1720T bStaley tune

[sobdiver]

I recently purchased a 1720T for my wife.  I wanted her to have a lightweight gun that was easy to use and accurate.  The 1720T is definitely filling the bill.
 With the help from some posts on this forum I did a bstaley tune.   It was a little bit of a challenge at first to find info on how to tear down the 1720 and do the tune, but as it turns out it’s very easy and I may put together some video instructions.
To do the tune I used four square 70D #113 o-rings.  I enlarged the transfer port to .097.  The O-rings are installed between the hammer and the valve.   They fit perfectly inside the tube and since they are flat on the sides create a very consistent surface (round o-rings might squash together inconsistently when struck  by the hammer.   Here’s the tune I have achieved:



Here’s what I believe I’ve learned and understand.   Feel free to correct me if I have anything wrong.  Turning the striker CW (clock wise), makes it stick out further, which makes the stroke shorter. (the verbiage on this confused me at first).   Without the oring buffer in place the more you turn the striker CCW, the longer the stroke and the more power you will achieve.   The opposite happens with the buffer in place.   Here’s why: the higher the pressure  in the tube the more pressure behind the valve stem.  So when the hammer strikes the valve stem, there is more resistance.  As the gun drops in pressure, the hammer will push the valve stem in further releasing more air.   With the orings in place it will limit how far the valve stem can be pushed in, which when adjusted correctly can flatten out the shot curve. If you make the striker too short, (long stroke) the hammer striker won’t hit the valve stem and the gun won’t go bang.  If you make the striker too long (short stroke) the orings won’t have an effect because the hammer will never hit the oring bumper. 
At first I was tuning for a FPS goal somewhere near 800FPS and I had some good success. Then I started to figure out that there seemed to be a better sweet spot for the striker for efficiency and a little flatter string.   When the striker is in the proper zone you only want to make micro adjustments, turning it clockwise will increase the FPS and CCW will decrease the FPS.  When I turn my striker up from 1 1/8 CW to 1 1/4 CW  my peak FPS gets closer to 800FPS, it’s still a very nice shot string, but I don’t get quite as many shots and it’s not quite as flat.  Anything much above 1 1/4 starts to get out the sweet spot zone and peaks too high relatively and isn’t very efficient.
In addition to the Bstaley I polished the tube and added some graphite powder so the hammer is a little smoother.
I’m very happy with how the gun is shooting.  Here’s some cherry picked 5 shot groups when we had some brief spells of no wind on a recent camping/shooting trip:
 



I’m having so much fun with Susie’s gun, I’m now considering getting another one for me.  It really likes JSB/AA 8.4’s and 7.87’s.   At 50 yards when there is no wind it can pretty consistently do 1/2 “ or better 5 shot groups.  Did I get lucky and get an exceptional 1720t? If I get another one I’m hoping it’s just as good or I will be disappointed

[KnifeMaker]

You did a fine Job Rick, and I would say you definitely won the Barrel Lottery! 


Woo-Hoo!!! Now if you can just win again for your own that would be a double Woo-Hoo!


Knife

[FuzzyGrub]

The 1720T carbine is one of my favorites.     You have the Bstaley buffer down, just fine.  Myself, tuned to 15fpe w/10.3g for 22-23 shots.  As you said, not as efficient at that power.   If you do try tuning for more power, you can go to 0.110" on TP before the valve exhaust needs to opened.  You are at max hammer preload, so a slightly heavier spring would be needed, too. 

FWIW, the oem LW barrel gives you much better odds than a typical crosman one.   

[Frank in Fairfield]

First...I am not a tuner.
I did the bStaley tune on my 1720T with the hopes of shooting pistol FT.

TP=.109
HT= 1.5CW
HS=2.5CW
Spring=.041’x.300”x1.5”
4 o rings
2600-1800psi

With 7.9 CPH= 25 shots @   807fps & 11.4fpe
With 10.34 AA= 25 shots @ 730fps & 12.1fpe

[GLPalinkas]

I LOVE my Crosman 1720T. Got it 2 years ago at the Crosman FT event when they were selling them really inexpensively.
So, I shoot Field Target and wanted to try the BStaley tune so I could use it in a rifle FT WFTF match. Long story short, I am a big fan of several posters on this site, Jason (NerovousTrigger) and John (FuzzyGrub) who walked us all thru the tune in this thread: https://www.gatewaytoairguns.org/GTA/index.php?topic=86564

However, after I did the BStaley I ultimately decided that I would install the Huma regulator as I had already drilled the tp to .094. The thread suggests a Huma and I used the stock spring. Easy to tune now. Basically after setting the stroke all the tuning is done with the hammer spring. I did install a Challenger end plug so I could adjust the hammer spring externally. Paul Porch told me how to fine tune the trigger so I am ready for FT with her. I am using JSB 10.34 at 700 fps, about 11.25 FPE and getting 36 great shots. It falls off the reg around then but with the correct tune the fps rises only slightly and by the time it falls below 695 I am getting 40 shots. Amazing with that little air tube.

Best thing I ever did to an air rifle.

ps Yes, I know most are using the 8.4's in their 1720T's but I like the 10.34 better although she shoots the 8.4 ok. Just a little more weight to allow the skirt to seal better before Elvis leaves the station and I can deal with the slightly loopier trajectory.

Gary
Venice, FL

[sobdiver]

Since I'm maxed out on the hammer preload I would like to try and experiment with a heavier spring and see what happens if I try and up the power a bit with more preload instead of extending the striker a touch.  I am also interested in the regulator idea.  There is a good chance I'll have another 1720T on order this Friday and since I would want my gun to top Susie's, I might consider the regulator route for that gun I've already been researching the Huma and Lane regulators and have watched several of the Lane YT videos. 

