FAS 6004 Longer Barrel Project

[WyoMan]

Got started on this today. These are the parts I needed (especially the gun  ):



The barrel is a 12mm o.d. LW blank in .177. There are some weaver mounts that need D/T'd into the top of the lever and some rings that will give me a 20 MOA drop compensation.
The other parts are a sleeve and brake for the exposed part of the barrel.

But first, I ran a few over the chrony after the barrel was cleaned... it's shooting about 7 fps faster than the first one I got (everything looks fine):


I took it apart and made some measurements for the new barrel... decided to start on the barrel first.
Using an 11" section from the breech end of the blank here... and cutting it a little long because I may need more than one try for the dovetail face groove (o-ring is on the barrel face).
I'm not going to use the choked section of the blank because of the energy reduction... it's a big enough deal when you only start with 1.8 fpe, LOL


This is always a good sign - I'm within a few thou of groove diameter and haven't broken thru. The bore should be pretty well centered:


The cut end (muzzle) faced and crowned:


I have to turn the barrel to .395" and make a taper to .472" (breech end), but should probably cut the face groove next...

Wyo

[aluminumfetish]

I think those pistols are amazing, I will be following this for sure.

[Bob Pratl]

I purchased a FAS 6004 with match grips a year ago and I think that it is a great 10 meter target pistol. It is extremely consistent which makes it very accurate. I will also be following this thread.

[Rob M]

subscribed (-'

[aluminumfetish]

I had an IZH-46 before they got crazy expensive and also a Gamo Compact. I think this FAS is leaps and bounds ahead. If you don't mind me asking, what is your end goal / use for this little gem ? It'd make a wicked mousing rig, not to mention a laser of a target rig. The SSP's are brilliant, I am very anxious to see what kind of gain you get from this mod.

[WyoMan]

Thanks, guys. I don't have any progress to report for now... waiting on tooling and I thought I had everything 
I'm liking like this pistol more and more... especially since I got the first one up to the 330s with 8.44 gr. It punches pretty clean holes and is very accurate.

Bob, you're right. They are very consistent - single digit E.S. with a great two-stage trigger. I like the smooth feel you get from the leaf spring.

Mitchell, I hope to push the velocity up to 350 - 360 fps so I can extend the range a bit. SSPs struggle at high elevation but I plan to use this mainly for 10m target shooting. I'm also anxious to see how much gain you get from the longer barrel.

Wyo

[Bob Pratl]

Gary, I'm glad that you mentioned it, the trigger is one of the main factors in why I purchased a 6004. With the 4 adjustments I was able to set it
the way I like, 1 pound, very smooth, crisp and no creep. It's about the same weight as my S&W 41 and by far cheaper to practice with. Bob

[JCBinWV]

Gary - I really enjoyed your other thread w/ your first 6004 & I'll be watching this thread to see how this goes as well!   There's not a lot of info/tuning on these guns that i've found so far.  Really only found these two threads here on GTA, and one over on TargetTalk.  I've been interested in the FAS since a read an article in the ole Airgun Letter about the 604 some 20+yrs ago!  Held off buying the 6004 when they first came out for fear of spotty QC issues typical of "new" production....

Couldnt' resist any longer!!!  I've got one on the way from AoA that should be here this weekend...  Can't wait to get it in my hands & see how it compares to my Izh, Daisy 747 & the P17.


jc

[WyoMan]

Hi JC... The Airgun Letter... wow ... 20 years is a long time, LOL.
Glad you'll have one this w/e. They are a really nice pistol and I hope you enjoy it as much as I do.

In the mean time, while I'm patiently waiting on tooling, I decided to shim the piston to remove about half of the piston deadspace.



After the JB Weld is cured, it will be cut to .010" thick and coated with cyanoacrylate.

Finished the sleeve / brake for the section that extends outside of the frame:


The sleeve is from 1/2" Delrin tube stock and was drilled .375". I had to use a 3/8" steel rod insert (looked like a shish kabob) to turn down the section that fits inside the brake. The Delrin wall thickness in the turned down section is only .030" thick.

Fits together like this:


The setscrew will secure the pieces to the barrel.

And speaking of the barrel, here's what it should look like when it's done:


The section beyond oem length (7.52" max) needs to be turned to about .375" because the longer barrel will have to go in at an angle.
And, you'll also have to remove the latch assembly to have the necessary clearance. But the good news is that it's a reversible DIY drop-in 

Wyo

[Rob M]

similar mounting as the p17.. where that back clamp does all the alignment ?

[Hoosier Daddy]

I have had a 6004 on my list for some time, very interested in you project!

[CraigH]

I do love that barrel crown picture.         Well, all the rest, too.   

[JCBinWV]

Gary - quite interesting!  in the other thread you mentioned using JB Weld with the shim, but i didn't pick up exactly HOW you used it to MAKE the shim.... The pick above explains it all!  Brilliant.  How difficult is it to tool after its cured?  And what's the purpose of the coating of cyanoacrylate?   Shame FAS didn't use a piston seal in the design similar to the IZH 46.

So are you sticking w/ the round o-ring for your barrel/breech seal?  or going w/ the square profile for better contact?

I just rcvd an update from USPS & mine should be delivered today.  (needless to say, its gonna be a loooong day ...........  ;-)

keep up the good work & thanks for sharing!

jc

[WyoMan]

similar mounting as the p17.. where that back clamp does all the alignment ?

Yes, very similar, Rob... but the 6004 has a more robust clamp. Somewhere in between the P17 and the Alecto and HW 45 - which produce more than twice the fpe.
Also, the front of the barrel is aligned / secured by the barrel o.d. fitting into the i.d. of the lever (just like the others). And when the sights are attached to the lever, it's all fixed with no relative movement.

