• The AGN App is ready! Search "Airgun Nation" in your App store. To compliment this new tech we've assigned the "Threads" Feed & "Dark" Mode. To revert back click HERE.

Tuning Taipan Transfer port question: .20 cal build

Jump to latest Follow Reply
T

Tonykarter

Member
Nov 14, 2017
76
2
Texas, United States
You guys that have been through the Taipan...is the ID of the transfer port BORE (not the port size) the same on the .22 as the .25? I am building a .20cal Taipan Long and wondering if I will need to have a TP machined to .20 spec, or can I use the .22's TP. I own both .22 and .25 Taipan's, but would rather not have to disassemble the .22 to borrow the .22's TP, but rather use the .25 TP instead. Hence, my question regarding the common size of both, or different?



Any other mods you would suggest to make this thing as precision as possible? Not a power build, is for benchrest at 50+yards. Estimate I will be shooting it at 820-880fps with the heavy .20 pellet. THANKS!
 
The Vets have a dual transfer port design, so technically two different air passages. Kinda unique in that regard. As for size difference of those dual ports from the .25 to .22 I can't help you there.

I also have plans to make a .20 Veteran (actually paying a buddy to make it). My Vet Short is going to be converted to .20. The .20 barrel that came in my Raptor is going in the Short. A tested and known to be superbly accurate barrel. 

I've done inspections (pulled the barrel on my Long and studied the schematics) and it seems like it just needs barrel machining to work. I shot a couple .20 pellets through the current .22 (not accurately of course, just for testing) and am getting a good seal with the .22 probe. I plan to use the the .22 probe, and the .22 single shot tray for the .20.

The trickiest thing to figure out for mine is that that the .20 barrel I'm using is a 16mm so it'll either need the od reduced to 15mm, or the scope tower machined down to fit a 16mm barrel. I also havent decided on length. It'll have a possible 18 inches once the step down is cut off. That would make the Short 5 inches longer than OEM length, so around 29 inches. I'm kinda thinking of having my buddy cut it to maybe 16 or so inches of barrel length, for a 27 or so inch OAL. 

Since the Short in .22 is really a 32 and under fpe gun, we're talking about optimal speeds for the .20 JSB offerings. I was thoroughly impressed with the .20 accuracy and wind resistance, etc. I'm very excited to have a .20 Veteran in the near future. NSA has mentioned that he will have .20 slugs shortly as well. That could be fun too (especially cuz with a couple extra inches of barrel those .20 slugs should be able to be pushed even faster than 32fpe).
 
Upvote 0
If talking "Veteran" it is CALIBER specific having a hole threw it that must hold pellet centered to the barrel bore that butts up against it.
Click to expand...

I see what what you're saying, as the smaller .20 will create a step that the pellet has to bump over as it is "chambered." Could this problem be remedied with a simple cone shaped lead? (if, in my case, using the .22 transfer port for the .20)
 
Upvote 0
Tony, can a .177 thimble be purchased and drilled out to .20 cal, and a 22 probe machined to match?



A thimble is a great idea, but I wouldn't know where to order one. Can you point me in the right direction?
Click to expand...

Click to expand...

The only place I've seen with any parts for the Taipans is Talon Tunes. And by thimble, I think he's talking about the transfer port. It is basically a thimble in the Veteran. 

vet transfer port.1599689805.jpg


That is a picture of the transfer port in the Veteran (Thanks MtnGhost). 

The two oval holes are the transfer ports, the through hole in the middle of part, where I marked the red arrow, is the path the pellet takes as you close the cocking lever. The barrel butts up against this cylindrical transfer port/thimble. 

Two ways to approach this, as suggested by jarmstrong, if you could buy this part for a .177 Vet, it could be opened up to .20 where the pellet goes through it (red arrow). This way would also require a .20 specific bolt.

The other way, which I suspect would work, just use a .22 transfer port/thimble. Obviously the .20 pellet will fit through the .22 sized hole. I just think you'd need a cone shaped lead in the barrel to avoid the step down from the .22 diameter hole of the tranfer port/thimble to the .20 diameter barrel, Otherwise, there's going to be a 90 degree step that the .20 pellet hits as it transitions from tp/thimble to barrel. This manner would allow you to keep the .22 bolt (much more simple). 

This is the oring that seals the bolt:

barrel oring.1599690339.jpg


It is BEHIND the transfer port/thimble. So, sequentially, brass piece seen here, then oring, then transfer port, then barrel. There is no oring groove cut into the barrel, nor oring between the transfer port and the transfer port/thimble. This, and my experimentation with a .20 pellet fired from a .22 Vet, all makes me think there won't be any sealing issues if the conversion to .20 is done by keeping the .22 bolt, oring, tp/thimble, and simple machining the barrel with the correct threads to fit the breech, and cutting the cone shaped lead to avoid the step down. 

(NOT a machinist so could be way off base here).
 
Upvote 0
Free bore leades no matter caliber MUST BE kept within a few thousands of the projectile. If there is any YAW present when the projectile enters rifling, the yaw will stay there threw the exit at muzzle.



This the exact reason why very few SLUG SPEC barrels with deep free bores shoot pellets consistently also. The JUMP and abrupt entering of barrels rifling is a crap shoot on having the pellet enter square & true. This is why in pellet gun barrels ( Correctly done ones anyways ) have the head of pellet into the rifling when bolt is closed. some the skirt too FWIW.
 
  • Like
Reactions: mmahoney
Upvote 0
Okay then, so to do it right, I'm going to need to get a transfer port machined with tighter ID, specific to the .20 pellet. Then I'm going to need that back brass piece machined, also specific to the .20 pellet. Finally, I'm going to need a new pellet probe assembly machined that mates with the other two and the o-ring to seal the back. Those first two pieces, if machined to the proper ID, should keep yaw to an absolute minimum and present the pellet to the barrel as square as possible. So that begs the question, what is the correct ID of the rear brass fitting and the transfer port for the .20 caliber?
 
Upvote 0
I'm going to use the .25 Long to do this rather than the .22. I am pretty sure that will require tuning the reg way down and some adjustment of the hammer to get it down into the 800's. A buddy of mine that lives a couple of houses down is a machinist and said he would make the transfer port, pellet probe assembly and rear brass piece for me. Question: What are the optimum metal alloys I want to use to make them?
 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu