GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: customcutter on December 26, 2021, 02:11:43 PM
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I'm going to finally start working on the BT65, trying to reduce the cocking force. I'm going to polish the inside of the hammer tube. Right now I can see and feel the machining marks on the inside. Then burnish it with some Tungsten Disulfide.
I've taken the valve apart and can't get the white delrin seat out of the valve. I've tried using a dental pick pushing from the hammer side. I don't want to damage it. Someone suggested replacing it with a seat made of PEEK. The existing stem has a taper that fits the seat. Should I make the PEEK seat with the same taper, or make a new stem with a flat surface and smaller surface area? Will this reduce the force needed to break open the valve? What about using a lighter spring to reseat the valve once it breaks open?
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Progress so far. I made a mandrel from 1/2" hardwood dowel. Then used 1/3 sheet of 150 grit to remove the rough machining. By the time I was through it was probably worn down to close to 400 grit. Then I cut a piece of 400 grit and repeated the process. Here are the results of polishing the hammer tube.
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After polishing with the 150 grit I could still feel some rough spots, so I looked at the edges on the hammer itself. I noticed a couple of high spots on the top next to the brass tube so I took them down with a file. It was slightly better, but not good enough. So I looked at the edges again on the hammer and noticed some sharp edges on the corners of the larger outer rings. I decided to buff them slightly and "break" the edges with the scothbrite wheel on my buffer. Much better, the hammer slides through now by only slightly tilting the tube rather than the almost 45* angle before. Next, I'll apply and burnish some Tungsten Disulfide on all contact edges.
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Here's a pic of the existing poppet for reference as far as the angle. Still haven't been able to remove the white delrin seat in the valve body. Looking from the hammer side of the valve there appears to only be about .010" visible above the brass valve body. I'm assuming that it's a press fit into the body.
For those who have made PEEK seats, would you stay with an angled shaft/seat arrangement, or make one with a 90* sealing seat?
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I haven't messed with peek seats but have done peek poppets and are easier to get to seal with a angle vs being 90 degrees is polish the hammer to mirror finish and also do the same to the poppet and stem
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As far as changing the valve return spring you can but it will increase your dwell time also so I'd try it with the original spring also if you can round and polish air ways in the valve transfer port side round any 90 degree corners and mirror polish the passage ways the valve should lift off the peak easier since it is a harder material and rounding 90 degree passage ways will help air flow quite a bit
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As far as changing the valve return spring you can but it will increase your dwell time also so I'd try it with the original spring also if you can round and polish air ways in the valve transfer port side round any 90 degree corners and mirror polish the passage ways the valve should lift off the peak easier since it is a harder material and rounding 90 degree passage ways will help air flow quite a bit
Mark, thanks for the replies. I'll stick with the angled stem/seat for now. The main focus at this point is reducing the cocking force. Once I do that I will seal 5 of the 6 ports on the valve body and work on transfer ports, etc. I need to check my scraps, check the local scrap yard. I might be better off making a new valve body, stem, and poppet. Before I get carried away and damage this one. :o
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I’m not familiar with the bt (although I’m learning hear).
It appears the stem of poppet is rather large compared to the poppet head. The stem is where the most significant closing force generally develops from. The spring is quite negligible when the stem is oversized. Also, Mann mentioned an increase in dwell time due to smaller spring. I may be wrong, but when people want a lighter cocking force/same fpe, anything that usually increases dwell GENERALLY helps. When the hammer strikes the stem, it has X amount of energy. Part of the energy is used to crack the valve and the rest is used to create dwell time.
You can increase dwell with less hammer strike by simply decreasing stem size. What are your stem dimensions?
What is the purpose of the black disk/bolt on the stem?
Enjoying your upgrade here.
Dave
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Stem does seem awful large I agree with you and don't know this valve either
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Depending on measurements on the the stem I would only reduce area directly behind the head to where it steps up I would take it down to just under .125 or 1/8 inch have had success down farther at like .100 to ..080 but starting to get thinner than I'd like to be leaving the step in there may have to 45 degree it but after that I'd leave that area alone being it probably steps up to fit the valve properly and seal the rear of it with small oring in there
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It is the sealing area that causes the closing force. Cutting it down in just the throat area only improves flow.
A bushing would need to be made to accommodate a smaller stem unless op proceeds with making a new valve body. At which point, it could be considered in the design.
Dave
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I’m not familiar with the bt (although I’m learning hear).
It appears the stem of poppet is rather large compared to the poppet head. The stem is where the most significant closing force generally develops from. The spring is quite negligible when the stem is oversized. Also, Mann mentioned an increase in dwell time due to smaller spring. I may be wrong, but when people want a lighter cocking force/same fpe, anything that usually increases dwell GENERALLY helps. When the hammer strikes the stem, it has X amount of energy. Part of the energy is used to crack the valve and the rest is used to create dwell time.
You can increase dwell with less hammer strike by simply decreasing stem size. What are your stem dimensions?
What is the purpose of the black disk/bolt on the stem?
Enjoying your upgrade here.
Dave
If you look at the hammer face it is slotted from top to bottom on the edge that strikes the stem.
The black disk threads onto the end of the stem and is held in place by the nut. So the hammer actually strikes the black disk, rather than the stem.
Stem measurements starting at the black disc are 2.1 long overall, .195" thick behind the black disk, then steps down to .157", .368" width at the poppet, .216" on the end that retains the spring.
