The purpose of this post is to share my experience tuning the .25 compact. If you are a newbie to PCP air rifles, as I am, than I hope I can shed some light on what you will need to accomplish this basic tune. I was surprised to find the new AMP Regulator in my .25 Compact which I received on 12/14/2018. There was no information, what so ever, from FX that I had it installed or how to use it. This required my having to return my original Huma Regulator to AoA and reorder directly from Huma. Switching out the regulators is pretty straight forward. Remove the air cylinder, of course after depressurization and loosening the 4 retention nuts, which unscrews quite easily. I removed both cylinder caps, you should have Two (2) 3 mm steel dowel pins to remove rear cylinder cap, and I used a Phillips screw driver to remove the fill port cap. I than used a 1/2" x 18" piece of PVC pipe to push the AMP Regulator out of the air cylinder. I also ran a micro fiber cloth through the cylinder to make sure it was nice and clean. I than installed the Huma Regulator. I lined the regulator vent hole with right side of the cylinders vent port. There are two holes drilled into the air cylinder with the AMP Regulator. One port is for the regulator adjustment access and the other port is for venting. The right side port is for venting the regulator and is covered by the stock. There is a little rubber ball that fits into the adjustment port on the left side of the cylinder. It's purpose is to cover the hole and make it more aesthetically pleasing. Reassemble and make sure you check that your piston is properly positioned which is 28.55 mm from the back plate. I must say, before I received the Huma Regulator, I started to experiment with the AMP Regulator and had it firing at 917 fp/s with a low of 904 f/ps and I believe I was right around 24 shots or 3 mags. At any rate, they were scooting along pretty good. Some of you, with the AMP Regulator may find adding another regulator is unnecessary. I will take my rifle out tomorrow and make the fine tuning adjustments to the Huma. Guess I'll find out if this tune was worth it or not. At least, my HS adjuster did not have loctite applied which is sweet. So, we shall see.
Perhaps the most annoying modification is replacing the FX Manometer. If you purchase a Wika Manometer, it does not come with a o-ring. The Huma Regulator does come with a o-ring. Hubb at Huma Air advised me they use 2 different size o-rings, 3x3 mm and 4x2.5 mm. I purchased the 3x3 mm o-rings from McMaster Carr. They are very efficient and pretty much have every o-ring you can imagine. I had the same issue others have mentioned which is a slow leak when the manometer is perfectly aligned with the air cylinder. I gave it another 1/2 turn and it seems to be holding well. However, my gauge now has the Wika label upside down. I have ordered the the 4x2.5 to see if this o-ring does better. When using Huma or Wika gauges it is recommended to use o-rings. To do so it is suggested you should remove the 4 mm bushing that FX uses. It is not easy to get out. I had to insert a screw and pull it out. This action pretty much makes the bushing unusable IMO. When using the o-rings do not torque them down with a wrench. Hand tighten is fine. If you keep the plastic bushing in place you will need to torque it down. To remove the FX Manometer you will need a 11 mm thin wrench. The 1st wrench, adjustable, I purchased was a little to big and as a result damaged the FX gauge. I have since purchased a Capri Tools 10 mm x 11 mm thin open wrench from Amazon for $7.19 fits perfectly. The reason for replacing the FX gauge with a Huma or Wika manometer is that they are more accurate and you can use more air pressure. Not sure about going 300 Bar however I am at 260 Bar at this time and no leaks. I also had to order a new dust cap, part # 19544, for the gauge and fill port. The new dust port on the compact .25 has a flange which hits the gauge precluding it from seating correctly. You can grind this flange down or do as I did and order the old dustcover without the flange. I also ordered a new FX manometer and Three 4 mm bushings. Now, If I decide to,I can return my rifle to it's original OEM condition.
