New Year, new... project

[YEMX]

When I finally got some free time, weather turned to garbage.  So I didn't get to test fire today.  The next week isn't looking too good either 

Here's the new scope mount:

[Sbak]

i think im missing something, what does the offset mount do? why not just use traditional rings? not trying to be a downer, it looks really good i just haven't figured out the benefit yet

[YEMX]

i think im missing something, what does the offset mount do? why not just use traditional rings? not trying to be a downer, it looks really good i just haven't figured out the benefit yet

As previously stated, with the standard rings that I had, the rings were mounted all the way forward on the breech, and the scope was also pushed as forward as it could go in the rings.  The sight picture worked-ish, but it really needed to be a touch more forward to be perfect.  But I had no more forward adjustment.  Hence the new mount- I have much more adjustment available to me, and now the eye relief is proper, and the sight picture is correct.

In case you were wondering, I set the LOP properly before I epoxied in the mag lock for the folding stock, so I can't move the LOP (which is already proper for me anyway) to help with scope alignment, or I'll lose the mag lock feature. 

[Motorhead]

Nice job .... Pretty too!!

[Arkmaker]

Looks awesome!


You are a testament to preservence. More pics please 😛😛

[YEMX]

Nice job .... Pretty too!!

Many thanks!  Not as gorgeous as your Raptor!! 

Looks awesome!


You are a testament to preservence. More pics please 😛😛

Much appreciated!  I don't know about all that- "glutton for punishment" would probably be more accurate!  I'll definitely take more pics during the bipod extension build, and once the whole thing is done.  Looks like a week of rain in the forecast, so I'm not sure when I'll be able to  get initial numbers for y'all.  I wish I had an indoor set up...  But even with the LDC, this thing would be way too loud to shoot indoors.  Outside is quiet enough, though not at all "backyard friendly".  Not that I would shoot this thing in the backyard.   

[YEMX]

Well now, lookie what came in the mail today!



Gotta order up some aluminium, and then I can get to work!  For as thin as this tube is, there is surprisingly little flex!  Bad news- I won't be able to use my "over-bore" bipod.  There's not enough clearance, as this tube ends right at the end of the tank.  Which is fine.  The tube more than clears all the important bits!  I'm stoked!

Although, I have a little adjustment forward, so I might be able to scoot the whole thing forward and maybe I'll have JUST enough clearance to use the over-bore bipod...  Hmmmm...

[Motorhead]

Interesting under thingy out onto the front rest ?

[YEMX]

Interesting under thingy out onto the front rest ?

Yessir- it's the CF tube that's going to be the bipod extension.  I just mocked it up to see if it would clear everything from the drop block forward.  I'm going to make some aluminium end caps for both ends, and an inner support ring for the front mounting ring at the rear.  The front will have a section of M1913 to mount a bipod. 

Oh- and I moved the main mount as forward as I can, and I still don't have enough room to clear the tank with the over-bore mounting block.  No biggie though.  The M1913 rail will be exactly where I want it- just past the end of the tank.  I'm happy.

[YEMX]

Okay...  We've got a brief respite from the rain (it'll be back for the rest of the week), so I took her out to shoot.

Start pressure: 3600 psi
End pressure: 2700 psi
Reg set to 2800 psi
Slug weight: 61.7 grains
Total of 12 shots

Only going to count 9 shots (for my purposes), as those are all on the reg.  Hammer is adjusted to only crack the valve and no more.  I might, for S&G's just crank it to 2900 psi, but I don't want to set it right at 3k psi.

I've got some blow-by at the TP, but I kind of expected that.  I'll figure out how to seal that up, and see what happens then.  Next time I go out, I'll keep it at 2800 psi output for a full string, then refill and do a full string at 2900 psi to see if there's any difference.  If there is none (or not enough to matter) I'll keep her at 2800 psi. 

Numbers are still lower than I'd like, but given the OAL of the barrel (26"), the output of the reg (2800 psi) and the blow by at the TP, it's actually right at where I expect it to be.  I wrote down the gross numbers, no decimals- unless it was something like ".96"  then yeah, I rounded up.  But that was just for the last recorded shot. 

