This is long but seemed to fit this posts discussion. It's not meant as a how-to but simply what I do and if you're considering doing a break barrel reseal, might be of interest.
I got into airguns over a decade ago and the majority of the guns I've owned have been spring/ram powered. The first two were Chinese clones of the TX200 (B40) and the R9 (B320). The B40 was too heavy for me considering how I use my airguns and is the only lever cocking rifle I've owned. Both of these had issues that required work and modification. What I know today about tuning break barrel airguns started with those two rifles and I've been inside every break barrel I've owned (R9 and multiple siblings using the same basic power plant, R1, HW30, BSA Lightning XL, and a couple older Haenels). My all time favorite is the R9 platform in 177 and I have several. I feel the R9 power plant is ideal in 177 generating speeds in the upper 800s and at times lower 900s at approx 3000 feet pending on the pellet used. I use a spring compressor on every break barrel gun I work on.
What I do to these guns is as follows:
1. open them up and remove all components and notice how the piston seal fits the tube
2. clean up the air tube and piston/seal with alcohol - wipe the lubes off the remaining components
2a. inspect the seal for damage and if replacing it, remove and set aside
2b. measure the spring wire diameter (if used) and count the coils. The wire diameter x the coil count will give you a close estimate of the compressed size.
3. debur the inside edges of any opening in the air tube (holes, slots, etc) which can damage the seal as it's installed
4. I like to cross hatch the air tube using a finer grade of sandpaper (not shinny and not too course) allowing a lite skim amount of lube to stay in place
If replacing the piston seal:
A proper fit of the seal to the air tube is critical. Too tight or loose can affect the speed and too loose will make the shot cycle harsher than needed. If it's too large you can reduce the diameter using sandpaper ideally while it is being turned by some sort of tool. If the seal has a wiper section (not on the leading edge) determine if that is the spot that needs reduction. Use calipers and test fit frequently. I like a seal to have some resistance and prefer about 3-5lbs of effort to push the seal and piston in the tube where it will be used. I've seen the tube tighter at the rear than the front so don't use that section to test fit. I used a food scale to determine the amount of effort needed after I used trial and error to get what I think is a good fit. If the transfer port is plugged and the piston is in the working zone it should stop movement of the piston.
I've also found the seal design can make a difference in speed. A parachute design is better suited to an air tube that has variations in the inside diameter.
Mod the transfer port?
I've seen discussions on changing the transfer port diameter and have not done it to any of my guns. I did recall seeing discussion on this matter and did a Google search for " change port size of spring powered rifle " which brought up many posts on the subject.
Piston buttons:
I like to use ARH buttons on the rear of a piston. Properly placed they keep the rear of the metal piston from rubbing on the compression tube itself. I use a good quality brand of super glue to keep them in place and take care about cleaning the area they are to be placed. I have had to sand the buttons down to fit the tube and keep in mind - many of the tubes I've seen vary on inside diameter at the rear. If proerly placed and sized, the cocking seems smoother. They are not needed but they have became part of my routine when resealing a break barrel. I've only seen one come off and that was when I used a cheaper glue.
If replacing a spring:
Of course using a spring that will generate the power desired is the goal. I typically aim at getting as much power as I can given the space available and have found the R9/HW95 platform in 177 can generate speed close to 900fps with medium weight pellets at approx 3000' elevation.
I dislike a spring powered gun that has a lot of twang and/or buzz. I often make a delrin spring guide and top hat that fits the inside diameter snuggly. The spring will expand during compression and if the guide doesn't fit properly you get the twang/buzz to some degree. If a fit is too tight, the shot cycle will be affected (speed and consistency). I like a solid "thump" type sound from a shot cycle.
If the spring is too short spacers can be used to generate more power in most cases but if too long (with/without spacers), you get coil bind and will not be able to cock the gun. I can't count the times I've had this occur while trying to find the maximum compressed length.
A spring has a tendancy to twist as its compressed so I polish the spring ends plus I like to add 'smooth' metal washers if I feel the spring will not twist smoothly.
Spring kits:
I've never used a spring kit since I buy/make components needed. Some spring 'kits' use a sleeve around the spring itself but I have never used one so can't say anything about their use.
If replacing a ram/strut:
Not a lot you can do to a gas ram unless it's designed to have internal pressure changed. I don't have much experience with this type of power plant so can't say much about it.
Lubes used:
I've used lube from ARH (AirRifleHeadquarters) most of the time but recently started looking at synthetic lubes. I haven't used them yet but based on what I've seen on the forums, they are worth consideration.
Using moly from ARH, I very lightly coat the working area of the air tube (enough to say it's not bare metal), then apply a small amount to the piston seal behind the leading edge and if buttons are used on the rear of the piston I cover them. I also lube the spring guide with moly.
I like to use ARH tar on the spring OD but not too much. It's quite sticky and moly may be just as good if the guide fits properly.
Lube Tune (what I got in a purchase))??
Many years ago I bought a RS2 off of gunbroker and when I recieved it, I found the spring area completely filled with what looked like the grease one puts into a grease gun. The seller obviously didn't like the twang/buzz (LOL).
I've seen posts on this and never tried it since I do the full routine.