I'm not sure why there is an o-ring behind the poppet in atmospheric pressure?
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Depending on measurements on the the stem I would only reduce area directly behind the head to where it steps up I would take it down to just under .125 or 1/8 inch have had success down farther at like .100 to ..080 but starting to get thinner than I'd like to be leaving the step in there may have to 45 degree it but after that I'd leave that area alone being it probably steps up to fit the valve properly and seal the rear of it with small oring in there
Yes, the thicker section right behind the black disk is the tolerance for guiding the stem in the valve. I'm not sure why the o-ring is there though as this is behind the pressure/seal on the poppet and in atmospheric pressure?
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Here is a different picture with the parts laid out. Trying to show the slot in the huge (93 gram) hammer. I couldn't get a pic of the inside of the valve showing the delrin seat.
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The point that is .195” (with the oring) is the point (diameter) that BECOMES THE SIGNIFICANT CLOSING FORCE once the valve cracks open. The pressure inside the throat makes the stem act like a piston, forcing the hammer back and allowing the valve to close. Once pressure drops, it’s just a guide for the stem. The oring is to keep air from leaking into hammer area during the shot cycle. Most don’t use one due to drag ( I don’t).
Another hammer force robbing area is that plastic disk. It doesn’t transfer energy very efficiently.
Dave
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Better flow will increase the power it should also lift off the peek seat easier to being peek doesn't flex like derlin does increase of power and dwell can hurt efficiency by lightening the stem and increasing flow it should help opening but and if you change the spring to lighten it up more it will or could be worse on efficiency you want a balance and is why I said to try it with the original spring first as for the oring some valve designs have it to seal the stem for blow by when the valve is open usually blow by is so minimal that isn't needed
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FYI
A stem .195” od develops a closing force of roughly 60# at 2000psi
A stem .125” od develops a closing force of roughly 25# at 2000psi
Dave
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I just didn't want him to have to sleeve the valve the valve or make a new one otherwise I agree with you and understand what you are saying
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The point that is .195” (with the oring) is the point (diameter) that BECOMES THE SIGNIFICANT CLOSING FORCE once the valve cracks open. The pressure inside the throat makes the stem act like a piston, forcing the hammer back and allowing the valve to close. Once pressure drops, it’s just a guide for the stem. The oring is to keep air from leaking into hammer area during the shot cycle. Most don’t use one due to drag ( I don’t).
Another hammer force robbing area is that plastic disk. It doesn’t transfer energy very efficiently.
Dave
Thanks for the explanation. I thought the main closing force was the HP air escaping past the flat back side of the poppet area. I can see where the air passing the thinner section also would push against the stem forcing it to close. I guess the 45* angle is more efficient at getting air to the transfer port area, instead of a 90* step. Also if were a 90* angle it would be a stress riser on the stem.
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I just didn't want him to have to sleeve the valve the valve or make a new one otherwise I agree with you and understand what you are saying
Of course. I’m certainly not trying to say this is a have to change thing. I was just wanting to make sure all of the areas that rob power from the hammer strike were known. Efficiency is a different item as well but you shouldn’t have to deal with a hard to cock hammer for good efficiency.
The 45 degree taper at the seat may help a little with air flow but it’s main advantage is dependable sealing of the poppet. This along with soft poppet material make for a more dependable gun….at the expense of harder cocking force. The manufacturers don’t care as much about easy to cock as they do about dependability (meaning less returns).
Dave
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No they don't care depending on what size your peek seat is you could make the poppet head smaller decreasing opening force to but need to know the size of the seat and throat and poppet head size
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FYI
A stem .195” od develops a closing force of roughly 60# at 2000psi
A stem .125” od develops a closing force of roughly 25# at 2000psi
Dave
Thanks. Are closing force and sealing force different? I would think that the area of the pressure side of the poppet would be 200-300#? I've never used the formula although I've seen it posted a few times in some of the threads I've read on balanced valves, etc.
The black disk is actually steel, I checked it a few minutes ago with a magnet. I thought it was to hard for plastic and it didn't deform at all when I used pliers to remove it from the stem. It might still flex slightly when struck by the hammer, but I would think minimally.
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No they don't care depending on what size your peek seat is you could make the poppet head smaller decreasing opening force to but need to know the size of the seat and throat and poppet head size
For now I've given up on removing the delrin seat and replacing with a peek seat. If I can come up with a way of reducing the cocking force needed I'll pursue the peek seat. Then again my only option may be to try and make a balanced valve system.
I just used a bathroom scale and tried to measure the force needed to cock the hammer. I measured 4 times and got readings from 14.8 to 16.4#, and that is without the hammer spring adjuster being inserted. I only had the hammer tube section resting on the scale and used a wooden dowel to push the hammer down. It feels like a whole lot more when trying to use the small bolt handle. :o
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The Hatsan BT65 is an old platform and if I had handled one before buying I probably wouldn't have. It is extremely heavy for me with my lower back issues so I spent a lot of time making a bullpup stock (much easier to handle), so I don't want to sell it. I also know that it won't get much use with the hard cocking issue.
If you want to learn more about the gun/valve set up here is a YT video explaining most of the mods that were done by him. I usually play YT videos from 1.5-2.0 speed. https://www.youtube.com/watch?v=Jqr4ps8IggE (https://www.youtube.com/watch?v=Jqr4ps8IggE)
Here is a link to rsterne's mod's he did to his AT44 many years ago also. It is very similar design in the valve body, but the hammer is much lighter and strikes the poppet stem instead of the black disk. Also the hammer spring appears to be much smaller and the adjuster is mounted in the hammer instead of in the rear of the spring. https://www.gatewaytoairguns.org/GTA/index.php?topic=33903.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=33903.0)
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Are closing force and sealing force different?