FPS    FPE

865    102
879    105
872    104
875    104
872    104
872    104
869    103
872    104
862    101
----------------- AM NOT COUNTING THESE
852    99
856    100
843    97- 2700 psi END

So again, preliminary numbers.  So next time I still won't be shooting for groups.  I'm still going to be in test phase.  But I'm VERY pleased- we're over 100 fpe, and the TP doesn't have as much blow-by as I thought it would    So yay me!  I have successfully made my first working AG part! 

Now to figure out how to seal this TP.  I didn't machine very much clearance at all.  I'm thinking about buying some flat, thin rubber (but what kind?) washers to use.  I don't have room for an oring. 
 

[Rallyshark]

That's certainly an improvement from the fist numbers!  I'm curious to see what it does once you get the TP sealed up.  I'm also curious about what it will do at 3000 psi   I don't know how much that transfer leak is hurting things, but I'm thinking it probably has a wee bit more juice in the cards.

[YEMX]

I was mulling things over whilst at the hardware store trying to find something appropriate to seal the TP with...  Once I figure out this TP sealing issue, I'll re-shoot at 2800 and skip 2900 and just go to 3k psi output.  If I'm filling to 3600 psi and shooting down to around 2800 now, and only getting about 9 shots, I can't imagine how few shots I'll get from 3600 to 3k psi... 

[FuzzyGrub]

Tom,  I didn't try to search back through the thread to see what kind of TP you are using.  I've used some latex rubber tubbing pulled over brass tubing. 

https://www.gatewaytoairguns.org/GTA/index.php?topic=153928.msg155694680;topicseen#msg155694680

[YEMX]

It's an aluminium TP I made.  I think I know where it's leaking- right where the breech and TP meet.  The TP has a taper on it at that spot.  Overall fit is tight- also, there's an oring seal on the valve side- the TP "snaps" into that o-ring with some authority.  You know when it fully seats! 


Funny you mention that TP design- I was thinking about that exact set up while at the hardware store!  But again, I'd have to re-make the TP.  Which I still might do.  I have a better cut off set up, and I can now do a square shoulder, where as before due to my cutters, I couldn't. 

I've been kicking around making one from delrin as well...

[mackeral5]

Tom. I know sealants are generally frowned upon and messy, however......  I often use Loctite 518 anaerobic sealant for similar challenges.   My crude fabrication methods often result in less than ideal sealing surfaces especially on transfer ports.  I would almost be willing to guarantee you that with a little 518, that transfer port will seal.  Of it doesnt, 518 is easily removed with acetone on a paper towel/qtip...

On another note, don't be surprised if stopping transfer port leakage yields results not exactly in alignment with what you would expect.....

[YEMX]

I'm going to try to make one from delrin...  I've already boogered 3 of them But I'm getting there!  I think it's just because I was tired.  So I finally just quit for the evening.  I want to try to make it even tighter and maybe try some of that loctite 518 if for whatever reason I'm not getting the seal I want.

I'm not really expecting a huge increase in velocity- that's going to come from increasing output pressure.  But I'd feel better if there wasn't any leaks from the TP.

[Motorhead]

Yes, mechanical transfer ports sealed via CRUSH can work, but BOTH mating surfaces must also be parallel and flat.
using a material such as ACETAL which has some yield, needs to be generally made to have .010-.015" of crush maximum or the breech will bend in the bottom of magazine slot creating misalignment of the probe into barrel.

[Arkmaker]

Great numbers! I sorta wish I had something that hit that hard. (Other than pb's).

[YEMX]

New TP didn't work...    I made one from Delrin...  It does seal better than my original TP, but it's not perfect, and there's some other stuff I don't like about it.  I also ran into the issue that Motorhead described- I made the TP a touch too tall.  No worries- I'm going to make another one from aluminium.  This time, I've got the tooling to make a flat shoulder.  I've also got some Loctite 518 on order.  I WILL get this sorted.   

[YEMX]

Great numbers! I sorta wish I had something that hit that hard. (Other than pb's).

Thank you!  Yes, I'm happy the numbers have gone up- but I still want to solve the TP leak issue, and see what 3k is going to do.  I'm not expecting much, but my goal is only 16+ fpe more...  So who knows?

You could build a Brod... 

Also, I'm going to just test 2900 psi and 3k psi, no sense being lazy about things this late in the game, is there?  Curiosity is getting the better of me.