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bordurat
PostPosted: Fri Apr 03, 2020 7:17 pm 
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Posts: 6
ulricbb , do you have pictures of you modified piston head?
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bordurat
PostPosted: Fri Apr 03, 2020 7:20 pm 
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Posts: 6
airmec wrote:
ulricbb wrote:
haha, no the big hole is not thru the piston.

in my first picture, you can see a small hole in the side of the piston, that hole connect to another small hole in the bottom of the big hole, (both small hole are at 90 degrees.

alright, now i want to cut that piston, does someone know how much i have to remove, and where a have to drill the new hole, for the catch mecanisim...


I measured the standard, ''short'' piston at 5.820'' (+/- 0.010''), from the end of the skirt to the face under the seal. You will need to cut a new sear notch, but you don't need to touch the cocking slot. Position of the sear notch is critical for engaging the sear, so cut the notch the same exact distance from the end of the piston's skirt that it is now. Be aware that the piston is surface hardened, so better to use carbide tooling. Ideally, you'd want to anneal the piston's skirt, and then re-harden and temper it so the sear notch will last without deformations (safety first!). Also you may want to order the full-power gas ram, part number BT9M22-00-5A. That should take your rifle in the 900s.


Does the short piston have a venting hole or not (do you have a picture of the head of the piston?)
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ulricbb
PostPosted: Fri Apr 03, 2020 7:43 pm 
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Joined: Thu Apr 02, 2020 4:06 pm
Posts: 17
Location: North shore Montréal
i dont have pictures of the modified piston....i threaded the hole and insert a screw, with the head about 1/32 deeper the the piston surface, i will add jb weld tomorow....

i also ordered the gas spring from autralia, customairseals 48 all in on ebay, because everyone in canada si back order....

look at my 2 shot, front and back(10 yards). both with gamo Rocket Pellets 9.6g on a range hood stainless steel:

top: with only the piston plug.
bottom: piston plug and shorten


Attachments:
IMG_20200403_154707.jpg
IMG_20200403_154707.jpg [ 342.88 KiB | Viewed 1236 times ]
IMG_20200403_154749.jpg
IMG_20200403_154749.jpg [ 376.42 KiB | Viewed 1236 times ]
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FirstTimeShooter
PostPosted: Fri Apr 03, 2020 8:09 pm 
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Posts: 5
Dukemeister wrote:
I have to laugh. I guess I had one just like it - honestly I don't remember it at all. I do remember plugging small bleed holes, but not the bigger blind hole. Anyhow, the bigger hole won't increase power, it will provide some dead air volume that could prevent piston slam. By plugging the small hole it will bring up the power. When I saw your picture I thought the blind hole was a through hole.


I also recently purchased a Crosman Fire Nitro Piston .177 air rifle and was also shocked to see that version of the piston. Do you know what will give more fps - plugging the larger blindhole or just leaving the blindhole as is? I understand that plugging the small bleed hole will help increase fps but still unsure about the larger blindhole. Any information on this would be super helpful and appreciated :D
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Dukemeister
PostPosted: Fri Apr 03, 2020 8:13 pm 
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Posts: 4163
Location: Kingston, ON
Yep, you got more power. Now you need to get a chrony to find out what it's doing. Honestly, it's an indispensable tool for properly tuning a gun. And they are relatively cheap nowadays, so consider getting yourself one. If we weren't in physical distancing mode, you could link up with a forum member in your area and use their chrony. :drinkers:

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FirstTimeShooter
PostPosted: Fri Apr 03, 2020 8:19 pm 
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Joined: Fri Apr 03, 2020 7:23 pm
Posts: 5
Dukemeister wrote:
Yep, you got more power. Now you need to get a chrony to find out what it's doing. Honestly, it's an indispensable tool for properly tuning a gun. And they are relatively cheap nowadays, so consider getting yourself one. If we weren't in physical distancing mode, you could link up with a forum member in your area and use their chrony. :drinkers:


sorry I guess I wasn't very clear. Do you know what option would make the gun shoot faster: (a) plugging the blindhole or (b) leaving the blindhole as is?
Yes as a newbie to this I have been noticing that device in many videos - will definitely look into investing into one seeing as how this craziness might not end for a while!
While I have you here: any suggestions on trusted websites to order parts from? I would like to order a stronger gas ram (BT9M as my current rifle only has the BT5M)
Thank you again for any help you can offer :D
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ulricbb
PostPosted: Fri Apr 03, 2020 8:49 pm 
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Joined: Thu Apr 02, 2020 4:06 pm
Posts: 17
Location: North shore Montréal
https://www.ebay.ca/itm/GAS-RAM-PISTON- ... 2749.l2649



