Author Topic: made an adjustable piston for the 880 (Read 48395 times))

Rob M · « **Reply #80 on:** September 30, 2016, 12:47:53 PM »

those are REALLY good numbers. i think you said the gun was supposed to push 500 fps stock?? or am i confused.. 810 is faster than a stock 397! Now to get the number of pumps down.. wish you were closer, wed convert it to big bore stroker in no time since ive already dont the leg work researching where to get the tube and what sizes are ideal.what was the gun pushing on 10 pumps before the mod??

bhh · « **Reply #81 on:** September 30, 2016, 01:09:44 PM »

Yes, it was suppose to push 490 stock, but this is the reduced power version. The normal version claims 800, but online reviews have it around 100 fps faster than my reduced power version. I think the only difference is mine has a shorter piston that stops .175 short of the valve. Nevertheless, mine started out shooting 10.5 gr pellets at 450 with 10 pumps before the mod. IIRC.

I'd like to try the larger tube. Any info would be greatly appreciated.

But next up I want to see what reducing valve volume does.

Rob M · « **Reply #82 on:** September 30, 2016, 01:31:20 PM »

the valve is soo small ill tell you what will happen.. from pump 1-5 the velocity will go up , or stay about the same. from pumps 10 up you will either not be able to pump anymore, or the velocity will not climb.. your new max numbers will likely be closer to 700 fps, but with less strokes. u can try it and see what happens. But ur wayy better off pushing higher pressure with a very solid pump arm mechanism

bhh · « **Reply #83 on:** September 30, 2016, 07:33:04 PM »

I'm sure you're right, but it sure is fun to experiment. Sounds like I'll need to build a new cocking arm.

Anyway, curiosity got the best of me and I picked up the full power version of my rifle today. Kmart had them for $35.

The piston looks a lot like my modified one - plastic back half that connects to the pump arm with one o-ring and a foam wiper, and a front half with an aluminum head with one o-ring.

30 pumps gives 720 fps, 10 pumps gives 630 fps. I'll bet a few layers of aluminum tape would have it right up there with the adjustable piston.

Rob M · « **Reply #84 on:** September 30, 2016, 07:36:47 PM »

maybe .. the dual orings u have is a bit of an advantage.. give it a go.. seems like u already spanked the stock numers

Rob M · « **Reply #85 on:** September 30, 2016, 07:37:28 PM »

ok yea , id just reinforce the pump arm with a strip of steel till the connection point blows up like mine did lol

bhh · « **Reply #86 on:** October 01, 2016, 12:20:10 PM »

I made a reducer. It reduced the valve volume by .9 cc.

From the 4th pump onward it pumps about as hard as the previous version at 10 pumps.

Results:

1 pump - 262
2 pumps - 388
3 pumps - 470
5 pumps - 532
6 pumps - 585
7 pumps - 600
8 pumps - 625
10 pumps - 650
15 pumps - 690
30 pumps - 709
40 pumps - 702

So, I actually lost speed from 6 pumps on. 5 pumps were the same. I'm sure barrel length comes in to play now with the small volume of air.

It is crazy quiet at 4 pumps and below; the hammer strike and valve reset are louder than the shot. This would be a great mod for basement shooting or bird pesting at close range It is also much quieter for the rest of the shots.

Now I'll increase valve volume a little at a time and see if there is a sweet spot.

Rob M · « **Reply #87 on:** October 01, 2016, 01:10:50 PM »

Quote from: bhh on October 01, 2016, 12:20:10 PM

I made a reducer. It reduced the valve volume by .9 cc.

From the 4th pump onward it pumps about as hard as the previous version at 10 pumps.

Results:

1 pump - 262
2 pumps - 388
3 pumps - 470
5 pumps - 532
6 pumps - 585
7 pumps - 600
8 pumps - 625
10 pumps - 650
15 pumps - 690
30 pumps - 709
40 pumps - 702

So, I actually lost speed from 6 pumps on. 5 pumps were the same. I'm sure barrel length comes in to play now with the small volume of air.

It is crazy quiet at 4 pumps and below; the hammer strike and valve reset are louder than the shot. This would be a great mod for basement shooting or bird pesting at close range It is also much quieter for the rest of the shots.

