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Author Topic: TJ's 257 twist rate verification and Disco air tube max safe pressure?  (Read 409 times))

Offline rualert

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     I know this must have been brought up before, but apparently, my Google foo is not up to par today. So like the title states, I just need to verify that the normal TJ's 257 barrel twist rate is the 1 in 14. The second, should be simple for this group, what is the safe max working pressure for a Disco tube?
Again I apologize in advance if this is just my searching of the forum not being up to par today, but I appreciate all assistance prior to starting my next few builds.

Thak you all,
Casey
  • New Port Richey for now

Offline Rick67

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Re: TJ's 257 twist rate verification and Disco air tube max safe pressure?
« Reply #1 on: September 13, 2022, 09:10:01 PM »
Magnum Air Power (MAP) says Disco tubes can be filled up to 3k PSI, especially if you have his upgraded torx screws.

I don't have a Disco tube but do have stainless Don Cothran tubes with MAP screws.

Don Cothran says his tubes are rated for 3K PSI.

I have done the 3K mark on several occasions but found out that a substantially lower pressure works best for me; i.e., more consistent shots.
  • Abq., NM, USA

Offline Rick67

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Offline rsterne

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Re: TJ's 257 twist rate verification and Disco air tube max safe pressure?
« Reply #3 on: September 14, 2022, 01:44:29 AM »
Providing the proper valve screws are fitted, the tube is OK for 3,000 psi.... The 25-20 TJ's liner is 14" twist, they also have a 25-35 liner that is 10" twist.... and although not listed they have a mandrel for a 7" twist as well....

Bob
  • 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).

Offline rualert

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Re: TJ's 257 twist rate verification and Disco air tube max safe pressure?
« Reply #4 on: September 14, 2022, 11:56:08 AM »
     Thank you all, I have grade 8 fallen head cap screws in shear so I thought I was alright, just wanted to be safe. I have a very deep respect for HPA, and understand how quickly it can seriously hurt you or worse.

As for the twist rates, I plan to use the available bullet molds, and some of the available cast slugs, even if I need to start off buying from members until I have my casting setup in place.
all the big bores are forcing me to gather casting equipment and learn how to proceed.

Thank you all,
Casey
  • New Port Richey for now

Offline Rick67

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Re: TJ's 257 twist rate verification and Disco air tube max safe pressure?
« Reply #5 on: September 16, 2022, 07:27:14 PM »
MAP screws are a very tight fit on Don Cothtran tubes, and they look good polished to go against the tube's bead-blasted finish.

If you would notice, they are shaped like shortened cap screws and would be proud when installed.

For the bottom one, I reshaped it to a dome shape so as not to interfere with the trigger assembly.



  • Abq., NM, USA

Offline rualert

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Re: TJ's 257 twist rate verification and Disco air tube max safe pressure?
« Reply #6 on: October 12, 2022, 10:52:50 AM »
     Thank you all for the input and great pointers to help keep me safe. It's just been a while since I had access to my shop and tools due to work sending me across the country for a few years. Now back in the shop and have had to pull notes on an existing build, I had in progress, thus the prior questions.
Glad I had those notes, and a good deal of my pointers were directly from Bob, so thank you sir, and everyone else.

Casey
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Online bear air

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Re: TJ's 257 twist rate verification and Disco air tube max safe pressure?
« Reply #7 on: October 12, 2022, 12:47:48 PM »
Please keep us posted on how your project is coming along. Sounds very interesting.
  • Sioux City IA, USA
Psalm 107:14  He brought them out of darkness and the deepest gloom and broke away their chains

Offline rualert

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Re: TJ's 257 twist rate verification and Disco air tube max safe pressure?
« Reply #8 on: October 13, 2022, 05:56:43 PM »
     Will do that, now just working through the honey-do list so I can get back to my lathe again!

Casey
  • New Port Richey for now

Offline rualert

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Re: TJ's 257 twist rate verification and Disco air tube max safe pressure?
« Reply #9 on: October 13, 2022, 06:01:14 PM »
     Guess I should add I just received a package from Mr. T.J. with a couple of .257 barrels, sO I have an aF TalonDor (Talon SS with all Condor hot rodded parts to make some barrel bushings and a breech for. might also need a fresh hammer to stay in the 115-gram weight range as Doug advises. The other may well end up in an AEA bolt gun since I have enough power to push them from it. although the project gun may well also have the umph. Things to ponder. Need to find Bob's 257 Condor thread again and re-read his settings and tests.
Fun times indeed.

Casey
  • New Port Richey for now

Online bear air

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Re: TJ's 257 twist rate verification and Disco air tube max safe pressure?
« Reply #10 on: October 13, 2022, 10:26:32 PM »
Bob's a genius when it comes to ag' s.
  • Sioux City IA, USA
Psalm 107:14  He brought them out of darkness and the deepest gloom and broke away their chains

Offline rsterne

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🇺🇦 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).

Offline rualert

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Re: TJ's 257 twist rate verification and Disco air tube max safe pressure?
« Reply #12 on: November 23, 2022, 03:05:55 PM »
     Thanks, Bob, I do enjoy your work and insight. I posted a WTB and acquired a Condor frame, so my build will be on that frame setup. I guess this might turn into my build thread unless that should be elsewhere. I think staying here may just be the right place since I'm making a ton of the parts myself, but will be asking how to reach Doug for one of his monster valves.
That said, thus far the barrel and the corresponding Carbon fiber sleeve have arrived, and I just finished making an almost 114-gram brass and Delrin heavy hammer. Not exactly like your's Doug, but like several, I picked up over the years before the Talon tunes forum seemed to go dry. I think maybe a guy from the UK made them, very nice but the heavier one wasn't heavy enough, and would not slide over the TJ's barrel at .500. I'll get some pics up shortly, and get a bit more in-depth as I get started with the Condor valve for now, and get the 257 barrel machined along with some new tight bushings.

Casey

P.S. About tie I built a dedicated slug shooter and surpass my personal best long-range shots from air power.
  • New Port Richey for now