FirstTimeShooter wrote:
Dukemeister wrote:
Yep, you got more power. Now you need to get a chrony to find out what it's doing. Honestly, it's an indispensable tool for properly tuning a gun. And they are relatively cheap nowadays, so consider getting yourself one. If we weren't in physical distancing mode, you could link up with a forum member in your area and use their chrony. :drinkers:


sorry I guess I wasn't very clear. Do you know what option would make the gun shoot faster: (a) plugging the blindhole or (b) leaving the blindhole as is?
Yes as a newbie to this I have been noticing that device in many videos - will definitely look into investing into one seeing as how this craziness might not end for a while!
While I have you here: any suggestions on trusted websites to order parts from? I would like to order a stronger gas ram (BT9M as my current rifle only has the BT5M)
Thank you again for any help you can offer :D
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FirstTimeShooter
PostPosted: Fri Apr 03, 2020 9:02 pm 
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Joined: Fri Apr 03, 2020 7:23 pm
Posts: 5
[quote="ulricbb"]https://www.ebay.ca/itm/GAS-RAM-PISTON-SPRING-NITRO-GAMO-CROSMAN-BENJAMIN-60KG-177-22-AIR-RIFLE-GUN/153295973100?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I was looking up some different sites and stumbled across this:
https://www.customairseals.com/product/ ... o-crosman/
believe it is the same ad that you just posted for me but from the actual retail seller - might be more legit
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ulricbb
PostPosted: Fri Apr 03, 2020 9:18 pm 
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Joined: Thu Apr 02, 2020 4:06 pm
Posts: 17
Location: North shore Montréal
yes, same seller, item, price...

i felt more secure with ebay-paypal-credit card....cant go wrong

FirstTimeShooter wrote:
ulricbb wrote:
https://www.ebay.ca/itm/GAS-RAM-PISTON-SPRING-NITRO-GAMO-CROSMAN-BENJAMIN-60KG-177-22-AIR-RIFLE-GUN/153295973100?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I was looking up some different sites and stumbled across this:
https://www.customairseals.com/product/ ... o-crosman/
believe it is the same ad that you just posted for me but from the actual retail seller - might be more legit
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Jetronic
PostPosted: Sat Apr 04, 2020 1:26 am 
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Joined: Mon Mar 30, 2020 5:50 am
Posts: 18
FirstTimeShooter wrote:
Dukemeister wrote:
Yep, you got more power. Now you need to get a chrony to find out what it's doing. Honestly, it's an indispensable tool for properly tuning a gun. And they are relatively cheap nowadays, so consider getting yourself one. If we weren't in physical distancing mode, you could link up with a forum member in your area and use their chrony. :drinkers:


sorry I guess I wasn't very clear. Do you know what option would make the gun shoot faster: (a) plugging the blindhole or (b) leaving the blindhole as is?
Yes as a newbie to this I have been noticing that device in many videos - will definitely look into investing into one seeing as how this craziness might not end for a while!
While I have you here: any suggestions on trusted websites to order parts from? I would like to order a stronger gas ram (BT9M as my current rifle only has the BT5M)
Thank you again for any help you can offer :D


Plugging the big hole will be faster bit can reduce accuracy with heavier pellets
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airmec
PostPosted: Sat Apr 04, 2020 5:10 am 
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Joined: Thu May 07, 2015 8:30 pm
Posts: 1950
Location: Eastern Townships
bordurat wrote:
airmec wrote:
ulricbb wrote:
haha, no the big hole is not thru the piston.

in my first picture, you can see a small hole in the side of the piston, that hole connect to another small hole in the bottom of the big hole, (both small hole are at 90 degrees.

alright, now i want to cut that piston, does someone know how much i have to remove, and where a have to drill the new hole, for the catch mecanisim...


