Discovery - Adjustable Transfer Port

Discovery - Adjustable Transfer Port

Joined: November 4th, 2010, 7:35 pm

November 6th, 2011, 10:13 am #1

After several thousand rounds through my Marauder it is time for a lightweight sporter that can be shot in the standing position. This Discovery will replace my springer. I have a nice used .177 Disco on the way and then some tuning will start. From what I have read it is likely that even 10.5 gr pellets will be moving a bit too fast for best accuracy...My experience shows 880 fps is ideal and much faster accuracy then suffers.

I am looking to buy (no lathe...) a fixed transfer port with a smaller id or an adjustable port.

Any comments on barrel bands when using a 6.5" suppressor would be great...Do I use a second band near the end of the barrel? Do you guys place shims on your bands as shown on the TKO site?

Thanks,

Lou
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Joined: March 28th, 2002, 6:54 pm

November 6th, 2011, 5:21 pm #2

if a flat string at lower power is your goal. Lower fill pressure is likely the result, nice if you are pumping.
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Joined: November 4th, 2010, 7:35 pm

November 6th, 2011, 6:02 pm #3

After several thousand rounds through my Marauder it is time for a lightweight sporter that can be shot in the standing position. This Discovery will replace my springer. I have a nice used .177 Disco on the way and then some tuning will start. From what I have read it is likely that even 10.5 gr pellets will be moving a bit too fast for best accuracy...My experience shows 880 fps is ideal and much faster accuracy then suffers.

I am looking to buy (no lathe...) a fixed transfer port with a smaller id or an adjustable port.

Any comments on barrel bands when using a 6.5" suppressor would be great...Do I use a second band near the end of the barrel? Do you guys place shims on your bands as shown on the TKO site?

Thanks,

Lou
Any tips on the best method to lighten? Can one drill small lightening holes in to accomplish some weight savings? Thanks for any advice.

Lou
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Joined: November 17th, 2006, 3:51 am

November 6th, 2011, 11:51 pm #4

Have ground/filed big flats (pretty much the sides of the srtiker are just along for the ride, the top holds the pin and the bottom acts as a sear..so can pretty much just take away the sides).

Others got lathed...but they are hard and will take a TC lathe bit. Can anneal them soft, lathe them (and they come out prettier this way), then harden them again (either heat harden the whole part or case harden the outer layer (KaseKnit).

Do have to say, the best combination of shot count has come from a medium lightened striker and a slightly strangled off transfer port. Allows almost a full fill pressure (close to 1800psi).

The striker force sets the fill pressure...its the force that knocks open the valve. Get the striker very light, and it just can't work up the "oomph" to open the valve at higher pressures. Does save gas, as the valve tends to open and close faster with a lighter striker. I'd lighten and test, not going any lighter than will open the valve at 1600-1800psi.

At that point, you have the operating pressure pretty well set. To get more shots, have to control the gas release to the pellet.

Would be good to start trying smaller transfer ports. May find that a slightly smaller transfer port does little to change velocity, but adds a few shots per fill. Humans don't intuit circle area worth a crap...going from .12" to '1" doesn't seem like much...but its going from .0113CI to .0079 CI.

Ideally, you'd stop reducing transfer port size once you hit the energy level you wanted...but if you want "all I can get" then don't do EITHER the light striker or the smaller transfer port.



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Joined: November 17th, 2006, 3:51 am

November 7th, 2011, 12:09 am #5

Had a glitch...one shot was 2fps too slow...ignoring that one, would be 21 shots inside of 10fps and +18 foot pounds per shot.

Other folks have managed better, and i;ve not finished fiddling with it so I may as well.

Page from notebook (and if you haven't started keeping notes...would be worth while to do so):
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Joined: November 4th, 2010, 7:35 pm

November 7th, 2011, 10:10 am #6

After several thousand rounds through my Marauder it is time for a lightweight sporter that can be shot in the standing position. This Discovery will replace my springer. I have a nice used .177 Disco on the way and then some tuning will start. From what I have read it is likely that even 10.5 gr pellets will be moving a bit too fast for best accuracy...My experience shows 880 fps is ideal and much faster accuracy then suffers.

I am looking to buy (no lathe...) a fixed transfer port with a smaller id or an adjustable port.

Any comments on barrel bands when using a 6.5" suppressor would be great...Do I use a second band near the end of the barrel? Do you guys place shims on your bands as shown on the TKO site?

Thanks,

Lou
My Marauder tuning has been a great lesson in the physics of PCP guns. That's why I would work with whatever fill pressures the Discovery liked and reduce transfer port volume to reduce velocity and possibly flatten string. My Marauder is tuned for a 2150 psi max fill, so with the Discovery's lower fill demands there should not be a problem.

Would you share how you strangled down the transfer port volume or does anyone know where to purchase? Thanks.
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