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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

Carbon fiber tube questions

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Spacebus:
It's become popular to put a CF tube on the naked Stormrider/PR900/Chaser/CP2/etc. 12mm OD barrels and then tighten the LDC against the tube and whatever the tube is butted up against (barrel band or the receiver). Is a 12 x 14 OD tube with a 14 x 18 OD tube over the outside stronger than one 12 x 16 CF tube? Mostly the idea is to put tension on the barrel, and I assume it also helps some with the rigidity of the noodle barrel. I'm trying to make a lightweight "bull barrel" for my Bandit.

These questions arise after reading about Bob's dual tank BR guns. One of the guns is using concentric CF tubes within each other for rigidity in some parts of the build. It got me thinking about doubling up on CF tube for my bottle bandito. My idea is to try and keep some form of barrel band in conjunction with the tensioned sleeved barrel, like many OEM shrouded barrels with bands (like my Eagle Claw).

I know these SPA/Snowpeak guns don't have the most robust barrel mounting system, and maybe I should only use barrel bands that are indexed, like the front sight holder/barrel band on the Stormrider/PR900 and the band on the Eagle Claw. I don't know of any way to index a barrel band for the Bandit, I've just been torquing the barrel band as tight as I feel safe (I've had to cut one off) and using a set screw through the top. This clearly isn't enough since I had a problem on my last hunt.

I've tried the CF tube with my Stormrider and I think it helped prevent shift, but I also removed a "floating" barrel band at the same time, which might have been what actually helped. I'm mostly interested in figuring out how to make the barrel on my bottle bandito carbine more rigid/robust. I'm also keen on eventually getting the Buck Rail AR conversion kit (https://buck-rail.com/product/diana-ar-conversion/) and using the MLok style band/tube shroud. I just don't see how I'll keep the MLok shroud from rotating about the air tube. I also noticed that the part of the barrel sleeved with the CF tube was still flexible enough to pinch with just my hand around both the barrel and air tube when I had it on the Stormrider. This is why I initially asked about the 18mm CF tube.

Is BR open to custom jobs? If the AR grip had some notches/cutouts on the front with corresponding tangs on the MLok shroud this would make the Bandit/Chaser like the Stormrider in having an indexed barrel band.  My custom tube shroud would also have a 14mm ID for the barrel band (maybe even with an O ring groove!) so I can use a full length 14mm OD tube and then put a 18mm od tube in front of the band and a touch longer than the 14mm tube and use the tapered moderator to center and tension the whole thing against the receiver, MLok shroud, and grip.


Is this going to actually help anything? I take my bottle bandito into thick bush hunting small game like snowshoe hares and squirrels. Sometimes my barrel bumps into trees, branches, etc. even though I try to be careful while moving. Other times I slip, trip, or otherwise fall and the gun hits the ground or some other hard surface. When carrying my Army service rifle this was never a problem, though I wasn't hunting small game. There's nothing more frustrating than having a barrel shift while I'm actively hunting and ruin the whole day. I injured a squirrel on my last hunt because of a barrel shift.  I hope this is comprehensible, thank you for reading all of it!

rsterne:
The reason I used two concentric tubes in the design of my dual tank benchrest is that I could not get a single tube that would do the job.... I would have preferred that.... The stiffness of a barrel is basically proportional to the 4th power of the outside diameter, so if you double the diameter, it will be 16 times as stiff.... Assuming you glue the tubes together, a 12 x 14 inside a 14 x 18 would be stiffer than a 12 x 16 and almost as good as a 12 x 18 (depending on the glue strength).... Gluing it to the barrel will help quite a bit as well, although tensioning the barrel by putting compression on the tube may be just as good (or better, who knows?)....

Bob

Spacebus:

--- Quote from: rsterne on March 05, 2023, 02:24:27 PM ---The reason I used two concentric tubes in the design of my dual tank benchrest is that I could not get a single tube that would do the job.... I would have preferred that.... The stiffness of a barrel is basically proportional to the 4th power of the outside diameter, so if you double the diameter, it will be 16 times as stiff.... Assuming you glue the tubes together, a 12 x 14 inside a 14 x 18 would be stiffer than a 12 x 16 and almost as good as a 12 x 18 (depending on the glue strength).... Gluing it to the barrel will help quite a bit as well, although tensioning the barrel by putting compression on the tube may be just as good (or better, who knows?)....

Bob

--- End quote ---

I was thinking about gluing the barrel to the inner tube and using the outer tube for tension. This all ultimately hedges on my ability to figure out a barrel band that can't rotate. I need to find my feeler gauges and figure out the barrel to tube clearance.

mackeral5:
This is another area I have somewhat followed along in Bob's footsteps. 

I really like sleeving my short barreled guns with CF, say 18" and less.  What's not to like---short stiff barrels that do not rust, at least not externally.  Bull barrels without the weight. 

The jury is still out as to how I feel about longer barreled guns, say 24" or so inches and up. 

The key, IMO is counterboring your breech (accurately) to accept the CF tubing.  The counter bore should be as deep as your breech allows.  The cf should fit snugly in the counterbore. 

I've used both Loctite green retaining compound and JB weld to attach the CF.  Lately I've been using more JB Weld. 

Tensioning----unless you have the ability to precisely locate and fabricate the tensioning system, it will be a challenge to not have a wandering POI.   

The gun pictured below has  a .500 OD .300 bore TJ's barrel that is sleeved in a layer of 13x15 cf which in turn is sleeved in 15x18cf.  At present it is averaging around 1.5-2" at 100 yards. I am going through the gun piece by piece, system by system to confirm stability, with a goal of getting groups down in the 1" and less range.  The gun has performed this way, but it is very tricky to get it to do so.
 No coffee, absolutely perfect follow through is required on every shot.  I am convinced with a more stable barrel system the gun won't be so twitchy. 

I have 3 other barrels for this gun (in various stages of completion) in .22 and .25, all of which are of the epoxy/CF sleeve configuration.  But they are all in the 22-24" range, barrels are more skinny so thicker CF, and all are planned to be used at 50-70fpe vs the 24.5" .300 which is typically tuned at or above 100fpe.

It does not help matters that my shooting requires that I have a big moderator hanging off the end of my barrels....



I haven't given up yet but I am coming around to accepting that ultimately I may have to farm out the work to someone who is capable of fabricating a precision tensioning system--perhaps something similar to AAA's tensioning system.     

Baco:
i was under the impression that BR tri rail had 2 barrel supports, one near the breech and a kind of bbl band at the end + screws to tighten up everything

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