I measured the standard, ''short'' piston at 5.820'' (+/- 0.010''), from the end of the skirt to the face under the seal. You will need to cut a new sear notch, but you don't need to touch the cocking slot. Position of the sear notch is critical for engaging the sear, so cut the notch the same exact distance from the end of the piston's skirt that it is now. Be aware that the piston is surface hardened, so better to use carbide tooling. Ideally, you'd want to anneal the piston's skirt, and then re-harden and temper it so the sear notch will last without deformations (safety first!). Also you may want to order the full-power gas ram, part number BT9M22-00-5A. That should take your rifle in the 900s.


Does the short piston have a venting hole or not (do you have a picture of the head of the piston?)


The short piston in my detuned Crosman steel spring rifles does have a small hole drilled in the face, but the long one in my TR77NPS doesn't (don't bother with the center mark, it's just a machining mark). See attached pics:


Attachments:
IMG_6670.JPG
IMG_6670.JPG [ 130.62 KiB | Viewed 1204 times ]
detuned_TR77NPS_piston.JPG
detuned_TR77NPS_piston.JPG [ 25.8 KiB | Viewed 1204 times ]

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airmec
PostPosted: Sat Apr 04, 2020 5:30 am 
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Joined: Thu May 07, 2015 8:30 pm
Posts: 1950
Location: Eastern Townships
Dukemeister wrote:
I have to laugh. I guess I had one just like it - honestly I don't remember it at all. I do remember plugging small bleed holes, but not the bigger blind hole. Anyhow, the bigger hole won't increase power, it will provide some dead air volume that could prevent piston slam. By plugging the small hole it will bring up the power. When I saw your picture I thought the blind hole was a through hole.


Sorry Duke, I don't agree with that; more ''dead'' air space in front of the piston will provide a lower compression ratio, thus increasing piston slam because of a lower pressure air cushion. This is why chevota sands his seals, to up the compression ratio; simply put, it works sorta like a car's engine: with higher compression you get more power.

Jetronic wrote:
Plugging the big hole will be faster but can reduce accuracy with heavier pellets


Sorry again, it's the opposite with heavier pellets. They will tame the shot cycle better, travel slower and be better stabilized, increasing accuracy. Very often heavy pellets are recommended in magnum springers for that very reason.

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ulricbb
PostPosted: Sat Apr 04, 2020 6:28 am 
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Joined: Thu Apr 02, 2020 4:06 pm
Posts: 17
Location: North shore Montréal
How does he do that?
He sands the back side of the seal?
Make sence, how much material can i sand?
I guess, the importent is the seal must be a bit larger than the piston front surface...

[quote="airmec"][quote="Dukemeister"]
This is why chevota sands his seals, to up the compression ratio; simply put, it works sorta like a car's engine: with higher compression you get more power.
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airmec
PostPosted: Sat Apr 04, 2020 7:00 am 
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Joined: Thu May 07, 2015 8:30 pm
Posts: 1950
Location: Eastern Townships
ulricbb wrote:
How does he do that?
He sands the back side of the seal?
Make sence, how much material can i sand?
I guess, the importent is the seal must be a bit larger than the piston front surface...

airmec wrote:
Dukemeister wrote:
This is why chevota sands his seals, to up the compression ratio; simply put, it works sorta like a car's engine: with higher compression you get more power.


No actually it's the front side. You want to leave about 0.015'' to 0.020'' of seal material over the center dovetail. Easy to do on a lathe, more delicate by hands. Be aware that this seal mod alone won't yield a lot of power, it's more like a ''fine tuning'' procedure, when the rifle has been extensively modded and you want to extract the very last bit of available power you can get.

''I guess, the important is the seal must be a bit larger than the piston front surface...''

Absolutely, you don't want to sand to the point you get to the taper part of the seal.

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bordurat
PostPosted: Sat Apr 04, 2020 10:24 am 
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Joined: Fri Apr 03, 2020 7:08 pm
Posts: 6
ulricbb wrote:
i dont have pictures of the modified piston....i threaded the hole and insert a screw, with the head about 1/32 deeper the the piston surface, i will add jb weld tomorow....

i also ordered the gas spring from autralia, customairseals 48 all in on ebay, because everyone in canada si back order....

look at my 2 shot, front and back(10 yards). both with gamo Rocket Pellets 9.6g on a range hood stainless steel:

top: with only the piston plug.
bottom: piston plug and shorten



but still with low power ram right?
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