Help tuning- <12 ft lbs. For those in the know
Hi there,
I know most of you are used to work on much higher power, i wonder if you could give me some advice with regards to setting a consistent power/speed for my needs.
My rifle arrived in uk already set up by Ed, at 11.5 ft lbs.
The hammer spring screw is almost all out, with about 3 threads still in.
I wanted to check its consistence so i chronoed it on several occasions.
My aim was to get 570 fps with jsb exact 15.9 grain, wich translates to 11.5 Ft lbs and thereabouts, which is a safe limit i don’t want to exceed.
Anything above 582fps would be above the limit.
I have found however inconsistence between shots, up to 20fps, so i’m obliged to keep the speed at 550fps, to avoid breaching.
550fps is too slow and it changes the poi a lot beyond 50yds.
The changes in speed occur both during the same refill, and from a fill to another.
I.e, i set it a 570 and i think i got a good consistence, then refill and find out 20ps dofference.
I don’t think temperature influences that much, as such changes can be seen in a matter of minutes.
I fill at 220 bar (my bottle gauge) which is 210 on the gun’s one.
I think the power is higher to start with and then goes down and settles at 170bar, but you appreciate police will fill at 200 and start counting from there!!
Initially i thought the spring was beddin in, and needed to be broken in before settling at its final elasticity, but i’ve shot about 2000 pellets and i guess i should have happened already (or do i need more?)
Im currently trying to make veeery small adjustments at time, rather then moving the screw too much, slowly incresing, let’s see what happens.
However i would muh appreciate your thoughts with regards on how to obtain the best speed consistence.
I hear you unscrew the regulator 1/3 of turn and then decrease the spring tension, i guess i should do the opposite, so that more power needs to be applied from the hammer to discharge the air. This way i can tighten the screw a bit more, as right now i think it is so decompressed that it doesn’t “get” or “keep” the fine adjustments i make to its tension.
I hope you know what i mean.
Anyway i would much prefer to find a solution without having to strip down the gun.
I thought wih a regulated rifle i should have not bother with this shite, but it now seems i can’t enjoy using it as im always there checking the speed.
That’s very disappointing i must say.
Any help appreciated.
Cheers.
All Replies
Update:
I got some nylon washers:
7mm OD, 3mm ID, 0.8mm thick.
I managed to mount one retaining the rubber oring underneath it.
Without oring i was getting a puff of air on the face.
My reg is still @ 12:45 (75bar).
As expected i had to increase the hst as i had lost a good 100fps with the choking.
However i can’t get more than 540fps now, as even if i increse the hst further the speed doesn’t increse any more.
That’s a good point, as it is here we wanted to get.
So now i need to re-increase the reg pressure a bit so that i can get a speed of 570.
BUT HOW MUCH SHOULD I INCREASE THE REG PRESSURE?
I recall that you told me that a good situation is when one reaches the wanted speed at a point where even with further hst increase, the speed doesn’t change
I reckon I’m a tad below that point, so the moment is crucial.
Just a reminder for my attempts and then you tell me where to move the reg.
Reg @Stock 12:00 = 130 bar
Reg @ 12:07 = 125 barÂ
Reg @ 12:15 (1/4 turn clockwise)= 110 bar
Reg@ 12:45 (3/4 turn clockwise)= 75 bar
Would 80bar be enough to allow me to get 570fps, still keeping the situation that further hst tension would still give me 570fps?
Would 90bar or 100bar more appropriate? (so that the reg has still pressure to let me increase the speed to 580+?
Given we agree for a pressure, where is it in the reg position? (12:30? 12:40?)
Ed, any thoughts? You said you tuned your reg at 100, where should i move the reg screw then to reach 100?
Any advice on how to move forward welcome, i’ll disassemble it tomorrow.
Cheers
The reason why I told about 100 bar of reg is quite simple — having the pressure less you have risk that hammer will met the bronze hexagon, damage it and the valve rod will not move smoothly, you will got another problem.
Thanks bigtoe,
Next step from where im now is to increase the reg to 80-90.