[moorepower]

I LOVE my Crosman 1720T. Got it 2 years ago at the Crosman FT event when they were selling them really inexpensively.
So, I shoot Field Target and wanted to try the BStaley tune so I could use it in a rifle FT WFTF match. Long story short, I am a big fan of several posters on this site, Jason (NerovousTrigger) and John (FuzzyGrub) who walked us all thru the tune in this thread: https://www.gatewaytoairguns.org/GTA/index.php?topic=86564

However, after I did the BStaley I ultimately decided that I would install the Huma regulator as I had already drilled the tp to .094. The thread suggests a Huma and I used the stock spring. Easy to tune now. Basically after setting the stroke all the tuning is done with the hammer spring. I did install a Challenger end plug so I could adjust the hammer spring externally. Paul Porch told me how to fine tune the trigger so I am ready for FT with her. I am using JSB 10.34 at 700 fps, about 11.25 FPE and getting 36 great shots. It falls off the reg around then but with the correct tune the fps rises only slightly and by the time it falls below 695 I am getting 40 shots. Amazing with that little air tube.

Best thing I ever did to an air rifle.

ps Yes, I know most are using the 8.4's in their 1720T's but I like the 10.34 better although she shoots the 8.4 ok. Just a little more weight to allow the skirt to seal better before Elvis leaves the station and I can deal with the slightly loopier trajectory.

Gary
Venice, FL

What psi is reg set? Shot count?

[Gwelo]

Since I'm maxed out on the hammer preload I would like to try and experiment with a heavier spring and see what happens if I try and up the power a bit with more preload instead of extending the striker a touch.  I am also interested in the regulator idea.  There is a good chance I'll have another 1720T on order this Friday and since I would want my gun to top Susie's, I might consider the regulator route for that gun I've already been researching the Huma and Lane regulators and have watched several of the Lane YT videos.

You probably know this but if you order from Crosman's website and use "AGNATION" as a promo code you save 25% off the $475.99 price. Net is $356.99. They used to have free shipping on Fri, not sure if still do.
If you have a better price/place to buy, spill!
 

[sobdiver]

Since I'm maxed out on the hammer preload I would like to try and experiment with a heavier spring and see what happens if I try and up the power a bit with more preload instead of extending the striker a touch.  I am also interested in the regulator idea.  There is a good chance I'll have another 1720T on order this Friday and since I would want my gun to top Susie's, I might consider the regulator route for that gun I've already been researching the Huma and Lane regulators and have watched several of the Lane YT videos.

You probably know this but if you order from Crosman's website and use "AGNATION" as a promo code you save 25% off the $475.99 price. Net is $356.99. They used to have free shipping on Fri, not sure if still do.
If you have a better price/place to buy, spill!

Yes, I was planning to buy at Crosman with the AGNATION code, and combine the Friday free shipping.  Thanks for looking out for me, because if I didn't find out about all the buying tips until after I pulled the trigger I would be pretty bent

[GLPalinkas]

I LOVE my Crosman 1720T. Got it 2 years ago at the Crosman FT event when they were selling them really inexpensively.

.......... Easy to tune now. Basically after setting the stroke all the tuning is done with the hammer spring. I did install a Challenger end plug so I could adjust the hammer spring externally. Paul Porch told me how to fine tune the trigger so I am ready for FT with her. I am using JSB 10.34 at 700 fps, about 11.25 FPE and getting 36 great shots. It falls off the reg around then but with the correct tune the fps rises only slightly and by the time it falls below 695 I am getting 40 shots. Amazing with that little air tube. .......

What psi is reg set? Shot count?

The reg is set when it comes from the supplier (I used trenieroutdoors.com) and it came about 125 bar. Using the instructions, I re-set it to "approx" 95 bar. The setting is not exactly precise so I am guessing around 96 bar or 1400 psi. I actually pulled it out several times to get a shot string where when it came off the regulator it didn't spike the fps too much so that I could get a few extra shots in the region I wanted.
I get 40 shots at about 11.25 FPE. Obviously, it depends on your goal as far as FPE. Mine was Field Target in the WFTF class which is limited to 12 FPE. My accuracy is outstanding at my current setting.

I don't wish to hijack the OP so if I can help in any other way, please pm me.

[sobdiver]

No worries about hijacking, regulator talk is helpful

[FuzzyGrub]

One of these days, I'll install a huma in my 1720T, and tune it to the same 800fps w/10.3g AA.  I do think I'd get a little better shot count (3-4) along with a bit tighter Es, than Bstaley. 

[sobdiver]

Since I'm maxed out on the hammer preload I would like to try and experiment with a heavier spring and see what happens if I try and up the power a bit with more preload instead of extending the striker a touch.  I am also interested in the regulator idea.  There is a good chance I'll have another 1720T on order this Friday and since I would want my gun to top Susie's, I might consider the regulator route for that gun I've already been researching the Huma and Lane regulators and have watched several of the Lane YT videos.

You probably know this but if you order from Crosman's website and use "AGNATION" as a promo code you save 25% off the $475.99 price. Net is $356.99. They used to have free shipping on Fri, not sure if still do.
If you have a better price/place to buy, spill!

I can verify that free shipping Friday still works.  As a matter of fact I successfully placed my order on Thursday night, so it would appear that the Free Shipping begins at midnight EST