Playing Around With Co2 Tuning - Airguns & Guns Forum

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• playing around with co2 tuning

« previous next » Print Pages: [1] Go Down Share This! Author Topic: playing around with co2 tuning (Read 2590 times)) Ribbonstone GTA Senior Contributor Posts: 12030 playing around with co2 tuning « on: April 03, 2014, 07:15:38 PM » The basic question is this: Am I nuts for setting my co2 this way? Not really looking for an energy goal, just looking for a decent/balanced setting and accepting whatever energy the system can make. Something useful for inside and outside in the spring.Recently re-converted a PCP (HiPac) 5mm 2250 back to 12gr. for warm weather use. Shot it a bit, but realized it would be best to completely pull the gun apart, clean, lube, go back to a lighter spring, a “power adjuster” end cap, a standard Crosman valve, and re-tune it.Spring came from my parts box, but I’ve lost track of what Crosman co2 it came out of. Might be a 2240, 2250, 2300, or a 2260 but it looks like a standard Crosman 2240 spring. End cap started off life as a Discovery end cap and I just use the existing threaded hole as my power adjuster (added a little set screw as well).Looks long barreled, but most of that is shroud, there is only 11.7” of barrel inside that shroud.Got to thinking about how PCP valves operate over a range of pressures. Co2 valves are the same system (basically “whack it with a weight” valves). So co2 should also operate well over a range of pressures.With co2, pressure and temperature are much more closely liked than with air. CO2 will self-cool/drop pressure as temperature changes. Rapid fire will cool the gun and drop the pressure.81F today, which is pretty fine co2 weather.Set the new spring to various preloads (from no preload to 6 turns in of the power adjusting screw) and shoot AS FAST AS I COULD LOAD. With a single shot, idea was to shoot about every 8-10 seconds.Bad news is that I had no way of getting an accurate reading of the temperature inside the gun as it self cooled.Chart:Preload from 0 to 6 turns.6 very rapid shots at each setting.First surprise: thought it would take more shots than 6 to see a difference. Evidently valves cool down fast. Speed drops faster than you’d guess by the temperature of the bottom tube. Thinking about that, realize that all the gas “knows” is the temperature of the 12gr. bulb it is stored in and the temperature inside the valve. Because each of those things is a loose slip fit into the tube, they are not in full contact to the air tube, so the temperature change we can feel on the outside takes time to conduct to the outside.What we normally do is shoot at a reasonably slow pace to allow the gun to come to some kind of equilibrium. May shoot fast or slow for the first shots, but as we go along, at the same pace of shooting, the temperature stabilizes at some point lower than ambient temperature.With no preload to about 4 turns in, the cooler the gun got, the faster it shot. Makes sense, as it’s like a weak striker spring in a PCP starting out at too high pressure.Someplace about 5 turns in, the velocity didn’t increase ( “3” is not enough to really count as it is within the normal variation between shots). At 6 turns in, velocity dropped as the gun cooled and pressure dropped. If it were a PCP, would think that the striker hit was set for the highest pressure and velocity decreased as pressure dropped.Made the assumption that at someplace around the 5 turns setting the valve had enough self-regulation to handle the change in pressure (temperature) caused by rapid fire.Decided to try 4 2/3 turns of preload over a new 12gr., still shooting rapidly (trying for a 6 shot a minute pace).Can see the problem? How to tell if the gas is running out or if the temperature/pressure just dropped past the valve’s ability to self regulate?Decided that once the velocity dropped, just walk away from the gun and let it warm up. IF the shots after the warm up were back to normal, then it wasn’t out of gas yet, just too cold.Going to have to check how many shots on a 12gr. if it shot at a sane pace of about 2 shots per minute (even though the velocity is the same when cool, it is using more gas to get there).MORE POWER?Am thinking that, like a PCP, once you found the right operating pressure, going faster would be a matter of gas flow more than anything else. Valve volume, transfer ports, valve stems, and a “clean” gas flow. BUT, unlike air, the more gas you flow per shot, the more cooling, so it’s likely to get complicated getting more power and less temperature sensitivity. Logged Louisiana rsterne Member 2000+fps Club GTA Senior Contributor Posts: 27131 GTA Forums Person of the Year 2017 Real Name: Bob Re: playing around with co2 tuning « Reply #1 on: April 03, 2014, 08:38:17 PM » Absolutely correct.... CO2 can be tuned to self-regulate, and you know when you're there when the rate of fire doesn't change things much.... I've been talking about this for a few years now, but few seem to listen.... I have a 1750 that shoots within a 10% ES from just out of the frigde at 35*F right up to nearly 80*F, peaking at about 60*F.... What changes dramatically is the shot count, a lot fewer in cold weather.... You have to give up a bit of velocity to achieve this type of tune.... but when you consider that higher velocity is only in warm weather, and then only if you are shooting a shot a minute, does it really matter.... especially when you consider you may only get half the number of shots to get that last bit of velocity....Bob Logged Coalmont, BC, Canada The only thing necessary for the triumph of evil is for good men to do nothing.Stand up for what you believe in, my friends! Ribbonstone GTA Senior Contributor Posts: 12030 Re: playing around with co2 tuning « Reply #2 on: April 03, 2014, 09:12:50 PM » Would guess with my normal slow firing pace could go up to 6 turns in. Vel doesn't change much with 3 shots in 25-30seconds , which is probably 8 or 9 times faster than I'd normally shoot. Might work out better for the hot season to come.First noticed this when I bulk filled a 2260. Even shooting at a steady pace and not letting the rifle cool down, found that as the gun ran out of gas, it would shoot faster. The last couple of shots per fill were the fastest of a string. Finally it hit me that the striker spring was a bit weak, so when it was starting to run out of co2, the pressure in the tube started to fall for the first time.Was going to use two indoor co2 match type rifles that are already slow (like 460-470fps) for this test. Know they get even slower when brought outside in warm weather and can come close to valve lock in hot weather. Problem with those for testing is that they move so little co2 per shot, is impossible to load and shoot them rapidly enough to cool them down, so I'd have to force cool them. Logged Louisiana Print Pages: [1] Go Up « previous next » GTA » All Springer/NP/PCP Air Gun Discussion General » PCP/CO2/HPA Air Gun Gates "The Darkside" (Moderators: Rocker1, only1harry, splitbeing) » playing around with co2 tuning

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