Precihole PCP

[vsraja]

I think our Indian market needs a multi-pump air rifle,which has a recoil-less firing cycle similar to a PCP.It also has the integrated pumping mechanism, hence no need of any tank or a pump to recharge it.Also it was way cheaper (we can see many of them are cheaper than break barrel air rifles) and less maintenance needed.Hence it suits well for many of the Indian casual plinkers where hunting was banned.It was sufficient for a short range target practice and plinking.Also it suits many veterans and young shooters at the starting stage.Hence it suits them well as their first air rifle.

Pros of a multi-pump air rifle:
1)Recoilless(Accurate)
2)weightless
3)No need of extra accessories for recharging
4)suitable for target practice
5)cheaper than a pcp (atleast)
6)easy maintenance

[sam 47]

Stayed up late last night after studies reading and trying to understand PCPs. I asked Tom Gaylord of Airgun Academy blog to give the links to some articles so that it would save me long time searching. Posting some relevant portions of the articles...

How a PCP valve works
The information above illustrates how a powerplant and its firing valve can be set up to release just a portion of the air stored in the reservoir, keeping the rest for follow-on shots. All it takes is some thought to enlarge the reservoir to get even more shots per fill and to adjust the valve to use that compressed air as sparingly as possible. But something else creeps into the equation at this point.

With the Benjamin multi-pumps described above, each successive shot was less powerful until all the air was exhausted. But PCPs don’t work that way. A PCP will continue to shoot all its shots within a reasonably tight velocity spread, even though the air pressure inside the reservoir is constantly dropping. They can do that because when the valve releases air, it stays behind the pellet and holds the valve open for a brief time. If the barrel is long enough, the pellet stays inside for some time and allows the air pressure behind it to continue to build because the valve has not yet closed.

If the valve did close, then each shot would be a little slower than the last. But because the air valve remains open just a little longer each time, more air leaves the reservoir. Yes it is pressurized a little less each time, but there is more of it because the valve remains open just a little longer and that balances things out. As a result, the pellet gets a longer push from lower pressure air, which keeps the pellet velocity more or less the same.

Run out of barrel
At some point, though, the pellet has to leave the muzzle and the push has to stop. When that happens, the pellet velocity starts dropping with every successive shot and we say the gun is off the power curve.

Power band = 1000 psi?
GunFun 1 mentioned that he has noticed that many PCPs seem to have their power band — the pressure at which all the shots seem to go out at about the same velocity — in a range of pressures that’s about 1,000 psi, high to low. But he then said that his Talon SS is only filled to 2700 psi and runs out of steam at 2000 psi, which is only 700 psi. The lesson here is that 1000 psi is not a magic number, any more than a fill pressure of 3000 psi is magic. And please note that the Talon SS has a 12-inch barrel, although I don’t know if GunFun1 has replaced his barrel or not. I’m just saying that a shorter barrel will have a narrower power band.

When I worked at AirForce Airguns I used to take angry calls from customers wanting to know why their AirForce Condor could only be filled to 2650 psi, when it “should” have filled to 3000 psi. They tried putting in more air, but their gun just shot slower when they did. They were still getting the top velocity the gun could give (1,250 f.p.s. with .22 caliber Crosman Premiers) and they were getting it over 20 shots, which is all a Condor will do at top velocity, but they wondered why they were being “cheated” by having their gun stop 350 psi below the place where it “should” stop.

The power curve
These shooters did not understand how precharged airguns work. You don’t use an arbitrary fill pressure to determine the gun’s power. You use a chronograph. You fill the gun until any higher pressure results in slower shots. That pressure is the maximum fill pressure — regardless of what number that turns out to be. Then you shoot the gun until the velocity starts dropping off rapidly. Fill it again and note the pressure at which the tank begins to accept air. That is your lower pressure limit.

The band of pressure between the highest fill pressure and the lowest pressure at which the shots are still stable is called the power curve. Don’t try to make that curve conform to certain numbers. Just find out where it is and live with it. The high number is your maximum fill pressure and the low number is the point where your gun needs to be filled.

As it turns out, many times the power curve for a particular airgun will be about 1,000 psi., but it doesn’t have to be. It is whatever it is, and you find that out with a chronograph. Typically PCPs with shorter barrels will have narrower power bands, as will the more powerful guns. A lower-powered PCP and one with a longer barrel will have a larger band of pressure. But, until you use a chronograph to find out, you’ll never know for sure.

What should you do?
Now that you know this, what should you do about it? Glad you asked. I’m assuming you want to apply it to a precharged airgun. First, get a chronograph. You don’t need a chronograph to enjoy a precharged airgun, but you will never know exactly where the power band is without one.

Use the published fill pressure as a starting point — a guideline. I have seen plenty precharged airguns without a regulator whose maximum fill pressures were not what was published or even what was engraved on the side of the gun. If it says 3000 psi, expect something between 2800 and 3100 psi. That’s why you test every airgun.

I have found that the lower the fill pressure the closer the number usually comes to the actual maximum. I have owned two different Daystates that filled to 2600 psi, and they both tested to within 100 psi of that. A hand-built gun like a USFT is probably tested by the builder before you get it. If a gun like that is off, it will be because your gauge doesn’t agree with the maker’s.

