Air Gun Home :: View topic - Marauder tuning graph, just a start! 3 pellet weights.

69Hotrod69 · Veteran Member

Did some Chrony testing need to do more adjustments to see whats really going on but at least it's a start.

Hopefully Bob, with his experience let me know where I should start making changes. All input will be greatly appreciated.

69Hotrod69 · Veteran Member

Looking at the data it seems to me that the settings are to high for the pellet weights?

Any ideas?

rsterne · Moderator

You basically have too much hammer strike for the pressure.... It is relatively (but not completely) independant of pellet weight.... You are striving for a shallow curve with the initial velocity starting about 4-5% below the peak velocity.... climbing slowly and then as flat as possible across the top.... and then gradually dropping to whatever you feel is a suitable velocity to end the string at.... I use a 4% drop (ie 96% of maximum) for the minimum velocity I figure is workable.... but you will require less variation than that at extreme ranges and can use more at close ranges or when just plinking.... Rather than reduce the hammer strike, you could, of course try increasing the fill pressure.... The curve for the 21 gr. pellets looks fairly flat at your 2500 psi starting pressure.... With those pellets, you would end the string at about shot 16-17 (96% of 830=797 fps).... Starting from 3000 psi you might get about 30 shots averaging ~31 FPE.... Mr. Green

There is a slight effect due to pellet weight.... For instance, if you set the gun up for a curve as described above with 18.1 gr. JSB Exact Heavy (my favourite pellet for BC and accuracy).... you will get a curve that is shorter (ie fewer shots) with a light pellet and it will tend more towards the type of curve you have now.... the first shot being (nearly) the fastest.... If you use a very heavy pellet such as an EunJin then the whole curve will shift towards a lower pressure and you will usually gain shots in the string.... You may not be able to use the same starting pressure, but you will probably be able to use a lower ending pressure.... Alternately, of course, you could crank in a bit more hammer hit (spring preload and/or travel) and get more power but fewer shots.... For a given pressure range, lighter pellets require a lighter hammer hit.... Wink

BTW, if you use an image hosting service such as photobucket, you can post full size images in your thread....

Bob

69Hotrod69 · Veteran Member

Thanks Bob,

Your Help is allways Invaluable! I got the idea now, just need to start playing with adjustments.

I'm going to try filling to 3000 and see what the string looks like. I love the JSB Heavys also, but this Marauder even with the new crown doesn't seem to like them Evil or Very Mad

I was initially trying to get 30FPE with the JSB Heavy but since it won't shoot them I'll see if I can't get her tuned for the Kodiaks.

It's kinda funny my R3 2260 Carbine shoots almost anything since I worked the barrel. It being regualted at 1900PSI it is a tack drver at 25 yards it's only limitation is my ability to hold her still.

Opened a photobucket account will start making my posts look a little better.

Back to the Chrony!

packrat · Senior Member

Actually, all you have to do is click on the picture and it goes to full size...nice looking graph BTW, easy to read.

sniper · Silver Status Member

I'm currently without a scuba tank. My next one will
hopefully be bigger than the last.
I look forward to finally doing some
adjustments on mine since I've had it almost 2 years. Rolling Eyes

Good graph!

69Hotrod69 · Veteran Member

Packrat, Bob was just following up on a question I had asked him in a PM about the Full size image post. Smile

Sniper, Your in SoCal area right? By the way I hand pump, Embarassed

its good exercise and I cant afford Gym membership cuz of my new found obsession with air rifles. Laughing

sniper · Silver Status Member

Yeah, I'm a freeway trip from you.scuba Tanks are like "cruise control".
once you have it you never go back.

69Hotrod69 · Veteran Member

I was thinking about getting an old scuba set up 3000psi and just hand pumping to get to 3000 after initial fill. I dont mind 50 or so hard pumps but I hate the easy pumps before I get to around 1800psi.

sniper · Silver Status Member

If you're gonna go with tank go top shelf. I did that very same thing with a cheap used 3000psi tank. now because of it's age and grade of metal my dive shop won't fill it. I have it on consignment for less than half of what I paid for it. Evil or Very Mad

Since I will own pcp's forever I wish I would've saved longer and bought a really nice tank. that's this year. I'll be lucky to be shooting my mrod by summer. Evil or Very Mad

filling with a tank takes all of 7.5638 seconds. Laughing

donec · Senior Member

69Hotrod69 · Veteran Member

I used to dive in the USN so I know a Little about tanks my old navy buddy owns a dive school so I should be able to get a descent aluminum for next to nothing. You must of had one of the old 70,s early 80's bottles they had cast the aluminum incorrectly and the bottles are illegal for shops to fill now. A good Alum bottle will last a very long time as long as the threads don't get corrosion thats the main reason they fail visual. I cant see paying 600+ for a set up, but then again I'm a stay at home dad amd don't have that much income for hobbies.

sniper · Silver Status Member

1979 to be exact. Crying or Very sad

69Hotrod69 · Veteran Member

Bummer!!

69Hotrod69 · Veteran Member

The only pellets this thing shoots is Kodaks/Barracudas! and I'm not that impressed with those still get zingers. My 2260Barrel reworked the same as this consistanly gives ragged holes at 25yds. I think the choking must not be very good?

The tune however looks Good. and its in the range I like to pump in 2000-3000. Over 30shots at 30+FPE Twisted Evil

Now if I can get it to shoot straight I'll be a very happy man.

Bob was right the 3000PSI looks very good for these settings.