Tuning How to lower SD on unregulated pcp's?

[LancasterAirgunner24]

With my Hatsan AT-44 QE 177 and Beeman Chief 2 plus 177, im getting average SD of around 20 over 40-50 shot strings ( i have them both shooting 900ish fps at 2000psi fill pressure ).. What can be done to lower the SD? I want to get the SD as low as i can before i decide where i want to set them up to shoot the two mags per fill..

 

[EPG]

I just have the stock hammer and spring in there, all i did to it was sand and smooth off the edges to reduce friction on the hammer as it moves back and forth.. what kind of increase in weight should i be looking at adding to it? i havent weighed the hammer but im not opposed to it and messing with that.. a return spring on the outside of the air cylinder right? ive heard of the o-ring stacking but i feel as though more simple things can be done first..

I love unregulated rifles and I’m always tweaking and testing on mine. Picture is of hammer springs I’m currently testing in my unregulated Daystates (Daystate is nice in that they seem to always use 18mm OD springs - so easy to swap across rifles).

As thomasair and thammer said, you can try a stiffer valve return spring or a heavier hammer. If your hammer is hollow, it’s easy to add some weight (melted pellets, etc) inside it.

I’m really experimenting with hammer springs. I’ve found amazing differences you can achieve with different springs.

I’m focused on my Daystates lately. Even my regulated Daystates may benefit because Daystate seems to use very high regulator pressures in their HP rifles. I don’t need the extreme velocity for target shooting, so I’m experimenting with lighter hammer springs to drop the peak of an unregulated shot curve into say the 150bar range. Then I’m hoping I can drop a regulator into the rifle set for 150bar and the rifle will be operating at nice velocity & efficiency point.

It doesn’t cost much to try different springs - $3 for 5 springs on AliExpress, lol. And it’s reversible - just swap the original spring(s) back in.

-Ed

 

[LancasterAirgunner24]

As Thomas air stated springs can be a huge help. In addition to the return spring a heavier shorter (just shy of the hammer touching the valve stem) prevents hammer bounce and saves air so you retain more of it extending that curve. If it already makes the power you need there's no reason to touch the ports.

Honestly, 900fps with 8.4g Norma for the beeman and 9.1g Norma for the hatsan to me will provide a clean kill shot on most small critters and allow me to plink at 50+ yards.. that to me is right where i wana be with my air rifles.. I just finished graphing my new results and needless to say, im plenty satisfied with the results! ill post the updated graph now. as for bounce and sound of the function over the course of the shot, its not bad at all, its a good "THUNG" and i dont hear a bunch of wasted air. both of them are now i think functioning in copasetic manner enough to move to slinging pellets down range and shooting groups! I dont see the need to do anything with ports honestly. its just a good way to ruin your gun and not be able to go back. i rather mess with things i can repeat and go back too if needed.

 

[LancasterAirgunner24]

Guys.. i think i did it haha 3/8 turn on the hammer spring for the beeman and 1/8 turn on the hatsan and i am very happy with the results! Time to put the chrony away and start shooting groups and messing with Chairgun!

Final Results:

Beeman Chief 2 plus 177. (40 shots)
Fill: 2000psi
Pellets: Norma 8.4
HI: 929
LOW: 890
AV: 911
ES: 39
SD: 10

Hatsan AT-44 QE 177. (30 shots)
Fill: 2000psi
Pellets: Norma 9.1g
HI: 930
LOW: 902
AV: 918
ES: 28
SD: 8

Thank you guys for your input, i do appreciate it! All my tuning consists of chrony work, hammer adjustments, fill pressure adjustments to eliminate wasted air and get the guns shooting good and not being over worked.. good hearing helps too lol

 

[LancasterAirgunner24]

Your Hatsan isn't going to be able to be flattened much more at all. Your first shot to peak is around 30fps difference. Not much improvement to be had there.

Only ways to flatten are to either turn the hammerspring in slightly or need a smaller transfer port.

1/8 turn on the hammer spring is all i did to get the new results from the prior.. i dont mess with ports ever, i feel as though like i just did you can achieve satisfactory results with minor altercations first.. new ES is 28 and SD is 8.. that to me for an unregulater pcp is just where i wana be.

 

[LancasterAirgunner24]

Your approach is a good way to get into airguns - learn how things work and then make an informed decision on what/where you want to buy into.

I also believe that good quality equipment is worth while investing in and buy the best I can afford.

Just a comment on SD and ES numbers, I agree that they are an excellent indicator of (power plant) performance but there are other factors (like harmonics) that determine overall performance. Look at the whole picture.

Cheers!

Ive been shooting air rifles since i was just a little guy but recently i picked up these two for good prices on Pyramyd air around christmas so ive been just digging deeper into it since and glad i did! Quality will always beat quality, but sometimes my wallet feels otherwise haha working with what i got! Next is shooting groups and just letting the gun tell me what it wants to get the tightest groups i can! trigger work, harmonics if needed, clean/maintained barrel and crown and the most important ME! every shot, the same breathing, movments, timing, trigger pull, rest etc.