New plinking gun

[eeler1]

Nice to see another airgunner/machinist on board. I've got a Marauder that was the ancestor of your gun. Now that I'm living in the city, can't shoot like you anymore, not jealous, just wishing I didn't have to drive to shoot.

 

[FOMOGO]

Hey Shad,Glad to see you back,was wondering where you went to now I know,again glad to here about your nuptials. Rick

Same here, congrats on the marriage, and the new plinker. Been pretty out of touch myself for the last 3 months and still have at least a month to go before I get back home to a somewhat normal life. Good to see you back, always enjoyed your posts. Cheers, Mike

 

[JPigg55]

A few questions, please:
1. Every shot will decrease the pressure reservoir pressure slightly. Is the some sort of regulator to provide a constant pressure for each shot? If not have you noticed any change in down range ballistics from first to 40th shot?

There are many YouTube videos that answer this, but, as Ogberi stated, most PCP's don't use a regulator.
Basically, two factors affect muzzle energy and velocity. One is the pellet mass (i.e. weight in grains). The other is speed.
Speed is determined by the differential pressure acting across the pellet as it moves down the barrel (i.e. acceleration).
On a PCP, the hammer is basically a weight that is accelerated by a spring that is compressed when you cock it.
When fired, this gives the hammer some amount of kinetic energy as the spring accelerates it towards the air reservoir valve.
Based on reservoir pressure, this determines the time and amount the valve is open and, as a result, the amount and pressure of the air released.
So at full pressure, the valve is only slightly opened for a short time. As the reservoir pressure drops, the valve is opened more and for longer releasing a larger amount of air at a lower pressure.
This pressure (actually differential pressure) behind the pellet starts to accelerate it down the barrel. As the differential pressure decreases so does the acceleration.
So here two factors affect total velocity based on acceleration, the amount of differential pressure as it moves down the barrel and time the differential pressure acts on the pellet.
Time is mostly a function of barrel length, the longer the barrel the more time the pressure can act upon the projectile.
The pressure, or more correctly differential pressure, is a function of expansion (volume) and barrel length.
As an example, at full pressure lets say the valve releases 1 cc of air at 3000 psi. As the pellet moves down the barrel this volume increases and the pressure resultantly decreases.
For this example let say the pellet moves the first inch down the barrel increasing the volume behind the pellet to 2 cc's. Based on Boyle's law (I believe), the pressure behind the pellet is now only 1500 psi and at 4cc's the pressure is now 750 psi. So as the pellet moves down the barrel, the differential pressure drops as does the acceleration.
Know lets say this dropped the reservoir pressure to 2800 psi. Since the valve will have approximately the same kinetic energy when fired, the valve will be open further and longer releasing more air at a lower pressure.
For the example, let's say it releases 2cc's of air at 2800 psi. The pellet must move twice as far down the barrel to get the same relative pressure drop, i.e half the original pressure.
So for the example, let's say it's 2 inches (1 cc per inch) until the pressure drops to 1400 psi and 4 more inches before it drops to 700 psi.
So in the first scenario, the pellet moves 3 inches when the pressure drops to 750 psi, but in the second the pellet has to move 6 inches before the pressure drops to 700 psi.
Even with a higher initial pressure, the pellet acceleration drops more rapidly in the first scenario due to the faster drop in differential pressure from the ever increasing volume behind the projectile as it moves down the barrel until it reaches the end of the barrel.

That's why if you look at a graph of pressure vs velocity, the muzzle velocity of a PCP air gun for any given pellet weight tends to increase slightly as the reservoir pressure drops to a point where the reservoir pressure lowers to where velocity starts to drop again.

 

[RJSakowski]

So there is a regulation mechanism to attempt to maintain constant velocity through the pressure drop in the reservoir. Thanks for the explanation!

 

[682bear]

My understanding of this is that the pressure in the reservoir is what closes the valve... so at full pressure, it closes the valve quicker, as the reservoir pressure drops, it takes longer for the lower pressure to overcome the striker spring and close the valve... thereby releasing slightly more air to push the pellet...

So, yes, it is self regulating...

-Bear

 

[Mikebr5]

I am an NRA instructor and about 6 months after Sandy Hook I had to change my teaching... I had a LOT of rimfire ammo before that... shocked me to run out.
Centerfire is no fun teaching for 1st time students for a few reasons, cost being right up there for most people, but I did teach some on SKS. Still not ideal.
I have a passel of children, most grown, but I still shoot with them on occasional family get together days. We started looking into the PCP and I was amazed at the improvements from the pump air guns from my childhood, like the Crosman 760.
My wife picked up a Benjamin Marauder in .25... Amazing gun. I love it but don't get to play with it enough.

