Experimenting with the 1720T - 20.33 FPE

[GadgetX]

I have been experimenting with mods on a 1720T.  Would like a 20 -25 shot FPE >15 tune somehow.

Members here sent me a few mod parts and I thank them very much.  I was able to shot a max power 10 shot string average of 887 fps with a 10.65 gr pellet.  Max power was 927 fps (20.33 fpe), but as most guessed it went down from there. 

Mods are .110 port, mod valve stem and with spring 1.5" x .30 x.042.

I have tested it many times with original spring (0 striker, 7.5 spring) which gave the highest shot count (count was 25-30), Stiffer spring which gave the highest FPE.  Varied the port from .080, .097, .110.  Decrease in shot string was not significant.  When I added the stiffer spring the shot count was in the mid-low teens.

May look for a spring 1.75" x .30 x .038.  For some reason just estimating, this seems like it would be the sweet spot.

Will post result strings next week when I get home from travel.

Again thanks to all members of this fantastic forum.

M

[FuzzyGrub]

Your goal is definitely achievable with the oring buffer.  Leave that spring, and do a complete shot string at the initial settings I sent you.   Start a little high at 3100psi. 

[GadgetX]

Here is were I am now.

10.65 gr Barracuda match, stiffer spring, modified valve stem & .110 port.  3000 - 2250 psi fill.  Striker at .25, spring at 6.5. FPE 14.98 - 17.02.  26 shots.

I would not mind if the FPS was flatter around 820s. 

M

795.8
802.5
814.4
818.9
824.7
835.6
836.6
845.0
843.8
848.1
847.6
846.4
848.3
846.6
843.4
error
837.8
835.9
832.6
826.9
818.7
812.5
808.6
806.1
799.4

[FuzzyGrub]

If you cut the first two and last three, it is not far out.  Take a turn off the preload and see where you are at.  Then very, very, small adjustments to throw.

PS: You are getting better flow with that valve stem.

[BigTinBoat]

Here is were I am now.

10.65 gr Barracuda match, stiffer spring, modified valve stem & .110 port.  3000 - 2250 psi fill.  Striker at .25, spring at 6.5. FPE 14.98 - 17.02.  26 shots.

I would not mind if the FPS was flatter around 820s. 

M

795.8
802.5
814.4
818.9
824.7
835.6
836.6
845.0
843.8
848.1
847.6
846.4
848.3
846.6
843.4
error
837.8
835.9
832.6
826.9
818.7
812.5
808.6
806.1
799.4

Did you put the O-rings in? I think I'm at about .25-.5 on striker and like 4 on the spring. I start and end right at 800 with a peak of 832 for 23 shots, with 10.3 AA

[GadgetX]

I will get back later next week.  Off to Mardi Gras this week.

Thanks for the tips I will try next weekend.

M

[BigTinBoat]

Decided to get my 1720 out and run a string. Pumped it to just past the 3K line on gauge. Here are the #'s (I bumped up my external spring adjuster about 1/8 turn) Pellet - 10.3 Air Arms
801.7
808.9
820
822.6
826.8
833.5
837.1
838.9
838.9
841.2
846.9
843.5
840.9
843.4
841.6
839.9
841.7
835.1
835.1
825.7
829.3
821.3
815.3
800.1

If we throw out the 1st and last shot I got 22 shots under 4.4% spread (throw out the 1st two and last shot and it's 21 w/i 3.7%)
Average FPS - 833
Average FPE - 15.87

And at 10m here is the target with all 24 shots. (the bottom Diamond) I think my gun likes the AA pellets. And the best part? 7 pumps to charge hose and 24 more pumps to fill back to 3K. Efficiency is just about 1.4FPE/CUIN (according to the Sikes Calc)

And I have a Hill Depinger in my tube so you will probably get at least 1 more shot, but I think the difference the depinger made is worth 1 shot.

By comparison the center diamond is 20 shots with my Daisy 901 at 10m

[GadgetX]

Folks,

Anyone know the specs of the stock spring in the 1720T?

Stock is 1.75" long, .3" OD, has 14.5 coils, wire is ~.032 by measurement.  Have no clue on Rate (lbs/in), Max Deflection (in) or Max Load (Lbs).

Also when they talk about a #7, #10, #12 spring are they talking about the Max Load or the Rate?

Any clue or help would be appreciated.

M

[BigTinBoat]

Folks,

Anyone know the specs of the stock spring in the 1720T?

Stock is 1.75" long, .3" OD, has 14.5 coils, wire is ~.032 by measurement.  Have no clue on Rate (lbs/in), Max Deflection (in) or Max Load (Lbs).

Also when they talk about a #7, #10, #12 spring are they talking about the Max Load or the Rate?

Any clue or help would be appreciated.

