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Air gun question re PCP guns


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#1 HD Rider

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Posted 20 September 2013 - 10:22 PM

I was watching some YouTube tests of PCP guns and noticed that each shot seems to have varying air pressure resulting in varying muzzle velocity. My question is why doesn't this cause a loss in accuracy?

In The tests I was watching, accuracy wasn't affected by this. Is it that the difference in pressure is so small that it causes no ill effects?

Seems that with regular firearm cartridges, using powder, slight variation in powder weight, bullet weight or even case thickness can cause problems. It seems that slight differences in air pressure on PCP guns should result in the same issues.

#2 Brant

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Posted 21 September 2013 - 07:09 AM

It does if the variability is great enough and it depends somewhat on the distance they are shooting to show up on targets. Many of the higher end airguns like the Matadors or Crickets use internal regulators to keep the velocities very consistent. Regulators add to the cost of the guns. Other high-end guns like Daystates use specially designed valve systems (Harper valve) to achieve the same results.

 

By limiting the fill pressure range one uses in a given airgun you can minimize this variability on some of the less expensive guns. For example you can shoot a Marauder from a fill of 3000 psi down to about 1000 psi but the velocity of the shots will have a lot of variability - especially at the beginning, middle, and end. Instead, you can fill it to 2500 psi and only shoot it down to 1500 psi and get a much tighter range.


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#3 crazyhorse

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Posted 23 September 2013 - 07:28 AM

Roughly speaking you can live with at least a velocity difference of 20 FPS and still have good accuracy. That has been my experience.

For competition, I have two rifles with regulators that maintain a constant 4 FPS differential thru out the entire shot string and they are very accurate. It also is important to have a good barrel and decent crown.



#4 Air Rifle Hunter

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Posted 23 September 2013 - 08:08 AM

Like CrazyHorse mentioned, a difference of 20 FPS between starting velocity and peak velocity won't show too much difference. I don't have any guns with regulators so I do my best to tune them to have a 20 fps difference or better to keep accuracy consistant over a determined number of shots.

A chrony, pellets and shooting time will help you to find the sweet spot of your PSI and you can then determine starting and ending fill pressures from that point.

#5 ratassassin

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Posted 23 September 2013 - 09:27 PM

.22 Long Rifle seems so much simpler. :)

#6 Air Rifle Hunter

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Posted 23 September 2013 - 09:42 PM

A .22 LR is simpler, but it is much easier to find .22 pellets than .22LR ammo right now (at least in my area).

#7 Bisley

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Posted 23 September 2013 - 09:54 PM

.38 spcl's. You can reload them cheaper than many places are selling .22's for, less than $10 for 50rds. Cheaper if you really get a miserly powder. They are the grown up version of the .22, and a kick in the  :eck05:  to shoot in a lever gun. And in the rifle, it don't care if you feed it rile or pistol primers, so you can use whatever you have on hand B)

#8 Brant

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Posted 24 September 2013 - 05:51 AM

It depends. I shoot 98% of my airgun shooting right at my house. Even a legally silenced 22 would be louder and cost me about $600 after the Fed stamp and say Sparrow silencer plus subsonic ammo. Then there is the issue of bullet flight distance. Pellets are high drag and have limited range. If you want stealthy in most states there is virtually no limit what you can do to an airgun since it isn't a firearm. CA is a different story. Accuracy has become a whole new debate with the latest airguns depending on how much you want to spend on them. I know a guy in Sweden with a Sako Quad that competes with a Steyr airgun and they go back and forth and he uses expensive match ammunition and a March scope on the Sako so he has about $4k invested.

.22 Long Rifle seems so much simpler. :)


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#9 russinbaja

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Posted 26 December 2013 - 07:27 AM

I love to shoot and where I live (Baja) powder burners are not an option. I got into airguns years ago down here with a 22 RSW 48 side cock in . It is very accurate and I took rabbits out to 60 yds. My friend want one for his farm so I gave it to him. Then I started trying the break barrel guns and never found one to hold zero for me. About 2 weeks ago I brought down a 177 Marauder. OMG I haven't really gotten to know it yet but everything about it is awsome. The first time I shot it I thought there was something wrong with it because it is so quiet. When I checked out the target I saw the pellet had passed thru 3/4" ply backing at 30 yards. Compaired to a spring gun there is no kick which means the scope will hold zero. With a PCP airgun it really doesn't get any simpler. Air it up and shoot. I have an air bottle so that makes it that much easier. I'm getting about 30 strong shots before I top off the air at a time. I bought 3 magazine for it that hold 10 shots each so that works out well. One frustrating thing about airguns is that each one has a pellet that it will shoot really well. I have a pretty good selection of pellets built up over the years so I'm trying to find the one that will give me a dime group and 25 yards. That's both fun and frustrating. This is only my 2nd post so if there is any interest I'll continue post my learning experiences as I go. Oh, yesterday a couple colladed doves (concidered a pest) landed out beyound my targets and I took shot and dropped it like a stone. the seconde one just looked around. That's how quiet this rifle is.

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#10 russinbaja

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Posted 08 March 2014 - 02:22 PM

Having a lot of fun bunching paper. Not getting the dime size groups I drempt of but 25¢ groups at 25 yards is just fine with me. Only a few collard dove here now but I managed enough to cook up. I have some raspberry chipotle sauce and thought that sounded good for a marinate. I added sherry, orange juice, garlic, green onions and salt & pepper. Let it soak over night and cooked the whole thing on low heat for an hour. I'd do that again. I breasted the dove before soaking them. I read the Marauder forum and many folks there modify their marauders. I'm happy right now with how mine shoots right out of the box.






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