Tuning Air Venturi Avenger - Barrel Stiffening

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SkeeterHawk

SkeeterHawk

Member
Oct 23, 2021
689
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Florissant, Colorado, United States
Hello Air-Gun Enthusiasts!

I have been working on stiffening the barrel of my Air Venturi Avenger and have come up with (what I think) is a "solid" solution for this gun, so I thought I'd share the results of my research.

I love the Avenger, but I didn't like how the barrel was floating in "outer space" like it was. I plan to shoot this gun long distance accurately, so I thought that this was the most logical place to start. Reinforcing the barrel with Carbon Fiber (CF) isn't as easy as thought since CF tubes come in a tolerance that is + or - the nominal size. This means that it is a "crap shoot" if they will fit inside each other perfectly or not.

I bought the following for this modification (not counting what I bought that I didn't use because it was slightly off the "perfect" size)

  • Carbon Fiber Tube - 11mm I.D. 12MM O.D. 500mm Long
  • Carbon Fiber Tube - 12mm I.D. 15mm O.D 500mm Long
  • Carbon Fiber Tube - 15mm I.D 19mm O.D 500mm Long
  • O-Rings 2mm cs with 18.5mm I.D 70Duro

I had to use 80grit emory cloth attached to a dowel to ream out the inside of the CF tubes that were too small. Here is the jig:

01_SandingJig.1650259565.jpg


This allowed me to ream out the 12MM ID tube a whole lot, and the 15MM ID tube a little so that the whole assembly could be assembled with a rubber mallet. No epoxy was used for this assembly.

I finally got the inner and middle tubes to come together.

02_InnerAndMiddleCF.1650259680.jpg


Here is how they looked like from the end

03_InnerAndMiddleCF_Aligned.1650259701.jpg


So, I had to cut the inner CF tube assembly to 15 1/2" long so that it would allow the Donny adapter to fit snugly. I sanded this assembly down about 1/16" so that I could insert an o-ring between the inner CF tube and the back bushing to give the assembly a little "slop" and make it so that the Donny adapter could be tightened snugly against the aluminum shroud.

Here are the inner CF tube assembly next to the outer tube.

04_Inner-Mid_NestTo_OuterShowingLength.1650259863.jpg


You have to cut 2.75" off of the back of the aluminum shroud so that the whole thing will mate snug. You will have to re-drill the hole for the mounting screw and taper the hole for the flat head screw.

11_Suppliment_AluminumShroudTrim.1650260638.jpg


Here is the Donny adapter bottomed out against the inner CF shroud. Note that the barrel is covering up the "breather holes" in the Donny adapter.

05_DonnyAdapterBottomoedOutAgainstInnerCF.1650260079.jpg


Here is the adapter removed so that you can see the gap between the inner shroud and the barrel.

06_DonnyRemoved.1650260016.jpg


After installing the outer CF shroud over the inner CF shroud assembly, you can see that the barrel assembly is ready for the Donny adapter to be inserted.

07_EndOfBarrelWaitingForDonny.1650260178.jpg


For reference, here is how the Donny Adapter looks installed into just the new CF assembly.

08_DonnyInstalledNoAluminumShroud.1650260284.jpg


Adding the O-Rings to the outer CF shroud will give consistent spacing between the barrel and the aluminum shroud. Here are the 8-o-rings installed.

09_O-RingsInstalledForSpacing.1650260356.jpg


So the result is the barrel looking out of the end of the shroud assembly...

10_BarrelCenteredInShroudBeforeFinalDonnyInstall.1650260395.jpg


That is a beautiful sight!!

Now the Donny Adapter will simply thread onto the end of the shortened aluminum shroud, and seat snugly against the barrel assembly. I believe that this will also allow me to use a barrel tuner for the Avenger.

See you at RMAC with this beast!!
 
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There is a lot to be said for "peace of mind", plus my gun can now do things that it couldn't before (harmonic barrel tuning). I was already getting really good groups at 50 yards (within 1") just supporting the gun from a door frame, so I may see a marginal improvement there. I am making a lot of changes over the next couple weeks and am pushing my home range out to 92 yards so I can practice for the bench rest. I've never gone out to 100 yards yet and figured that locking down the "spaghetti noodle" inside the shroud will improve my chances of success regardless. Besides, carbon fiber is cool stuff, eh?
 
