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PostPosted: Thu Aug 26, 2021 10:27 am 
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Location: Ontario, Canada
I'm curious as to the piston length used in the various detuned .177/495fps Crosman nitro-piston rifles. If they are 170mm or longer then it would be possible to chop the piston to bring power up. I think my full power Crosman NP uses a 150mm piston. Do they use a piston bleeder hole in these .177cal NP rifles? A 700fps NP might be a nice shooting rifle.

Yup, I've had my FAC/PAL for over 40 years.


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PostPosted: Thu Aug 26, 2021 11:56 am 
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Length doesn't matter, or something like that. Actually, Crosman used/uses so many different combinations of piston and spring that it really depends on the specific model and time frame. In the early days of the B18/19 colones (Phantom/Quest) the de-tuning was done with an extra long piston that could be cut to make it PAL. Different springs were used in .177 and .22 cal to keep them below 500 fps. Later, they put a bleed hole in the regular piston head to drop the speed, this was the common method when they introduced NP rifles. Various NP springs were used along with the regular compression piston. So, you should strip and examine your compression piston and see if there are any markings to identify the gas spring to get an idea of what to do next. :drinkers:

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PostPosted: Thu Aug 26, 2021 6:39 pm 
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The reason I asked is because CanTire now has the Crosman Fire NP on sale for $140. A 495fps rifle doesn't interest me much but if it was something I could tune to 600-700fps then it might be interesting. So I guess I should have asked what piston Crosman is using in the Cdn detuned Fire NP in 2021. Hopefully they use a longer piston. Possibly someone here has taken one apart to tinker.

I had one of the old .177cal Crosman Quest rifles with the extra long pistons. I think the piston was 200 or 210mm. The barrel would only cock to 90*. I eventually chopped it a bit to get speed up to mid 600s.


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PostPosted: Thu Aug 26, 2021 9:37 pm 
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If the fire NP gun is anything like the Crosman Phenix, which I suspect it is, then it’s likely a long piston that keeps it below 500fps. A while back I did some tests with it and the best results were with a short piston and the stock gas ram. I tried long piston with full power gas ram and that didn’t work at all. Full power gas ram with short piston was too powerful for .177.

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PostPosted: Thu Aug 26, 2021 11:00 pm 
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I currently have a full power Crosman Fury NP that shoots hard at just over 900fps with 7.9gr. Cocking effort is different when compared to springs. It's very smooth but strong right through the cocking stroke. Snappy recoil that can kill scopes.

I checked the pistons and rams available from Crosman. They list a different ram and piston for the detuned .22cal NP. I can't find a listing for the .177cal NP parts. This makes me wonder if they drill the bleed hole for .177cal (same weak ram & longer piston), but I'm uncertain.

Gravel Agency has 3 rams listed but no detailed descriptions. According to Crosman, the -5A is the full power ram. The -1A is the detuned ram for .22cal 495fps. I'm not sure about the other ram (the -1).

https://store.gravelagency.com/en/catal ... 5M22-00-5A


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PostPosted: Fri Aug 27, 2021 8:20 am 
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BT9M22-00-5A Is the full-power gas ram, BT5M22-00-1A is the low power one.

I saw a BT9M with a short drilled piston in a <500 Benji, and there are BT5M gas ram with long piston in my <500 Trail NP and TR77NPS. A friend of mine has a full power Trail NP with a BT9M gas ram and regular, non-drilled short piston, he's getting in the neighbourhood of 740 fps in .22 with a 14.3 gr pellet. HTH.

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PostPosted: Fri Aug 27, 2021 10:49 am 
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My full power .177cal Crosman Fury NP shoots 8.64gr H&N FTT at 880fps and 7.9gr PHP at 920fps. It's been shooting the same speed for over 3 1/2 years and many thousands of pellets. I'm actually surprised the NP has lasted this long.

The NP sure is an interesting power plant. It’s powerful and very smooth. Cocking effort is high from the beginning to end with no noticeable build-up like a wire spring has. No friction is felt during cocking and obviously no spring vibrations felt during the shot cycle. It has a very fast lock-time and a unique sound when shot but it can be hard on optics. The double recoil is quite snappy.


