Air Gun Home :: View topic - 850 HPA conversion, fill equipment and Velocity test results

rbva · Member

I got the .177 850 converted to HPA a little while back

The Scuba tank arrived this week, I got a 80cf 3300psi tank, $5.00 to fill.
and got a carry strap. boot and valve cover with it.... note, it's a boy tank

I had to Mill two small 3mm deep groves in valve facing side of the yoke to get it to fit correctly, the K valve on the tank has bigger than normal shoulders and wider on one side.

After this is it fit perfectly:

The gun was a breeze to fill from here

Took it out back and put a few shots over the chrony:

It got a high of 871fps and a low of 848fps (quite a spread)
then it seemed to settle down to around 860fps.(855 to 865 over 20 shots)

I was hoping it would be a bit closer to 900fps. I think I'll take off the tank and test the output pressure before I do any more to it.
If possible I'll try to get it to 1300psi. That should get it to just a hair under 900fps.... right where I like it.

23ib0d0n · Moderator

Have you changed valve / flow dynamics? Flow, ports and spring tension make huge differences at lower operating pressures. This one took some serious effort to seal up properly. Twisted Evil

rbva · Member

I just got done with opening up the valve and the velocity is up at 915fps average now with about a 4fps deviation.
next we'll do a bit of port work. Smile

Rogerflat · Silver Status Member

That's a pretty rifle. Is she loud at 900 fps?

rbva · Member

Thanks, no not loud at all ..... very quite in fact. The sound of the pellet hitting the backstop is by far the loudest thing.

AirGunEric · Site Admin

Nice job- and very useful info for people looking to work on their AM850!

broommaster2000 · Moderator

That's hot. Mr. Green

Good work, and thanks for the documentation.

4950cycle · Member

I love repeatability in an airgun. I like PCP. This looks like an answer that dosn't cost $1,500 or as bulky as a Shinsung. I would like to see something like this in a .22 at 900 + FPS with 14-15 grn. pellet. Ya gotta love where this may go. COOL RIG

rbva · Member

After spending a few months playing with the 850, I think that I've
figured it out.
The speed on the 177 is up over 980 fps. to get it higher will be easy,
but will start getting too close to supersonic. I might push it past 1000fps
just so that I can decrease the pressure and increase the shot count...
but for right now, I'm enjoying the speed and accuracy.
oh... I also transferred it back into it's black stock, it looks much better.

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StevieLaner7777 · Moderator

Sleek!
If those rifles weren't so expensive over here I would be doing just the same as what you've done with yours.

Stevie Thumb Up!

H · New Member

Hi,I am looking at doing something similar but there is not much technical info on springs/spacers/adapters?Can you help?

rbva · Member

Try "The 850 Resource" over here:

http://www.network54.com/Index/84463

Everything you need will be over there.

cliffspot · Veteran Member

So Roald, seems you are getting all the bugs out! Tell me when you can get mine to 850 in 22 cal and I will be happy to outshoot my friend's AA410! That is the coolest "My 850 does 850 in 22!" Hahahaha! What pressure are you running? 1300psi?

rbva · Member

Hey Cliff! hows it going? geeze I haven't had time to surf for a while Smile

We are running 1400psi (1410 at 3000psi down to 1380 at 1400)
Shot count has taken a knock with the higher velocities though. Down to around 100 shot now.
but not bad for a 22 at just under 800fps.

broommaster2000 · Moderator

Hey guys,

Do you think the 850 .22 can go up to about 800 Fps on CO2 alone? I already have a bulk fill kit.