Experimenting with the 1720T - 20.33 FPE

[FuzzyGrub]

You can use 4 orings instead of 3 orings and two washers.  It just means that the throw adjustment will be have more turns.  About one additional turn, in this case.  On a BSB, the throw adjustment is the velocity adjustment.  The farther you turn the throw in for velocity, you also decrease your throw.  I like to have as much throw as I can. 

As far as regulators in Prod/1720T, search for some posts by Scott (motorhead).  He did some extensive testing with a Milo regulator.   At these power levels I doubt you will get any more shot count, given the loss of air volume for regulator and plenum needed for this power level.

Rob and I both had similar tunes of about 15FPE @ twenty something shots.  Keep in mind we are using the slightly lighter jsbs than your h&n's.  Your fps should be somewhere slightly lower or slightly lower shot count.

PS: The good thing about springs that are too long is, you can make them shorter. 

[BigTinBoat]

Rob,

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

No I didn't. Based on all of the stuff I found on several different articles/posts .109 seemed best so that's where I started, and then left it.

[GadgetX]

Did you guys check the port size of the valve itself?  The transfer port that John sent me is larger that the port in the valve.  I drilled my extra transfer port at the same size as valve that I will try.  It does not seem like a port larger than the port size in the valve would work any better than a port of the same size.  Did you guys drill the valve port also?

M

[BigTinBoat]

  Did you guys drill the valve port also?

M

I did not drill mine. Didn't even take it out when I first did the mod

[FuzzyGrub]

I have drilled them out for other applications, but I thought the valve  exhaust was the 0.110".   If the tp was slightly larger, should not hurt, and might help if the barrel tp is slightly mis-aligned with the valve port. 

[GadgetX]

Went to shop and got some good measuring equipment.  My stock valve port is exactly .109 which is 375 ten thousandths less than 7/64" drill.  My stock breech port is .130.  The transfer port John sent is .126.  I drilled my extra red transfer port to exactly 7/64" which is .109375. This should be ideal.  So far the only 1.75 springs that allow full travel are 7.16, 8.21 lb.  9.84 SS springs you lose ~ 3/4 - 1 turn on the Hammer Spring (HS) adjustment.  The back ordered 9.04 lb spring should be here Monday.  Looks like solid length of 1.75 springs have to be < .985" in order for AG to cock properly and allow full HS adjustment.  Any 1.75 springs in SS seem to be too "fat" and don't allow gun to cock properly on full Hammer Spring adjustment.  Will report back with shot data in a few days.

Take care,

Thanks Guys,

M

[GadgetX]

Well I shot a tin and a half today trying different configurations.  Results were disappointing.  But got to love PCP so easy to shoot reload. 

Results:

Both the 7.16 lb & 8.21 lbs 1.75" were just to light.  Lots of shoots but nothing over 790 fps.

The 9.84 lb 1.75" spring shots were over 850 fps but could not adjust toward sweet spot because HS had such little adjustment.  11.88 1.75" spring had literally no adjustment but fired 11 shots over 900 fps.  Will try 9.04 lb 1.75" spring when they arrive on Monday.

The best tune has been John's 9.91 lb 1.5" spring which string was in my 3rd post.  Rob's 11.4 lb I was able to squeak out a respectable 14 shots 877.8 - 897.1 fps.

I played with the striker adjustment from 0 to 3 turns.  Still puzzled what changes except less Fps.  I could not see the string flatten out or peak differently.

M




 

[FuzzyGrub]

Not sure what happened to the tp.  Maybe I drilled one, but sent another by mistake?  I don't think it is going to impact your tune much.  Go back to where you were and make very small adjustments in throw, like 1/8 T. 

[GadgetX]

Thanks John.  You are right about small adjustments. 

When tuning, in general terms, what flattens out the string?  AG seems to start low and peek at 2500 or so.  This AG would be the cat's meow with a regulator.  I am guessing that is why they go to double tubes.

Thanks,

M

PS - Found this document which has helped me mucho.  https://docs.google.com/document/d/1wsnI6_GJHqhD13YGlihlBpQzb_X91qmCsdCxT4iQtMA/edit

[FuzzyGrub]

FWIW: If you go double tube, you can't use a reg.  The air inlet from the 2nd tube is right where the reg has to be.

When close, I lower the throw very slightly, and sometime increase hammer preload.  and the opposite.  Going with a higher fpe usually has the consequences oh having higher Es.

[GadgetX]

New spring 1.75" 9.1 lb.  Best string - Hammer 0  HS 5.25  3000 - 2000 psi  10.65 gr  No BSB

788.0
790.8
801.8
807.9
812.2
819.7
823.4
835.5
836.1
845.8
848.8
850.6
854.8
853.8
855.4
851.6
847.9
844.8
837.7
832.4
825.6
822.2
816.3
806.7
798.1
774.6

Everytime I use the BSB I get more peak and less shots.  If I go to HS 6 no orings I get flatter curve with ~20 shots.  I have to order more pellets.  Shot over 800 in the last week.

This is how I tuned with orings.  load 2500 psi, turned striker out to I hit my goal FPS.  Played with HS.  Tried 3, 3.5 & 4 orings.  Gun is much quieter until I get to 2500 psi.

I feel like a I have failed.  Set my goal too high.  Need more air.  When I set my HS at 6.5 I get 13 shots 842.7 - 880.3 fps.  This would be good for hunting with spare air tank to refill often. 

Will continue when I get some more pellets.

M

[FuzzyGrub]

Try a lower goal for your peak.  Say 800-810fps with those 10.65g.

PS: I have been busy on some mods and fixes to the Prod rifle in Blaster clothing.  Fixed a very slow leak, changed shroud, and free-floated the airtube.  I have a few parts coming to finish this off.  I will get back to some tuning with 1720T and brothers Prod.  I have a WAR anti-bounce hammer coming to try as well.

[GadgetX]

John,

Why do you need a anti bounce with a ring tune? 

I also have come up with an interesting tuning tweak on the BSB.  I put a digital caliper in the slot between the hammer and the end of tube slot.  I increase the striker until the caliper shows some decrease from striker touching piston valve.  With 3 orings that is about .35 of a turn.  When I have tested the FPS this has always been the sweet spot, no matter what the HS adjustment.  If I could just figure out the hammer spring adjustment this easy, it would become a AUTOMATIC tune.   

Got pellets in yesterday, going to shoot a few hundred or so today.  I will let you know if I get any good strings.

M

[FuzzyGrub]

Why do you need a anti bounce with a ring tune? 

I want to see how it compares to the BSB.  I don't plan to try both together. 

I have heard how quiet it has made some Mrods, and picked up one of the Prod blems that were for sale. 

[GadgetX]

Well going to leave the 1720T at this tune.  3100-2000 PSI, Striker .4, HS 6.25.  Three orings and one washer.  9.04 LB 1.75 spring.

798.9
808.6
814.3
817.5
822.2
828.7
835.2
840.7
835.3
844.9
841.7
852.2
852.9
851.3
856.8
848.0
844.6
843.3
839.1
836.2
837.1
828.0
824.5
820.7
824.5
816.3
809.9
805.3
796.3

This is the best I have done. with the 1720T.

Thanks to all. 

M