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Messages - Mintie

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1
Modifications / Re: PCP airgun design
« on: December 29, 2018, 10:30:08 PM »
Either way there still needs to be a volume of air between the one way bottle valve (if it has one) and the valve face which would be considered the "plenum". The general rule is that you will need 1cc of volume in that space for each fpe you are wanting to get.

2
Modifications / Re: PCP airgun design
« on: December 29, 2018, 03:11:28 PM »
I think the tube would be a much better way to go, make sure your ID matches an easily available reg from Huma in case you choose to regulate it in the future.

3
Modifications / Re: PCP airgun design
« on: December 29, 2018, 08:06:44 AM »
Ahhh right sorry I didnt click to what you were getting at, you are asking about using a bottle without having a reg on it? That would mean it cant be removed from the rifle while being pressurized and it couldnt be swapped to another bottle under pressure in the field. The inside neck thread on most bottles is M18 so by the time you have a male thread inside that your "bottle neck" is probably going to be 8mm or less which might end up being restrictive to the flow through the valve, it would probably perform better with a plenum space to feed from.

4
Modifications / Re: PCP airgun design
« on: December 28, 2018, 10:47:46 PM »
Yes you will need a plenum between the regulator and the firing valve, the general rule is 1cc per fpe you are chasing but that also depends on caliber etc too. Generally the plenum is a solid piece that the reg screws into and it then screws into the other half of the valve, the valve spring is usually seated against the end of it.

In an unregulated rifle the whole tube in front of the valve is effectively the plenum, some unregulated rifles use a pot infront of the valve that sort of regulates (just by having a very small hole in it) the amount of air that the valve has available to use which can help to flatten out the shot curve.

On specific info and your engineering questions you will need to speak to Wingman.

5
For Sale, Wanted, Spotted / Wanted - Gamo G1200 Co2 rifle
« on: December 20, 2018, 03:39:08 PM »
Let me know if you have one to part with, any condition is fine as I will strip and tinker with it anyway.

Cheers

6
Hunting / Re: Summer plinking
« on: December 20, 2018, 03:37:32 PM »
Would love to grab a G1200 to tinker with, let me know if you see another one for sale Mike. Need to get those pellets off to you too!

7
For Sale, Wanted, Spotted / Re: Wanted to buy
« on: December 13, 2018, 04:08:27 PM »
Hi Mintie. Has the trigger been enhanced at all please? Cheers. Richardo

Hi Richardo,

I haven't done any work on the trigger, Not sure if the owner did himself or not. I believe they are the same as the discovery trigger, not bad off the shelf but certainly room for improvement.

Cheers

8
For Sale, Wanted, Spotted / Re: Wanted to buy
« on: December 13, 2018, 02:11:38 PM »
Nice one. I've never fired one of those, but if you need info on it, mintie, our in house crosman aholic will help for sure.

This ones already been across my bench, its running pretty hot and wearing a nice little silencer now.

9
For Sale, Wanted, Spotted / Re: Wanted to buy
« on: December 13, 2018, 09:04:17 AM »
I know the rifle well and I am somewhat jealous. Well done.

10
General Airgun Discussion / Re: Pellets
« on: December 04, 2018, 02:06:02 PM »
All yours mate, Whats your address?

The springers sound interesting, Send them along to me and I will see what I can do with them

11
General Airgun Discussion / Re: Pellets
« on: December 04, 2018, 09:17:40 AM »
If these are the ones you are after I have 2 and a bit boxes worth here for you if you want them, you have given me stuff before :)




12
General Airgun Discussion / Re: Pellets
« on: December 03, 2018, 11:23:25 AM »
Which pellets were they mate? I have a few boxes of killwells here

13
General Airgun Discussion / Re: bulk filling co2 airguns
« on: December 03, 2018, 11:03:49 AM »
CO2 is interesting stuff, you probably know this stuff but I will outline its properties in terms of airgun performance for other future sody enthusiasts.

 - The pressure of the gas CO2 changes quite a bit with the ambient temperature, nominally its around 850psi, As the temp drops so does the pressure.
 - So long as there is liquid CO2 in the vessel the gas CO2 will be at a constant pressure (depending on temp)
 - As each shot is taken and the pressure of the gas CO2 in the vessel drops the liquid evaporates to replace the gas to the same pressure, this evaporation causes the vessel to cool down rapidly
 - The amount of temp drop per shot is relative to the size of the vessel and how much gas you are removing from the vessel for each shot. For example if your valve is using enough gas to need .2 grams of liquid CO2 to evaporate to replace the gas used for each shot and the vessel is only 12 grams then that vessel will cool down much more with each shot than the same valve working with a 36 gram vessel as the percentage of gas taken to vessel size is 3 times as much.
 - CO2 cool down is what kills accuracy and performance in rapid fire applications that use 12 gram cartridges, each rapid shot drops the temp further and further which drops the pressure of the gas CO2. I have recorded more than 200fps (from 380fps down to 160fps) difference between shot 1 and shot 8 of a CO2 pistol fired quickly. 2 ways around this are much slower shooting which allows the vessel temp to come back up to room temp (or you can help it along with hand warmers etc) or a larger vessel which will handle the drop in pressure better because of the bigger ratio of gas taken per shot to liquid present to evaporate and replace it.
 - High powered applications can also cause temp to drop dramatically with each shot too, A maxed out 2250 will only get 10 shots per 12 gram cartridge so the amount of evaporation required to replace the gas from each shot is huge.
 - Power can be linked to barrel length and also pellet weight, CO2 expands at a slower rate than HPA so the longer barrels give it more of a chance to expand to its best potential, heavier pellets also give it a chance to expand more with a bit more time before they leave the muzzle so tend to produce more FPE


When the liquid CO2 has all been evaporated the pressure of the gas drops off very quickly with each shot, and this is where some CO2 gun designs are much more efficient than others - Take the Crosman 2250 as an example where the cartridge is pierced directly into the valve VS the QB where 2 cartridges are both pierced and fill the whole tube with pressure. The QB will end up depleting the liquid CO2 much faster as it has had to evaporate to fill the whole tube with gas before any shots are taken, it will still shoot fine while there is still some liquid CO2 left but once the liquid is gone the tube full of gas will drop power fast with each shot.

CO2 is a very good power plant for airguns as it essentially self regulates to a constant pressure so long as there is enough time given between shots for the temp to stabilize. It can be tuned in most setups to achieve 12fpe and more if you really want to push it. Its just a shame it cant really produce the same sort of power as HPA.

14
General Airgun Discussion / Re: Importing airguns
« on: November 28, 2018, 02:30:18 PM »
Ask them for a more comprehensive reason why it was declined or ask under the OIA what reasons would be good enough for its approval.

15
Modifications / Re: Spring Rifles
« on: November 27, 2018, 08:53:28 PM »
Chasing power gains in springers is a pretty tough task, there are tradeoffs with everything you do and you often end up with a harsher shooting cycle.

Have you got access to a chronograph? It would be good to know what its shooting at now, if it's close to factory spec I would probably just leave it at a bit of a clean and polish up inside,  if it's a bit lower than it should be you could look at a new spring and seals.

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