Very different. Let’s take an example with a 1/8” stem and a 1/4” valve throat operating at 2000psi.
The sealing force (force holding the poppet closed) is a product of the throat area (0.049 sq in) and the pressure (2000psi) = 98lbs
Actually something more than that depending on the sealing margin—the overlap between the poppet and valve seat—but at least 98lbs.
The closing force (force acting to close the valve after it is knocked open) is a product of the stem area (0.012 sq in) and the pressure (2000psi) = 24lbs
So we are talking about something in the neighborhood of a 4 to 1 ratio. Note we are ignoring the effects of the valve spring and the sail effect but those are comparatively small in most cases.
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Are closing force and sealing force different?
Very different. Let’s take an example with a 1/8” stem and a 1/4” valve throat operating at 2000psi.
The sealing force (force holding the poppet closed) is a product of the throat area (0.049 sq in) and the pressure (2000psi) = 98lbs
Actually something more than that depending on the sealing margin—the overlap between the poppet and valve seat—but at least 98lbs.
The closing force (force acting to close the valve after it is knocked open) is a product of the stem area (0.012 sq in) and the pressure (2000psi) = 24lbs
So we are talking about something in the neighborhood of a 4 to 1 ratio. Note we are ignoring the effects of the valve spring and the sail effect but those are comparatively small in most cases.
Thanks for the explanation. I thought they had to be different. However, I don't understand using the radius of the stem for the sealing pressure? I would think it would be the widest part of the poppet pushing against the seat? Which is .367" or .1057 sq in generating 211# of force at 2000PSI? Or is my math incorrect or my thinking that the back of the poppet would generate the sealing force?
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Yes, the widest part of the poppet that is actually forming a seal is what will determine the force holding it closed. That is what I was trying to describe when I brought up the sealing margin (overlap).
Your math checks out perfectly.
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Jason always explains things quite well, thanks.
Consider this though, although the holding force and closing force may be a 4 to 1 ratio, the distance the hammer needs to travel against the larger force is significantly less than the distance it has to travel against the smaller force. I don’t have the formula handy but you can figure out what that ratio is of fpe to crack vs fpe to open/dwell.
My suggestion would be to try a different poppet with a small diameter stem. Of coarse a sleeve with a step to keep it from being blown back toward hammer would need to be made. This would be a couple pieces you could make, insert in valve and do no harm to existing parts. And still have reliable sealing. If you don’t like the results, simply remove and put old parts back. No loss other than time spent making the parts.
Dave
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Yes, the widest part of the poppet that is actually forming a seal is what will determine the force holding it closed. That is what I was trying to describe when I brought up the sealing margin (overlap).
Your math checks out perfectly.
Thanks Jason. That's why I asked for the clarification. Been almost 50 years since my high school geometry and physics classes. I kept telling myself PiRsquared, but somehow I was doing the actual math PisquaredXRadius. :o Couldn't figure out why I was getting different numbers from you and Dave. Palm slap to forehead DOH!
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Jason always explains things quite well, thanks.
Consider this though, although the holding force and closing force may be a 4 to 1 ratio, the distance the hammer needs to travel against the larger force is significantly less than the distance it has to travel against the smaller force. I don’t have the formula handy but you can figure out what that ratio is of fpe to crack vs fpe to open/dwell.
My suggestion would be to try a different poppet with a small diameter stem. Of coarse a sleeve with a step to keep it from being blown back toward hammer would need to be made. This would be a couple pieces you could make, insert in valve and do no harm to existing parts. And still have reliable sealing. If you don’t like the results, simply remove and put old parts back. No loss other than time spent making the parts.
Dave
If I can figure out how to get the existing delrin seat out, that would be a great option.
Another question, if I decide to make another valve should I stick with brass, or could I possibly use Al (not familiar with the tensile strengths of either one)? I still haven't looked in the scrap pieces to see what I have on hand. My lathe is capable of SAE or Metric threads although I've only tried cutting them a few times. I know 200bar is nothing to play around with, which is the recommended high pressure rating on the reservoir.
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I don’t think you would need to remove the delrin seat to try what I suggested but again, I’m not 100% familiar with the valve.
Many valve bodies are made from aluminum but there may be something about the design that warrants brass. I’m not sure.
Dave
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I don’t think you would need to remove the delrin seat to try what I suggested but again, I’m not 100% familiar with the valve.
Many valve bodies are made from aluminum but there may be something about the design that warrants brass. I’m not sure.
Dave
Thanks, I hadn't thought of leaving it in, other than fewer seams would possibly be mean less chance of leaks.
I need to check, but IIRC the existing cylinder is Al. I guess I could measure it for minimum thickness if I decide to use Al.
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Disassembly of the breach and hammer tube/trigger assembly isn't to hard getting it back together and functioning properly has been a PITA. I've probably taken it apart and re-assembled it 15-20 times today. I couldn't get the trigger sear to catch the hammer. It would go back far enough to catch the anti-bounce lever, but wouldn't catch the sear. I thought there was something wrong with the trigger mechanism so I worked on it several different times thinking it needed to be in the fired position, then the cocked position, but no matter what I tried the hammer wouldn't go back far enough. Finally I took the hammer out and inserted it into the trigger assembly to confirm that it was supposed to go in and which position fired/cocked the sear needed to be in. I realized that there was a guide on the hammer that wasn't lining up properly with the grove on the trigger assembly. (You can see it in the #2 reply in this thread).
Finally I started putting the breach back on the lower assembly, no matter what I tried it didn't want to seat properly. Then I realized that the hammer was caught by the anti-bounce lever. I compressed the spring enough to release the anti-bounce and success.
Thought I would add this for anyone else working on a BT65, and also for myself. If it happens again hopefully if I don't remember the "tricks" I'll find them in a search.
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OK, another question about poppet design. I know from reading probably 1000's of post on power mod's that the rule of thumb for transfer ports, etc. is that sizing should be 75-80% of the pellet size. I think that is the actual diameters not surface area. I guess the poppet stem major diameter less the minor diameter should yield an area equal to 75-80% of the pellet size?
.25X.8=.2, so .1x.1=.01, .01x3.14=.0314sq inches.
The original poppet major diameter was .195"
.0975x.0975=.00950625x3.14=.0299sq inches.
The minor diameter was .157"
.0785x.0785=.00616225x3.14=.01935sq inches.
.0299-.01935=.01055sq inches. Wow, approximately 1/3rd the area of 80% of a .25cal pellet, or is my math off again?
Is there a "rule of thumb" for poppet stem and throat measurements based on pellet size???
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No rule of thumb on the stem diameter in the ‘guide’ area (your .195 area). This only effects closing, not flow.
The stem diameter (area) in your throat area is subtracted from the throat area to determine flow in that area.
Dave
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No rule of thumb on the stem diameter in the ‘guide’ area (your .195 area). This only effects closing, not flow.
The stem diameter (area) in your throat area is subtracted from the throat area to determine flow in that area.
Dave
Thanks, I simply assumed that the throat area was the same size as the "guide" area. :o Time to pull out the bore gauges.
Just remembered I found a delrin seal in a bag of o-rings last night. It measures .265" throat. Time to re-do the math.
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I'm trying to follow along but am not sure what is meant by the guide area.
Is it represented somewhere on this diagram? I know the Hatsan valve design deviates from this a bit...
(https://i.imgur.com/O4kSyIy.gif)
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Ken, if it would help you play with the numbers, I'm attaching a copy of my porting worksheet...
(https://i.imgur.com/i3UumA6.gif)
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Hey Jason,
I’m referring to the portion of valve body the stem rides in as the guide. The part that is a close fit to stem immediately in front of hammer.
Dave
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Jason, Yes, the guide area is the section of the valve where the stem exits toward the hammer. On mine that section of the stem has an o-ring on it. Dave explained to me that it stops air escaping into the hammer area.
On my poppet it is threaded and has a flat disk that threads onto the stem and then a nut to lock it in place. The hammer has a large slot down the middle of it, and there is a spring loaded arm/lever that is pushed back by the bolt when cocking. That arm rotates and slides in the slot on the hammer. I'm not sure why it's there other than excessive cocking force. Hatsan did away with that style hammer and arm in their next model the AT44. Also made it a side lever cocking.
Thanks for the porting sheet. I will definitely down load and save. When I re-calculated based on the "throat" in the spare delrin seat I came up with 110%+ based on the 80% porting of transfer ports to pellet size.
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I just realized it's been 15+ years since I've made any spreadsheets. Who knew that corporate stuff was useful. :o
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I've re-assemble the rifle. It is a lot smoother, but not much lower on the cocking force needed. I'm going to tune it to around 900fps and see how the shot string goes. At least I'll have some starting data for comparisons.
I've had the gun torn apart and scattered all over my wife's kitchen counter for the last 2 days, so I better give it a rest while I'm still ahead. In a couple of days I'll tear it down again and start on the new peek seat. Need to try and source some different springs as well.
More questions have come up concerning a seat made of peek. The original is white delrin I'm guessing, and the spare one that I found in the bag of parts is flat on both sides. The seat that I extracted is shaped to the cone on the stem, presumably by pressure. My understanding is that peek is much harder. So I should machine the peek seek to match the cone on the stem? Should I also try to lap it in with something like valve grinding compound to insure a good seat?
Thanks again for all the help everyone is offering.
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The more ‘cone’ in the seat, the larger the sealing diameter, the higher the cracking force needed.
Also, when lapping, the softer material holds the compound while the compound cuts the harder material. Your poppet is good so I suggest NOT lapping with compound.
What can be done, however, is cut your seat square and BURNISH it with the poppet. If done gently, this will make a minimum sealing diameter and true up the seat with a very mild cone.
Dave
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Thanks again Dave. I received some .5" natural peek last week. When I get ready I'll follow your advice. ;D
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My first attempts at Hatsan tapered seats were difficult. The most successful PEEK seats I made were 90° square cut, no bur, no additional operation. Because of PEEK's high compression strength tapered seats deform less are prone to leak with any surface deviance, while the 90° corner crushes a bit making a good seal. Just a hard first fill seats the valve.
I turn the outer diameter, then drill the smallest desired center bore, face, groove for oring, and then parting tool no other operations. I usually make a few, increasing the bore diameter for a tuning set, while the peek is set up, reduces waste material.
Explore using a brass slug in your hammer to increase opening force without increasing spring force.
You should be making full strings to see what you are trading with different set ups.