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PostPosted: Fri Aug 27, 2021 11:55 am 
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I just picked up an aged Phantom .22 non-pal and it needs some TLC. I am not sure if I want to bump it to PAL territory or not.

Is there anything that can be done on these NP engines to make them more scope friendly?

Thanks
Rob27


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PostPosted: Fri Aug 27, 2021 11:59 am 
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Rob27 wrote:
Is there anything that can be done on these NP engines to make them more scope friendly?

There is a scope mount that mitgates the double recoil.

https://www.airgunsource.ca/us/diana-bu ... tubes.html

Pricey though. Not in stock at AGS either but there should be other sources and perhaps similar models from other manufacturers.

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PostPosted: Fri Aug 27, 2021 12:55 pm 
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jckstrthmghty wrote:
Rob27 wrote:
Is there anything that can be done on these NP engines to make them more scope friendly?

There is a scope mount that mitgates the double recoil.

https://www.airgunsource.ca/us/diana-bu ... tubes.html

Pricey though. Not in stock at AGS either but there should be other sources and perhaps similar models from other manufacturers.

Drifting off topic, but this article may be of interest for anyone planning to go with a recoil absorbing scope mount:
https://www.airgunnation.com/topic/dian ... res-a-fix/

Also the Chinaware stores have the knock-off Bullseye and Diana scope mounts for cheap.
https://www.aliexpress.com/item/4000960 ... 623d5b83-3
Probably made in the same factory by the same hands that make the name branded ones, just saying.

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PostPosted: Fri Aug 27, 2021 1:15 pm 
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Hi Todd.

Esteve sent a chart to me regarding velocities with various piston lengths and springs in his Optimus.

With a full power "D" spring and 8.2gr pellets:
Short piston -965fps
Med piston. -800
Long piston. -620

With the "B" spring, the velocities are 835, 675, and 475, respectively.

Might be worth trying a long piston with the full power strut in your Fury NP. Looks like it could generate the velocity you're looking for. Recoil should be a lot less since the reduced stroke causes a reduction in the time the strut can accelerate the piston, so the piston is moving slower at the end of its travel. Should make for a short, snappy and smooth stroke. I bet it would be a great shooter.

Maybe there's a member here with a long B18 piston they don't need/use anymore...

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PostPosted: Fri Aug 27, 2021 6:02 pm 
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I like the long distance capability of the full-power Fury NP. Maybe one of those modified recoil absorbing mounts will work for this rifle.

A few days ago I took out the Fury NP and wasn’t even coming close to making hits at 75 yards. I checked on paper and the POI was about 3" to 4" left. It took 24 clicks to get it back sighted in at 75 yards. Then I shot at the 75-yd gong and hit it on the first shot. Then made about 6 or 8 misses. I checked again on paper and POI was now right of the bullseye. I had to click it back 24 to get centered again. Then I did some shooting with it at 30 yards and switched rifles. Yesterday I had it out again and made a couple of hits on a small gong at 50 yards and then a bunch of misses. I checked on paper and the POI was way left again. I adjusted it to center and after a while I was missing again. Checked on paper and POI was a few inches high. I went to 30 yards and got it set up for center hits at 30 yards and then put it away. I’ll see what happens on the next shooting session.

When I got home from shooting yesterday I checked all the scope and stock screws on the Fury NP and everything was still tight (with Loctite). The barrel hinge still seems snug and not sloppy at all. I had cleaned the barrel prior to shooting yesterday so it definitely wasn’t fouled. The rifle still has lots of power so the strut is fine. All that’s left to suspect is the scope. The Leaper/UTG fixed 4X is a durable scope and they call it their “True Strength” scope series. It’s been on that rifle for over 3 years and has seen many thousands of shots. I’m starting to think the scope’s adjustment parts have taken too much double recoil from the NP. The scope still “clicks” when I make adjustments, POI does move when adjusted and the crosshairs look fine. It just doesn't stay adjusted.


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