Avenger / Leviathan project 60 FPE in .22

[Lathaniel]

I am working towards producing  60+ FPE on my .22 Leviathan using DIY/ low cost mods.thebudea is to make 60FPE accessible within a cheap platform, staying true to the cheap platform and not adding $100's to the price. Thus far I have got it just shy of 56 FPE with a total of R750= $50. I will share my learnings, the do's and don'ts and would appreciate other people's inputs.

The first thing I did was to correct the low POI . At full elevation on the scope, the POI was 5cm low at 30m. This was actually a quick and easy fix, though it took a lot of thought, trial and error to fix. The rear barrel shroud stabilizer was too tight, forcing the stabilizer to be misaligned with the barrel, shroud and stabilizer, forcing the barrel to face down.
Remove barrel shroud, using an Alan key loosen the grub screw, until it is in perfect alignment with the shroud, reattach the shroud, and your POI is fixed.
Next, I drilled the barrel and transfer ports to 5mm, my barrel port was 4mm, and the transfer port was already at 5mm. Remember to always deburr after drilling, I used a knitting needle and 800 grit sand paper. I will be honest; I was disappointed with the modest 3 FPE gain, still the gun was running 43 FPE at this stage.
This is where I spent some money, I bought an extended plenum. An extra 10cc of air, and with a small modification to the stock, I used a drill and file. I gained another 2 FPE. As an aside, to install the extended plenum, one needs to remove the air bleed valve. This should be simple; however, there is a hidden grub screw between the air and trigger blocks. Please remove this before, unscrewing the bleed screw cap.
A friend told me that it's possible to remove the valve return spring. I did thus, however, due to filling with a small Chinese compressor; I could not get the valve to seat. In the end, I took a very light spring off of an electric motor bush that happened to fit perfectly, and just like that, I was on 50 FPE.

If changing the valve spring had such an effect, that got me thinking of the hammer. I tried shimming it from the rear, as the parts diagram shows a spring washer in the 0.25. However, the sear would not engage at this point. So, back to the drawing board, In the end I took a 5mm machine screw, with a wide head, and filed it down to fit into the hammer, with the screw part, into the spring. 56 FPE, though my shot count was affected, I'm now only getting 15 shots per fill.
And this is where disaster struck. Checking ports, I noticed that the valve port is very small. After removing the valve stem, it is equivalent of a 3.5mm hole. To get this, convert the diameter of the valve hole and stem to area, then subtract the stem from the valve port area, and convert back to radius then to diameter. This is clearly a large bottle neck. I drilled the port to 6mm, which puts the valve port at just over 5mm, perfectly balanced. However, the valve would no longer seat unless I put the OEM valve spring back, which pushed my power back down to 50FPE. I am currently having a new valve, with the correct port sizes, machined, with an expected cost of R500= $25. Hopefully, with this installed, we will reach the 60FPE.

In the interim, I have started playing with the trigger. I read somewhere, possibly here, about a trigger mod to improve it. On that concept I stripped the trigger, and took the trigger tension screw out, and placed it in the rear hole, closest to the trigger, and placed the "blank " I removed into the trigger tension screw hole. It took some adjusting before the safety would work. But now, I believe the trigger is much lighter than stock. That said, I will need to wait for my new valve before I can properly test it.

I will keep this post updated on developments; if anyone has other ideas or opinions, I would appreciate it.

[ranchibi]

Lathaniel, nice work and mods on your Avenger! I hope you reach your 60 FPE tune. I wonder if you get someone to fabricate a drop down block (will have to cut stock to attach) so you could run a larger carbon fiber reservoir to attain more shots and maybe increase your plenum volume more easily.

[Lathaniel]

Hello and thank you. There are people here running that block and tank, I had a chat to the one guy today, and he reckons he gets around 200 shots per fill, on his 500cc bottle, with it set to shoot 18gr JSB at 905 fps. That is incredible. I know Doux silencers here in SA did a large order for export to America recently.
It is definitely on my to-do list, but quite pricey at the moment, hopefully prices stabilize, or I manage to save a bit. But the Leviathan is incredibly slug hungry.

[sb327]

I may have missed it, what weight projectile are you using?

