Tuning Impact MK II does NOT like freezing Temps

[nervoustrig]

Air pressure does indeed rise and fall with temperature.

However it turns out this relationship is fairly serendipitous to the typical hunter who stores his gun indoors and then heads out into the cold. As the gun's temperature decreases, the regulated pressure will begin to fall and the seat will open up to allow the pressure to top off. On a fine enough scale, there is some amount of hysteresis to it but from a practical perspective, it's not something to be concerned about. Other effects like lubricant viscosity, air density, material contraction, etc. conspire to affect things but the plenum pressure is a small consideration at best.

Then we have the other scenario, bringing a cold gun back into the warm indoors. That will cause the plenum pressure to rise. The reason is because the air is trapped, so to speak…the increased pressure simply causes the regulator to close harder. Depending on how the gun is tuned and how much of a temperature/pressure rise we're dealing with, there may be a change in POI. But if it is tuned carefully, this effect can be minimized. That is achieved by tuning your regulated rifle more like an unregulated one, operating somewhere near the peak of the bell curve. In this way, pressure changes do not affect the extreme spread to any meaningful extent.

To give some perspective, a 30F increase in temperature will cause a 2000psi setpoint to climb by 113psi. Meanwhile it's not uncommon for conventional (unregulated) PCP to hold a 1-2% ES over a range of 500psi, so that wouldn't really be an issue for a regulated PCP adjusted to the velocity knee.

 

[Strobing_NYC]

I use a carbon tube sleeve thing I device made for removing air from PCP"s while filling, as well as I 2 large inline filters with the little balls that change color when wet and cotton filter @ the end of it before going into a CF tank and then into gun.

I have a HPDAVV 60S air compressor and 2 Yong Wangers. 

So normally used for woodchucks/coyotes/other medium to small nuisance animals in sensitive environments. Due to the accuracy and low noise levels its perfect for my work. Went to sight in with a thermal scope for Night Beaver work in about 31° Temps. The gun sounded and shot like a totally different gun. No power nadda..

My work around for now is going to be putting hand warmers around the plenum and reg to see if that helps. As I don't have time to take apart and remove all extra silicone and lub. It's just amazing to me that not many others have had this issue and why isn't it talked about more. There are a lot of shooters in the north that I'm sure like to shoot year round. So there has to he a semi easy solution to theis issue. It's not FX Impact specifically from reading above but purtains to MKII Impact in my case with power plenum



Thank You for all the discussion

 

[Airgun-hobbyist]

I use a carbon tube sleeve thing I device made for removing air from PCP"s while filling, as well as I 2 large inline filters with the little balls that change color when wet and cotton filter @ the end of it before going into a CF tank and then into gun.

I have a HPDAVV 60S air compressor and 2 Yong Wangers. 

So normally used for woodchucks/coyotes/other medium to small nuisance animals in sensitive environments. Due to the accuracy and low noise levels its perfect for my work. Went to sight in with a thermal scope for Night Beaver work in about 31° Temps. The gun sounded and shot like a totally different gun. No power nadda..

My work around for now is going to be putting hand warmers around the plenum and reg to see if that helps. As I don't have time to take apart and remove all extra silicone and lub. It's just amazing to me that not many others have had this issue and why isn't it talked about more. There are a lot of shooters in the north that I'm sure like to shoot year round. So there has to he a semi easy solution to theis issue. It's not FX Impact specifically from reading above but purtains to MKII Impact in my case with power plenum



Thank You for all the discussion

I shoot outside in freezing conditions alot, and I just move my scope accordingly and try to plan ahead. However, last year I had set up the Impact in just about freezing conditions for .25 caliber for nighttime coyote hunting, but then taking it out in 20° freezing weather in an unheated blind it was way off because of being well below freezing. The pressures and sound of the shot told the story, as well as the point of impact change.

dIn your case, it does not have to do with the Power Plenum in the MKII specifically, but regulated pcp's getting used in sub-freezing conditions in general. The Impact is loaded with different metals and different types and sizes of o-rings throughout the whole rifle, as well as lube on the hammer and valve rod. Therefore, it is the expansion and contraction rates of dis-similar materials at different temperatures that is effecting the thing. Internal air pressures are greatly effected and translates to how hard the hammer strikes and how fast the valve opens too.

A non-regulated PCP does much better for this type of winter pesting, as there are much less moving parts and o-rings and the shot cycle works off of plenum space and pressure. Therefore one thing that would be important to keep an eye on would be fill pressures. If filled to optimal working pressures while outside in the freezing weather, it would becom overfilled once returning to the warm conditions inside (if you did not shoot it down before returning to the warmth.)

