Bottled Disco Frankengun (Help!)

[aPpYe]

Okay, so I put a tissue on the front part of the breech, where it meets the barrel and it popped very noticeably  when I fired a pellet.  I guess this means the leak is the transfer port after all.  Is a transfer port made completely from polyurethane (95a) not going to work?  Is the material still too soft?  I opted for that in lieu of PTFE because I wanted the transfer port to stay the same shape between a bunch of rebuilds.  At some point, I do plan on keeping the gun assembled for a long period of time, but for now, while I am continuing to take it apart and put it back together (sometimes several times a day), I need a transfer port that is going to survive many rebuilds...

Since my last post, the barrel port and the valve face are now filed perfectly level and polished for a good seal.  This did add another ten to fifteen thousandths to the needed size of the transfer port, so I am going to have to make another.  Third time's a charm I hope...

[Gerard]

My second attempt at fitting a 95 durometer urethane transfer port works great, with zero tissue flutter on firing a JSB 18.13gr at 700fps. Checked both sides with a single ply of tissue and nothing moved but the trigger, hammer and pellet. The first one leaked slightly. It was an easy fit, no effort to insert it into the hole in the cylinder. So I made the second seal a bit harder to snap into place and it's working great. It is also squished between barrel and valve by about 0.012".

[aPpYe]

Cylinders would have been fantastic, and it what I originally did, using a mill.  It wasn't until I got home that I realized that it milled them both oversize and the valve/tube one off center.  I think the bit was bent or something.  Once I got my 3/8" polyurethane rod in, I put it in and saw that the valve had a leak at the poppet, and I ended up ruining the valve trying to fix it.   

With the new valve, I just filed a flat.  Yesterday, I also filed the barrel itself flat (the breech still has a nice round hole, so placement should still be easy) because on closer inspection I discovered that the bit left a high spot around the edges, which I thought might be the cause of the leak.

Anyway, I will also go with somewhere between .010" to .015" oversized to make it squish in there really well.

[aPpYe]

Okay, so total distance between the valve exhaust should be .277" ...  Yeah, I filed the @$%^ out of the barrel.  Both surfaces are perfectly flat as far as I can tell, and polished with 320, then 500 grit sandpaper.  I have higher grits but it seemed pretty shiny and smooth with 500...  I always put a film of silicon grease on each side of the transfer port before installation.

I made a transfer port that is .290, and I drilled a 1/8 hole through it just so the gun would work and I could test a shot or two.   Once I have a port that does not leak I will open it up to match both the valve and the barrel ends. 

I still get a puff of air...  I feel it on my cheek.  Perhaps facial hair helps with this!  I won't bother with tissue until I am not able to feel it.

Firing a pellet with a clamp on the front of the breech does seal things better (I feel less "puff") but not completely.  The breech screw was upgraded to 8-32 and all screws are nice and tight.  I don't know if this means I should go shorter or taller with the transfer port, but I will make one at .300 and another at .285 and see what happens.  I am also wondering if I should purchase a second barrel band so it can hold it things more tightly at the breech end...

This project is trying my patience!

[aPpYe]

FINALLY!!!!!!!!!!!!!!!

.300 did it.  At least with the 1/8 hole in there.  I also moved the barrel band to the breech (though I don't know that it was necessary) and really tightened the @$%^ out of all the screws.  I may be ordering a second band for the muzzle end tomorrow to avoid the changing poi issues I see people have complained about...   Since it is regulated, however,  I won't have the problem with changing tube pressure bending things around.  I guess I can see how it behaves with the barrel "floated" like that...  the barrel sure does flex around though!

Here's to hoping that opening up the transfer port doesn't cause me pain and heartache. 

[aPpYe]

Okay then!  Gun is done with final assembly (for now!) and I shot a five shot string with an arbitrary spring/ssg setting (basically turned in just before coil bind and a lot of preload).  It produced a 12fps spread with a maximum of 929fps using jsb 16.2gr.  Tomorrow I will actually tune the thing, and calculate efficiency...

[nervoustrigger]

Very nice, Patrick, I'm glad to hear you whipped it into shape.  I've been following but haven't had much to contribute.  Keeping my fingers crossed that the heavy .177 pellets group well.  A 30fpe .177 would be interesting for some distance shooting.

[aPpYe]

You and me both!  I have probably 100 of the jsb 16.2gr, so probably enough to tune and maybe get a few groups in.  Depending on how well they do, my next ammo order will include some more Jsb 16.2 gr, and some h&n 15gr to try, and I guess I'm gonna have to see how piledrivers work out.  They're a bit pricey, but still considerably cheaper than .22lr...  The 15gr are priced really well ...

