Home tuning.
Posted: Fri Jun 12, 2015 7:54 am
Over the last fortnight, I have been very busy with my two Air Arms rifles. My HFT 500 has been the main focus of my concern, seemingly unable to outshoot my Ultimate Sporter. It would group okay for 3 or 4 pellets but had never shot a 10 shot group without at least a couple of flyers. I had also experienced missing targets in HFT competitions and unsure why I missed them, mostly putting it down to user error.
The anti-tampers have been removed on both rifles, so I eventually plucked up the courage to delve deep inside the workings of my HFT 500. My first surprise came when I found that the transfer port o-ring seal was split in two! The next surprise was the amount of black grease clinging to the hammer rail. Obviously, the inside of the hammer was coated in the sticky gunk too! Then finally, when stripping the firing pot, I was very surprised to find that the firing pin wouldn't come out of it's housing within the pot. It had to be teased out. I found a couple of surface tags on the stem, so smoothed them down. Then I cleaned and polished all moving internal parts. On re-assembly, the rifle was shooting over the legal limit, so I had to empty the air cylinder and start all over again. I surmised that all that cleaning and polishing must have got the internals working far more efficiently, so then set out to adjust power output via the firing pot filler/measuring valve. This took quite a few attempts to get right, having to fill and empty the rifle on each occasion which proved to be a bit of a ball ache, but I suppose time, if not patience, is on my side.
Eventually, I settled on a setting that Woki had suggested to me, then fine tuned the power output with the venturi screw. It is now running at a very consistent 770fps and is extremely efficient with the stored air. More importantly though is the fact that my HFT 500 is now grouping exactly how it should. I'm hoping to get to round 2 of the North West Gauntlet at Fort on Sunday, we'll see how it performs on the day.
I found it so easy to work on my HFT 500, I decided to do exactly the same thing with my Ultimate Sporter. Although there was plenty of thick, sticky gunk inside the rifle where it shouldn't have been, the actual finishing of the component parts was much better than my HFT 500. So all this one needed was a good clean and polish. In fact, there was little difference in power output afterwards, so a tweak on the venturi screw was all that was needed.
One thing that did come to light though, was just how fragile the transfer port o-ring seal can be. You have to be very, very careful when re-assembling an Air Arms PCP not to nudge the o-ring out of its very shallow housing. So a message was sent to Neil Price (UK Neil), ordering a number of his upgraded transfer port seal set's. Each set consists of a thin metal washer and an o-ring. The o-ring is positioned around the washer within the transfer port housing, pretty much eliminating the chance of the o-ring moving when re-assembling. Also, the metal washer will then protect the fragile o-ring from the blast of air that travels through the transfer port. Cracking idea and very cheap peace of mind.
My Ultimate Sporter is now shooting incredibly well. Lovely tight groups, even when mag fed. I am so pleased I worked up enough confidence to have a go at tuning my rifles. The result is far more than I ever hoped it would be, plus I have the added benefit of being able to understand my rifles better. The reward of seeing how much my two Air Arms rifles have responded to an internal clean, polish and small upgrade is immeasurable.
Mike.
The anti-tampers have been removed on both rifles, so I eventually plucked up the courage to delve deep inside the workings of my HFT 500. My first surprise came when I found that the transfer port o-ring seal was split in two! The next surprise was the amount of black grease clinging to the hammer rail. Obviously, the inside of the hammer was coated in the sticky gunk too! Then finally, when stripping the firing pot, I was very surprised to find that the firing pin wouldn't come out of it's housing within the pot. It had to be teased out. I found a couple of surface tags on the stem, so smoothed them down. Then I cleaned and polished all moving internal parts. On re-assembly, the rifle was shooting over the legal limit, so I had to empty the air cylinder and start all over again. I surmised that all that cleaning and polishing must have got the internals working far more efficiently, so then set out to adjust power output via the firing pot filler/measuring valve. This took quite a few attempts to get right, having to fill and empty the rifle on each occasion which proved to be a bit of a ball ache, but I suppose time, if not patience, is on my side.
Eventually, I settled on a setting that Woki had suggested to me, then fine tuned the power output with the venturi screw. It is now running at a very consistent 770fps and is extremely efficient with the stored air. More importantly though is the fact that my HFT 500 is now grouping exactly how it should. I'm hoping to get to round 2 of the North West Gauntlet at Fort on Sunday, we'll see how it performs on the day.
I found it so easy to work on my HFT 500, I decided to do exactly the same thing with my Ultimate Sporter. Although there was plenty of thick, sticky gunk inside the rifle where it shouldn't have been, the actual finishing of the component parts was much better than my HFT 500. So all this one needed was a good clean and polish. In fact, there was little difference in power output afterwards, so a tweak on the venturi screw was all that was needed.
One thing that did come to light though, was just how fragile the transfer port o-ring seal can be. You have to be very, very careful when re-assembling an Air Arms PCP not to nudge the o-ring out of its very shallow housing. So a message was sent to Neil Price (UK Neil), ordering a number of his upgraded transfer port seal set's. Each set consists of a thin metal washer and an o-ring. The o-ring is positioned around the washer within the transfer port housing, pretty much eliminating the chance of the o-ring moving when re-assembling. Also, the metal washer will then protect the fragile o-ring from the blast of air that travels through the transfer port. Cracking idea and very cheap peace of mind.
My Ultimate Sporter is now shooting incredibly well. Lovely tight groups, even when mag fed. I am so pleased I worked up enough confidence to have a go at tuning my rifles. The result is far more than I ever hoped it would be, plus I have the added benefit of being able to understand my rifles better. The reward of seeing how much my two Air Arms rifles have responded to an internal clean, polish and small upgrade is immeasurable.
Mike.
