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PostPosted: Mon Apr 06, 2020 6:55 pm 
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Joined: Sun Apr 05, 2020 7:58 am
Posts: 7
Great... thanks for the info.


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PostPosted: Tue Apr 07, 2020 4:52 am 
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Joined: Mon Mar 30, 2020 5:50 am
Posts: 18
Air PNB wrote:
Hello all new to the forum, but not to air guns although I've never opened many up to upgrade them, just finished plugging the small bleeder hole...made a huge difference in accuracy and up'd the power by depth of penetration into half inch plywood...thanks to you folks. I of course also purchased the p. auto rem.hunter express, first nitro piston air rifle, I also rebuild nitrogen charged shocks the rebuildable kind that you find on snowmobiles, bikes, quads, sxs etc.. so I have nitrogen tank gauges and all the bits and pieces to facilitate shock rebuilding. So my question is has anyone heard of modifying the nitrogen cartridge itself, increasing the nitrogen charge in it, I have done similar to "non rebuildable shocks" by adding a small self sealing port to allow for discharging and recharging the nitrogen. The though is increase the speed and ftlbs of the piston which in turn should affect the end speed/power?

Thanks


Yes, the original theoben springs had a valve so you could adjust the pressure inside. Theres an optimum pressure though and going over or under results in less energy at the muzzle. Theoben got rid of the valve later on because people over pressured the springs and got weak guns if not broken. Weihrauch also used a theoben with adjustable pressure. Also they become near impossible to cock...

With steel springs its the same, above a certain point a stronger spring doesn't get you more power. Bit you do get big biceps from cocking...


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PostPosted: Tue Apr 07, 2020 5:34 am 
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Joined: Thu May 07, 2015 8:30 pm
Posts: 1556
Location: Eastern Townships
Air PNB wrote:
Hello all new to the forum, but not to air guns although I've never opened many up to upgrade them, just finished plugging the small bleeder hole...made a huge difference in accuracy and up'd the power by depth of penetration into half inch plywood...thanks to you folks. I of course also purchased the p. auto rem.hunter express, first nitro piston air rifle, I also rebuild nitrogen charged shocks the rebuildable kind that you find on snowmobiles, bikes, quads, sxs etc.. so I have nitrogen tank gauges and all the bits and pieces to facilitate shock rebuilding. So my question is has anyone heard of modifying the nitrogen cartridge itself, increasing the nitrogen charge in it, I have done similar to "non rebuildable shocks" by adding a small self sealing port to allow for discharging and recharging the nitrogen. The though is increase the speed and ftlbs of the piston which in turn should affect the end speed/power?

Thanks


Hi and welcome Air PNB, my first question would be: Do you have your PAL? Modifying your rifle this way will make it shoot over 500 fps, giving it the same legal status as a ''real'' firearm. And you know what ''they'' say: No one can ignore the law.

As for adjustable gas rams, they're available on the net, just do a google search it's easy. But putting an even stronger one in your rifle may not give higher power, and could also give you a very harsh firing cycle, hold sensitivity and less accuracy. It'll also be harder on scopes, and induce premature wear in your rifle. Main concern here is the volume of the compression chamber, this is what mainly determine the potential power of your airgun. When you reach 16-18 ft/lbs of energy with the B19 platform, it's about maxed out.

Here's a link to an energy (and other stuff) calculator: https://www.pyramydair.com/airgun-resou ... Units&u=14

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PostPosted: Thu Apr 09, 2020 4:20 pm 
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Joined: Fri Apr 03, 2020 7:08 pm
Posts: 6
So with piston head plugged ( threaded + screw and flushed with jb weld) no other modifications ( piston still long with original low power gas ram )

crosman 7.4g wadcutter = 564 fps

crosman 7.4g pointed = 571 fps

crosman 7.4g destroyer = 523 fps

Next chrony readings will be when I receive the full power gas ram and then I will see if I leave it like that or if I also shorten the piston.


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PostPosted: Thu Apr 09, 2020 5:35 pm 
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Joined: Sun Apr 05, 2020 7:58 am
Posts: 7
Thanks for posting bordurat.
I'll be watching for the next installment... :D

Much appreciated.


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PostPosted: Mon Apr 20, 2020 12:58 am 
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Joined: Sun Apr 19, 2020 11:19 am
Posts: 1
I also picked up this rifle and really interested in everyone’s progress with the mods/upgrades.
Any updates?


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PostPosted: Sat Apr 25, 2020 6:26 am 
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Joined: Sat Apr 25, 2020 6:12 am
Posts: 3
I am another who fell under the Princess Auto deal so good you cant pass it up spell. I mean seriously....under $100can was too good to say no. This is the second time I've stumbled across a price that literally pulled my credit card from my wallet before I could stop it. An Umarex Forge for under $120can including shipping and taxes.....I have stopped going to Princess Auto's website since I dont have anymore room for another gun. :lol: But now I am here trying to see about increasing the performance of the Remington. I'll be following this thread as I am very interested in how the different mods turn out...oh and thanks for posting the results so far.


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PostPosted: Mon Nov 23, 2020 12:28 pm 
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Joined: Mon Nov 23, 2020 11:59 am
Posts: 1
I just bought the PA special and got similar velocities as posted by others:
Unmoded- 487 fps ave of 10 shots crosman 7.4 pointed
Blind hole and bleed hole plugged with Fastweld 10- 550 fps ave 10 shots crosman 7.4 pointed
Piston shortened and new sear hole cut into piston- 595 fps ave 5 shots crosman 7.4 pointed

The piston was shortened the minimum amount ie I cut the piston off at the forward end of the "sear hole." This ended up about 0.460" shorter (overall piston length) and a dimensional copy of the "sear hole" recreated the same distance from the new trailing edge of the piston. I will tell you the surface of the piston is VERY hard steel, not to bad to shorten with a high speed small cutting wheel but very hard to make the new "sear hole." Hint: the new sear hole does not have to be as square as the original, just the front and back surfaces the sear rides on need to be flat. You will need to break the hard surface of the piston steel with a small dia pointed high speed stone (dremel?) and then drill it with a drill press to start the new sear hole.

I didn't think steel this hard could come out of China! A hacksaw just kind of polishes it!

If I did it again I would shorten the piston more but I didn't want to push it to far and have it fail to load properly.

Get a PAL everyone!!

PS I live at ~3600 ft ASL, this may affect velocities!


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PostPosted: Sat Dec 12, 2020 1:43 am 
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Joined: Fri Dec 11, 2020 9:46 pm
Posts: 1
Just wondering if anyone has just replaced the nitro piston with the full power version (BT9M22-00-5A) and tested the results? Would be nice to know the increase with just that modification.


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