I do know that the jsb 10.3gr produced reasonably consistent sub 1" groups at 55 yards, so maybe I gained a little efficiency with those.  I can definitely shoot them faster!  I also have two tins of 13.4gr jsb's to try...

[aPpYe]

Okay, I still haven't had a chance to actually tune it yet.  A brake job, the wrong set of pads, and another trip to the auto parts store put a stop to that.  Oh well.

I did play with it for a couple of minutes though (in the dark) and found something kind of interesting.  More testing required I guess.  I backed the stop nuts for the SSG way back to the end of the rod, well out of the way of any hammer/spring travel.  This effectively disables the SSG, no? 

All shots were fired using 16.2gr JSB Beasts.

Now, If I am remembering this correctly, starting with the RVA (the one that comes on a Challenger) turned out 1.25 turns (the maximum preload possible, 1 turn out will not cock, as it hits coil bind), I took a few shots that were all in the mid 930's ... I then backed the RVA way out (perhaps 9 turns?  I did not pay close attention) and took three shots.  978, 977, 978.  The power went UP!  That's also awesome consistency, but of course, each shot likely used A LOT of air, and I would not want to tune the gun this way.   I took a quick shot this morning before work, backing it out further to exactly 12 turns and found it was at 925, so it looks like the knee is in there somewhere. 

This leads me to believe that this particular spring (2261-009, from the Disco EVP) somehow hits harder with something less than full preload.  Or something else is going on ...  Perhaps I am imagining things?  Can someone shed some light on this? 

New brakes are on the car, and barring any disasters.  I will verify these results tonight, and hopefully tune it ...

[aPpYe]

Okay.?  I guess I was imagining things...  Maybe I grabbed summer 13.4's without realizing it ... Or alien hairless elves from the planet mergatroid...  Anyway, I was unable to reproduce 978 with any setting on the RVA with the ssg nuts removed.  The plateau is around 940 with these pellets, so I will shoot for 915-925 or so with as little preload add possible while maintaining a small gap.  I am pretty close now... 

I also ordered one tin each of JSB 16.2gr, H&N 15gr, Eunjin 16.1gr, and some 21gr piledrivers.  I am going at least one of these will group well.  I have read anecdotal reviews on all of these that go either way, so I guess I will have to find out for myself..

[aPpYe]

All right!  I still haven't had a chance to tune for efficiency because I don't have enough jsb 16.2gr pellets left to run a string...  More on the way.  That being said, the 16.2gr JSB Beasts have DEFINITELY replaced the 10.34gr as my top pellet!  After cleaning the barrel and extending my probe a little further, I am CONSISTENTLY getting .5" (and even below!) 5 shot groups at about 40 yards when shooting at 900-910fps, scoped and bag rested.  Normally, my long range here at home is more like 55 yards, but a large burn pile sitting in the way says otherwise.  But just look at these groups!


The 13.4gr Monsters seem to group well too, but I didn't get the chance to really test them out, and find their optimal velocity.  That will be tomorrow.  The Beasts are obviously a tighter fit as they load into the barrel, which may account for the better accuracy.

[aPpYe]

Dang!  It's been nearly six years since I posted on this!

Anyway, over the last few days I have been machining (milling machine and lathe versus by hand with rotary tools) on a new bolt, valve body and barrel.  I am going with a Maximus barrel, hopefully it shoots as straight as the old one!  Besides assembly and testing all I really have to do now is to mill an oblong barrel port and blend a (95a Polyurethane) transfer port.  The porting should theoretically start at 97.75% at the exhaust port, tapering down to 97.5 at the barrel port, and finally 97.13% behind the pellet, allowing for the (.030") pin probe.  I had ideas about going to 100% by machining a retractable pin into the bolt (or going with Bob's "j-breech" idea) but I just want to shoot this thing.  If I remember right, I was somewhere around 1.7 fpe/ci before, so perhaps that'll go up a little with the more precise machining and the longer barrel.  I will tune it to 30-35fpe with JSB Beasts.  I'll probably try some of the .177 slugs I see on the market as well.  Grouping on paper is the most important factor to me, really.

The gun has been sitting in pieces for years now, so once I have it reasonably tuned and shooting straight without leaks, I plan on leaving it that way for some time.  Famous last words, I know.

QUESTIONS!

I would like to fit an air stripper ...  Does anyone know of one that fits a .177 Maximus barrel?  If not, perhaps there is one that will fit with some light machining?  Suggestions welcome!

