Chrono check.

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Timmytree
Posts: 920
Joined: Sun Feb 15, 2015 11:50 am

Chrono check.

Mon May 07, 2018 9:33 pm

Does anyone ever try a chrono check in hot weather? My Prosport has hardly been touched since the last strip down in October last year. It has a TbT guide fitted with 2 slim AA washers. It settled nicely at about 775 fps with AA Fields in 4.52, Healthy but not too close to the limit, somewhere around 11.3 ftlbs.
I did a quick check tonight and got a string between 789 and 794 fps with one shot peaking at 797 fps, far too close! I removed both washers and it dropped to high 750s, one washer back in and it was at 778 to 780, thats ok and it feels good. Interesting that one washer dropped the fps by 10 to 15 fps but the second one dropped it by a further 20 fps. That suggests to me that maybe the PS would benefit from a slightly stiffer spring but less preload. I'll repeat the test midweek when the temperatures have dropped a bit, if the fps reduces then I'll know that I need to add a washer for winter and remove one in summer!

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tonyc
Posts: 86
Joined: Mon May 29, 2017 10:55 am

Re: Chrono check.

Wed May 09, 2018 12:56 pm

I don't have a springer now which is close enough to the limit to need regular testing but I do check my PCPs and their power is temperature dependent. I did extensive testing on a HW110 (my AA's are affected, less so) together with changes in lubrication which resulted in less variation - still about 0.5-1fps per degC. I'd suggest the causes are mobility of the lubricant and reduced friction in warmer weather.

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Sake-san
Posts: 551
Joined: Mon May 18, 2015 7:28 pm

Re: Chrono check.

Fri May 18, 2018 8:08 am

The usual culprit is the piston seal... it's a problem that all FT springer shooters encounter especially in more southern Eu countries / regions where we have a very significant seasonal & daily temp range. Having thoroughly tested (along with many others) a very broad selection of classic parachute type seals they all exhibit temperature sensitivity through expansion & contraction. A common finding is that the V-Mach seal (when sized correctly) seams to suffer the least, possibly due to the composition being less sensitive to temperature related expansion / contraction.
A properly sized o-ring seal will virtually eliminate the problem and has become the standard fix for many, many shooters.

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gary martin
Posts: 687
Joined: Thu Feb 19, 2015 8:21 pm

Re: Chrono check.

Fri May 18, 2018 4:23 pm

Tim, I have experienced temp shift in the way that Sake San has mentioned. Though mine was the opposite to yours Higher in cold temp prob down to piston seal not expanding as fast and travelling comp tube quicker in the initial stage of stroke. Lower in very warm temp, piston seal softer giving greater friction slowing the cycle down. This is just my theory as I don't have access to equipment to measure locktime.

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Sake-san
Posts: 551
Joined: Mon May 18, 2015 7:28 pm

Re: Chrono check.

Fri May 18, 2018 6:49 pm

Exactly the experience of myself and many others, power drops in warm / hot temperatures (seal expansion) and increases in cooler / cold temps (seal contraction). Adding / subtracting washers and even weighed summer / winter pellets = competition circuit fixes. Or just go with an o-ring seal....
TX200/Gary Cane/Sightron SIII 10-50x60
TX200/Gary Cane/Sightron SIII 10x42
TX200 test / analysis gun

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