Dave

[Lathaniel]

At the moment, I'm using the .218 23gr H&N HP slugs. I'm getting between 1040 and 1050 FPS. The thought is that when I've reached my target, I can use 27 or 30 gr slugs, and be between 950-1000 fps, which from what I understand, seems a good speed for long range accuracy using slugs

[sb327]

Heavier slugs should yield you a few more fpe. You may be right at your target goal with heavier slugs.

Dave

[Lathaniel]

Thank you. As soon as I get my valve back, I will try the heavier slugs, much appreciated

[Lathaniel]

So instead of just waiting for the new valve, I decided to work on the trigger. In tests, without air in the gun, unfortunately it seems to have a single action, with a much crisper and cleaner break.
For those that are interested I will detail the process below.
1) Remove the trigger, a pin easily pushed out of the breech block, top and closest to the muzzle.
2) Remove the trigger tension grub screw.
3) Remove the "blank" grub screw, from the rear of the trigger, closest to the trigger.
4) Insert the trigger tension grub screw into the hole left by the blank grub screw.
5) inside the block, under the trigger, us the safety lock grub screw. You can find it easily by engaging and disengaging safety with the trigger out. Loosen this a little bit, if you don't, when you adjust the new screw to get a lighter break, there will be a point, with very little gain, where the safety does not engage.
6) Optional add another screw to where you removed the trigger tension screw and replace the spring. If you don't do this, the trigger may seem a bit loose when not cooked.
7) Reassemble trigger
Adjust the trigger to your liking, using the rear 2 screws.
9) Test the safety when you are happy, if it does not engage,  either back the safety screw out, or make your trigger a bit stiffer.
10) Do the bump test, in a safe manner, make sure that the adjustment is safe before being happy with it.

[Lathaniel]

OK, so getting a new valve seems to be an exercise in futility. I can't seem to get delrin, peek or even acetal to make a new poppet here in SA. I was busy importing some delrin, but a week later I was told they don't ship here. I looked at after market valves, but sadly, while I believe they would be worth every cent  it is purely unaffordable for us in sunny south africa.So I made a metal poppet, I will attach a photo. Sadly this resulted in a decrease in muzzle velocity, 23gr slugs now only pushing 1000 - 1010, meaning a decrease of fpe, so sitting around 51 fpe now.  Not to mention the incredibly annoying slow leak I now have.
After accepting that, that is what it is, I chanced upon the old poppet, took the vernier and measured it, the back is wide enough to seal, so I drilled a new hole, put the valve stem in the back, polished the new sealing face, and have filled the old hole, with epidermix to prevent leaks, now it's a waiting game, but I have full confidence it will work

[ranchibi]

Hope it works for you!

[Booder98]

5) inside the block, under the trigger, us the safety lock grub screw. You can find it easily by engaging and disengaging safety with the trigger out. Loosen this a little bit, if you don't, when you adjust the new screw to get a lighter break, there will be a point, with very little gain, where the safety does not engage.

If you've adjusted the screw to where the safety will no longer engage, you can replace that safety grub screw with an M3x10mm screw.  That will give you a little more room to make the trigger lighter and still let the safety engage.

[Lathaniel]

Found something that my little brain can't understand. Gamo Pro magnum 15.43gr is shooting at 940 fps, whereas jsb jumbo monster 25.39 gr is shooting at 980 fps, how is this possible. Thanks in advance

[Baco]

Found something that my little brain can't understand. Gamo Pro magnum 15.43gr is shooting at 940 fps, whereas jsb jumbo monster 25.39 gr is shooting at 980 fps, how is this possible. Thanks in advance

what chrony?

are you using the stock 3.5mm valve port?

as you drilled barrel/transfer port if you use the stock valve porting you waste more air i believe, you'd want the opposite so air gets strangled and creates more pressure behind the pellet, otherwise there's higher dwell which favours heavier pellets

i'd balance the porting then play with valve stem length and bstaley or FFH/SSG


you can use a hardened steel drill bit as valve stem to test things


fpe is already higher than the .25 for your gun so congrats on that

[Lathaniel]

Hello, thanks for your reply. I have done quite a bit if work so far, opened barrel and transfer ports to 5mm, valve to 6mm, with a reworked poppet ( i need to make a new valve stem, the one i have is ~ 3mm shorter than standard), ultra light valve return spring, and weighted the hammer and shimmed the spring a bit. Also put a plenum extender in.
I'm using the chrony F1, and my shot strings are very consistent ~ 2fps exterme spread.  I was just very confused to see the opposite of what I expected, but the dwell time makes sense. Im aiming to shoot 30gr slugs when I can find them again, pellets seem in short supply at the moment. So your theory means I should gain more than I expected.

