Experimenting with the 1720T - 20.33 FPE

[FuzzyGrub]

Is there some reason to use SS spring? 

No not really.  MC has music wire precision springs, too.

[BigTinBoat]

Well looking around Century has the best selection of springs.  If my guessiments are close the stock spring is 6 lb.  Not sure exactly what the 1.5" spring John sent me (in gun) is, but the 1.5" spring that Rob sent me is ~ 16 lb I think. 

Here what 1.75" x .30" springs I plan to order:

7.5, 9.6, 11, 13, 16 lb

If you guys need any I can order you some since you have to order $40 worth.  Just PM me.

Trial and error has put me on the .110 port, which is the largest without modifying the valve.  Even if I modify valve I think anymore will bring my shot count down too much.  I want 20-25 shots.

Did anyone modify the barrel end spacer?

M

The spring I sent is 11.4lb. (max load) I found a link to it.
Material: High Carbon Steel Music Wire
http://www.zoro.com/i/G2170594/

[GadgetX]

According what I have read Music Wire (Steel ASTM A228) springs are the best for fatigue applications.  SS springs are mainly for corrosive environments or higher temps (> 250 f).  Other parts of this puzzle are the stock spring is left handed and the 1.5 springs you guys sent me are right handed.  Doesn't seem like it matters...

M

[GadgetX]

The spring I sent is 11.4lb. (max load) I found a link to it.
Material: High Carbon Steel Music Wire
http://www.zoro.com/i/G2170594/

Good info thanks Rob !!  The zink coating made it slightly larger I guess.

So 9.91 lbs & 11.4 lbs at 1.5".  So I am going to order 9.6, 11 & 13 lb 1.75" inch springs.

Thanks guys,

M

[GadgetX]

I found a pack of 10 SS compression springs.  1.75" x .3" x .042" 9.84 lb for $13 shipped.  They are RH coil but shouldn't matter.  Also free returns offered.

This seems like a good SS spring.   If they work well I will share...

Mike

[BigTinBoat]

I found a pack of 10 SS compression springs.  1.75" x .3" x .042" 9.84 lb for $13 shipped.  They are RH coil but shouldn't matter.  Also free returns offered.

This seems like a good SS spring.   If they work well I will share...

Mike

Wouldn't mind trying one if it helps flatten the curve.

[GadgetX]

It only gets better...  Google to the Rescue !!

Packs of 10 springs in 1.75" x .30" in 8, 9, 10, 11 lb on the way in.  All returnable $13 shipped a pack

Enough to share if they work well.  This should help the bolt cocking issue I was having with the 1.5" springs.

Will report back with results.

M

[BigTinBoat]

This should help the bolt cocking issue I was having with the 1.5" springs.

Will report back with results.

M

What issue were you having?

[FuzzyGrub]

This should help the bolt cocking issue I was having with the 1.5" springs.

Will report back with results.

M

What issue were you having?

Yea, what issue?   Can't think of any issue that the longer spring is going to help fix.  I thought you were just trying other configs.

If binding, there are a couple of other things to check.

[GadgetX]

The bolt was not always engaging with 1.5" springs.  Put original back in and no issues... 

M

[FuzzyGrub]

The bolt was not always engaging with 1.5" springs.  Put original back in and no issues... 

M

Spring engages sometimes, and not others???   or sear did not latch? 

I have 1.5" springs in both of my 1720T and they always engage and latch. 

Just checked: Both Prod and 1720T share the same spring part number: 1700-009

I suspect something else is causing issue.

[GadgetX]

Ok trying to put my arms around this oring tune.  John suggested I try 3 orings and 2 washer spacers.  Tune seemed to want ~3/4 of a turn on striker.  I took out the spacers yesterday leaving just the 3 orings and the striker seemed best a 0 turns.  Zero turns actually gave me a more FPS with same shot number between 3000 - 2200 psi.  Confused as always...

