Making a mess of my 1720T project, help!

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qball

qball

Member
Apr 13, 2020
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CA, United States
So I got Thea 1720 pistol from AGN for fun target shooter but it came with really low power tune. After reading all the threads I can find on AGN and GTA I promptly drilled out the TP and added spacer trying to get more power while waiting for hills Airgun’s 0.105 TP and 42 hammer spring to be shipped. Of course it didn’t do much but thankfully the TP and hammer spring arrived very quickly. Installed the 42 spring and TP and BAM! 900FPS with @2400 PSI and then 800 FPS @ 2000 psi. In and effort to flatten out the shot curve I install a .4 inch Section of rubber tube(Beasley mod?), messed around with the hammer throw and was only able to flatten it out a little bit.


So what am I doing wrong? I’m thinking I need to got back to the stock 0.067 TP but where can I get that? Is a 100 dollar regulator my only cure for the wild shot string?


any help is appreciated!
 
You need a 0.080 (maximum for flat shot string anything over then velocity will drop straight down with every shot) P-Rod OEM TP and everything else left all bone stock as factory set and fill to 2900-3000psi. Simple. Hammer spring that's other than factory does you no good unless you install a regulator which this pistol doesn't need that shoots perfectly fine without one. Add a B Staley O-Ring mod to reduce hammer bounce to save air if you wish.


 
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Why on earth would you ruin the higher power 0.067 OEM 1720T factory TP and not drill out the smaller restrictive TP that came included as a spare as a swappable low power 10 meter TP with that pistol instead? Doesn't make any sense at all.
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Hey we all do regrettable things sometimes once we dig into something. 

From the sounds of it the pistol may have already had the smaller TP installed and no other TP came with it.
 
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I got the 1720T second hand and pretty sure I got the restrictive one TP, it was tiny! 


Sounds like I just wasted 60 bucks on after market parts. Hahahahaha! whats the best source for OEM TP and spring? Can’t find anything on crossman.com. 

Another problem is I don’t see the speed really picks up till around 2500 PSI. Guess I can just crank up the OEM spring and the 0.067 TP will restrict airflow when hammer has enough force to open the valve? I’m stating to get a hand of it and suspected my TP is way too big. Might just bite the bullet and get the Huma regulator, is there a better one? 
 
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I got the 1720T second hand and pretty sure I got the restrictive one TP, it was tiny! 


Sounds like I just wasted 60 bucks on after market parts. Hahahahaha! whats the best source for OEM TP and spring? Can’t find anything on crossman.com. 

Another problem is I don’t see the speed really picks up till around 2500 PSI. Guess I can just crank up the OEM spring and the 0.067 TP will restrict airflow when hammer has enough force to open the valve? I’m stating to get a hand of it and suspected my TP is way too big. Might just bite the bullet and get the Huma regulator, is there a better one?
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If the gun chronied in the 450-550fps before tinkering then it was indeed the smaller restrictive TP meant for 10 meter shooting.

Why would Hill sell an oversized TP that's larger than 0.080 specifically for a 1720T application? That just doesn't make much sense it's all downhill when going larger than 0.080. Maybe for a P-Rod the oversize TP and spring application would be more fitting since its a 22 instead.

The 1720T and 1701P are the simplest guns to bump the power up with very minimal investment and tinkering just by swapping P-Rod 0.080 OEM TP. Nothing else needed and no regulator needed they are that consistent. Adding a regulator may even give you less shots because it takes up volume in an already small capacity air tube and you lose the overall pressure remaining manometer reading as well.

You might be better off buying an FX Impact.

I will post Crosman OEM part numbers shortly.
 
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Crosman OEM Part #s...

2220-014 P-Rod TP

1720-014 1720T high power TP

1700-014 1720 low power TP

130-036 TP seal

These parts are only a couple of bucks each from Crosman.

You dont need a hammer spring because you already have the OEM 1720T factory spring that you use.

When done fill to 2800-2900psi to tune just with HST adjustment for a flatest possible shot curve and once set perfect you may fill to 3000psi.

If you insist on installing a regulator you are on your own and are introducing a really money wasted unnecessary variable to the gun that's one more thing to go wrong with the potential dreaded unexplained unexpected unwanted first shot reg creep (Yep even HUMA) that misses your target rather than perfect dead on 100% from shot #1 till the last unregulated shot.
 
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While the 0.105 TP is too large for a conventional tune, it should be fine for a BStaley mod. I use 0.110" TP which is equal to the oem exhaust port. Larger is usually not a problem and can eliviate some alignment issues between valve and breech/barrel. I get 22-23 shots at 15fpe w/10.3 AA. 4% Es. I haven't heard of using a rubber tube for the bumper, though.
 
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While the 0.105 TP is too large for a conventional tune, it should be fine for a BStaley mod. I use 0.110" TP which is equal to the oem exhaust port. Larger is usually not a problem and can eliviate some alignment issues between valve and breech/barrel. I get 22-23 shots at 15fpe w/10.3 AA. 4% Es. I haven't heard of using a rubber tube for the bumper, though.
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That's awesome to hear, I read the tube thing on one of AGN or GTA thread but think I'll go find the proper O-Rings to try. Which hammer spring are you using? Stock? I'm looking to around 12-13 FPE and hopefully 30 flat shots.

Thanks!
 
Upvote 0
If the gun chronied in the 450-550fps before tinkering then it was indeed the smaller restrictive TP meant for 10 meter shooting.

Why would Hill sell an oversized TP that's larger than 0.080 specifically for a 1720T application? That just doesn't make much sense it's all downhill when going larger than 0.080. Maybe for a P-Rod the oversize TP and spring application would be more fitting since its a 22 instead.

