TEXAN BARREL SWAP
Select Gate
READ GTA FORUM RULES BEFORE POSTING
GTA Forum Help Desk
GTA Announcement Gate
Dealer Area
GRIP
AirgunWeb Airgun Videos
Airgun Repository of Knowledge
Vendors and Vendor Videos
AirGun Expo 2021
Airgun Expo 2022
Contests and Giveaways!!!
Welcome New Members
In Memoriam
GTA Contributing Members
Shot Show Videos
Hajimoto Productions
Airgun Detectives
Air Gun Gate
BB Guns and Such
"Bob and Lloyds Workshop"
American/U.S. Air Gun Gates
European/Asian Air Gun Gates
PCP/CO2/HPA Air Gun Gates "The Darkside"
Air Archery
Vintage Air Gun Gate
Air Guns And Related Accessories Review Gates
Hunting Gate
Machine Shop Talk & AG Parts Machining
3D printing and files
Buyer's, Seller's & Trader's Comments
Bargain Gate
Back Room
Target Shooting Discussion Gate
Target Match Rules
Shooting Match Gates
Field Target Gates
The Long Range Club
100 Yard Match
Discussions By States
Welcome,
Guest
. Please
login
or
register
.
Did you miss your
activation email
?
1 Hour
1 Day
1 Week
1 Month
Forever
Login with username, password and session length
Home
About
Help
Old GTA
Gallery
Search
Stats
Login
Register
Advertise Here
GTA
»
All Springer/NP/PCP Air Gun Discussion General
»
PCP/CO2/HPA Air Gun Gates "The Darkside"
»
Big Bore AirGun Gate
(Moderators:
Rocker1
,
GTA-Airgunner
) »
TEXAN BARREL SWAP
« previous
next »
Print
Pages:
1
[
2
]
Go Down
Share This!
Author
Topic: TEXAN BARREL SWAP (Read 2170 times))
shortshell
Shooter
Posts: 22
yes
Real Name: Ron
Re: TEXAN BARREL SWAP
«
Reply #20 on:
April 11, 2022, 06:01:10 PM »
Valves were made from 316 Stainless steel which is quiet hard. There has been no sign of thread metal striping & the threads have been on and off many times over the weeks during testing. In actual fact the threads are not a problem.
Logged
Australia, Eatons Hill
rsterne
Member 2000+fps Club
Bob and Lloyd
GTA Senior Contributor
Posts: 26956
GTA Forums Person of the Year 2017
Real Name: Bob
Re: TEXAN BARREL SWAP
«
Reply #21 on:
April 11, 2022, 06:59:09 PM »
Sorry, but I must agree with Marco.... I would not trust those bottle threads at high pressures.... Besides being very roughly made, they look way out of tolerance.... This is what they should look like....
Please be careful.... At 3000 psi the force on 18mm threads is 1183 lbs. and the minimum safety margin to failure is about 2 tons....
Bob
«
Last Edit: April 11, 2022, 07:10:32 PM by rsterne
»
Logged
Coalmont, BC, Canada
🇺🇦
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).
shortshell
Shooter
Posts: 22
yes
Real Name: Ron
Re: TEXAN BARREL SWAP
«
Reply #22 on:
April 11, 2022, 08:25:38 PM »
If you look closely the finer thread on the left is a drager air scba thread & the coarser one is actually the Texan thread which is a 7/8 x 14 lee reloading die thread that was finally cut with a die after starting it on the lathe. I had to reshape the picture to a smaller size so it may not show its true shape. Maybe I should not have posted the picture as both bottle & texan threads show no damage & tighten without stripping.
Logged
Australia, Eatons Hill
BSJ
Marksman
Posts: 490
yes
Real Name: Brian
Re: TEXAN BARREL SWAP
«
Reply #23 on:
April 12, 2022, 09:41:56 AM »
Logged
VT (The Islands), USA
MJP
Member 4400+Fpe Club
GTA Senior Contributor
Posts: 2136
I'll make it real. For me.
Real Name: Marko
Re: TEXAN BARREL SWAP
«
Reply #24 on:
April 16, 2022, 04:22:31 PM »
Sad to say but nothing to do with picture quality, that part is trash as the thread is substandard.
I value my own life and people around me so much that I have remade parts with better threads than this. If it's not smooth and in correct dimensions then its not good. Every rough spot is a stress riser and potentially start for a failure.
Do not gamble with your life, remake or get the part properly made.
Marko
Logged
Finland
Impossible just takes a little bit longer to achieve.