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Thanks, that pretty much sums up my plan. Other than the hammer already weighs 90+grams. I want to maintain FPE, but most importantly reduce the cocking force needed. I've even considered trying to fab some type of cocking lever like on the AT44.
I ordered a piece of 1/2"x12 natural and it is labeled .500, which is what I got when I measured the spare delrin seat with a caliper. I'll dig the mic out when I start cutting. Thanks for the idea of making a few hadn't thought of that so I'll probably do 2-3 to save set up time.
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I aired up the BT65 earlier to 100 bar, shot it 3 times to make sure the valve was seated. Then I filled it to 200 bar and let it sit for a few hours. As expected it dropped to almost 190 bar. IDK if it was heat from filling or leakage, so I topped it back at 200 bar and let it sit another hour. The hammer spring was backed out flush with the back of the gun and I haven't cut a channel in the stock to back it out more, so I went with the setting I had.
It was still holding 200 bar so I loaded some 24.7gr Vortex Strike .25 cal. The magazine holds 9, I thought it was 10 so I had 1 mis-fire. I fired 3 magazines and it was almost dusk so I had several ERR's. Here is the shot string.
938/961/ERR/956/968/ERR/962/964/980/EMPTY MISFIRE/ 165BAR
975/963/975/ERR/979/973/ERR/972/969 137BAR
963/ERR/ERR/921/925/ERR/ERR/901/ERR
As it sits I think I'm looking at 20 good shots. Just over 2 mags. I'll try to get the new peek seat made and get some more info. Still need to find some springs, forgot about that. I know I have a couple of spares for my Evanix Rainstorm when I ordered it.
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With using peek it's harder so you don't need as big of a poppet head which helps with the cracking force may have to sand the peek using the poppet to help get the shape and to get it to seal I would color the seat made of peek and start with like 800 grit fold the paper in half and push stem threw it then push the stem into the valve and on the poppet seat sand until the sharpie marker is gone I'd do it a couple times the I'd go to 1500 grit and do the same color the seat with the sharpie and spin the poppet around on it till all the marker is gone I would also polish the poppet to a mirror finish find out what the hole size in the seat is and measure poppet head peek is alot strong and I'd take poppet head and make it about .060 of a inch larger than the seat hole is should lighten up cracking force quite a bit to either need to lighten the spring up or the hammer then or some of each
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Never had any luck burnishing in a peek poppet I've had to lap it in with some good metal polish to I had good luck with the sanding I described and also lapping in with metal polish
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Never had any luck burnishing in a peek poppet I've had to lap it in with some good metal polish to I had good luck with the sanding I described and also lapping in with metal polish
Thanks for the suggestions. I'll try burnishing first and if it doesn't work, I'll move onto other options.
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I managed to get 2 peek seats made today. 1 has a .250" opening same as the old seat, and the second is .225". I had to use 1.5mm o-rings, as I don't have any 1mm like the originals. Burnished both with the stem, by chucking the stem in the tailstock. I left the stem at the original diameter for now.
Just inserted the .250" seat into the cylinder and hit it hard with a few blast of air. Finally got it to partially seal and aired it to 100 bar, which it's holding for now. Going to let it cool off, then take it to 200 bar before calling it a night. I'll check in the AM to see if it's leaked down.
Time to dig out 1 of the Evanix RS II hammer springs and see if it will fit.
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I found the Evanix springs. It measured:
2.8" long, .48" wide, .051" thick with 11 coils and I cut it 10 coils. The Hatsan spring was:
2.6" long, .492 wide, .056" thick with 12 coils. So it should have been stronger.
Re-assembled everything and it feels a little better. I'll try a shot string tomorrow and see what happens. Cylinder holding 200bar for now.
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I shot another 3 mags this morning with the mods. Tried loading the Caldwell Chronograph app onto my tablet. Can't get it to work for some reason, I know most people use cell phones? This was the original readings:
938/961/ERR/956/968/ERR/962/964/980/EMPTY MISFIRE/ 165BAR
975/963/975/ERR/979/973/ERR/972/969 137BAR
963/ERR/ERR/921/925/ERR/ERR/901/ERR 105BAR
This is this morning readings, with the peek poppet, and slightly weaker modified spring:
988/992/1003/1004/1013/980/empty/1003/993/990 160bar
987/986/982/973/967/958/956/947/936 130 bar
937/935/925/918/905/895/892/881/878 105 bar
Not sure what to make of the readings. It appears that the valve is easier to knock off 938vs988 with a weaker spring. I need to find a weaker spring for sure. Right now both springs are backed off completely AFAIK. Should I try cutting another coil or 2 off? I read another thread last night that said cutting coils actually made springs stronger! (Doesn't make sense to my 2 brain cells.) :o I looked through Amazon last night looking for compression spring kits. Didn"t find anything suitable so far. As soon as I get the cocking force reduced more I will start with the other mods in the video.
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FWIW your original spring was around 14.5~ lbs and your second spring from the evanix is around 11.2 lbs/in
Both have some heft, you could try to get down to 8 or 9 lbs, I think that rating can be found at mcmaster and its so common maybe a member here has one around that.
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Clipping coils increases spring RATE. When you say an 11 lb. spring, you are really meaning 11 lb/inch of travel.
If you compress that spring 1”, it will push back with 11# of force. Clip it down to 1 coil left and it will push back with same 11# force with just a minimal amount of travel. But it obviously doesn’t have the equivalent stored energy. Which is what we want.
