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 Post subject: Reduce power on 1740
PostPosted: Sat Jun 23, 2018 3:35 pm 
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Joined: Mon Jan 20, 2014 10:32 pm
Posts: 758
Location: Burlington ON
What is the best way to reduce the power on a 1740 (built from a 2240)?
I snipped a few coils off the hammer spring to get about 65 good shots out of a CO2 and assume I need to do something else like that and either snip more or put a longer one back in (or maybe compress it with washers or something).
If that is right, is it harder or softer spring the way to go?
Or something else entirely?


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 Post subject: Re: Reduce power on 1740
PostPosted: Sat Jun 23, 2018 3:44 pm 
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Joined: Mon Aug 15, 2016 11:00 pm
Posts: 309
smaller transfer port hole I think is the most convenient, then harder valve spring then lighter hammer spring, using RVA is very subjective on what you want to end up with.


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 Post subject: Re: Reduce power on 1740
PostPosted: Sat Jun 23, 2018 4:09 pm 
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Joined: Mon Aug 08, 2016 7:23 am
Posts: 2776
Location: Somewheres near the Atlantic
pistolero wrote:
smaller transfer port hole I think is the most convenient, then harder valve spring then lighter hammer spring, using RVA is very subjective on what you want to end up with.


Ive used 1377 transfer port and clipped a hammer spring. I got like 140shots at 360 fps...


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 Post subject: Re: Reduce power on 1740
PostPosted: Sat Jun 23, 2018 4:17 pm 
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Joined: Thu May 07, 2015 8:30 pm
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Location: Eastern Townships, P.Q.
You could also reduce the valve volume by adding a sleeve inside, and maybe a nylon spacer behind the valve to reduce dwell. The smaller TP is a good idea, I use that on my own 1740, along with a clipped spring. IIRC, I get around 430 fps with a 7.9 grains pellet.

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 Post subject: Re: Reduce power on 1740
PostPosted: Sat Jun 23, 2018 4:59 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8973
Location: Coalmont BC
It has been a while since I built my 1740, but if I was going to do it again I would use the lightest hammer spring that would keep the velocity under 500 fps with a 7.9 gr. pellet.... while having a small gap between the spring and hammer to help prevent hammer bounce.... Alternately, if you have the skills and time, an even better solution would be to use a stock 2240 spring and make an SSG to preload the spring to provide such a gap.... The lightest hammer you can make would also help conserve CO2....

While this is not what you are asking about, here is what I did recently with a stock 2260 (.22 cal with a 24" barrel)….

Image

The shot string with the SSG fitted produced 627 FPE total energy from one 12 gr. CO2 cartridge.... a number which as far as I know has never been exceeded.... Using the same technology in .177 cal will yield a much higher shot count (even with a shorter barrel), although not quite as much total energy.... Here is a previous 1740 I built with a 10" barrel, before I came up with the idea of an SSG.... The best results were with a 0.109" transfer port, a lightweight hammer, and a much shortened 2240 hammer spring.... but I have no doubt the SSG could increase the shot count even further....

Image

Image

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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 Post subject: Re: Reduce power on 1740
PostPosted: Sat Jun 23, 2018 5:45 pm 
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Joined: Mon Jan 20, 2014 10:32 pm
Posts: 758
Location: Burlington ON
Thanks all for the fast replies. I didn't realize the transfer ports came in different sizes so probably the easiest (I always like easiest...) is to switch it out for the 1377 one.
Next question is where to get one? CSS carry most parts but I only see the .22 one but could ask.

(this will probably be a duh moment but "SSG" Bob...?)


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 Post subject: Re: Reduce power on 1740
PostPosted: Sat Jun 23, 2018 6:41 pm 
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Joined: Thu May 07, 2015 8:30 pm
Posts: 1184
Location: Eastern Townships, P.Q.
PM sent.

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 Post subject: Re: Reduce power on 1740
PostPosted: Sat Jun 23, 2018 8:59 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8973
Location: Coalmont BC
"Stopping Spring Guide".... an adjustable length spring guide that preloads the hammer spring and stops it, just before the hammer hits the valve stem.... The hammer "coasts" the remaining distance, opening the valve with only it's momentum.... When the valve closes and throws the hammer back against the spring, the preload on the spring resists that action and the hammer doesn't bounce and reopen the valve a second time (after the pellet has already left the muzzle), which wastes air.... A short stiff spring, fitted with a small gap, does a similar thing, but has slightly more tendency to bounce, and is harder to cock (not an issue on a CO2 gun)…. Here is a conventional RVA (rear velocity adjuster) and one that incorporates an SSG.... These fit a Disco / 22XX tube....

Image

The preload on the spring is adjusted with the small nuts screwed onto the end of the spring guide and locked together.... The gap between the end of the guide and the inside of the hammer is adjusted with the bolt in the end cap.... The guide slides through a hole in that bolt, and the O-ring acts as a cushion at the end of the stroke.... A preload of 3-5 lbs. on the spring is typical, with an optimum gap of about 1/16-1/8"....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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 Post subject: Re: Reduce power on 1740
PostPosted: Sat Jun 23, 2018 9:34 pm 
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Joined: Mon Jan 20, 2014 10:32 pm
Posts: 758
Location: Burlington ON
Wow, look at that - thanks Bob. Never heard about that before, very interesting indeed!


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 Post subject: Re: Reduce power on 1740
PostPosted: Sun Jun 24, 2018 8:33 pm 
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Joined: Thu May 07, 2015 8:30 pm
Posts: 1184
Location: Eastern Townships, P.Q.
:wink:


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 Post subject: Re: Reduce power on 1740
PostPosted: Mon Jun 25, 2018 8:13 pm 
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Joined: Mon Jan 20, 2014 10:32 pm
Posts: 758
Location: Burlington ON
That looks like one well made, precision part! :-D


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