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Adding barrel stiffness W/O carbon tubing & TJ's 3 groove barrel

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Motorhead

Motorhead

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Nov 1, 2018
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Here a few weeks ago I received a Prototype / first production TJ's .22 barrel Liner in the 3 groove configuration from "Troy Hammer" ( Web name )
At 26.5" Long and 1/2" diameter it is surprisingly stiff ( They are hammer forged of better steel than typical AG barrels ) .... but not really as stiff as wanted being shot at a very high power level exceeding 50 fpe it shakes pretty good EVEN under tension from shroud putting barrel in stretch.

So, not being a fan of Carbon Tubes over barrels/liners ( Stiff yes, but Carbon vibrates !!! ) Yes like a good fishing pole carbon transmits vibrations very well indeed.
We went with 6061-T6 aluminum tube epoxied to the TJ liner. Out front at muzzle machined up an air stripper / diverter to get as much pressure pulse into shroud space as possible.
At the breech end a machined aluminum shoulder washer was fitted keeping it a tad loose so it would conform and flush up with face edge of breech when shroud pushed against it firmly.
At the washer to tube sleeve we prepped surfaces and placed a fillet of JB weld epoxy allowing it to cure to a non flowing thick toothpaste consistency. Then assembled barrel back into action, attached shroud parts and snugged it back into tension leaving it for 12 hours to cure.
End result is the flange washer now sits FIRMLY and EXACTLY flush to breech face. This stops any barrel deflection / bend where barrel exits the breech. The shroud is thin wall Stainless steel ( Quite lite actually ) and then @ 6" from end into heavy wall CF and a cap on threaded end tightens it all up into a stretch tensioned assembly.
* Only did this in 2 parts due to in house material length limitations, tho does look nicer I'm thinking.

Damn it is stiff once snugged up with no detectable side / side motion unless really pushed on.

Now as to the 3G TJ's ..... unchoked and bore of .2175 with 18-1 rifling it shoots .217 slugs in the sub 25 grain range just stellar. Been shooting 20.2 NSA at or above 1060 fps and JSB 25.4 monster pellets @ 970's having both show very good consistency in testing done thus far. These barrels can be purchased threw TROY being he owns the mandrel that makes these barrel possible.

Just some fun late summer fabrication & testing.

Scott S

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ALL...of the manufacturers just need to...PROVIDE A "PROPERLY" designed barrel in their guns..! If the gun is designed to shoot a 30gr. pellet / slug at 1000fps, it SHOULD do so without problems, such as vibrating, or wave forming barrels during the shot.
If the gun is designed to shoot an 8gr pellet at 600fps, then yeah, fine, provide the paper thin barrels that are currently being provided, and hidden under .63" or .75" diameter shrouds.

I agree about crutches being required, being it ANY (carbon fiber, aluminum, or Titanium) external sleeve over a barrel to "attempt" stiffen it. This is a very poor method for trying to stiffen a piece of tubing. And to make matters even worse, from things that I've read in the forums and seen in YouTube, most users aren't doing the assembly of these two pieces even sorta correctly.

The manufacturers are just going as CHEAP as possible to get the pellet downstream of the receiver. And possibly to cut a few ounces off the total weight of the gun. The Swedish guys being the worst, most obvious offender.

Short barrels rule !

Rant over...

Thanks Motorhead for bring this topic up so I could provide my rant !

Mike
 
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MikeVV said:
ALL...of the manufacturers just need to...PROVIDE A "PROPERLY" designed barrel in their guns..! If the gun is designed to shoot a 30gr. pellet / slug at 1000fps, it SHOULD do so without problems, such as vibrating, or wave forming barrels during the shot.
If the gun is designed to shoot an 8gr pellet at 600fps, then yeah, fine, provide the paper thin barrels that are currently being provided, and hidden under .63" or .75" diameter shrouds.

I agree about crutches being required, being it ANY (carbon fiber, aluminum, or Titanium) external sleeve over a barrel to "attempt" stiffen it. This is a very poor method for trying to stiffen a piece of tubing. And to make matters even worse, from things that I've read in the forums and seen in YouTube, most users aren't doing the assembly of these two pieces even sorta correctly.

The manufacturers are just going as CHEAP as possible to get the pellet downstream of the receiver. And possibly to cut a few ounces off the total weight of the gun. The Swedish guys being the worst, most obvious offender.

Short barrels rule !

Rant over...

Thanks Motorhead for bring this topic up so I could provide my rant !

Mike
Click to expand...
If we're going to throw out the Sweden name .... Seems near every model or version of a existing model has some sort of "Fixes" or "Crutches" being applied.
Now to keep things from becoming a blow out from the fan base .. we're done .. Nuff said.

When WE AS AG USERS & Tweakers take any platform modifying to use other fitted parts, increase power etc etc etc .... There will come a time where creative "Fixes" or "Crutches" need to be applied to get correct function / accuracy. This such a case !!! 26" of 1/2" barrel tube is for most AG's is Very Long !!