I’ll wait to see what happens to my current setting when i choke the port.
I haven’t checked its size, sorry, but i think it is around 5mm, someone else might reply to you moire accurately…
you are running the gun low pressure high volume, this will work and will be consistent but you will suffer hammer bounce and it will be wasteful.
What size is the stock transfer port?
What size is the barrel porting (if it has any) or the port that exits the air behind the pellet?
I seriously feel you would do MUCH better with a reg at 90 to 95BAR .177 or 85 to 90 in .22 ( I like 90 for .22), less bounce and regs seem to work better a little higher and here is the important bit…coming off reg will not result in a power spike upwards for a few shots.
The key will be getting the reg to cycle on each shot, ask Ed what volume of air is held behind the exhaust valve, you may find it better to reduce this volume so ensuring the reg cycles each an every time. Remember the Edgun is an FAC gun detuned for sub12, it will be setup for large volumes of air used on each shot, this may not allow the reg to cycle at its best and may result in a poor shot to shot consistency.
Simply adding some Acetal as a spacer in the exhaust area is all thats needed to get the reg cycling better…just remove some air volume and replace it with plastic…such as a thick spacer washer or sleeve.
Again, before saying that’s sorted with Ed’s theoretical advice i’d wait to see how it works in practice. For instance he predicts that lowering the pressure to 100bar will need increasing hst tension, whereas in practice what happens it’s just the opposite.
However, there is no controversy that narrowing the port will reduce the amount of air, hence will allow to increase hst tension.
I shall try that. I’ll keep my reg pressure where is is now (around 70 bar), as right now, even with stock port, it keeps a quite decent consistency (with the exception of temperature changes).
I’ll get a custom made washer soon (3mm inner diameter).
I have actually checked the size of the port area (where the oring sits) and it is 9mm diameter not 8, not that will make much of a difference anyway.
Cheers
most UK PCP’s are most efficient with 90BAR reg pressure, 3.8mm transfer port and around 3mm barrel porting.
if the transfer port is removable a new unit could be machined up, not sure on the barrel porting though
Yoda, In your O ring kit, I also included a few of the smaller ID Teflon O rings, for you to try in the transfer port, and a new HST screw that has more threads on it.
You should have your stuff within the next couple of days.
ed you echo my thoughts exactly there things are very extreme in this country, the goverment points the finger around the world but is afraid to look in the mirror..
Ed just confirmed what I said in my 1st message.
Yoda Ed is correct a 100 bar is fine but “after” you choke the transfer port, aka make it smaller.
Derek, come to Russia, we do not care about the stupid laws here 🙂 Having read about all the situations you live in West countries and remembering that the leaders of your countries claim USSR as a authoritarian regime I have nothing to laugh since you are now living under the real dictatorship of not the best people of your civilization and not the best principles. That guy also told me, when I asked him if it was true that in UK while someone is invading in your house the owner of the house cannot protect himself, that it is not true, one has right to defend himself but has no right to hurt an invader! To me that is the most stupid thing I’ve ever heard! And that completely describe the situation you live in and I am very sorry for that, hope you will kick off all those idiots with their multicultural, political correctness etc and will come back to us, normal people 🙂
Yoda, the situation is quite simple — I used to have my reg. set to 120 bar, it was enough to reach the speed of the pellet about 265 m/sec, no more, no matter what hst you have, as I began to use heavier pellets I had to increase the pressure after reg. in order to keep the good air consumption and increase the speed. When I tune a reg down to 100 bar I have more constant shots with lower speed and normal hst, so that is not a theory, that is my experience.
Hi Ed,
Thanks for stepping in.
I shall try Narrowing the port, and subsequently increaing the hst.
Just one thing though, you wrote that decresing the reg pressure to 100 will require incresing the hst “and the inconsistency will disappear”…
That’s not correct:
If the reg pressure is decresed to 100, with the same hst tension,the speed actually goes up quite a lot, and the hst needs to be loosened to keep speed under limit.