Summary:
I find it's rewarding to do your own tune and if any of this helps others looking at trying to upgrade their guns -- good.
I got into airguns over a decade ago and the majority of the guns I've owned have been spring/ram powered. The first two were Chinese clones of the TX200 (B40) and the R9 (B320). The B40 was too heavy for me considering how I use my airguns and is the only lever cocking rifle I've owned. Both of these had issues that required work and modification. What I know today about tuning break barrel airguns started with those two rifles and I've been inside every break barrel I've owned (R9 and multiple siblings using the same basic power plant, R1, HW30, BSA Lightning XL, and a couple older Haenels). My all time favorite is the R9 platform in 177 and I have several. I feel the R9 power plant is ideal in 177 generating speeds in the upper 800s and at times lower 900s at approx 3000 feet pending on the pellet used. I use a spring compressor on every break barrel gun I work on.
What I do to these guns is as follows:
1. open them up and remove all components and notice how the piston seal fits the tube
2. clean up the air tube and piston/seal with alcohol - wipe the lubes off the remaining components
2a. inspect the seal for damage and if replacing it, remove and set aside
2b. measure the spring wire diameter (if used) and count the coils. The wire diameter x the coil count will give you a close estimate of the compressed size.
3. debur the inside edges of any opening in the air tube (holes, slots, etc) which can damage the seal as it's installed
4. I like to cross hatch the air tube using a finer grade of sandpaper (not shinny and not too course) allowing a lite skim amount of lube to stay in place
If replacing the piston seal:
A proper fit of the seal to the air tube is critical. Too tight or loose can affect the speed and too loose will make the shot cycle harsher than needed. If it's too large you can reduce the diameter using sandpaper ideally while it is being turned by some sort of tool. If the seal has a wiper section (not on the leading edge) determine if that is the spot that needs reduction. Use calipers and test fit frequently. I like a seal to have some resistance and prefer about 3-5lbs of effort to push the seal and piston in the tube where it will be used. I've seen the tube tighter at the rear than the front so don't use that section to test fit. I used a food scale to determine the amount of effort needed after I used trial and error to get what I think is a good fit. If the transfer port is plugged and the piston is in the working zone it should stop movement of the piston.
I've also found the seal design can make a difference in speed. A parachute design is better suited to an air tube that has variations in the inside diameter.
Mod the transfer port?
I've seen discussions on changing the transfer port diameter and have not done it to any of my guns. I did recall seeing discussion on this matter and did a Google search for " change port size of spring powered rifle " which brought up many posts on the subject.
Piston buttons:
I like to use ARH buttons on the rear of a piston. Properly placed they keep the rear of the metal piston from rubbing on the compression tube itself. I use a good quality brand of super glue to keep them in place and take care about cleaning the area they are to be placed. I have had to sand the buttons down to fit the tube and keep in mind - many of the tubes I've seen vary on inside diameter at the rear. If proerly placed and sized, the cocking seems smoother. They are not needed but they have became part of my routine when resealing a break barrel. I've only seen one come off and that was when I used a cheaper glue.
If replacing a spring:
Of course using a spring that will generate the power desired is the goal. I typically aim at getting as much power as I can given the space available and have found the R9/HW95 platform in 177 can generate speed close to 900fps with medium weight pellets at approx 3000' elevation.
I dislike a spring powered gun that has a lot of twang and/or buzz. I often make a delrin spring guide and top hat that fits the inside diameter snuggly. The spring will expand during compression and if the guide doesn't fit properly you get the twang/buzz to some degree. If a fit is too tight, the shot cycle will be affected (speed and consistency). I like a solid "thump" type sound from a shot cycle.
If the spring is too short spacers can be used to generate more power in most cases but if too long (with/without spacers), you get coil bind and will not be able to cock the gun. I can't count the times I've had this occur while trying to find the maximum compressed length.
A spring has a tendancy to twist as its compressed so I polish the spring ends plus I like to add 'smooth' metal washers if I feel the spring will not twist smoothly.
Spring kits:
I've never used a spring kit since I buy/make components needed. Some spring 'kits' use a sleeve around the spring itself but I have never used one so can't say anything about their use.
If replacing a ram/strut:
Not a lot you can do to a gas ram unless it's designed to have internal pressure changed. I don't have much experience with this type of power plant so can't say much about it.
Lubes used:
I've used lube from ARH (AirRifleHeadquarters) most of the time but recently started looking at synthetic lubes. I haven't used them yet but based on what I've seen on the forums, they are worth consideration.
Using moly from ARH, I very lightly coat the working area of the air tube (enough to say it's not bare metal), then apply a small amount to the piston seal behind the leading edge and if buttons are used on the rear of the piston I cover them. I also lube the spring guide with moly.
I like to use ARH tar on the spring OD but not too much. It's quite sticky and moly may be just as good if the guide fits properly.
Lube Tune (what I got in a purchase))??
Many years ago I bought a RS2 off of gunbroker and when I recieved it, I found the spring area completely filled with what looked like the grease one puts into a grease gun. The seller obviously didn't like the twang/buzz (LOL).
I've seen posts on this and never tried it since I do the full routine.
Summary:
I find it's rewarding to do your own tune and if any of this helps others looking at trying to upgrade their guns -- good.
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