Accuracy wise .. Not taking pictures, but at 80 yards we're easily inside a Nickle diameter if shot is taken cleanly !!! Shooter error prevails as it always does but seldom admitted too. Face palm

This is not a target gun !! .. this is a Hunter / Pester to kill poop with. O' its accurate enough.
 
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nomojo65 said:
Yes, no tension only “maybe” adding some stiffness to the barrel? I think I miss understood putting your TJ liner under tension.
Click to expand...
Tensioned indeed ... The shroud is compressed against the breech when the end cap at muzzle is tightened.
So ending result is Barrel is being pulled on while shroud is in crush. That has the assembly acting as if the barrel is 1" in diameter. ( Shroud O.D. size )
The original WAR as well JSAR used this methiod of barrel pull tensioning with great success, tho parts to do so have evolved over time.
 
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airgunmike56 said:
I have never had a FX gun, But my Mutant, Prophet, Cricket, I can take the barrel out and use it as a weapon NO FLEX, I do not understand making barrels that Flex and bend, I have not had the barrels out of my Vulcan and Uragan out yet so I am not sure if they bend or not, But I would bet my last dollar they don't.
Mike
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Because the @ 20" of barrel is @ 15mm diameter and screwed into receiver, then the scope towers clamp onto the barrel and in turn clamp onto the air tube X2 places. All that is left unsupported is forward of front scope tower. Generally from 4 to 12" pending bullpup ?
 
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Glem.Chally said:
You happy with the barrels accuracy?
Click to expand...
Thus far it has shown itself to be very accurate & consistent. Come next spring when I'm out in the Alfalfa fields shooting belding ground squirrels at 20 to 150+ yards, open exposure to the winds etc ... will I really get a better feel for how it does alongside more typical LW or CZ barreled rifles.
 
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Motorhead said:
Thus far it has shown itself to be very accurate & consistent. Come next spring when I'm out in the Alfalfa fields shooting belding ground squirrels at 20 to 150+ yards, open exposure to the winds etc ... will I really get a better feel for how it does alongside more typical LW or CZ barreled rifles.
Click to expand...
Nice! Thanks.
 
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Looks like a fun project!

While I agree fishing poles do vibrate but they are literally paper thin plus they are designed to bend. At same exact diameter a multidirectional or even unidirectional carbon tube is unbelievably stiff, structurally carbon is much stiff than aluminum at same weight or thickness. I’ve put all my weight on a 3mm thick tube and sucker won’t even show a hint of bending, it’s quite mind boggling. New 787 airplane is basically all carbon!

However at our power level that aluminum tube should be more than stiff enough. My only concern is the different thermal expansion rate of steel barrel and aluminum sleeve. Another good thing about carbon is they are very inert or has very little thermal expansion plus acts as excellent insolation to keep the steel barrel relatively constant in temp. I have never seen a aluminum reinforced center fire barrel but carbon wrapped barrel has proved to be exceptionally good like proof research or Christianson arms barrels. But firearm barrels have crazy amount of heat to deal which is why hammer forged barrels are looked down upon. Keep in mind what we can buy is carbon fiber in resin or epoxy while carbon fiber is actually relatively good at conducting heat the epoxy is not, epoxy to resin ratio differs but it’s safe to say we do not have the space age high modulous carbon tube with low resin ratio so the carbon tube we buy generally has low heat conductivity which is a good thing for our use case since we don’t have heat from fire to expel like firearm barrels and insolation is good at keeping the steel barrels temp constant especially hammer forged barrels, granted we are dealing with so little heat and power I doubt if the hammer forge barrel get left out in the sun would really change the POI……if it does then it’s a really bad barrel. LOL
 
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On that note ... The sleeve of aluminum is NOT under tension. It does not touch air stripper. Epoxy used a semi hardening "Finish Cure" type that when cured remains just a tad elastic or soft never becoming brittle hard. My thought being when the aluminum thermal expands down it's length this connection / bond can semi shift with it.
Tho understand we're not stiffening a fully floating barrel here !! Only thing we're do is damping vibration and having the tensioned shroud do the stiffening.

It's what i had ... with some propane torch heat it would slip right off easy enough.
 
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As long as it’s not the original JB weld which has melting temp 550 degrees the normal quick epoxy has melting temp of 250 which is pretty easy to do by leaving the barrel in the oven. Most epoxy I know will crystallize and solidifies fully cured but as long as it’s even then don’t think there will be much of a problem unless the extrusion isn’t even/under tension then it might shift the POI as it heats up. Now and days I don’t see that being a problem with much better quality extrusions we can buy today.

Either way it’s fun to experiment, we certainly isn’t lacking heat these days so easy to shoot a few shots with the gun in the morning and leave the gun in the shade outside till afternoon and check POI again. Don’t think you will run into too much issues.


Edit: If you decide to take it off and try something different then I would not use torch as it will create hot and cold spots no matter how careful you are, oven is the way to go…….if the mrs lets you.😅
 
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Indeed on the extruded aluminum tube wall thickness changing @ .008" one side to the other.
Thought about lathe truing it up, then felt it would alter the stress relieved properties of the tube .. so did not.
I will be shocked if POI moves around under such tension, tube expansion or otherwise.

Only TIME will tell ... hey where's my beer ?
 
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