The point is, you only discover the power band of a PCP by testing for it. The test is simple if you have a chronograph. Without it, you are just guessing.

Last tip — worth the price
My last tip today. What if you don’t have a chronograph and can’t afford one? Is there any way to know what your power band is? Yes, there is.

You may not know the velocity the gun is delivering, but you can discover where the power band is by shooting a large group of shots at a target long distance away. First, fill to where you think the maximum is. Then start shooting at a target a long way off — at least 40 yards. If the pellets walk up in the beginning, the gun was over-pressurized. If they group together and then start to drop, the gun was on the power band until the pellets started to drop. That’s when it came off the power band. I actually did this with my first Career 707 rifle.

Just remember, you don’t need a lot of extra equipment to enjoy an airgun. But if you want to understand the technical parameters, some equipment is vital.

Dear Veerbhadra,

For 6K I assume the TANK PH supplies would be of an easy to carry to field size with low volume just sufficient to fill the gun for a few times in the field. What I want to know is whether it would be possible to fill this small tank using the pump supplied with the gun? Of course it would take a lot more time and physical effort and I don't think I can do it myself due to my poor shoulders. But I can get one of my plantation workers to do it for me. If it could be done what kind of adapters would be required to connect the pump's output to the tanks input?

Thank You,
Best Regards,

GNV

Sir, I know the question is for Veerbhadra, but I am sharing with you what I found out. Assuming you manage to get the right adapters and the tank and the pump are rated for the same pressure, still it is going to be a very hard work. The simple reason is that the volume of the air tank is much more than the gun reservoir, atleast 5-10 times. So it will take I think as I have found out 14-16 hours of labour (allowing time for man and pump to cool down in between), and strokes bordering on the 15k-20k mark. Specifics will vary with the specifics of the tank, but I don't think a simple cheap handpump will be able to take the strain of filling it, unless the tank is the size of a small fire extinguisher.

[kanwar76]

Why one needs to fill up tank with pump rather than straight filling the gun up?

Or again am I missing something

[sam 47]

Why one needs to fill up tank with pump rather than straight filling the gun up?

Or again am I missing something

You are not missing anything sir. People fill up guns directly with pumps. I think GNV sir is wanting to know if he can use the pump to fill up the tank also, so that he can carry it when shooting in the field. That way, when he runs out of air in the field, he can quickly fill it up with air from the tank, without the trouble and pain of having to pump it in the field.

[kanwar76]

Why one needs to fill up tank with pump rather than straight filling the gun up?

Or again am I missing something

You are not missing anything sir. People fill up guns directly with pumps. I think GNV sir is wanting to know if he can use the pump to fill up the tank also, so that he can carry it when shooting in the field. That way, when he runs out of air in the field, he can quickly fill it up with air from the tank, without the trouble and pain of having to pump it in the field.

I always thought carrying pump will be easier than carrying the tank in the field but then you learn something new everyday

[sam 47]

I always thought carrying pump will be easier than carrying the tank in the field but then you learn something new everyday

Depends on the size of tank. Pumping for 200 times with high pressure pump wastes a lot of precious time and effort. The smaller tank will also fill up for 1-2 times, and until the gun runs dry for 2-3 times in succession in a sub 15 fpe gun, that's a lot of shooting, easily way more 100 shots.(well, in most guns.)

[pratik_mahale]

I always thought carrying pump will be easier than carrying the tank in the field but then you learn something new everyday

Depends on the size of tank. Pumping for 200 times with high pressure pump wastes a lot of precious time and effort. The smaller tank will also fill up for 1-2 times, and until the gun runs dry for 2-3 times in succession in a sub 15 fpe gun, that's a lot of shooting, easily way more 100 shots.(well, in most guns.)

Hi Sam,

How much you paid for those tanks.
Can you give the details like the size & weight of the tanks
How many times you can fill your PCP with the smaller one

[jatindra Singh Deo]

I always thought carrying pump will be easier than carrying the tank in the field but then you learn something new everyday

Depends on the size of tank. Pumping for 200 times with high pressure pump wastes a lot of precious time and effort. The smaller tank will also fill up for 1-2 times, and until the gun runs dry for 2-3 times in succession in a sub 15 fpe gun, that's a lot of shooting, easily way more 100 shots.(well, in most guns.)

Cool off mate , I know you mean well .We have veterans here you are dealing with and more often than not our assumptions don't add up on the field to those we made in theory .This is the reason why we put up questions to people who have field experience.Spend some time preferably hands on ,I assure you ,the experience will be very revealing . I have gone through this process and have come out a wee bit wiser if not more .Happy Shooting !

Regards
Jatin

[sam 47]

Cool off mate , I know you mean well .We have veterans here you are dealing with and more often than not our assumptions don't add up on the field to those we made in theory .This is the reason why we put up questions to people who have field experience.Spend some time preferably hands on ,I assure you ,the experience will be very revealing . I have gone through this process and have come out a wee bit wiser if not more .Happy Shooting !

