Tuning De-Tuning my new Beeman AR2078B .177

[Kgphotos]

I recently received a new Beeman AR2078B. It's a great fun rifle for ten meter shooting. I'd like to reduce the velocity to make it quieter and get more shots per fill. Right now it is getting 635fps with an 8 grain wadcutter and its giving just over 40 shots on a single CO2 cartridge before I see a slight drop in impact on the target. My goal would be to reduce the velocity down to the 550-575 fps range. I believe that would make it a bit more quiet (not that it is super loud ) and offer up a few more shots per fill.
My plan is to slowly clip coils on the hammer spring and see what that gets me. I have also read where people have tried to shed a little weight from the hammer itself. I will try the spring first. I can purchase the whole hammer kit from Archer Airguns so I have a back-up plan in case I mess anything up. I think if I take it slowly and use my chronograph I can slow walk it into the velocity range I'm looking for.
I'd like to run this plan by everyone here just in case I'm overlooking something important. This is my first QB/AR78 style rifle but I have confidently worked on my FX air rifles internals as well as a couple Marauders. Thanks for reading,
Kenny

 

[John "spysir" Blount]

Indoors at a controlled temp that might work but somewhere above 90 degrees even the factory spring will experience valve lock.
If you can find the correct size tubing or some other seal, choke down the transfer port.
John

 

[Treefrog]

Very cool!

You can do that without having to cut the spring. I've been experimenting with the 'BStaley mod' and restricting the transfer port for a while. I'm getting 93 shots from a pair of cartridges and 55 from one. It's quite a bit quieter now, too.

Here's the thread on it. - https://www.airgunnation.com/threads/an-economical-approach-to-co2-for-the-qb78-series.1310296/

Cheers,

J~

 

[nervoustrig]

Right now it is getting 635fps with an 8 grain wadcutter and its giving just over 40 shots on a single CO2 cartridge before I see a slight drop in impact on the target.

I just wanted to note something in the ballpark of 300fpe per cartridge is a good goal for a long-barreled .177. Your current result works out to about 285fpe so that suggests the hammer strike is pretty close to ideal.

Of course it is true that trading off some velocity will likely yield not only more shots but also a higher total FPE so by all means pursue it. I just wanted you to know you shouldn’t need to make drastic changes to get there. A subtle hammer buffer (bstaley) as described by Treefrog is a good approach, and isn’t subject to a widening extreme spread the way reducing hammer strike sometimes does.

 

[Kgphotos]

Thank you gentleman. I appreciate you taking the time to help me out. I have played with the ’bstaley’ mod in the past with my dad’s Marauder so I am a little familiar. I like that idea since it is not a permanent mod.
If I decide to also experiment with transfer ports where would I look to purchase a transfer port with a smaller opening. As I look around everybody has plans for a larger port for more power but not a smaller port.

Another question regarding efficiency. I understand that the ‘bstaley’ mod reduces the hammer strike on the valve therefore releasing less gas per shot. And I understand that a reduced transfer port restricts the flow of gas to the pellet resulting in lower velocity. But the reduced transfer port change must not contribute to efficiency since the volume of gas released by the valve does not change. Isn’t that correct?
Thanks again. I knew if I asked here I would get the advice I need and even learn a few things.​

Kenny

 

[Treefrog]

Kenny,

It's my understanding that the co2 in the cartridges stays liquid and then boils off when the pressure is reduced by opening of the valve. That means that reducing the amount of time the valve is open (with the BStaley mod) also reduces boil-off-time and the quantity of gas released. A reduced transfer port size will reduce how quickly the pressure drops when the valve is opened, thus also reducing the amount of gas boil-off. So it's a win-win when the two are combined. That's how I remember a friend (the guy that originally imported these guns) explained it.

Frankly, I'm glad to see others exploring greater efficiency instead of more power. We're certainly a minority...

Cheers,

Jeff

 

[John "spysir" Blount]

Mine is a QB78 on HPA so don't really know exactly what to expect on Co2. Also have a custom valve & stem so...
Just a picture of the lightened hammer and the Felt "stopper" (like a bstanly before it's time) made for a table leg or such.

John

 

[Kgphotos]

Kenny,

It's my understanding that the co2 in the cartridges stays liquid and then boils off when the pressure is reduced by opening of the valve. That means that reducing the amount of time the valve is open (with the BStaley mod) also reduces boil-off-time and the quantity of gas released. A reduced transfer port size will reduce how quickly the pressure drops when the valve is opened, thus also reducing the amount of gas boil-off. So it's a win-win when the two are combined. That's how I remember a friend (the guy that originally imported these guns) explained it.

Frankly, I'm glad to see others exploring greater efficiency instead of more power. We're certainly a minority...

Cheers,

Jeff

Treefrog, do you happen to have any links for the orings and reduced transfer port seals that you use in your QBs? Thanks,
Kenny

 

[JimBentley]

These guns are a real treat to shoot. I’ve never tried to turn one down, but a simple Mod would make it silent

 

[Treefrog]

Treefrog, do you happen to have any links for the orings and reduced transfer port seals that you use in your QBs? Thanks,
Kenny

Hey Kenny,

The o-rings are size #113. You can find them at just about any good hardware supply place.

I made the transfer port seal from the plastic of an unused toilet lid. (Us welders do tend to keep scrap piles.) I drilled out the nipple end of a used co2 cartridge with a 1/4" bit and used it as a punch (in a vise) to make a slug, then drilled the inside of that out to what I wanted. Pics attached. You need one about .243" wide and .120" thick. Mine was a bit tall and I had to file it down some.





Cheers,

Jeff

 

[RickH]

I have a 2078A and get about 60 shots out of a pair of CO2 cartridges shooting 10 meter matches In .177. Your round count on a single CO2 sounds pretty good, I’d leave it alone.

Rick H.

 

[Kgphotos]

Hey Kenny,

The o-rings are size #113. You can find them at just about any good hardware supply place.

I made the transfer port seal from the plastic of an unused toilet lid. (Us welders do tend to keep scrap piles.) I drilled out the nipple end of a used co2 cartridge with a 1/4" bit and used it as a punch (in a vise) to make a slug, then drilled the inside of that out to what I wanted. Pics attached. You need one about .243" wide and .120" thick. Mine was a bit tall and I had to file it down some.

View attachment 457032

View attachment 457034

Cheers,

Jeff

Thank you for the detailed instructions. This is going to be a fun project. I am also a welder. Well at least I own a welder and attempt to weld stuff. I’m just a hobby level welder. I like to make targets for my air rifles mostly. I know what you mean about keeping scrap piles of stuff. Thanks again,
Kenny

 

[Treefrog]

No worries.

Since your gun is new, you might want to give the barrel a thorough cleaning, then push a pellet through from the muzzle to ensure that there aren't any machining-burrs left on the inside of the transfer port near the breech. Mine had a huge one and it needed a little work with the dremel. Accuracy really improved after it was cleared. A lot of us lap our new QB barrels too. It helps with accuracy and makes cleaning faster.

Jody at weldingtipsandtricks on youtube is the man if you're learning to weld. He knows his stuff.

Looking forward to seeing the results of your gun mods here.

Cheers,

J~

 

[Kgphotos]

Thanks Treefrog. I plan to give the barrel a good cleaning this weekend and also lap/polish the bore. I am also going to do a little work on the trigger. The trigger is not terrible but it does have a bit of "creep". I will probably try dropping that o ring in as well as see what difference it makes on the tune. Thanks again for all of your help.
Kenny