Air Venturi Moving Groups

[MT shooter]

Hi All,

New to the forum, searched through the threads, but wasn't able to find a topic that seemed to line up with my question below, so thanks in advance for any wisdom the group might be able to impart here.

I just received my first proper air air rifle an Avenger .177. Put a Vortex 4-12 50mm scope and bipod on it and have been really impressed with its precision. Stock hammer spring position, ~4200psi charge with 2000psi reg.

Shooting mostly at 50yrds in my back yard, and I find as I shoot the groups are great, roughly dime size, but they'll move as I shoot by as much as 2in, then create a new group that is dime size again, always laterally. Typically seeing this over the course of 60-80 shots in ~30min or so.

Seems as though if I let the gun sit, it'll shot back at its zero position. No environmental corelations like wind, temperature, etc.

Maybe it needs to be cleaned more frequently? Just variability from the barrel heating up?

Has anybody seen this and if so know how I best go about remeding the variability?

 

[RickH]

Your gun is cursed and must be dealt with by a gun exorcist such as myself. Send it to me immediately and if I am unable drive out the demon I will drop the gun in a deep pool of water so as to drown the evil spirit and save you many years of fear and frustration. Seriously though it sounds like the gun is heating up which can cause this kind of shift in grouping. When you take a break things cool down and work as they did with only a few shots. It’s hot out now and that’s not helping. I’d be curious to see if it continues to do this in the fall with cooler temperatures.

Rick H.

 

[JaceSpace1369]

Hi All,

New to the forum, searched through the threads, but wasn't able to find a topic that seemed to line up with my question below, so thanks in advance for any wisdom the group might be able to impart here.

I just received my first proper air air rifle an Avenger .177. Put a Vortex 4-12 50mm scope and bipod on it and have been really impressed with its precision. Stock hammer spring position, ~4200psi charge with 2000psi reg.

Shooting mostly at 50yrds in my back yard, and I find as I shoot the groups are great, roughly dime size, but they'll move as I shoot by as much as 2in, then create a new group that is dime size again, always laterally. Typically seeing this over the course of 60-80 shots in ~30min or so.

Seems as though if I let the gun sit, it'll shot back at its zero position. No environmental corelations like wind, temperature, etc.

Maybe it needs to be cleaned more frequently? Just variability from the barrel heating up?

Has anybody seen this and if so know how I best go about remeding the variability?

Avengers are notorious for POI shifts, there are several threads speaking to this and fixes. You'll have to use the search engine, I can't recommend any particular thread as I have not owned any avengers or read on the deeply enough but I have seen several threads about this same issue and members giving advice.

 

[engfred]

Hi MT shooter,
Welcome to reality.
I also got an Avenger and also experienced the same with POI shifts.
The problem is that the design and support have not enough axial stability.
I ended up designing a new front part of the stock - see other Avenger threads.
First I designed and tested the concept of clamping 3 nos. 3d printed parts together on the two the pressure pipes.

Then after successful test I redesigned the 3d model to adapt to the rear stock part.
See below

Then I Installed and tested - Success no more POI shifts - BUt I did a lot more - Trigger - Airstripper -Barrel etc.

But Maybe there is Hope for you with a Bipod that can rotate freely like an Accutac FC4 G2. But I know its probably just as expensive as your rifle.
You can also buy a cheap Tripod from china - Alieexpress / Temu or others 40 USD + an adapter from Arca Swiss to Picatinni - Like I did for testing:
This is very stable and makes it much more easy to shoot different targets due to it can turn freely.

I normally use the fixed Accutac, but in the future I will only be using the Accutac FC4 gen 2 or the Tripod solution. Try setting up a A3 sized Benchrest target at 30 yards and shoot - You will note a big difference. (Image showing my latest rifle - Image with my temporary extended rail - Now I got the original Extended rail = much more steady). I still have the Avenger shoots great - I havent tested it on the Tripod but I will do and show shooting result and images.

 

[MT shooter]

Wow, thanks engfred! Sincerely appreciate such a detailed report and those are some great looking builds! Few questions for you:

• "the concept of clamping 3 nos. 3d printed parts" <-- what is nos?
• What is an airstripper?
• I bought a UTG recon 360 bipod that can be made relatively loose, maybe I'll try loosening it up and see if the POI shift reduces.
• What is the vertical cylinder sticking out of the bottom of your Avenger build?
  