Regards
Jatin

Thanks mate. My bad on posting based on nothing but secondhand information. Never again a post by me on the subject of pneumatics.

[Big Daddy]

Thanks mate. My bad on posting based on nothing but secondhand information. Never again a post by me on the subject of pneumatics.

Come on Sam, that's not the spirit.

Sometimes it gets dirty and mucky and needs a whip master to set things right. That's why we have mods.
I do not agree with Jatin's statement as even new bees have the right to express in their own free will, in their own wisdom. But then this is his view and I have to respect his right to express his opinion. Don't get demotivated. Its all part of a health forum.

BD

[GNV]

Why one needs to fill up tank with pump rather than straight filling the gun up?

Or again am I missing something

You are not missing anything sir. People fill up guns directly with pumps. I think GNV sir is wanting to know if he can use the pump to fill up the tank also, so that he can carry it when shooting in the field. That way, when he runs out of air in the field, he can quickly fill it up with air from the tank, without the trouble and pain of having to pump it in the field.

This is exactly what I mean. For 6K I am guessing that PH would supply a small capacity tank/bottle and I want to know is it possible to charge that tanks with a Pump if one has the necessary adapters.

[Rudransh]

Yes if tank is under 500cc capacity so it will be more feasible to fill it in time of few hundreds pumps.more than 500cc it can but you will not like the number of pumps you have to pump it up and also not advisable for pump life.

My two cents buy a pump keep it handy and don't let the gun empty topping the reservoir is more easy and quick than filling from zero.

Regards
Veerbhadra

[22cal]

I think unless one has access to scuba filling pump...The excitement might not sustain for long.

Basu

Basuji, getting access to a SCUBA filling pump or 'High Pressure Breathing-air compressor' is not an easy thing. Here in Koklata, not a single rifle club has it's own HP Breathing-air compressor. These rifle clubs spend lot of money for shooting lanes, motorized pulleys, electronic scorers but not on Breathing-air compressors. High pressure Breathing-air compressors are expensive and very delicate. One can acquire a HP compressor for just above 3 lakhs, but maintaining it is quite difficult.
In Kolkata only Kolkata police (river police) and Sea Explorers Institute have their own HP compressors. Kolkata Police does not allow civilians to use their compressors, but Sea Explorers Institute does (only to some selected few). Sea Explorers Institute always remains crowded with trainees from Indian Navy, Police and other Govt. disaster management teams from all over India. So they never get their HP Breathing-air compressors idle. They have enough reasons for not opening their compressors to public. (Though they are an NGO, they are not greedy enough to earn some extra income).
In the year 2012 or 2013, a lady named Rajpreet Warna started a recreational SCUBA center in Salt Lake area, called Bubbles & Fun. They had a portable Breathing-air compressor. But I do not know the current running status of her organization.They had a presence on Facebook too.
Access to a HP Breathing-air compressor is relatively easier if you stay in a coastal city with at least one recreational dive center. Among landlocked cities, Bangaluru have two such centers. These private recreational dive schools should happily fill your PCP with good quality compressed breathing-air, but they may charge a premium price for a single recharge. Usually they fill up a 12lit standard SCUBA tank for 150 to 300. They may charge the same amount for your PCP rifle tank for each fill. If you have a SCUBA tank of your own, you can get the tank filled from any dive center for just 150 and fill your PCP tank many times from that SCUBA tank (with the help of a proper adapter). A new aluminum SCUBA tank costs 25k and above, almost same price for a PCP air rifle. This is the price of cheaper aluminum tanks, the steel tanks cost almost double and they are much heavier than their aluminum counterparts.
In Kolkata, one can easily get used aluminum SCUBA tanks in scrap market of Thanthania, Bidhan Sarani, near the ancestral house of Piku (I mean where the film was shot ). Here in Kolkata, some gunsmiths refurbish those tanks and fit an adapter to resell them to local PCP owners. The aluminum SCUBA tanks are prone to wear and tear and have a risk potential if not properly maintained and checked at regular interval. Even an aluminum tank, never used under water, becomes risky as it gets old (time and number of refills). Aluminum is a soft metal and the stress and strain of filling it every time makes it prone to accident. With nearly 200Bar pressure in it, it becomes actually a bomb waiting to explode. I shall never suggest anyone to buy an used SCUBA tank from a scrapyard and use it for PCP rifle refilling. I have every piece of my own diving gear but I never went for a SCUBA tank because they are expensive, they have a very limited life, and they are extremely inconvenient to carry around. I never owned a PCP rifle (or pistol), or otherwise I might have thought in the other way.

[Big Daddy]

Most of the tanks available for pcp users are second hand imported tanks. However there are some reputed and ethical dealers in Bombay who sell great stuff. If one is buying such a tank, it's always wise to pay INR 1,500 and get an hydrostatic test done. Better safe than sorry.

BD

[GNV]

Just now I received a copy of the manual of PH PCP. You can see the specifications below.

capture2.jpg

capture3.jpg

capture4.jpg

Gun's Reservoir capacity and number of usable shots per fill were however not given in the manual.