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I finally got some trigger time this morning on the Avenger with the modifications, and I am SUPER pleased with the results!!! I just put six pellets through the exact same hole at 50 yards just standing with a door frame as a "rest". That was by far the best group that I have shot with that gun yet, so I would attribute that to the barrel stiffening. I can't wait to get this on a bench and see how far out I can go.

So, to answer the question "Was it worth it?" I'd say definitely! I shoot this gun all the time, and this was a marked improvement on the performance that I am used to. These mods cost me around $40, plus some time, and I have increased the performance of this already good performing gun. I call this mod a winner!

Happy shooting! I'll be smiling more now :)
 
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Have you had any more range time with it lately?
Click to expand...

Yes, I sure have! I haven't pushed my range out to 92 yards yet, but I was testing pellets yesterday at 65 yards with a moderate (12mph) cross wind, and I was able to get 0.6" groups consistently. Unfortunately, I don't have really good data before and after because I recently got a really solid bi-pod (Accu-Tac FC-5 Gen2) and rear bag (Armageddon Gear Pint-sized game-changer), so this makes a huge difference in how solid the rifle is. That said, I was getting bigger groups at 50 yards before even using foam for a front rest and my fist at the rear. Anyway, I am starting to think that the reason why the occasional flyers that we all get from the Avenger have more to do with the spaghetti noodle whipping around inside the shroud.

Where did you buy the Carbon tubes? I checked several places I use, but they didn't have those sizes.
Click to expand...

I got everything off of E-Bay, but the shipping is slow, so you have to be patient. I have put a few orders in because as I mentioned, the tolerance is a crap-shoot. Anyway, here are links to the products that I actually used for this conversion. I hope that what you need is in stock when you order...


If there was an 11mm ID by 15MM OD, that would be perfect and you could only use two tubes. I couldn't find that "holy grail" so I had to use two pieces for the inner shroud.

Another thing to note was that I "won the lottery" with the 11mm ID tube as it fit just snug all the way down the barrel, so that was perfect. I didn't want to use epoxy or anything on the actual barrel. On my 2240's, I used metal foil tape on the barrel so that it would make a tight fit to the carbon fiber. Anyway, there you have it. I hope that this helps!

Shoot safe and straight!

Jonathan
 
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They look awesome, Kevin! I hope that you are in a position to give a little more definitive before and after results once installed. I have installed CF over just about every barrel in my arsenal. Besides the fact that they look really cool once installed, I could see a noticeable improvement in each one. The one that made the least difference was on my 2240 with a 24" 0.177cal barrel. The CF is the thinnest of all of my guns on that one, and that was the one where it made the smallest difference. I don't have room to make that one thicker unless I change something, so I may just live with it. It shoots accurately at 75 yards, so I don't know how much more to expect from a 0.177 shooting AirArms 10.3gr Heavy Diabolos.

Anyway, thanks for posting the pictures, and we're looking forward to hearing how you reinforced the barrels.
 
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@skeeterhawk thanks for sharing all this. Very much appreciated. Did you get hit with any additional customs fees upon delivery/receipt of the carbon fiber tubes?



@lennyk For other applications, I've had success cutting a very thin slit in wooden dowels, then slide the sandpaper in, and roll around the the dowel. Tape or glue might work too.
 
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how did you attach the 80grit to the dowel ?

did you drill with water so the emory would not clog ?
Click to expand...

I just used Gorilla Duct Tape. That stuff is so strong, it is awesome!

I actually pulled it out every 2-3 passes and "flicked" the debris off with my finger. It was pretty easy to tell from the dust coming out of the tube that the sandpaper was clogged. Since I was using tape to hold the emery cloth in place, I wouldn't introduce the water element. My only advice here is to take it slow and don't try to use sandpaper that is too big. If it is WAY too big, and you can still manage to hold it, the friction will heat up the tube and melt the epoxy holding it all together and make a mess. Otherwise, if you are feeling "frisky" and think you can hold it, I broke two dowels trying. My advice is to take it slow. You won't regret the time.

@skeeterhawk thanks for sharing all this. Very much appreciated. Did you get hit with any additional customs fees upon delivery/receipt of the carbon fiber tubes?
Click to expand...

No, thankfully all that was in the price. On E-Bay, just watch the shipping costs. As long as you don't get scammed there, all costs should be rolled in...at least that is my experience with well over 100 purchases within the last 2-3 years.



@lennyk For other applications, I've had success cutting a very thin slit in wooden dowels, then slide the sandpaper in, and roll around the the dowel. Tape or glue might work too.
Click to expand...