  
• Also, any chance you'd be open to sharing the CAD on your stock? Looks great and I'd love to experiment with it if you're open to it.

Thanks again!

 

[engfred]

Wow, thanks engfred! Sincerely appreciate such a detailed report and those are some great looking builds! Few questions for you:

• "the concept of clamping 3 nos. 3d printed parts" <-- what is nos?
• What is an airstripper?
• I bought a UTG recon 360 bipod that can be made relatively loose, maybe I'll try loosening it up and see if the POI shift reduces.
• What is the vertical cylinder sticking out of the bottom of your Avenger build?
  View attachment 480064
• Also, any chance you'd be open to sharing the CAD on your stock? Looks great and I'd love to experiment with it if you're open to it.

Thanks again!

Hi Mike,
The cylinder you marked with red is an external Plenum.
This means a larger chamber for regulated air = More power or / less air consumptions.
Airstripper means a part that separate the "dirty" air behind the projectile away from the projectile. In my case a 3d printed part that separate and divert the dirty air back in the shroud.

Send me a private message with your email address and I will forward the 3d files for the modificated front stock.
Be aware my Avenger is gen 1 - the stock has changed on the newer versions !

Regards from Denmark

 

[MT shooter]

Hi Mike,
The cylinder you marked with red is an external Plenum.
This means a larger chamber for regulated air = More power or / less air consumptions.
Airstripper means a part that separate the "dirty" air behind the projectile away from the projectile. In my case a 3d printed part that separate and divert the dirty air back in the shroud.

Send me a private message with your email address and I will forward the 3d files for the modificated front stock.
Be aware my Avenger is gen 1 - the stock has changed on the newer versions !

Regards from Denmark

@engfred I loosened up my bipod and pulled as much body pressure off my stock while shooting last night. 120rnds and zero POI shifts. I'll probably still look into the mods you speak of as it's a little impractical to shoot like that all the time, especially in really windy conditions. Thanks for the pointers!

Unfortunately the forum says I don't have permissions for a direct message, anybody know why and/or how to sort that out?

 

[Chief Ten-Beers]

You can get the Plenum extension on Ebay for about $40

 

[Firewalker]

Your gun is cursed and must be dealt with by a gun exorcist such as myself. Send it to me immediately and if I am unable drive out the demon I will drop the gun in a deep pool of water so as to drown the evil spirit and save you many years of fear and frustration. Seriously though it sounds like the gun is heating up which can cause this kind of shift in grouping. When you take a break things cool down and work as they did with only a few shots. It’s hot out now and that’s not helping. I’d be curious to see if it continues to do this in the fall with cooler temperatures.

Rick H.

Heating up? Um, no. In fact, releasing pressurized air into the atmosphere cools the gun.

 

[DeanB]

Black Arts barrel band solved my poi shifts, fairly cheap and easy install. You can adjust your poi with it then tighten down and will not move. OEM barrel band is crap.

 

[beerthief]

Hi All,

New to the forum, searched through the threads, but wasn't able to find a topic that seemed to line up with my question below, so thanks in advance for any wisdom the group might be able to impart here.

I just received my first proper air air rifle an Avenger .177. Put a Vortex 4-12 50mm scope and bipod on it and have been really impressed with its precision. Stock hammer spring position, ~4200psi charge with 2000psi reg.

Shooting mostly at 50yrds in my back yard, and I find as I shoot the groups are great, roughly dime size, but they'll move as I shoot by as much as 2in, then create a new group that is dime size again, always laterally. Typically seeing this over the course of 60-80 shots in ~30min or so.

Seems as though if I let the gun sit, it'll shot back at its zero position. No environmental corelations like wind, temperature, etc.

Maybe it needs to be cleaned more frequently? Just variability from the barrel heating up?

Has anybody seen this and if so know how I best go about remeding the variability?

60 or 80 shoots in 1/2 hour is very fast shooting , try slowing down ,

 

[Bramezy]

Heating up? Um, no. In fact, releasing pressurized air into the atmosphere cools the gun.

Hence all the condensation during a session!! We get it all the time when its warm out.