Preload washers on nitro piston

[Sovietik]

Do preload washers would make a difference on piston powered rifles?, I understand on springs it would in increase your fps, but on NP rifles I'm not sure, has anyone tried that before? I dont own a chrony so I cant test it by my self, just asking.

[Motorhead]

Will do little if anything.  Greater chance of rams piston bottoming out at full cocked position tho 

[Bullit]

The NP has it's full pressure from the moment you start cocking it, versus a spring which is more "progressive" build up to full pressure.  The same thing happens, in reverse, when fired.  While the spring may only have a percentage of it's max. force left during the end of it's stroke, the NP will still be exerting full value throughout it's stroke.  Adding spacers won't gain, with the NP powerplant,  and as posted above, slamming the piston into the breech will destroy your piston seal, and I'll bet it'll be a violent shooting cycle.  Good Question! 

[Scrambler82]

Can you replace the OEM NP with a higher pressure unit in any given Air Rifle ?

[Bullit]

It has been done with industrial rams.  But is not cheap, and not a "plug n play", deal at all.
There's old posts here that you can search out, and read about their efforts.

[Scrambler82]

Thanks bullit.
I was just thinking, still have a long way to go before I get there but it would be good reading.

[Kailua]

The Theoben gas piston pressure can be adjusted as well as the Hatsan gas pistons.  Not sure exactly what it takes to do so if you needed to do it yourself.  Some aftermarket gas pistons also have adjustable fill pressure in their pistons.  If that is something you may be interested in.

[Scrambler82]

I am really not sure what I want/need to get the job done.
Told by members of the site that what I have will do the trick.
I need to get it back from tuning. With the new trigger and give it a few shots, see what is happening.

Thanks for the input.

[MarkBrumbaugh]

The NP has it's full pressure from the moment you start cocking it, versus a spring which is more "progressive" build up to full pressure.  The same thing happens, in reverse, when fired.  While the spring may only have a percentage of it's max. force left during the end of it's stroke, the NP will still be exerting full value throughout it's stroke.  Adding spacers won't gain, with the NP powerplant,  and as posted above, slamming the piston into the breech will destroy your piston seal, and I'll bet it'll be a violent shooting cycle.  Good Question! 

I think the gas piston is the same as spring.  PV=nRT.  As the volume decreases in the cylinder, the pressure increases, and vice versa.  But I don't know that I would try to preload it with a washer.  It does have more pressure at the end of the stroke due to the preloaded pressure in the piston.  rather than preload with a washer, you would be better off if you could increase the latent pressure in the cylinder.

[Bullit]

LOL...   I'll bet you personally can start to compress a spring, well before you budge an NP.   I've got worn out Tailgate rams, that I STILL can just barely budge by hand !   The ramp up to full pressure is much quicker with the Nitrogen ram, versus a similar power spring used in the air rifle.   The spring is more progressive ramp up.

[Bryan Heimann]

Putting preload washers on the back end of the ram is pretty much pointless.  With the rod inserted into the piston, the design if the crosman nitro piston guns does not facilitate the use of piston weights.  You may boost power by adding weight to the piston if your gun is set up with the body of the ram in the piston, or if the rod-forward design does not have a notch where the rod inserts.  Because of the consistent force of the ram throughout the stroke, it is not likely that piston weights will give very good results.  Probably just increase the recoil.  Adding weights and spacers works better with coil springs because they exert less force as the piston goes down the tube, and they rely more on momentum of the piston and the amount of pre-load on the spring

[Sovietik]

That is what I thought, but was not sure ...piston has the load already from the starting point.   I'm really not trying to get a lot of more power just enough that when the gun settles down after the initial lube it remains at a decent fps. thanks all for the replys.

[Motorhead]

That is what I thought, but was not sure ...piston has the load already from the starting point.   I'm really not trying to get a lot of more power just enough that when the gun settles down after the initial lube it remains at a decent fps. thanks all for the replys.

Unlike a spring gun that typically slows a tad as spring takes a set ... NP guns generally speed up as seal breaks in and cyclic friction becomes less