[subscriber]

Lathaniel,

It is possible that you have mentioned your Avenger's pressure regulator setting in another thread.  Else, that is very much part of what determines maximum power for a PCP.

Hammer strike energy needs to increase with plenum pressure, else increasing pressure will limit how far the valve can open, and the valve dwell.

Now, it is possible that your regulator came from the factory with a sufficiently high pressure setting for max power.  I say max power, because you want to reach 60 FPE, but have reached 50 so far.

Perhaps setting the reg pressure up is so obvious that you started there.  Else, what others have done might be useful:




There have been a lot of Avenger tuning threads on GTA, and perhaps you have seen them.  Anyway, finding them via google is easier than using the GTA search engine:
www.google.com/search?q=site%3Agatewaytoairguns.org+.22+avenger+power+tune

[Lathaniel]

Thanks for the reply, I've got the reg set to 2700 psi, and the hammer spring all the way in, shimmed and hammer slightly weighted. Still shy of the 60. Before i started with the mids, 40 fpe was the best i could achieve, so 50 odd isnt bad, just a bit shy of where i want it. I have recently extended the valve length, which should assist a bit, however, the poppet isn't sitting flush now, so need to re face it ( hopefully get to that this weekend). Thank you for the links, I will read through them and see if there is anything I'm missing.

[subscriber]

2700 PSI sounds high enough to be useful.  Much more than that, and your shot count per fill may not be enough.  Depending on your fill pressure.  If you have a 4500 PSI source, then less of a concern.

In a much broader context, here is a thread about
achieving the maximum theoretical velocity from a PCP: 
https://www.gatewaytoairguns.org/GTA/index.php?topic=94054.0

Perhaps not relevant to the Avenger directly, and ultimately at the expense of efficiency.  The point is to identify and eliminate the typical bottlenecks.

One aspect you have already seen is that heavier projectiles are more efficient.   I don't know how heavy you could go, and if that would help much in achieving 60 FPE.  At some point the projectile may not be going fast enough for your purpose. 

950 FPS is usually fast enough for power, efficiency and a flat trajectory.  If you are shooting pellets, much faster than 950 FPS tends to not group as well at longer distances; and the pellets slow down so fast, the exercise is not very practical.  If you want to shoot over 1000 FPS, slugs are a much better bet.  Just keep them sub sonic.  1050 FPS or thereabouts.

Speaking of purpose; other than breaking 60 FPE, what is your purpose - if that is not a rude question?

[subscriber]

All of that said, Lathaniel, at 50 FPE you may already have exceeded what most .22 Avenger tuners have achieved, by a wide margin.

If you can't find heavier pellets, then perhaps some "low friction" slugs - if such an animal exists (cast, with narrow middle and rear drivebands).  I think you need at least a 30 grain projectile to achieve 60 FPE, considering the limited expansion volume of a .22 with a 22.75" barrel length.

[subscriber]

Delrin is the sold as acetal in SA. 

Plastem in Johannesburg has Acetal and Peek:   https://plastem.co.za/plastic-technical-data/

Contact: https://plastem.co.za/contact-plastem/


Engineering plastic supplier in Durban:  http://www.gartech.co.za/products.html#pom

DURBAN HEAD OFFICE
2 Teakfield Road, Springfield Park
Durban, South Africa

Tel: (+27) 31 579 9300
Email:admin@dems.co.za
Website: www.dems.co.za



More SA suppliers, here:  www.google.com/search?q=acetal+for+sale+south+africa

[Lathaniel]

Thanks for all that useful information.
I have recently gotten 30gr javelin slugs, and was getting around 910 fps with them. However, I let other people shoot, and it was double loaded, which I managed to shoot out, however, since then my muzzle velocity dropped to 825, so I have stripped and made a new valve stem, however it isn't sealing properly on the poppet, so I need to re face that, and hopefully I will be on. I will look at those suppliers you suggested, better to make a whole new poppet than fix the old one. I want to use it for pest control as well as long range shooting, 100m and up. There is a 300m gong shoot with air rifles happening soon, not far from where I live. So would be great to be able to do that. Are you also from South Africa?