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Mountain Man · Member

Well,where did everybody go?Too many rookie questions huh?Oh well,thanks anyway Rolling Eyes

rsterne · Moderator

My recommendations for a 1377 in .177....

Flat-Topped Piston and Valve
14" barrel
Otherwise, leave it alone

700 fps should be no problem.... maybe 10-12 pumps.... let us know....

Bob

Mountain Man · Member

Thanks for the reply and I will get back to you in a few weeks.It will probably be 5or6 weeks before I have it in hand and I will get back to you then Wink

Doc Sharptail · Member

I'm seeing 710-720 fps with a 24" .177 bbl on my ftp'd 13-77, at ten pumps, depending on the pellet. 700 should be doable with a 14" .177 bbl

I have yet to see anywhere near 700 fps with a 24" .22 bbl. Closest I've come is 650-660 with a 13-XX tube and valve. Even with a bored out valve, and lightest valve spring that I dare, I still start retaining air at 22 pumps- and 650 avg fps. There's a point of diminishing returns with the 13-XX that limits out beyond my somewhat limited ability.

So, I'd like to know how to get 700 fps and beyond out of a 24" bbl 22, on the 13-XX platform? This is an honest question- no ill-will intended...

Regards,

Doc Sharptail

rsterne · Moderator

HI Doc....

The only way I have found to get more than about 650 fps from a 13XX platform is to change the hammer spring for a stiffer one.... My 2289 with 14" barrel in .22 cal topped out at 650 fps at 18 pumps (with a 200 fps 2nd shot).... I changed the pump to one from a 2200 (my Uber-Carbine) and I was getting the same performance but with just 13 pumps.... By adding a velocity adjuster and cranking it to nearly coil bind (you have to have enough play to safely cock the hammer) I got it to 665 fps in 14 pumps.... ie the same performance you have, but in a 14" barrel.... (probably because of the increased preload on the hammer spring).... Cool

With a Discovery hammer spring and the adjuster cranked in just shy of coil bind I can get 765 fps (150 fps 2nd shot).... but that is at 24 pumps with the 2200 pump.... There is no reason you could not duplicate that (ie a good solid 100 fps increase) with about 34-36 pumps with a 13XX pump tube (although I have never tried that configuration).... All these velocities are with a 14" barrel.... Cool

My .22 Uber-Pumper was able to hit 795 fps with 14.3 gr. pellets with a 24" barrel and a 2200 hammer spring and stock 2289 valve volume.... It would defintely be over 800 fps with a Disco hammer spring.... That should occur at the same 34-36 pumps with a 13XX pump (ie the longer barrel will buy you about 35-40 fps).... With an extended valve (82% more volume than stock) I got over 900 fps using a 2200 hammer spring (I didn't have a Disco spring then).... but that took 22 pumps of a 1400 pump tube (which has nearly double the swept volume).... Shocked

From my experience, the point at which the valve retains air is the key to increased velocity.... A weaker valve spring helps.... but I find the heavier hammer spring to be more effective.... You will have to pre-cock the hammer before pumping, of course, or the air just rushes out the barrel.... Rolling Eyes

Bob

Doc Sharptail · Member

Thanks for the informative reply, Bob!

If I could quit buying scopes and air-guns for a while, I could get a pile o' parts, and do some experimenting of my own.

I'll keep the discovery spring in mind. The main purpose of all this is for hunting. I'm sure even a 50-60 fps increase will help me on the trajectory side of things. It's doable at the 650 mark, with close in head shots. I've had one too many experiences with pellets bouncing off the armoured feathers that the late fall grouse have around here, so hurried body shots are out of the question...

Lot's to work towards yet!

Regards,

Doc Sharptail

rsterne · Moderator

I found that with one of my velocity adjusters I could use a Disco spring and adjust it so that you didn't have to precock before pumping (faster reloading on Grouse).... and I was using a "set" sear spring inside the valve.... That also got me 650 fps with a 14" barrel and 14.3 gr. JSB Express pellets.... Cool

One thing I haven't tried is a stock valve spring with a Disco hammer spring cranked up until it will barely hold air when you start pumping.... My guess would be about 700 fps with a 14" barrel.... you could be the first to find out.... Twisted Evil

Bob

rsterne · Moderator

I pulled out my 2289 which I use for testing and had a go at trying different hammer springs today.... This gun has a completely stock (but flat faced) valve, transfer port and barrel port, including stock valve spring.... It is fitted with a flat-topped piston.... Obviously if you enlarge the ports you can increase the flow, which can be an advantage in .22 and larger calibers.... but I have found of limited value in .177.... All I was trying to determine was at how many pumps the gun reached its maximum velocity with the different hammer springs.... All testing was with JSB Expresss 14.3 gr. pellets.... Smile

Stock rear plug:

2289 hammer spring: 555 fps @ 18 pumps (270 fps 2nd)
2200 hammer spring: 620 fps @ 36 pumps (225 fps 2nd)
Disco hammer spring: 615 fps @ 30 pumps (275 fps 2nd)

Velocity adjuster turned in to 1/2 turn before coil bind:

2289 hammer spring: 580 fps @ 24 pumps (320 fps 2nd)
2200 hammer spring: 625 fps @ 40 pumps (no further gains)
Disco hammer spring: 645 fps @ 40 pumps (no further gains)

The 2200 hammer spring is about 3/8" longer than the 2289 and Disco springs.... therefore with the stock rear plug it has a higher preload.... The Disco spring is stiffer, however, and when adjusted to maximum safe tension while still allowing the gun to cock safely, it develops a higher striking force....

My conclusions are that if you have a stock rear plug, either the 2200 hammer spring or the Disco work great.... they both deliver about a 60 fps gain over stock (at 30 pumps vs. 18).... If you have a velocity adjuster, however, the Disco hammer spring is the best choice.... You can adjust it over the widest range of velocities, and it has the highest velocity when cranked to the max.... Note that with the stock internal valve spring, I never had to precock the gun before pumping, even with the Disco spring at maximum tension.... Cool

Bob