Maybe look to another non-regulated PCP rifle for winter season pesting.

 

[18.13]

Also air density comes in to play. I have shot when the temperature was 15 degrees and hitting .2 mils low and the same target when it was 109. .2 mils high. Just what Chairgun said it should be. .4 mils is about 1.4 inches at a 100 yards 

 

[TDK]

While I'm sure things discussed here like lube characteristics etc. play a role, I suspect the largest contributor to your velocity swing is regulator set point raising in the cold. I am NOT talking about any sort of temporary one-time change to the trapped air in the plenum, but the repeatable pressure setting the regulator returns to in operation. FX uses a plastic (likely delrin) reg piston, and that material has significant coefficient of thermal expansion. When the reg piston gets cold, it shrinks which requires the reg spring stack to have to compress further in order to seal. More spring stack compression, higher reg set point. Do some experiments and watch your reg gauge. The gun will obviously need to equalize in temp wth the environment first.

On my M3 I have a sekhmet digital reg gauge on the angled bracket so I can and have watched reg pressure like a hawk. An environmental temp drop from 70deg F to 40deg F results in reg set point going up 10 bar. The front reg uses the same piston and shifts in a similar manner, but isn't going to affect precision. The changes are very predictable for me, and I've done chrony work at the different temps/set points to see how many clicks I need on the micro adjuster to compensate. I need about 1 click on the micro adjuster for every 2 bar of reg set point increase to keep the same velocity. Taking an approach like this, it really doesn't matter what is causing temperature effects since you are just adjusting for end results. In my case I am using the reg pressure as an indicator of the temperature of the gun, but you could potentially do something similar by measuring or monitoring the temperature of the gun directly.

I think a lot of people are getting hung up on what the actual effects are of general air pressure drop with lower temperatures. Your gun tank pressure goes down like you got a short fill, but the regulator doesn't care (excluding the materials shrinkage discussed above). If the regulator has 220b of air pressure to work with, it doesn't matter if it is 30 degrees or 90 degrees.

 

[Strobing_NYC]

I have digital front tank and reg gauges as well as a Huma reg. 

 

[Corvid_hunter]

Going off topic here....rimfire shooters experience changes in cold weather and there is rimfire ammo made specifically for it. Biathlon ammo if I remember right.

 

[Strobing_NYC]

On topic my friend, my impact is almost up to .22 LR power and same line of thought we will take it

I'm going to try hand warmers tonight stuck on the impact and in the case. Maybe keep it in the case with a bunch of warmers until the shot is needed but then I would probably have major fog issues. Even been thinking of making a little hot tent in the back of my truck lol. This seems like a loosing battle and I'm not going to constantly be changing reg pressures and sighting in unfortunately. My best option so far is to try and find those pipe wraps that prevent freezing but find one or modify one to run off a USB battery bank and wrap the tank and main parts of the impact. 

 

[TDK]

I have digital front tank and reg gauges as well as a Huma reg.

Can you tell us how much the reg set point changes on that Huma reg with extreme temp swings? I have been eyeing a huma for the fact that they have a brass piston, but have yet to get direct feedback from a user on how they perform in this regard. This temperature sensitivity is the only complaint I have against the AMP.

You should still be able to use a similar compensation strategy to help: shoot with gun temperature equalized at a few temps and note the speed and adjuster clicks needed. Even better if you can shoot a target and confirm POI. This strategy would probably be more effective if you had one of the aftermarket 16 step power wheels for the MKII. On my M3, one click on the Macro adjuster is equal to around 4.2 micro adjuster clicks. Each micro adjuster click at my tune level is about 3.2fps.

 

[Strobing_NYC]

I can tell you that I normally have my reg @ 140bar and when I took it out of the case this morning from being in the cold the reg was up to 156.1 tank was @ 243

I threw some hothands on it before Goin out tonight I'll check when I get home to see if it helped. Also have the USB heaters on order. 

 

[TDK]

I can tell you that I normally have my reg @ 140bar and when I took it out of the case this morning from being in the cold the reg was up to 156.1 tank was @ 243

I threw some hothands on it before Goin out tonight I'll check when I get home to see if it helped. Also have the USB heaters on order.

When you say you took it out of the case and the reg gauge was at 156bar, it sounds like the expected one-time plenum pressure increase you get when taking a regulated gun from cold to to warm environment (due to the air trapped in the plenum). Did you dry fire a couple shots to see if the reg set point was still 140bar?

 

[brentritz]

I've noticed a little more 2nd reg creep after leaving it in the cold overnight. Of course, the bottle pressure also drops about 5lbs+- until warmed back up.