It is ok (and I prefer) some free flight to my hammers so it is ok to go pretty short.
Dave
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FWIW your original spring was around 14.5~ lbs and your second spring from the evanix is around 11.2 lbs/in
Both have some heft, you could try to get down to 8 or 9 lbs, I think that rating can be found at mcmaster and its so common maybe a member here has one around that.
Thanks Matt, I know there is a formula for calculating. I saw one on a site I visited a couple of nights ago.
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Clipping coils increases spring RATE. When you say an 11 lb. spring, you are really meaning 11 lb/inch of travel.
If you compress that spring 1”, it will push back with 11# of force. Clip it down to 1 coil left and it will push back with same 11# force with just a minimal amount of travel. But it obviously doesn’t have the equivalent stored energy. Which is what we want.
It is ok (and I prefer) some free flight to my hammers so it is ok to go pretty short.
Dave
Thanks Dave, it's a spare spring, so no harm in cutting it shorter. The spring rides inside a hollow section of the hammer and another hollow section at the rear which also houses the trigger, and hammer spring adjustment bolt. I'll take another couple of coils off and see where I'm at.
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I took the gun apart for what seem like the 100th time. :P I got the spring to where I had about 1/8" of free travel. First shot was around 500FPS, so I adjusted the HS to get 950, and aired the cylinder to 200bar. Here are the 2 earlier strings:
938/961/ERR/956/968/ERR/962/964/980/EMPTY MISFIRE/ 165BAR
975/963/975/ERR/979/973/ERR/972/969 137BAR
963/ERR/ERR/921/925/ERR/ERR/901/ERR 105BAR
This is this morning readings, with the peek poppet, and slightly weaker modified spring:
988/992/1003/1004/1013/980/empty/1003/993/990 160bar
987/986/982/973/967/958/956/947/936 130 bar
937/935/925/918/905/895/892/881/878 105 bar
Trimmed ERS spring trimmed and adjusted to 950fps:
948/965/957/962/967/965/961/969/937 165bar
978/960/966/985/981/960/959/972/988 145bar
961/964/962/963/953/942/935/954/929 115bar
Cocking is definitely easier and probably would be better at 900fps or with a 10#spring. Time to start working on the valve body. Any thoughts on lightening the hammer from present 93 grams?
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You could try it so the hammer is in free flight for the last .030 thousandths of a inch or a tad more with the heavier spring just cutting it shorter a little at a time that way it isn't preloading the hammer when uncocked and the 30 thousandths gap or tad more of free flight on the hammer will help with hammer bounce saving air also this is the basic idea of a ssg but you can load spring pressure on the ssg and still have 30 thousandths free flight on the hammer if you can make a peek poppet you can make a ssg pretty easy to do
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I vaguely remember the SSG from when I was active a few years back. Seemed like a Marauder Mod at the time. Isn't it basically a double spring? If so that would be increasing the cocking force again. Or maybe I'm confused about it, I'll have to look it up.
Thanks, Ken
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I'm not of much help on mods with the BT65, but I did pick one up last year. This is all very interesting.
I did notice they have a heavy hammer and spring, combined with the high flow valve they don't lend themselves to high efficiency/shot count (lol). But do make big power. (Even in .177)
The valve my gun came with was brass and one in the extra cylinder was steel. Made adding a regulator fun, as it worked in the old cylinder, but not the new (or vice versa). Also, there were different valve stems available for various power restrictions. All this is probably old news for those who tuned Hatsan's in years past, but there are still new owners now and then.
Hopefully you get things sorted to your liking. These are big guns in all aspects, looking foreword to your end results.
Take care
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No it is a single spring it stands for spring stop guide and works better at lower power tunes but still effective on higher power tunes to just not as much you can make a spring guide and a spring capture end drill and tap the longer end and you use a weaker spring and add spacers on the guide end to increase spring pressure with out increasing length or preload on the hammer leaving room for free flight and enough stifness to stop the hammer bounce just need to make 2 ends one with longer spring guide and one short one drill hole in the smaller end slide bolt threw and drill and tap the other end to capture the spring set it to correct length to give you 20 to 30 thousandths free flight and then you can increase spring pressure as needed with spacers on the guide end I made the guides out of peek and picked up about a 4 in small bolt to capture the spring take measurements and you set it back to same length with spacers in place to increase spring tension if needed you could probably order marauder springs think they are lighter 7 or 8 lbs
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How large is poppet head
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With 240 throat hole you could take poppet head down to .300 thousandths which would open easier yet and could use a lighter spring and possibly lighten the hammer too
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Thanks Zack, I've had this one 6-7 years. Got started on a bullpup stock 5 years ago and got away from the sport. Just getting back into it and want to make the gun a lot better than it was stock.
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Ssg
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With 240 throat hole you could take poppet head down to .300 thousandths which would open easier yet and could use a lighter spring and possibly lighten the hammer too
Thanks Mark. I've got some stainless rod I think. I may try making a new poppet, and keep this one so I can go back if needed.
I found this video on SSG's. You're right that would be pretty easy to fab. Not sure what I had it confused with but it was a spring within a spring.
https://www.youtube.com/watch?v=Hb303lT6IB0&t=14s (https://www.youtube.com/watch?v=Hb303lT6IB0&t=14s)
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Thanks for the pic Mark. Sometimes I'm a visual learner. Between your description and the video it sounds good. ;D
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I found this old post by Bob Sterne regarding hammer weights reading some old threads on tuning AT44's and BT65's.
