made an adjustable piston for the 880

[bhh]

Exactly. The screws are made of cheese and screwed into soft aluminum or plastic, and no matter how careful you are, things wear out just from taking it apart so many times.

[Rob M]

yep.. were i to do an 880 again, id do all my mods at once, and actually have a relaible sturdy 900 fps pumper..heck i probably would do 25 caliber.. But ive been too busy..

[bhh]

Yea, you should do it. I'm going to get an 880 and work it over like you did just to have an air rifle I can actually use. What were you getting at 15 pumps?

In other news, today I flared a pellet for a tight fit and pumped it up in the basement with 65 degree air rather than the 25 degree air outside.  960 fps. But really , who cares when I have to do that much pumping.  I'm going to limit myself to 20 pumps and see what I can get with that.

[Rob M]

add a delrin spacer , pump 20 chrono , and repeat till u hit the high of 20 pumps ( reducting volume gradually )
15 pumps was 805 ish

[bhh]

To bring this thread back on track, today Santa brought me a Daisy 880.  Looks like I'll be making an adjustable piston.

I also figured out why you broke pump arms so quickly while I was able to use/abuse my Umarex NXG for so long before it finally gave up. The Daisy pump arm is vastly inferior to the NXG. I've used sporks at KFC that are stronger than the Daisy pump arm. 

Baseline power from the 880 with CPHP 7.9gr:
10 pumps = ~650 fps
15 pumps = ~700 fps
20 pumps = ~750 fps

[Rob M]

thats great@@ a tad low on prelim numbers, i think my lasst one was 671 10 pumps same pells.yes, the spork pump arm is a joke.. the old metal ones are the opposite, and overkill

[airgunner53]

you say the old metal pump arms are a bit overkill, i feel it is better to have it and not need it than need it and not have it. still working on raising the funds for a crony i decided to use my modified 880 on 10 pumps only as it is very accurate, and seams to have the power i need. plus my added stroke helps possibly bump up what I'm actually pumping. seams to shoot hard and is dead on, all I need. if you do a search you can find the old metal pump arms for pretty cheep.

[Rob M]

yep.. if he posts a wtb he will find one, i did.. Funny, i had my 880 shooting 910 fps, but none of the 3 guns were ever accurate. my idea to thread and tension the barrel came after my 880 craze,. basically the barrel would be threaded 1/4-28 and a nut on the front of the shroud would slip in , grab the thread and then the user would turn the front nut to tension the barrel.. pretty dam simple.. Maybe one of these days ill get back to it.

[bhh]

Good to know that metal pump arms are out there. I might build one and try to coax a little more stroke out of it. My goal for this rifle is to have reliable shooter and not seek max power.

Interesting idea about the threaded muzzle.

[Rob M]

i think the adjustable piston with the stock felt oil wipe on it will make the gun a good reliable 800 fps shooter.

[airgunner53]

that was my idea, a god reliable shooter hence the wood stock and forearm and the metal receiver and pump arm. i am swapping out the barrel shroud for another older daisy shroud that i have that has an internal sleeve that feels heavier, but would protect the barrel that much more than the thin metal new barrel shroud. mine became inaccurate after the mods that i did, it used to shoot the CPHP pretty well, and after the chamber volume increase and stroke increase they just pepper the target. i now shoot the Beeman pointed at 8.53 grain as opposed of the 7.9 CPHP. also shoots the gold flights as they are also 8.5 grains. the heavier pellet makes a huge difference.

I have used plumbers tape on the barrel to help it seal and gives it a good fit. looking at possibly making a billet piston arm to increase durability.

love my little daisy.

[bhh]

Wow, that was easy. I did a few mods and new results (with CPHP 7.9 gr) are:
10 pumps = 742 fps
12 pumps = 788 fps
15 pumps = 825 fps

I quit at this point because it's cold and snowing outside and I didn't want to break the pump arm yet. At this point it is relatively easy to pump and I think it will last a long time if I don't go further.