If an engineer is not presented with a suitable problem, they will create their own!
shortshell
Shooter
Posts: 22
yes
Real Name: Ron
Re: TEXAN BARREL SWAP
«
Reply #25 on:
April 16, 2022, 09:55:34 PM »
You can rest at night Marco the valve in the photo was the first prototype that did not show the "Thread angle" properly in the photo to show it as the fine one on the left is a 1mmx 19mm pitch and as it is attached to a small S.C.B.A. escape bottle that did not need the TEFLON WASHER that is used as a plenum so the 2 valves & bottle were pressure tested at 5,500 psi at my old chemical plant test lab. This Bottle/valve only runs at 2.200psi anyway (I retired 20 years ago) The "stuffed" thread on the right is a bullet sizing die 7/8 x 14 & the final cut was with the correct die after lining it up on the lathe. It is only the Texan 458 (best slug size although the "Book" says .457 in the name) thread that attaches the valve to the Texan frame via a steel lock nut. The valve is 316 Stainless and is little hard but most rifle threads now use 314 SS as its easy to cut threads & I have cut many rifle & chambers in 314 SS & 4140 steel.
As It was a prototype No.1 of 2 That I had only taken the photo (note the Delrin poppet with a spring attached) of this one that I tested first so it did not get all the mods. I am in the process of making a final one No.3 with some extra mods & it too will be pressured tested.
I only posted "that " photo to show the poppet setup to those people who would like to see the internal & that the only mod needed to do to a swap barrel calibre was to change the size of exhaust holes in the "TOP HAT" but no one mentioned that only to knock the thread of a prototype.
As a foot note the .458 seems more accurate at 100m+ than the .30 but I have not finished making the .25 barrel.
Logged
Australia, Eatons Hill
shortshell
Shooter
Posts: 22
yes
Real Name: Ron
Re: TEXAN BARREL SWAP
«
Reply #26 on:
April 26, 2022, 11:00:50 PM »
This is a continuing information note for anyone thinking of a .457 Texan calibre change that I have been playing with as over here the shortage of powders & primers is converting quite a few people to airguns especially the big bores. I am not one of them as I have been playing with airguns for over 60 years plus many powder burners. I finished machining a .257" powder burner barrel with a 1 in 15" twist and 24"long. Using my No. 3 prototype valve with top hat (pressure tested) that is a bit smaller in its airways to the stock .457 unit that works a treat with the .308 barrel which is really just a reduction in the top hat discharge holes compared to the .457 top hat holes which has 5 holes each around 9/64" giving .07 square ins. The 4 holes in the No3 prototype top hat giving around .031 square inches had been drilled to 3/64" but when I replaced the .257 barrel I got tank dumps. So after a few goes on the calculator I found that the 4 holes may be too large in area. I then tapped a 1/16 UNF grub screw into one hole blocking it so the total area was reduced to just over .022 square inch area with the 3 holes & the tanks dumps were no longer. I have only tried 65gn .258" sized moulded lead slugs. It appears the top hat area & hole size must suit the calibre to prevent tank dumps on the big bore Texan.
Logged
Australia, Eatons Hill
shortshell
Shooter
Posts: 22
yes
Real Name: Ron
Re: TEXAN BARREL SWAP
«
Reply #27 on:
June 16, 2022, 11:18:50 PM »
Here is some more info to digest. After hundreds of .458, .308 ,257 slugs I found last week that I noticed on discharging some slugs I felt air coming out of the trigger slot in the frame. On disassembling the spring, hammer etc the rear internal O-RING was broken. This may have happened when replacing one of the barrels although I had machined a slight taper into the barrels so not to damage the O-RING. As replacing this o-ring is a pain I decided to cut a smaller o-ring into the breach end of the barrels that can be easily replaced with the action open. This appears to work as I got a few more shots per fill with the small air bottle untethered with the regulator removed. As the barrels protrude a little more it does not interfere with loading the slug sizes I use. Yes I had to redrill the 8 barrel holding grub screw holes in the barrels about 4mm more to allow the barrel o-ring to be fitted if needed.
Logged
Australia, Eatons Hill
shortshell
Shooter
Posts: 22
yes
Real Name: Ron
Re: TEXAN BARREL SWAP
«
Reply #28 on:
June 21, 2022, 11:14:25 PM »
Some more important info for anyone thinking of a barrel swap. I had fitted a .257 barrel from a powder burner & a stock 86gn .257 lyman mould & a CBE (Australia) 65gn. all checked at .257 but different lead mixes may change the measurement due to shrinkage on cooling & both have been promising but I decided to try a home made 42gn mould & sized it to .2585 (an experiment) but each time I shot it (6 times) I got a tank dump. As the other moulds worked fine I felt the sizing was wrong. I made another sizing die this time .2575 & I got only 3 tank dumps from about 8 shots. Another sizing die at .257 fixed the problem +30 shots. When fitting different barrels the old story of slugging the barrel is more important in the airgun world. Half a thou. oversize maybe ok(but not in my case) but no larger when sizing slugs. Airgun slugs do not need lube grooves but no more than a calibre of bore riding length & lube the slug. I test size all my moulded slugs as the lead mix can change. Another thing I have found is the air pressure on my big bores .457+ still works to around 1,100 to 1,200psi but I have not gone lower than that but the .25 does not like less than 1900psi due to the surface area of the base of the slug.