"Heavy hammers for high power, heavy pellets, and high pressures.... light hammers for less power, light pellets, and lower pressures (eg. regulated).... If you don't change the spring or preload, you get the same valve lift regardless of hammer weight, but heavier hammers give you longer dwell, releasing more air to drive heavier lead.... If you lighten the hammer, generally you have to increase the hammer spring preload a bit to shoot the same pellet at the same velocity....and when pushing the power limits this may make the gun hard to cock....
Bob"
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The dual spring was a tss they called it mostly used in mrod from what I remember it was also help with hammer bounce . I like the ssg it is easy to adapt it to other platforms
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AARGH! Just broke the head off of the small diameter bolt I found this morning in my collection trying to turn it down to fit the hole I drilled through the hammer adjustment bolt. I knew I should have used the 2x72 belt sander and turned it by hand. >:(
Luckily I have 2 more slightly larger diameter bolts that I think I can use, if I drill the opening it a bit larger. This time I'll turn the head down first before doing the other steps.
Don't know if I have any Delrin, may have to use the peek.
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Peek works too my last one I made was peek
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I got the second bolt to specs, made a piece from Al to thread it into, drilled out the hole a little larger in the hammer spring adjustment bolt. As I was assembling the SSG I realized this won't work. As it sits when the bolt is pulled back compressing the spring the 10-24 bolt will extend out the back of the rifle. When the bolt is released the head of the SSG bolt will catch on the hammer spring adjustment bolt.
I'm trying to figure a way to have the bolt head go through the hammer, but there is an arm that bolts onto the bottom of the tube. There is an allen head bolt on the bottom of the bolt probe. When you cock the rifle the allen head in the bolt probe catches the arm and the arm rotates as it pushes the hammer back. The small round piece specifically. The only purpose I can see for this arm is that it is spring loaded and would hold light pressure forward against the bolt probe maybe keeping it from rattling. That arm results in a slot cut in the face of the hammer almost .25"X1.5". That requires the large flat disk on the face of the poppet. :-\
If I drill through the hammer, that would create a rough spot for the rotating arm if I go back to the original configuration. The hole where the brass piece attaches to the hammer extends all the way through the hammer and is threaded. So an Allen head bolt could be inserted from the other side that the Allen head in the bolt probe could catch to cock the rifle.
Seems like the whole design is poor and other things were done in order to try to correct previous design flaws. I'm pretty sure at this point it is an exercise in futility.
Here's a pic in case someone sees something I don't.
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If I understand the ssg correctly, it essentially makes an otherwise stock spring into one that allows the hammer to be in free flight while still maintaining most all of the original energy for striking the valve. It also gives a less springy wall for the hammer to hit on the bounce, effectively debouncing it.
A non captive spring (one that allows hammer free flight) essentially does the same but not quite as well due to being more springy as the hammer bounces back into it. But it may be the best option in this situation where a guide gets in the way of other parts.
Dave
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Dave, I think you are correct. I was looking for a way to help de-bounce the hammer and increase efficiency.
Right now I'm going to assemble it without that swinging arm. It looks like I need to make a small piece to bolt to the top of the hammer to push the hammer back about 1/4" more to allow it to cock properly. Just to see what effect it has on cocking and the shot string. If that works, I might be able to make the SSG work.
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Do you have room or is the hammer housing set way down in the stock you could do a external ssg where the bolt comes out the back and is adjusted on the outside I'm not familiar with this platform otherwise like stated a shorter stiff spring allowing some free flight might be the easiest solution unless you can figure out a way to cock it differently
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I might be able to partially compress the SSG about 1/2 way, and shorten the bolt. That might keep the SSG bolt from extending past the back of the hammer spring adjustment bolt.
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Can you drill threw the hammer adjustment bolt and put the ssg bolt threw it and when you cock it the bolt would go threw the hammer adjuster bolt making it a external ssg which would stick out the back idk if that would work or not BT 65 supposedly uses there own hammer denounce device I don't know what it looks like but I read in the search are that it can be removed don't know if that will help or not
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Can you drill threw the hammer adjustment bolt and put the ssg bolt threw it and when you cock it the bolt would go threw the hammer adjuster bolt making it a external ssg which would stick out the back
That's the way it's set up right now. But the head on the SSG bolt will hit the back of the hammer adjustment bolt when it tries to go back in.
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I put the receiver back on the hammer/trigger tube. As suspected it liked about 1/4" of pushing the hammer back far enough to catch on the trigger mech. I tried taking the receiver back off and the tapered head bolt under the pellet probe stripped out. I tried finding and even making and oversize allen wrench to get it out. Tried sharpening a chisel and tapping it out reverse direction. After several hours of trying I decided to drill off the head thinking I would have about .020" above the lower tube to work with getting it out. The head popped off about .010" below the surface. I used a #29 drill .166" IIRC. I know I don't have any Ease Outs that small or if they would even work, I've never had any luck with slightly larger ones. At one time I had a set of the square shaped ease outs and they worked pretty well, but I can't seem to find them. I don't think I can get it out by cutting a grove with a dremel wheel for a flat screwdriver. Time to start a google search I guess.