The 1720T and 1701P are the simplest guns to bump the power up with very minimal investment and tinkering just by swapping P-Rod 0.080 OEM TP. Nothing else needed and no regulator needed they are that consistent. Adding a regulator may even give you less shots because it takes up volume in an already small capacity air tube and you lose the overall pressure remaining manometer reading as well.

You might be better off buying an FX Impact.

I will post Crosman OEM part numbers shortly.
Click to expand...



I told Tim that I would like to get around 12-15 FPE out of the 1720T and that's what he told me to try. Don't think it's working out but oh well, not a huge deal. I'm sure someone on AGN with a PRod could use the parts at a discount.



Are you suggesting 0.067 TP and 42 sized hammer spring? The spring I got with the gun seems really weak but could be limited by the TP. I honest don't need 15 FPE but really want a flat shot string for accuracy since it's no .25 when comes to putting down a squirrel.



I do have an Impact tuned for slugs, a dream-tac compact in 0.25 shooting 650 FPS for backyard but think I'm going to sell it because it's still kinda big(compared to 1720T and PP750) and overkill. I have a Artimes PP750 in .22 coming so the 1720T might just just be a paper target gun but I really liked how accurate it is and wouldn't mind making it a sparrow gun plus try the British style precise head shots on squirrels.
 
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Crosman OEM Part #s...

2220-014 P-Rod TP

1720-014 1720T high power TP

1700-014 1720 low power TP

130-036 TP seal

These parts are only a couple of bucks each from Crosman.

You dont need a hammer spring because you already have the OEM 1720T factory spring that you use.

When done fill to 2800-2900psi to tune just with HST adjustment for a flatest possible shot curve and once set perfect you may fill to 3000psi.

If you insist on installing a regulator you are on your own and are introducing a really money wasted unnecessary variable to the gun that's one more thing to go wrong with the potential dreaded unexplained unexpected unwanted first shot reg creep (Yep even HUMA) that misses your target rather than perfect dead on 100% from shot #1 till the last unregulated shot.
Click to expand...





Thank you so much for the info!!!!! I was kinda close to ordering the Huma regulator and their pressure gauge thingy totally over 200 bucks.

I'll get both the P-Rod TP and 1720T high power TP then a few TP seals.



Thanks again!


 
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Listen to Fuzzy! Nothing wrong with what you have. Just use 4 of the proper size orings for the BS buffer. I ran a 110 t port and heavier hammer spring and was able to get 30 12 fpe shots with 8.4 jsb.

The rubber tube thing your using is screwing things up for you. Run your hammer spring mid way in and get the throw where it's just starting to tap the valve for a starting point. Totally doable with what you currently have. Just get the right orings. 
 
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While the 0.105 TP is too large for a conventional tune, it should be fine for a BStaley mod. I use 0.110" TP which is equal to the oem exhaust port. Larger is usually not a problem and can eliviate some alignment issues between valve and breech/barrel. I get 22-23 shots at 15fpe w/10.3 AA. 4% Es. I haven't heard of using a rubber tube for the bumper, though.
Click to expand...





That's awesome to hear, I read the tube thing on one of AGN or GTA thread but think I'll go find the proper O-Rings to try. Which hammer spring are you using? Stock? I'm looking to around 12-13 FPE and hopefully 30 flat shots.

Thanks!
Click to expand...

If the "42" Hill refers to wire diameter, that should be close to the same spring I use.
 
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I ordered extra transfer ports directly from Crosman so I could drill them out myself progressively larger as desired. You do have to have the part number before you call, 1-800-724-7486 is the last number I used for ordering, they take credit cards.

The trigger pull weight is affected by the hammer spring tension; the higher the tension, the more pressure and friction on the sear mechanism, and thus a higher trigger pull weight.

To get more valve opening with less hammer spring tension (and also lighter trigger pull), I cut off a couple of coils from the valve spring. This, of course means disassembling the valve, so go ahead and plan on all new o-rings, and polish the valve stem to a near mirror polish.

The 1720 and P-Rod are similar. These will shoot more quietly with a higher fill pressure and a slightly more restrictive/smaller transfer port orifice size. I don't have all the data for mine handy, but I remember setting mine up for a max fill of 3100 or 3200 psi, shooting down to about 2600.

Good luck and have fun tinkering!
 
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While many people call the BStaley O-ring buffer a "hammer debounce" device, while it might help with that, I think its primary benefit is keeping dwell under control for the short barrels. The same valve spring is used in Mrods. Opening the TP up provides a short burst of air vs a longer slower one.

The oem hammer spring has changed over the years in the Prod and suspect same in the 1720T, which has the same part number. A Prod I purchased at the end of last year, had a 0.035" wire spring that was 1.75" long. Older Prods springs were 1.5" which is also what my 1720Ts had. The 0.042" wire springs I use with buffer are 1.5" long. I think they changed to the longer one, because some people were expierencing valve lock at 3Kpsi. The longer spring allows more pre-load, so a little more hammer energy.

The 1720T is a great tinkering gun like the Prod. They make a great little carbine. Mess up something, reasonable parts are just a phone call away. Have fun. :)




 
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Thanks everyone! 


switched to O rings and messed around with the hammer throw and spring tension and finally got a flat shot string of 25 12 FPE shots. However it’s a bit louder than I thought it should be and sounds a bit fartty guess I might have hammer bounce. Will try the heavier hammer spring to see if that helps reduce the initial low speed shot about 2700 psi. Definitely will order the TP first thing Monday so I can open the gun up a bit and it won’t be so sensitive.
 
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