I didn't build a new piston, but I filled the old one with JB weld and sanded it completely flat. I then put a flat washer behind the piston head with a thickness equal to the material I removed from the piston face.  Then I used a round file and extended the grove in the attaching shaft to let the piston assembly go towards the valve face about another .050". This lets the piston and valve contact firmly and the rubber bumper take up some shock and pressure.

I also made a longer/smaller dia. bolt probe, cut the breech end of the barrel to remove a sloppy leade, and opened the transfer port to .125".

This design is really efficient compared to the NXG.

I think I'm going to stop messing with this one and just have a nice rifle.

But I can't help but wondering:

A. Make a steel pump tube. I'll bet with a thinner wall and taking up all the space in the metal channel I could gain .040" in diameter.

B. Adjustable piston with about .010" clearance to the tube wall. The stock has a bunch of slop. I think Daisy doesn't want any chance of the piston hitting that soft aluminum tube. I'll bet the current system is wasting at least a pump's worth of air with all of the space.

C. Tweak stroke length. Maybe make a new thinner abutment out of ss or brass and then see if I can get a little more at the other end.

D. Metal pump arm, obviously. 

Guess I'll have to buy another 880. 

[Rob M]

those are very good numbers , and similar to what i was getting.. I wanted 20 pumps to be 900 fps with 7.9s , never got there, 895 was max.. at 23 pumps i hit 910 fps, but that was a custom piston.. You surely made more headway than most without machining any serious parts.

[bhh]

My plan with this mod was to optimize the way every stock Daisy part functioned to make it efficient as possible. It paid off more than I thought it would. 

So now I'm looking at my NXG project with this in mind. The breech has a sloppy, crooked throat and the probe doesn't push the pellet in far enough to seat firmly in the rifling.  Last night I made an extended probe and now I'll cut off the bad part of the barrel and make a new tighter leade.  Maybe I can hit 1000 fps after all. 

[Rob M]

well i certainly think the ngx is the more classical approach as far as the valve - piston relationship

[bhh]

Agreed. Seems like the dump valve is more efficient, however.

Anyway, I went back out and tried more pumps.

20 pumps = 869 fps
23 pumps = 864 fps

So it looks like I've hit the limit with what I currently have. I could tell I was really straining the pump arm starting at pump 17.

 

[airgunner53]

nice numbers, I am going to be buying a few abutments and going to experiment with them to see what I can do with them to increase stroke and also make them a bit thinner to make reduce clearance from piston to seal. if I am successful, I will be able to increase the stroke of the gun by one whole inch and would use less strokes to reach a good power to stroke ratio. Once again i have not crony, but I have some old sheets of meta and did some testing at 10 pumps and with the bee man pointed they would pancake agains it leaving a flat lead disk. I shot some lead free gold flights at it and id would leave a decent dent and on occasion would leave a small break in the metal, i pumped it to 15 pumps and it blew right through it I need to measure the metal that i was using. i was impressed to see it actually hit that hard. going to try the stroke mod to my .22 daisy and do the same test at 10 pumps to see what I can get out of it. love to see all the work that everyone is doing with their 880's took a rabbit the other day at 10 yards with 10 pumps with the Beeman pointed and had a pass through on a head shot I was happy to see that it has the power to do so, made lunch that much more enjoyable. I would love to get 800+ fps with 8.5 grain pellets.

[Rob M]

Agreed. Seems like the dump valve is more efficient, however.

Anyway, I went back out and tried more pumps.

20 pumps = 869 fps
23 pumps = 864 fps

So it looks like I've hit the limit with what I currently have. I could tell I was really straining the pump arm starting at pump 17.

 

you need a custom piston , make it smooth as glass and duel oring..those numbers will skyrocket

[bhh]

you need a custom piston , make it smooth as glass and duel oring..those numbers will skyrocket

Yea, I'm fighting the urge...

[bhh]

I will be able to increase the stroke of the gun by one whole inch 

I'm interested. 8 pumps would be like 10, 12 would be like 15. 

I would love to get 800+ fps with 8.5 grain pellets.

You might already be there, but without a chrono it's hard to tell how much you've improved your velocity.