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Bulletbob

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Jul 5, 2020
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N.C., United States Statesville Iredell county
So I broke out the chronograph and spent a few hours tuning and twisting screws. I watched several vidios before I started.
I set it at 6 turns on the big screw and 1 on the little screw { I forgot the proper names} 3000 psi fill. I shot three strings of 8.
st string was 377 fps with a low of 360 and a high of 387.
2nd string was 356 fps and 3rd was 432 fps
I tried 8 turns the eight shot string came out for a whopping 328 fps.
9 turns came out 452 fps averge for 8 shots
10 turns gave 422 fps.
all testing was done with crossman 14.3 Hp.
This is a preowned gun and I don't know the histroy. When I watch the vidieos they are showing much better fps . At this rate I am not shooting pellets I am lobbing them.
My point of impact is wildly vertical. By 4 or 5 inches at 30 yards.
Is there something I need to replace. The gun does not leak air.
Please someone help.
Thanks Bulletbob
 
I agree something is wrong. You went plenty far enough on the hammer spring to get velocity up around 650 fps. I couldn't get much over that with the stock .080 transfer port. I would start by checking to see of the gun is put together correctly and the hammer seems to be moving smoothly. Lube is not recommended but it cannot be rusted up either. The transfer port should be in place with little soft plastic pieces on the top and bottom of the aluminum transfer port. The barrel port must be directly above the transfer port.

If everything checks out then I would assume the hammer spring has been replaced with one significantly lighter. You could buy a stock one from Crosman inexpensively. You'd need to call them and reference the part number of the Prod part diagram. If you do not have one they will send you one.

I did not find the hammer throw to do much until I did a Bstaley tune - O rings around the valve stem. It is the inner screw. I mainly tuned with the screw with the larger hex size. And larger transfer ports. I found it possible to get over 800 fps but not with a reasonable shot count. I think 700-750 fps makes more sense but that means a bigger transfer port and if you do a Bstaley a stiffer hammer spring.
 
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Bobby, I would say to set your Prod as close to factory settings as you can. Here is a tune that should set you in a fairly good starting point.
Factory settings should be Hammer Spring (HS) around 6 T CW from full CCW and Hammer Throw (HT) 1 T CW from full CCW. Adjust HS between 6-4 T @3000<1500 PSI and see what your shot string looks like. Leave the HT alone for the time being. Focus on pressure and HS data. Fine tune with HT.

Patrick
 
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before doing any disassembly, shoot the pressure down a little bit and measure the velocity as you go.

It may be overfilled, as someone else mentioned, and you are getting partial valve block. Try letting the fill pressure drop down. Shoot it down to as low as 1,800 and keep checking velocities to see if you get a bell curve where it begins to rise and then drops off again. In the middle of that range will be your sweet spot fill pressure.

Since it's a used gun, you don't know what's been done internally. It was a good call to check for grease on the hammer which will slow it down. That needs dry lube like powdered graphite or powdered molybdenum disulfide burnished it to the metal sliding surfaces with no oil or grease to slow it down.

To get velocities around $700, I drilled out my transfer port. Trying to remember the size but it might have been around 105 in. I recall using a numbered drill bit but don't have my notes right now.

On the p-rod type of action the trigger pull gets heavier when you increase the hammer spring tension because of the way it's designed. The load of the hammer on the sear increases the pull weight. To get the same valve opening with less hammer tension and lighter trigger pull, I removed one or two turns from the valve poppet return spring to make it easier for the hammer to open the valve.

This, in turn, allowed the use of a higher fill pressure, somewhat less hammer spring tension, and the report was quieter.

These are my own mods and findings, somewhat non-standard, so I recommend having spare springs and transfer ports from Crosman parts before you start cutting them. Just throwing out some ideas.

Good luck with your tune up and adjustments.

Feinwerk
 
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@damienblack ,
My fill pressures go from about 3200 down to 2600 if I recall correctly and I shoot the jsb 18 gr with Krytech bike chain lube. The bell curve peaks out at around 705 FPS.

Use either a Donny FL sumo or Tanto and all I can hear is the action and the pellet impact. One drawback is I have to take the moderator off to fill the reservoir but it spins off and on quickly.

Marks PROD w DonnyFL Sumo Suppressor 20171202.jpg
 
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Feinwerk,
If I was smarter I would show you pictures if mine. The one I have has a custom made stock made of Walnut. It's less than 29 inches long. If I can ever get it to shoot it will be real handy.
After much testing and wasteing pellets I got a string of eight that was over 300FPS. NOT TOO GOOD.
my new guage showed up today and I have a spring and transport valve on the way.. I think I can I think I can.
I like your gun..
I think there is more wrong than spring settings.
Thanks for your help
 
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