 

[george wilson]

For heaven's sake! DON'T try shooting DEER or COYOTES with any pellet gun. It will MOST LIKELY injure the animal and cause it to live in pain forever. That is just cruel. There is a moral responsibility in killing animals to do it in a painless manner. Even a .243 center fire is often considered a minimal deer rifle.

I collect air rifles. A .22 with NO powder,just the primer,still seems to out penetrate all of them.

 

[JPigg55]

For heaven's sake! DON'T try shooting DEER or COYOTES with any pellet gun. It will MOST LIKELY injure the animal and cause it to live in pain forever. That is just cruel. There is a moral responsibility in killing animals to do it in a painless manner.

While I agree with your sentiment, I don't like blanket statements such as this.
There are plenty of air rifles capable of being used for hunting as long as they're used within their capabilities.
I believe it comes down to the person using it. I've seen wild boar dropped with a .22 as well as ones get up and run away after being hit 3 times with a 30-06.

I'm quite sure many here can tout examples both for and against air rifles for hunting. As well as opinions for minimum sized firearm to be used for game and the reasons why.
I recently watched a YouTube video of a .45 cal air rifle penetrating 3/4" plywood at 600 yards. Within some standards, this would equate to enough power and penetration to take a deer at that range, but in no way would I (or the video maker) ever recommend trying such a thing.
The actual point of this video (titled "How far can an air rifle kill") was more to do with safety for knowing what lies beyond your target. Pointing out the potential lethality of even an air rifle at extreme ranges.

Blanket statements like "A .22 is not a weapon for self defense" even though there is empirical evidence that the .22 handgun has a higher "One Shot Stop" percentage than many other larger caliber weapons (this was from data collected across the nation from police departments and hospitals dealing with handgun shooting resulting in a one shot stop or death. By the numbers, the only caliber to out perform the .22 was the .45) tends to get my goat.

To me, this is like saying "You can't make a quality part with a Harbor Freight benchtop lathe."
Sorry for the rant, I haven't had enough coffee yet. LOL
And I do agree 100% with George in that one does have a moral responsibility, but at the same time, I would try to kill a deer with a pea shooter if I faced starvation.

 

[strantor]

When I outgrew my Power Wheels truck and Red Ryder BB gun I upgraded to a go-kart and a Benjamin 347:

That was a long time ago but the gun still works just fine. That thing was a blast. I recently dug it out to give to my kids. The butt stock is all scratched to hell from putting it between my feet to pump it up. I remember that being quite a PITA. pump it ten times, put your single pellet in, aim the open sights, and let 'er rip! Miss, repeat. probably took 30+ seconds between shots. I was damn accurate with it too, no scope. Could hit a bird off a wire from 30yds away. I was probably more accurate as a kid than I am now.

 

[george wilson]

I don't recall the airguns being discussed being .45 caliber. There are some super large caliber air guns being made. In the Phillipines,I think.

In the early 19th. C.,some large caliber air guns were used by snipers in battle. French,if I recall correctly. They were so unsportsmanlike,the sniper using one would be executed. Their cast iron butt stock air flasks were pumped up by a large pump that looked like an early fire engine,pumped by several men. I don't recall how many times they could be fired before recharging.

Lewis and Clark carried one on their expedition. They awed the indians with it,since it was noiseless.

But,such airguns were and are in a completely different class than we are discussing here. Deer could be taken with such powerful air guns.

I am not a hunter,but once owned a perfectly nice Ruger #1 rifle in .243 caliber. Everyone kept saying it was insufficient for deer hunting. I can guarantee that it was many times more powerful than any air gun being discussed here.

My step father lived on a sort of farming community when he was young. He was told to kill a pig. He put out some food and while the pig was eating,he stood right over it,and shot it right in the brain. The pig just kept on eating!

By the way,Elmer Keith said that a minimum self defense caliber was a .357 magnum. He told a story about a sheriff ,mistakenly thinking a black cowboy for an outlaw,emptied his 9mm. Luger into the fellow. The cowboy said to him "Are you done shooting,white boy". Then he drew his .45 colt and killed the sheriff in one shot.

I think it was a bad move for the military to be re armed with 9mm automatics.

I'll stand with my blanket statement. If you are starving,I'd at least recommend a bow and proper arrows!