I originally outfitted this guy with an original iteration of Bob's SSG on a Challenger RVA, and I will likely use that.  I did purchase a TSS (P-Rod version?) some years ago that I may tinker with, but I don't like that I can't adjust both springs.  I've never even used it.  I'd also have to drill and tap the holes in it so I could mount it to this Discovery tube as well.  I want to be able to drastically adjust power levels like I could before.  This way, i can shoot at loud, full power here at my house (rural, in the mountains), and lower it down to some super quiet back yard friendly level when visiting family in L.A., and everything in between.  If I remember right, the gun barely made any noise when shooting at ~8fpe and was still precise and fun to shoot at ~30 yards at my folks place.  At lower power levels, I can easily shoot through an entire tin of pellets on one fill.  With the current regulator setting (1500 psi or so if I remember right), I was able to adjust from 30 fpe all the way down to not even opening the valve when releasing the striker.  I guess the question I have here, is more or less as follows:  The SSG was a brilliant idea that was pretty groundbreaking in terms of vastly increasing the efficiency of our guns.  Have there been any other improvements like this in the last five or so years that I might not be aware of?

[K.O.]

so ya want to add a stripper... need the 1/2 unf adapter from crosman... then ya gotta go to the red light district at Hastsanville...

https://www.airgundepot.com/hatsan-air-stripper-ha90100.html

[nervoustrigger]

Hi Patrick, good to see you around again.

An SSG is still a favored approach for eliminating air-wasting hammer bounce.

Another one you may not yet be familiar with is a “Cobra” valve.  It uses an internal chamber as an air spring to manipulate valve dwell.  The general strategy being to tune for a snappy shot cycle (low dwell).  See Scott’s excellent writeup for more info:
https://www.gatewaytoairguns.org/GTA/index.php?topic=139401

[aPpYe]

so ya want to add a stripper... need the 1/2 unf adapter from crosman... then ya gotta go to the red light district at Hastsanville...

https://www.airgundepot.com/hatsan-air-stripper-ha90100.html

I don't know if a thread adapter would work ...  Here is a picture of my barrels, the Maximus (the one I plan on using) on the left, followed by the barrel (same as discovery?) and muzzle brake thing that came with my 2400kt on the right.  None of these are threaded.

Hi Patrick, good to see you around again.

An SSG is still a favored approach for eliminating air-wasting hammer bounce.

Another one you may not yet be familiar with is a “Cobra” valve.  It uses an internal chamber as an air spring to manipulate valve dwell.  The general strategy being to tune for a snappy shot cycle (low dwell).  See Scott’s excellent writeup for more info:
https://www.gatewaytoairguns.org/GTA/index.php?topic=139401

Thanks!  Good to be around again.  I definitely caught the bug again!  By the way, have people broken the "2 fpe/ci barrier" yet?  That was the goal we were shooting for when I was last active.

I'll check this valve out!  That said, while perusing some of my old posts, I see that I mentioned an "art/sykes" valve a few times.  It seems I have forgotten what this is, and I can't seem to find any information on what it is or what it does.

[K.O.]

See no pic... the adapter is slip/glue on but I drill and tap and use a grub screw...

[aPpYe]

Whoops.  I added the pic. 

Okay, so perhaps I can drill the threads out of the air stripper itself then, mounting it directly to the barrel?  Then drill and tap a grub screw.  Would this work?  The knurled end of the barrel is about .440" at the end.  The rest of the barrel is more like .435" or so.

[K.O.]

My Maximus barrels are the same as the disco barrel... the adapter still works I drill and tap so the grub screw engages on the flat...

The other Knurled barrel I think is from a Maximus Euro or Hunter... which came with the adapter... I would have to dig to find the part #... but have to go very soon... will look tonight if hasn't been posted by then...

take a look at pic of fill port and muzzle..

https://www.airgundepot.com/benjamin-maximus-hunter-22-cal.html#gallery-3

can see it on the EU fpe version also
about 2 min in on vid...

[aPpYe]

Hm.  I found these:

• 6-2250XL-001 - Adapter, Silencer, UK
• GBMP-033 - Dust cover

These would allow me to attach the +atsan air stripper?  Does the adapter just press onto the barrel?

I didn't realize I got a EU version of the barrel.  That big ol' adapter is kinda weird looking.  Maybe I will just buy the stripper and see if it can be made to work before getting the adapters ...

[Rick67]

Hm.  I found these:

• 6-2250XL-001 - Adapter, Silencer, UK
• GBMP-033 - Dust cover

These would allow me to attach the +atsan air stripper?  Does the adapter just press onto the barrel?

I didn't realize I got a EU version of the barrel.  That big ol' adapter is kinda weird looking.  Maybe I will just buy the stripper and see if it can be made to work before getting the adapters ...

The Hatsan stripper is threaded 1/2-20, hence the adapter.