was almost able to get a 1.9mm bit in there. Pellets: H&N Baracuda Hunter Extreme 5.5mm 1.6g pellets.
---------------
After - using a 3.19mm drill bit, opening the port (after disassembly, cleaning, and reassembly). Same air ram. Pellets: H&N Baracuda Hunter Extreme 5.5mm 1.6g pellets.
Then as an additional test I used a different pellet: H&N Sport Terminator, 5.5mm 1.06g (much lighter). Averaged using 5-shot groups at 253 m/s, and 33.43j
---------------
Last note about accuracy. Shooting 20m wind-free range, I do believe the rifle was more accurate before the modification. It might be in my head, or me just shooting bad. But using 5-shot groups, I went from a quarter sized group to a 50-cent piece, or bigger. Admittedly, my normal pellet rig is a PCP Daystate, so the Gamo trigger feels like I'm pulling up a boat anchor! All said, the 3.2mm port did indeed open up the power and has negligible impact on the accuracy.
Before - using a drill bit, I measured the port as being just a smidge below 2mm. I didn't have a bit small enough, but I was almost able to get a 1.9mm bit in there. Pellets: H&N Baracuda Hunter Extreme 5.5mm 1.6g pellets.
- 177 m/s
- 179 m/s
- 181 m/s
- 177 m/s
---------------
After - using a 3.19mm drill bit, opening the port (after disassembly, cleaning, and reassembly). Same air ram. Pellets: H&N Baracuda Hunter Extreme 5.5mm 1.6g pellets.
- 239 m/s
- 228 m/s
- 215 m/s
- 225 m/s
Then as an additional test I used a different pellet: H&N Sport Terminator, 5.5mm 1.06g (much lighter). Averaged using 5-shot groups at 253 m/s, and 33.43j
---------------
Last note about accuracy. Shooting 20m wind-free range, I do believe the rifle was more accurate before the modification. It might be in my head, or me just shooting bad. But using 5-shot groups, I went from a quarter sized group to a 50-cent piece, or bigger. Admittedly, my normal pellet rig is a PCP Daystate, so the Gamo trigger feels like I'm pulling up a boat anchor! All said, the 3.2mm port did indeed open up the power and has negligible impact on the accuracy.
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The OP last visited AGN 2½ years ago.
My Gamo Magnum delivers 30 - 32 joules out of the box, depending on the pellet used. I changed the trigger set screw and now the trigger pull is 450 gram / 16oz which help a lot with accuracy.
Break barrel / springer / gas ram rifles deliver their maximum power at sea level and less at higher altitudes, about in proportion to the difference in atmospheric pressure. I am at 800m above sea level. 2600 feet.
Also, lighter pellets generally delivers more muzzle energy than heavier pellets, the opposite of a pcp.
My Gamo Magnum delivers 30 - 32 joules out of the box, depending on the pellet used. I changed the trigger set screw and now the trigger pull is 450 gram / 16oz which help a lot with accuracy.
Break barrel / springer / gas ram rifles deliver their maximum power at sea level and less at higher altitudes, about in proportion to the difference in atmospheric pressure. I am at 800m above sea level. 2600 feet.
Also, lighter pellets generally delivers more muzzle energy than heavier pellets, the opposite of a pcp.
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