M

According to the Century Spring Catalog one of their springs with those dimensions (other manufacturers should be equal or real close) will have the following specs:
Music Wire - Max load - 6.1lb , Rate - 6.0lb/in, Max Def - 1"
Stainless - Max load - 4.1lb, Rate  - 5.1lb/in, Max Def - .8"

When guys talk 7 or 10lb I'm pretty sure they are meaning Max load.
Middle of page "73". ( Is page 62 when the PDF opens on my computer)
http://www.centuryspring.com/pdfs/12-228compression.pdf

[GadgetX]

Hi Rob,

Yea I was figuring stock was #6 very similar to the MROD larger springs.  I am thinking of ordering a set of springs from Century that are the same length of 1.75" and have max load from 7.5 to 12 lbs.  Not sure if the wire diameter matters so I was going to get SS and Steel springs.  SS springs have a lower max load.  I once fine tuned a MROD and the best spring was about 10-11 lbs.

From my guessiment I am figuring 1.75" x .3" x .038 (Century 70902) or 1.75" x .3" x.04" (century 70921).

The 1.5" spring does not seem to work well with the 1720T bolt. 

Thanks !!

M

PS - Gun is louder than before.  Just curious, do they make a longer shroud with more baffles that can help quiet it down some?

[BigTinBoat]

Hi Rob,

Yea I was figuring stock was #6 very similar to the MROD larger springs.  I am thinking of ordering a set of springs from Century that are the same length of 1.75" and have max load from 7.5 to 12 lbs.  Not sure if the wire diameter matters so I was going to get SS and Steel springs.  SS springs have a lower max load.  I once fine tuned a MROD and the best spring was about 10-11 lbs.

From my guessiment I am figuring 1.75" x .3" x .038 (Century 70902) or 1.75" x .3" x.04" (century 70921).

The 1.5" spring does not seem to work well with the 1720T bolt. 

Thanks !!

M

PS - Gun is louder than before.  Just curious, do they make a longer shroud with more baffles that can help quiet it down some?

Spring works pretty good with mine. Are you having problems cocking? Mine is smooth cocking.

I bought mine used and it has a little 4" extension on it. I think it maybe have come from Marmot Militia. I think this is it here:
http://www.marmotmilitia.com/pistol-marauder-p-rod.html

[FuzzyGrub]

The refurb 1720T I got, did have 1.75" spring.  It is near identical to the disco spring, if not same.  The original prod one was 1.5", but I hear from some people that has been coming in 1.75" too.   I haven't had any issue using 1.5", but doesn't hurt to try a slightly longer one, as long as it does not bind. 

If you take spring length minus compressed length, times spring rate, equals max load.  Max load is what most people advertise for airgun springs.  You can measure your compressed length by pulling back the bolt and measuring where it contacts the spring, and then the distance at where it is fully cocked.  That difference times rate is the load you are set at.

MM shroud ext does help, but if you want more quiet at these power levels, look at Hill, TKO, or Clauge LDCs.  If you don't mind some DIY work, here is what I did:  http://www.marauderairrifle.com/forum/viewtopic.php?f=33&t=10961   I just sold both of my MM exts. 

[GadgetX]

Thanks John,

Thinking I don't want to remove the extension or LDC to fill the AG.

M

[williesurvive]

You don't have to remove the extension to fill the gun. I have 1 on my .25 m-rod and the 1720T. It will put the noise level back to what it was before the mods.

[FuzzyGrub]

Thanks John,

Thinking I don't want to remove the extension or LDC to fill the AG.

M

Yea, that would be a PITA.  I haven't had to do that though with MM ext, or Hill, or my DIY one.

PS: I have a piece of black electrical tape around the fill hose foster collar to prevent from scratching shroud.

[GadgetX]

Ahhh...  I went back where I had read this and it applied to the Clague with a shorter neck.  This begs the question of how much longer do they add to the AG?  Also does drilling the barrel end spacer holes out some help sound or performance?

I hope to fine tune the 1720T.  I am wanting to flatten the curve out some more.  Trying to find the 1.75" x .30" x .041 spring that is about 10-11 lbs max load.  Century I found out has a minimum order so searching around.

Thanks,

M

[FuzzyGrub]

The Hill adds 5.75" inches which is still not bad for carbine.  My DIY is slightly shorter.   The MM ext adds 3.3"

Don't bother looking in McMasterCarr for the 1.75" springs.   

BTW, I think you can shim the 1.5" springs a little.  Find some brass washers that fit in hammer recess and allow the throw Allen wrench to pass thru. 

 

[GadgetX]

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

[FuzzyGrub]

On a Prod, I have tried two small holes is the shroud, just ahead of the breech mount, with and without magic sponge, with no detectable diff in sound.

If you mean the airstipper, I drilled those out to 0.160".  Not sure how much that helps, but do it as matter of course.  You can go a little larger than that if you want, too.

The spring I sent you:
302 Stainless Steel Precision Compression Spring
1.5" Length, .3" OD, .042" Wire
Length  1.500"
Spring OD 0.30"
Wire Diameter  0.042"
Compressed Length  0.673"
Load 9.91 lbs.
Rate 17.38 lbs./inch
Additional Specifications Type 302 Stainless Steel—Meet ASTM A313.
RoHS Compliant


I would be interested in a sampling of springs.  I'll PM latter.

[GadgetX]

Thanks for the info.  I went and took it out to check.  My estimate was wrong because I thought it was a steel spring not a a SS spring.  Is there some reason to use SS spring?  From what I read Steel springs are more consistent and don't loose compression over time when compressed.

M