So to close this out, If one is inclined to complete this modification, you should have the appropriate knowledge, parts and tools. The knowledge is available on this forum as well as various instruction videos. If you don't have the correct parts, such as o-rings, you will have to stop and wait until they are ordered and shipped. Waiting is such a bummer when you are in the middle of a project. And, you need the appropriate tools in order to get top notch results. Minimally you should have a rifle vise, hex wrenches, standard wrench sizes, metric wrenches ( thin preferably), an o-ring removal set, a fine pick set, a electronic caliper, plastic see through storage containers, o-ring lube, silicone grease and chronograph just to name a few. Most importantly keep your work area neat and organized. If you drop, misplace or loose something, it can take time to find a replacement part. In the wonderful world of air rifles, finding a replacement part seems to be a deep dark secret. Clearly, the manufacturer wants you to buy parts from them. No wonder, a $3.00 bag of o-rings for $40.00. Any who, I am a newbie who likes to tinker. I find it a great way to spend a winters day while preparing for the spring hunt. And, being a "Professional Man Of Leisure" having fun is an area I am very familiar with. I Hope I have shed some light for those taking their 1st plunge into this addictive past time.
Regards,
Nick
Perhaps the most annoying modification is replacing the FX Manometer. If you purchase a Wika Manometer, it does not come with a o-ring. The Huma Regulator does come with a o-ring. Hubb at Huma Air advised me they use 2 different size o-rings, 3x3 mm and 4x2.5 mm. I purchased the 3x3 mm o-rings from McMaster Carr. They are very efficient and pretty much have every o-ring you can imagine. I had the same issue others have mentioned which is a slow leak when the manometer is perfectly aligned with the air cylinder. I gave it another 1/2 turn and it seems to be holding well. However, my gauge now has the Wika label upside down. I have ordered the the 4x2.5 to see if this o-ring does better. When using Huma or Wika gauges it is recommended to use o-rings. To do so it is suggested you should remove the 4 mm bushing that FX uses. It is not easy to get out. I had to insert a screw and pull it out. This action pretty much makes the bushing unusable IMO. When using the o-rings do not torque them down with a wrench. Hand tighten is fine. If you keep the plastic bushing in place you will need to torque it down. To remove the FX Manometer you will need a 11 mm thin wrench. The 1st wrench, adjustable, I purchased was a little to big and as a result damaged the FX gauge. I have since purchased a Capri Tools 10 mm x 11 mm thin open wrench from Amazon for $7.19 fits perfectly. The reason for replacing the FX gauge with a Huma or Wika manometer is that they are more accurate and you can use more air pressure. Not sure about going 300 Bar however I am at 260 Bar at this time and no leaks. I also had to order a new dust cap, part # 19544, for the gauge and fill port. The new dust port on the compact .25 has a flange which hits the gauge precluding it from seating correctly. You can grind this flange down or do as I did and order the old dustcover without the flange. I also ordered a new FX manometer and Three 4 mm bushings. Now, If I decide to,I can return my rifle to it's original OEM condition.
So to close this out, If one is inclined to complete this modification, you should have the appropriate knowledge, parts and tools. The knowledge is available on this forum as well as various instruction videos. If you don't have the correct parts, such as o-rings, you will have to stop and wait until they are ordered and shipped. Waiting is such a bummer when you are in the middle of a project. And, you need the appropriate tools in order to get top notch results. Minimally you should have a rifle vise, hex wrenches, standard wrench sizes, metric wrenches ( thin preferably), an o-ring removal set, a fine pick set, a electronic caliper, plastic see through storage containers, o-ring lube, silicone grease and chronograph just to name a few. Most importantly keep your work area neat and organized. If you drop, misplace or loose something, it can take time to find a replacement part. In the wonderful world of air rifles, finding a replacement part seems to be a deep dark secret. Clearly, the manufacturer wants you to buy parts from them. No wonder, a $3.00 bag of o-rings for $40.00. Any who, I am a newbie who likes to tinker. I find it a great way to spend a winters day while preparing for the spring hunt. And, being a "Professional Man Of Leisure" having fun is an area I am very familiar with. I Hope I have shed some light for those taking their 1st plunge into this addictive past time.
Regards,
Nick