So if the aim is to increse the hst, to reduce the hst looseness, then the reg pressure needs to stay high.
I appreciate that since you have not tried doing it in practice (for time constraint i gather from wha you write) you are just talking theory, but the actual response is quite different when actually done.
Regards
the guy who said that to you ed is a fool, turning his power up without having a firearm certificate could get him 5 years in prison and a £10,000 fine as well on top of that the sentence would mean he is banned from shooing anything for life..a fella i know who got caught selling copied dvds got an 18 months sentence, that also meant he couldnt shoot for 5 years he had to sell all his guns too..plus it puts a black mark on all the airgunners who obey the law.i am not being over serious we know many of our forums are monitered by agencys and anti shooters, so any GB or UK airgunners please dont follow that guys example if you love your sport 😉 😎
I am awfully sorry for not reading all four pages, probably there were some good advises already and I am sorry again for repeating them if there were any. I got the link to this topic from Alex (England) who buys some guns from me for selling them in England.
The situation is quite simple — the guns are initially designed for using definite pellets with definite speed to get the best accuracy/energy results. It happens so that it was JSB heavy 18 grain pellets and speed of the pellet withing 260-300 m/sec. So, based on that task all the gun was made, all the wholes inside, the spring tension and size, the weight of the hammer, the length of the barrel and the twist of the barrel, the working pressure after the regulator and the working pressure before it. Since normal people from countries with ubnormal weapon legislation want to take my guns as well but are afraid of the legislation I, based on their requirement have to downtune the gun to meet the energy limits. In some cased (to tell you truth in most cases) they uptune them after taking them in hands.One of my clients from GB, when he ordered a .25 from me and I asked him about the law restrictions told me “I don’t care about their fucking laws, I need that gun with that energy and I will have it!” So, there is no problem to downtune the gun just for the purpose of the delivery. But, if one wants to keep it withing the limits that can be a kind of problem. To have the gun with lower energy I have to change everything I mentioned before. As you should understand that is not possible at the present situation.
The best thing would be to downtune the regulator to 100 bar, in this case one will need to screw up the hammer spring and all the inconsistency will disappear, as the hammer will not be free at the very end of its movement. That is the only problem. The other thing which could help — to narrow the whole in the breech. Just a washer with the thickness of 1.2 mm and the outer diameter of 8 mm and the inner diameter of about 3 mm or 2.5 mm. In this case one will need to screw the hammer spring more and that will remove the looseness of the hammer.
Just out of curiosity:
What is the usual fps variation you get with your gun, 10fps? More?
Any difference you might have notice with number of shots fired or temperature or whatever?
Curious to know what is the level the gun reached after was tuned by cheshire gunsmiths.
Thanks!
been a while since my last chrono at the club and due another so will make a note of it but am sure it was not more than 10psi dont see a power change until 110 bar although in some of the cold weather we have had through nov to feb the gun was sluggish but then so was my others i still havent done a pellet count from 200 down to 110 but its over the hundred thats for sure and my version was quoted as 70 shots at fac i never got to fire the gun at 32ftlbs to test that though 😀
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Update
Fitted a 2.5mm (ID) washer on the port.
Reg moved to 12:25 (stock being 12:00).
Reg pressure should be around 95bar (not yet reached the reg coming off point as i haven’t shot so many shots).
Consistency is now great WITHIN THE SAME TEMPERATURE RANGE.
i.e. indoor, kept in the same room, has barely a 5fps difference across several shots on several consecutive days.
Still have to try shooting outside, with lower temp.
I have found that there is no way to keep speed constant with 15 degrees (Celsius) difference, as speed drops 15fps passing from 20 C to 5-7C.
I don’t know if the temperature affects the dynamic of the gasses or (more likely) th stiffness of the spring.
This has happened woth whatever setting i’ve used so far, so i guess it is a physical hurdle which is impossible to overcome.
Not a problem as worst case scenario speed drops.
And the Law is safe.
Now time for shooting some rabbits and leave this tuning shite alone.
Cheers all