That is a really good suggestion. The Gorilla tape was a champ for me, but I could see how that would work. Only thing is, if you have a lot of friction, that would weaken the dowel, and I broke them solid...so you may want to use the Gorilla Tape too.

I'm glad that my post seems to be helping my airgunning friends.

Cheers!
 
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SkeeterHawk said:
Yes, I sure have! I haven't pushed my range out to 92 yards yet, but I was testing pellets yesterday at 65 yards with a moderate (12mph) cross wind, and I was able to get 0.6" groups consistently. Unfortunately, I don't have really good data before and after because I recently got a really solid bi-pod (Accu-Tac FC-5 Gen2) and rear bag (Armageddon Gear Pint-sized game-changer), so this makes a huge difference in how solid the rifle is. That said, I was getting bigger groups at 50 yards before even using foam for a front rest and my fist at the rear. Anyway, I am starting to think that the reason why the occasional flyers that we all get from the Avenger have more to do with the spaghetti noodle whipping around inside the shroud.



I got everything off of E-Bay, but the shipping is slow, so you have to be patient. I have put a few orders in because as I mentioned, the tolerance is a crap-shoot. Anyway, here are links to the products that I actually used for this conversion. I hope that what you need is in stock when you order...


If there was an 11mm ID by 15MM OD, that would be perfect and you could only use two tubes. I couldn't find that "holy grail" so I had to use two pieces for the inner shroud.

Another thing to note was that I "won the lottery" with the 11mm ID tube as it fit just snug all the way down the barrel, so that was perfect. I didn't want to use epoxy or anything on the actual barrel. On my 2240's, I used metal foil tape on the barrel so that it would make a tight fit to the carbon fiber. Anyway, there you have it. I hope that this helps!

Shoot safe and straight!

Jonathan
Click to expand...
I'm a fan when it comes to dampening or eliminating harmonics. Very good choice for material, carbon fiber is light, strong and not a very good conductor
of vibration. Increasing wall thickness while straightening at the same time is a nice trick too.
Now, Using a "Whip Stick" to polish out the bore> Ok you were limited and you had to go with what you had. I get it. But a slotted tip rod, metal, wood, whatever, Can bell mouth the bore, Wrapping too much emery too tightly can "Pin Up" and heat up and seize although carbon is pretty much self lubricating. A flapper setup where you double over a strip of emery roughly2 1/2 the dia. of the bore. You stick it on the slotted rod in the middle, pick a rotation and roll the emery strip around the rod tip and stick it in the bore. use S-L-O-W rotation and support the rod near the mouth of the bore. Use enough rotation so the whipstick supports and Self Centers itself in the cylinder. If you use a rod as long as that shroud and you really hit the RPM's it's going to bow and whip and believe me - There will be no cheers in Mudville! You or someone else could get hurt faster than you can blink.
Generally speaking it is much easier to polish down the O.D. of the inside mating tube than the bore of the outer. If you have access to a lathe, even a wood lathe, Open, easy to see what you are doing, take measurements and it's much faster.
I think as things are or will be I hope, you may not need to get involved with a barrel tuner. The harmonics may be nulled enough as is.
 
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Jmac said:
I think as things are or will be I hope, you may not need to get involved with a barrel tuner. The harmonics may be nulled enough as is.
Click to expand...
I thought so too, but for grins I made a quick barrel tuner and was really surprised with the results. I just posted them here. I did see a difference when adding an adjustable weight to the end of the barrel after stiffening it. I don't think this would have worked without stiffening. Thoughts?
 
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revenger said:
I got a TJ barrel coming for my .25 avenger soon
Click to expand...
Would you mind giving us a link to the barrel and distributor you are using? Just wondering what your driving force is in changing out the barrel. Are you changing the twist rate, or getting it choked, ? I'm interested to know your goal.
revenger said:
Hoping for good results.
Click to expand...
Us too! 🤞 Keep us posted.
 
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SkeeterHawk said:
Would you mind giving us a link to the barrel and distributor you are using? Just wondering what your driving force is in changing out the barrel. Are you changing the twist rate, or getting it choked, ? I'm interested to know your goal.

Us too! 🤞 Keep us posted.
Click to expand...
TJ's Gateway, LLC
PO Box 531 Alexandria, KY 41001 US
(859)635-5560
[email protected]

It is just a barrel blank that I will have to get machined. The stock avenger barrel is choked and the TJ barrel is not choked. I want to be able to shoot slugs accurately and the stock barrel doesn't cut it. The TJ barrel will also be longer so I should be able to create more power as well. We will see.
 
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