Now I'll increase valve volume a little at a time and see if there is a sweet spot.

so in other words, my prediction was SPOT On?? lol, awesome , cool, that ya tried

Rob M · « **Reply #88 on:** October 01, 2016, 01:19:53 PM »

i think increasing the valve 40% will get ya to 900fps , or better, but the pump count may not go up..

bhh · « **Reply #89 on:** October 01, 2016, 01:39:06 PM »

Quote from: Rob M on October 01, 2016, 01:10:50 PM

so in other words, my prediction was SPOT On?? lol, awesome , cool, that ya tried

Yep! Except that pumping wasn't as hard as I thought and the pump arm didn't break - yet. Lol

Rob M · « **Reply #90 on:** October 01, 2016, 03:00:45 PM »

lol. well im excited to see what the valve increase does.. i dont see why you cannot get 900-1000 fps.. when i had one with added valve volume , i didnt have a chrony but heres the video

seriously think i was hitting 1000fps

bhh · « **Reply #91 on:** October 01, 2016, 04:24:35 PM »

Nice! That sounds like a .22 rimfire.

I'll have to ponder a way to increase the valve volume. I'll bet those threads are metric and I don't have any way to cut them.

Rob M · « **Reply #92 on:** October 01, 2016, 05:07:29 PM »

the sloppy idea is a dremel./Yes in real life it sounded like a 22 and i have a 22 so I know. lol/the way i did mine was add a gauge , so the channel leading to the valve was the additional volume. if ur not used to tapping NPT threads, DONT DO IT>> Anyway , id bore the rear valve plug on the lathe. drill bit and a boring bar could get some small gains.. then combined with dremel in the wall of the valve, u might have an easy time. You can thread metric on an imperial lathe, just need to know what ur doing.but id go the bore route.

Rob M · « **Reply #93 on:** October 01, 2016, 05:08:56 PM »

id have to see it in real life to have more ideas i guesss

bhh · « **Reply #94 on:** October 01, 2016, 10:51:31 PM »

I've been looking and thinking, and I just don't see much excess material. I think I can unscrew the halves about .040" and then remove a couple threads from the male end, but that would only get me a 10 percent increase. I can bore it thinner in some areas, but I don't want to make a hand grenade. I think my time would be better spent fitting a larger tube like you originally suggested.

Rob M · « **Reply #95 on:** October 01, 2016, 11:48:44 PM »

the interior wall on the daisy 880 is super thick . .400 roughly, so adding volume was no issue.. another idea, drill and tap a hole. then plug it only at the end. essentially what i had done with the gauge , but you would just have a plug.. the bigger tube would get the pump count down dramatically, but without a seriously solid pump mechanism and rigid piston assembly, it will not hit higher pressure. ( again more valve volume would be huge gains, especially combined with the bigger compression tube) if you can , share a pic of the compression tube configuration

Rob M · « **Reply #96 on:** October 01, 2016, 11:56:09 PM »

i looked it up on your other thread, thats a wayyyy better design than the 880. the cap that holds the check valve could surely use some boring.. and the valve body itself could use the drill/ plug method if you are confident in sealing it.the compression tube looks like real steel too, lol, thats a big difference. the 88o tube is a 4 inch piece of thin thin wall aluminum

bhh · « **Reply #97 on:** October 02, 2016, 12:51:40 AM »

I'll get some pics tomorrow, but it's a metal tube. As to the valve, there is no where on it that is .400 thick. Locations on the inside where it gets thick correspond with grooves or cuts on the outside.

Rob M · « **Reply #98 on:** October 02, 2016, 12:56:01 AM »

i saw there are slots and screw holes externally.theres definately ways to add volume, but having the pump compression tube bigger is a leap in the right direction no matter what to reduce the stroke count.. be nice getting 800 fos at 10 pumps or less

Rob M · « **Reply #99 on:** October 02, 2016, 01:06:25 AM »

I really wanna see you get to 1000 fps so i can go grab one and do the conversion with your r+d LMBO

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made an adjustable piston for the 880

Author Topic: made an adjustable piston for the 880 (Read 48395 times))