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I'd try the groove the top first and try to turn it out maybe add some heat also if you can the external ssg used a longer bolt and nuts on the out side then would use hammer adjuster screw to stop the spring slot of people put a oring between then nuts and hammer adjuster bolt then when fired the nuts of the ssg are sitting on the outside of gun does that make sense
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Now excuse me but i have a real hard time understanding why a SSG setup per regular couldn´t be had to work in the BT-65 too?
Hammers center is kind of hollow as is, and indeed that knurled nut at the valve big enough to cater to it.
Why on earth wouldn´t a regular SSG setup work if you just clearance for the bolt head running through the hammer?
That in turn would also render the use of the stock spring stop, just sans effect. Ie; set it to hearts desire as needed for being convenient with the SSG?
That said, plz run this by me cause you lost me...
Then again, the stock anti bounce device would make this rather moot in the first place no? Better maybe to just modify that?
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Would this work or not
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Like I said Idk the gun though and my not want that look that extra length could cut off behind the nuts once adjusted properly the bolt on that pic is the spring adjuster for preloading it
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Why not, but i guess you´d have to device some manner in to set unsprung length for the unit, and thus control hammer free flight.
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From what I've read the stock hammer denounce system or set up doesn't work very well kind of sux is what read
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The SSG can be made to work. I would have to make a longer hammer adjuster so that the bolt in the SSG doesn't stick out the back of it like in this photo. The other option would be to preload the SSG by about 1/2" and shorten the bolt so that it doesn't hang out the back. If the small bolt head sticks out the back of the hammer adjustment bolt then it will "hang" on it when the trigger is released.
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From what I've read the stock hammer denounce system or set up doesn't work very well kind of sux is what read
I know George (the guy in the original video I posted) did 2 or 3 different mods trying to improve the de-bounce system. He did not do a SSG, it looked like a simple mod.
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Ok I got ya sorry didn't know about that if you make ssg shorter the hammer might have to much free flight Only want 20 to 30 thousandths of a gap but some of it is trial and error so preload the spring and give it a go
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Yep, as soon as I'm able to get the screw out. I'll try the shorter bolt first, check the shot string. If that isn't good, I'll do the longer hammer adjustment bolt.
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Success! I tried welding a small nut onto the top of the 3mm screw, but way too small of a broken screw for that method to work. So, I watched Abom69 last night drill out and remove some 10mm bolts.
I optically (eyeballed in redneck) the piece to get the screw centered on the mill in the X and Y axis. Then I used a 1/8 end mill to flatten the top of the screw. Used a very small center drill to start a hole for the drill so that it wouldn't drift. Then I used a #40 drill bit to try and drill through the center. By the time I had drilled all the way through, about .200" it had twisted the screw into the brass piece about .100". So plenty to grab with a pair of pliers. All I need now is a 3mm tapered head replacement screw.
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Congrats on fishing out that broke off screw. Seems like the hardware is soft with this brand. Snapped off bolt heads on their springers in the past.
Funny thing, I seem to do a bunch of eyeballing myself. Usually followed by "seems 'bout right". ;D
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I do quite a bit of tlar engineering. Works most of the time and that’s good’nuff for me.
Congrats on getting the bugger out!
Dave
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Thanks guys, going to Lowes after lunch to see if I can find a longer bolt to make a hammer adjustment bolt. Also need a bolt for the SSG that isn't threaded the entire length and of coarse a 3mm flat head replacement.
I was surprised when Abom eyeballed centering the bolt he removed. He did explain that he likes to do it with a mill cutter turning the cutting edges 90* to align X and Y. Then flattens the bolt head for center drilling. Worked great!
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Turning the cutting edges 90 gets you really close. I do that when I start with a punch mark. I use a 1/6” bit, start the hole just barely, then switch 90 degrees on the flutes, dipping the bit in the hole to see which way it moves. Take out the error with the x and y, then it’s centered. Spot drill and then it’s ready to go. Sounds more complicated than it is.
Dave
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Finally got back on the BT65 today. The first SSG bolt was a 10-24 and threaded the entire length. It kept catching on the hammer spring adjusting bolt when it traveled through the center hole. I took a 1/4X20 SS bolt and turned the head down to .250, then I turned the bolt down to .177 (I was shooting for .185, but didn't measure soon enough :o). Then I grabbed a 10-24 die and cut threads on the last 5/8" approx.
I put everything back together and did a few dry test fires. It's not hanging up like the original 10-24 bolt did on the hammer adjustment bolt.
I'll try and get some shot strings tomorrow and see how adjusting the SSG affects velocities and air efficiency. It's been raining here all day, so this was a good project. Here's a pic of the original bolts and the modified bolt.
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Here's a pic of it assembled.
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I shot a few magazines today. With the hammer spring adjuster in the same place, I was getting a full 100fps less velocity. I thought it might have been the extra weight of the SSG bolt, so I removed it and basically the same velocities? ???
I screwed the hammer adjustment bolt in almost 1/4" to get back to original velocities. I noticed that with the SSG bolt installed I was getting 1 or 2 shots our of each magazine that were 30-40fps less than the rest of the mag. So I tapered the back of the SSG bolt and also the hole leading into the hammer adjustment bolt so that nothing could be catching. I would hoping that it would improve velocities as well. No luck. :( I shot 6 magazines and know less now than when I started. :o
I'm thinking possibly an o-ring on the transfer port may have gotten damaged during one of the hundred times of dis-assembly/assembly. I'm going to tear it back down, inspect/replace the o-rings, and put in the full length spring from the Evanix instead of the one that I cut down 2-3 coils, so that it is actually compressed about 1/2".