Logged
Australia, Eatons Hill
MJP
Member 4400+Fpe Club
GTA Senior Contributor
Posts: 2136
I'll make it real. For me.
Real Name: Marko
Re: TEXAN BARREL SWAP
«
Reply #29 on:
June 22, 2022, 07:06:39 AM »
You will get rid of any tank dumps with correcting the surface area problem concerning the tophat and barrel od on the breech sleeve.
Too big tophat and it has more surface area keeping it open, the flow is not enough to close the valve.
Now you mostly relying on flow restriction to close it.
Marko
Logged
Finland
Impossible just takes a little bit longer to achieve.
If an engineer is not presented with a suitable problem, they will create their own!
shortshell
Shooter
Posts: 22
yes
Real Name: Ron
Re: TEXAN BARREL SWAP
«
Reply #30 on:
June 22, 2022, 08:07:48 AM »
My Dumps were due to the slug being oversize & causing to much friction or restriction. I have my texan regulated to 2,200 psi. I found the oversize slugs about 15mm in from the breech. The Airforce manual even says a dump will happen if a slug/pellet is not seated completely into the breech & jams against the opening similar to being oversize. To accommodate different barrel calibres the 3rd valve I made I put grub screws into the top hat discharge holes to restrict air flow & it works perfectly. I just received a 15mm rod of PEEK for valve seals in case the Delrin gets a problem but has never caused me any .
Logged
Australia, Eatons Hill
MJP
Member 4400+Fpe Club
GTA Senior Contributor
Posts: 2136
I'll make it real. For me.
Real Name: Marko
Re: TEXAN BARREL SWAP
«
Reply #31 on:
June 22, 2022, 11:57:16 AM »
Like I said you get rid of any dumps by making the gun with correct dimensions.
Valve needs to be biased on closing by force via surface area difference, and it will close always and on all situations.
Your solution is a bandaid and unpredictable on pressure and bullet selected.
Kudos to you if it's good enough but there is a right way of doing it.
Marko
Logged
Finland
Impossible just takes a little bit longer to achieve.
If an engineer is not presented with a suitable problem, they will create their own!
shortshell
Shooter
Posts: 22
yes
Real Name: Ron
Re: TEXAN BARREL SWAP
«
Reply #32 on:
June 23, 2022, 04:02:27 AM »
Hi Marko, Do you mean to have the surface area of the valve material much larger than the exhaust port surface area of the valve material? I thought having a return spring was the help but the Texan did away with one. Having the valve material too large would restrict the air flow around the valve on opening. How would you suggest to do it.
Is not having a return spring the main cause of the problem as this is the only airgun without one & I have had or ever built?
Logged
Australia, Eatons Hill
MJP
Member 4400+Fpe Club
GTA Senior Contributor
Posts: 2136
I'll make it real. For me.
Real Name: Marko
Re: TEXAN BARREL SWAP
«
Reply #33 on:
June 23, 2022, 10:28:15 AM »
Return spring is useless, only helps when filling gun from empty. Its closing force is tiny compared to other forces in the system.
Tophat od needs to be small enough to cancel its opening force, the bigger the tophat od and surface area the more likely the gun is bound to dump.
Smaller od on the barrel and tophat is the way to get the gun to be consistent and not prone to dumping.
Imagine the pressurre pushing the bullet is also pushing against the tophat surface in side the breech sleeve. Large enough tophat and you are relaying mostly on flow over the poppet to close the valve.
And when you change to a smaller caliber with same od barrel and tophat you are in the gray area of to close or not to.
Ask me how I know.
Marko
Logged
Finland
Impossible just takes a little bit longer to achieve.
If an engineer is not presented with a suitable problem, they will create their own!
Print
Pages:
1
[
2
]
Go Up
« previous
next »
GTA
»
All Springer/NP/PCP Air Gun Discussion General
»
PCP/CO2/HPA Air Gun Gates "The Darkside"
»
Big Bore AirGun Gate
(Moderators:
Rocker1
,
GTA-Airgunner
) »
TEXAN BARREL SWAP