The new 1.75" hammer springs land tomorrow.  7.16, 8.21, 9.84, 11.88 lb.  They are 10 pack each so I will have more springs than I need.  Maybe I should offer a 4 pack assortment in the classified thread and try to recoup some of my $60.  They fit 1720T, 1701P and BP2220 pistols.  Or maybe change just my name to Mr. Spring!!   

Anyway look forward to a bunch of experimenting !!

M

[FuzzyGrub]

Yes, with three oring you will get more power, but you don't have the ability to turn it down from there.  The two 0.035" SS washers and three orings was for the 15fpe and have some adjustment to lower it. 

If you are right at the perfect tune for you. leave it there.  With the throw screw full CCW you don't have to worry about creep.  Many add a set-screw to the hammer to prevent creep of the throw screw. 

[GadgetX]

Mornin' John.  Not sure what is meant by "turn it down".  Seems like the same thing if you move the striker and the buffer out.  I guess I need to study up some more on the buffer.

 Thanks,

M

[BigTinBoat]

Mornin' John.  Not sure what is meant by "turn it down".  Seems like the same thing if you move the striker and the buffer out.  I guess I need to study up some more on the buffer.

 Thanks,

M

I can answer that. In your top pic the gun velocity cannot be lowered anymore as the striker is all the out. In the bottom pic you can turn the striker further out, hence "turning it down". (in velocity)
In theory (and likely in practice) both pics as drawn will shoot the same velocity.

[GadgetX]

Hi Rob,  I can see that you can "Tune it down" more.  Why not use 4 orings and turn the striker out some more.  Seems like the orings are acting as a anti bounce device also.  Why use 1/2 thickness washers as John recommends? 

If this AG had a regulator seems like you could get a almost flat 825 fps tune for 25 shots which would be ideal.

I am wondering exactly what effect the port size, hammer spring load have on obtaining my goal of a 25 shot 825 fps string with 10.65gr pellets. So many variables finding the best port size and spring load.  Add adjusting the striker & hammer spring makes it seem like infinite possibilities.  Good thing I am retired, but I better order more pellets...

My guess is that my 1720T will do best with port of .095 and the 9.84 lb spring, 0 striker and 7 hammer spring with 3 orings.

Be safe,

M

[BigTinBoat]

As John mentioned you ideally want the Striker set at zero to avoid any possibility of it moving. (I have a homemade "t" allen wrench made so that I know it is staying in the exact spot each time I take the gun out.)
Not sure on the regulator as it would take up some of the tube volume which is already only like 63CC's.

Nobody said it was going to be easy. I think sometimes we get lucky on a tune and hit it just right, if not it can be really hard due to all of the variables. And even harder, IMHO, due to the small volume of the tube.

[GadgetX]

I was considering a regulator but after watching this video  I can see that they would be better with a bottle type AG, because as you say, the gun has such a small tube. 

I know you and John have been experimenting with the 1720T a bunch.  Would love to hear where your guys guess is for port size and hammer spring load rating to achieve my goal.   From the factory I was getting a good shot string (>35 shots) but it was only low 600s fps.

M

[BigTinBoat]

Would love to hear where your guys guess is for port size and hammer spring load rating to achieve my goal.   From the factory I was getting a good shot string (>35 shots) but it was only low 600s fps.

M

I don't think you are going to get to 25 shots at 825.

With the .109 and the spring I sent you I am at 833 avg for 21 shots. I think without the depinger I would add 1 shot. If I took maybe an 1/8 turn off the HS I could add another for 23 total. Don't think 25 is possible.
I calculated my efficiency at 1.4 but it is probably higher as I do not know the volume of the depinger. Don't think it can get much better without some very very fine tuning.

[GadgetX]

Rob,

Did you try any other port size than .109?  If you did, how much did FPS fall off?

I got the 9.84 lb springs in.  From that I have discovered why you guys went to 1.5" springs.  More lbs equates to more coils.  Well the my 1.75" spring will not cock with HS more than 5.5 turns.  I checked the range and the adjustment unscrews at 6.5 turns.  Not sure this matters but will find out when it stops raining.

Will report back later this week with findings.

M