I have had a 6004 on my list for some time, very interested in you project!

Scott, order one now... if they're in-stock you'll have it for Christmas If not, then maybe by next Christmas - j/k

I do love that barrel crown picture.         Well, all the rest, too.   

Thanks, Craig. It's just a straight cut that is square to the bore. Pretty easy to cut an accurate crown that way, and I don't see any need for a recess.

JC, I hope you got your pistol today and are having fun shooting it!
The JB Weld is very easy to machine and it's not hard to get a decent finish. The CA is to seal the outer surface.
I've never tried a square o-ring for the breech seal. The round cross-section works just fine. What might need done is to cut a more pronounced chamfer on the breech end of the barrel. If you make a radius profile, you can get the barrel closer to the port bulkhead (more o-ring compression) without the barrel hitting the bulkhead... if that makes sense - thanks

Wyo

[WyoMan]

Finished the Piston:


And the Weaver mounts on the lever:




Everything is done except the longer barrel, and I wanted to do that first... But it's going to take some more time...

Wyo

[Rob M]

awesome work , love the dual groove piston

[JCBinWV]

Gary - mine arrived Friday, right about the time my twins came home from college (one expected, one not so much...) ;-)  I did manage to slip away once in a while for a little pistol break in...  Don't want to highjack your thread though - I'll post my feelings/impressions/etc in my own thread in a couple days once the "new toy greatness" wears off.

Back to your efforts - so that little bitty section of darkness on the face of the piston is JB Weld, huh?  Had no idea there were that many different types of JB Weld available, nor that you could do this type of work with it!  Is there a particular type you prefer?  And what happens if you don't coat the JB Weld w/ CA?

Of course the reason I'm asking - mine is a bit, shall we say "anemic" in the ole FPS/FPE dept as well. Might have to entertain mods of this type to get a little cleaner holes in my targets...

Thanks in advance for the feedback.

jc

[WyoMan]

Thanks, guys. Some more piston details...


Left - right: JB Weld shim (.010"), original face, UC90d 115 o-ring, felt oil wick, and a leather cushioning washer.
I had to make the cushioning washer because the lever opens far enough to crash the muzzle brake into the trigger guard. One more minor detail 
It will work fine now, have about 1/4" clearance and the entire piston will open to just beyond the intake hole.

JC, the JB Weld I use is the original formula (3960 psi). I give it 48 hr to cure before machining... just to be safe.
I don't know if you have to coat the machined surface with CA... I always do it. I suppose that a burnished finish would also work... maybe nothing is necessary.

Before you shim the piston, I would check your breech seal for leaks. That is one of the usual suspects for this platform...
Wet the breech o-ring with some non-detergent oil. Fire it a few times (with pellets, you want the breech pressure build), and check for spray patterns.
Also, check the o-ring for a dry spot that might indicate blow-by.
The piston shim is not a miracle solution. It takes the total firing charge and compresses it to a higher pressure. I find that it helps at high elev.... ymmv -

Wyo

[JCBinWV]

Gary - me and the breech seal are becoming quite well acquainted.  I noticed almost immediately after only firing a few shots that the breech was ROUGH and digging into the valve body.  I had to address that before it got much worse.  The breech seal is also snagging on the sharp top edge of the valve body and cutting into it. 

I removed the barrel and polished the breech face, smoothed/surfaced the chamfer properly and knocked off the chisel marks leading into the rifling lands.  Pellets seat smoothly and consistently with much less effort now!
 
Reassembling was tricky.  First couple shots across the chrony scared the &^^& out of me as I had LOST about 75fps!  WHOA NELLIE!  That's definitely the wrong direction.   that be the "blow by" you would be referring to...

Long story short, got that all squared away by doing what you described above.  Once I had the right barrel/valve body setup, my velocity increased from an avg 317fps with RWS Basic
To 340fps.  Not to shabby with all stock parts and just a little effort!

Not sure what I'm going  to do about the valve body cutting the breech seal though.... I simply flipped the cut section into the recess when I had the barrel out.  Already I can see the cut on the now facing side and it's only been ~75-100 rounds.  It's almost as if the barrel is sitting a tad too high and the oring isn't fully supported by the valve body.
 Will look at that closer as I shoot it more...

Love the idea of that leather cushioning washer!  I was noticing a small ding in the finish on my gun tonight where the piston rod hits the frame during cocking if you extend the lever all the way.  Dang it Gary!  There's another reason I need to go in!!  LOL

Generally speaking, so far, I'm really enjoying this gun even with these minor flaws.  Shame theyre there,  but nothing a little effort cant easily correct and improve.  Absolutely love the grip.  I showed it to a friend this weekend and the first words out of his mouth were "I want that grip on my T/C Contender!"  Speaking of which... mine doesn't seem to have any finish.  That's ok! I see some decent grain that may be enhanced w some diluted stock finish (so it soaks in...) I just happen to have handy.... 

now to stop shooting it long enough to address some of these...   

jc

[WyoMan]

Back to work on the barrel...

Face groove cut (shown with the oem barrel)


Lead-in and radius chamfer finished:


The radius chamfer allows the barrel to be positioned closer to the port bulkhead. Without this cut, the outside edge of the barrel will gouge the bulkhead (during the opening and closing of the lever)... preventing you from getting the barrel breech close enough to compress the o-ring for a good air seal.

JC, if the sharp top edge is cutting the o-ring, fold up some 600 grit and relieve the edge. My first one did that. It only took a few passes along the edge and the problem was solved.

Wyo