GTA

All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: doninva on March 06, 2016, 12:45:38 PM

Title: 1720T spring?
Post by: doninva on March 06, 2016, 12:45:38 PM

My 1720T has a 13CI bottle so air is not an issue. Am trying to get to 12FPE for field target. It is shooting 738 FPS with 7.87 pellets. I would like to get to around 800-810 FPS. It has a 1.730 X .300 X .035 spring in it with the stock hammer. Made one of Bob's SSGs and the ES is running under 10FPS for a string of 60 shots. Gun is extremely accurate. What spring would I need to get that extra 60FPS. Thanks, Don

Title: Re: 1720T spring?
Post by: Motorhead on March 06, 2016, 01:39:02 PM

I would do it via some valve massaging & perhaps a poppet spring change.
Getting valve to be more effecient will give better results that just striking hammer harder ... IMO

Title: Re: 1720T spring?
Post by: nervoustrigger on March 06, 2016, 02:35:32 PM

Don,

So the hammer spring is weaker than the stock one?

Also why start a new thread?  The previous one
http://www.gatewaytoairguns.org/GTA/index.php?topic=105598.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=105598.0)
contains essential information like the fact it's regulated and that you've opened the transfer port to 0.137".

The big piece of information we need is the regulator setpoint.  A stock 1720T will have no problem making 12fpe with only a ~0.094" transfer port down to about 2000psi. 

Title: Re: 1720T spring?
Post by: BigTinBoat on March 06, 2016, 05:37:19 PM

Quote from: nervoustrigger on March 06, 2016, 02:35:32 PM

The big piece of information we need is the regulator setpoint. 

Exactly

Title: Re: 1720T spring?
Post by: doninva on March 06, 2016, 10:30:04 PM

The regulator is set at 1400 PSI, I think. It's been a while since I did the conversion. Forgot I had started the other thread, man am I getting old. I will shoot it next weekend, in a match, and try to find a stronger spring. I may tear it down, as Scott suggested, and put a weaker spring in the valve. I have a light weigh hammer, I made, somewhere. Was hoping a little stiffer spring would get me close to 12 FPE without tearing into the gun again as it is shooting good. Don

Title: Re: 1720T spring?
Post by: BigTinBoat on March 06, 2016, 10:33:16 PM

Quote from: doninva on March 06, 2016, 10:30:04 PM

The regulator is set at 1400 PSI, I think. It's been a while since I did the conversion. Forgot I had started the other thread, man am I getting old. I will shoot it next weekend, in a match, and try to find a stronger spring. I may tear it down, as Scott suggested, and put a weaker spring in the valve. I have a light weigh hammer, I made, somewhere. Was hoping a little stiffer spring would get me close to 12 FPE without tearing into the gun again as it is shooting good. Don

You might get there with a stronger spring at 1400psi, but it will be close. Might need 1500-1600

Title: Re: 1720T spring?
Post by: Frank in Fairfield on March 06, 2016, 11:03:44 PM

My 1720T is non-regulated.
I shot 40 shots today at Diablo Silhouette on one fill 3000-2200psi.
7.33 graiins/833fps for 11.3fpe.

Spring: .330X.041x1.5"
4 ring BHB
PRod TP

I think 11.3fpe is fine for anything inside of 35 yards.