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Pellet gun tuning

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Pellet gun tuning

Unread postAuthor: sputnick » Fri Jan 23, 2009 4:55 pm

Hey everybody, a year ago I picked up a Gamo Expomatic 2000 (springer) for free at a dump, in perfect working order, with a decent scope. It has served me well so far, but now that I am comfortable with it, taking it apart, putting it back together, cleaning and shooting (penny at 60 feet consistantly) I want to see if there's anything I can do to ramp up the power and distance.

So if you have tuned an pellet gun, or know how to, let me know! I would love to see what suggestions you have.

I will post some pictures of my gun later, its a real keeper for a dump find...

Edit, PICS!!

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A better view of the homemade muzzle brake, (pre paint)
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The stock is pretty dodgy in some places,
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Yea so as you can see, a black/woodland camo paint job is in order, depending on how lazy/broke I am this weekend.
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Last edited by sputnick on Fri Jan 23, 2009 5:44 pm, edited 1 time in total.
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Re: Pellet gun tuning

Unread postAuthor: jackssmirkingrevenge » Fri Jan 23, 2009 5:19 pm

sputnick wrote:a year ago I picked up a Gamo Expomatic 2000 (springer) for free at a dump


Whoever put it there in the first place had the right idea ;) flog it on eBay and buy a decent German or British rifle ;)
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Unread postAuthor: Moonbogg » Fri Jan 23, 2009 5:22 pm

I have never tuned a gun but I have owned 2 precision rifles (Beeman Kodiac & Beeman S1). So I have a little experience. I know manufacturers and distributers often offer upgrade main springs or even sometimes a gas spring upgrade. In your case, simply replacing the old spring with a new one of the same type would likely result in power gain, after it breaks in of course.
Also, something else you could do since you got it for free, is sell it and use the money to go toward a more powerful gun.

EDIT:

jackssmirkingrevenge wrote:
sputnick wrote:a year ago I picked up a Gamo Expomatic 2000 (springer) for free at a dump


Whoever put it there in the first place had the right idea ;) flog it on eBay and buy a decent German or British rifle ;)


Can't sell air rifles on ebay...I tried :( I sold mine by going to an airgun forum and posting it in the for sale section. I got a call like HOURS later and sold it.
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Unread postAuthor: sputnick » Fri Jan 23, 2009 5:46 pm

Hey! Its not much, but it was still my first real pellet gun, It has sentimental value now! besides, if you look at the pics, I dont think anyone would pay decent money for that POS of a stock finish...
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Re: Pellet gun tuning

Unread postAuthor: Ragnarok » Fri Jan 23, 2009 5:51 pm

sputnick wrote:So if you have tuned an pellet gun, or know how to, let me know! I would love to see what suggestions you have.

My TX has a few mods I've done myself, but they relate to getting more accuracy out of it, not more power.

However, I can make suggestions as to how to get more power out of it. What's it's current spring dimensions and compression? - and what's it currently putting out?
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Unread postAuthor: sputnick » Fri Jan 23, 2009 5:59 pm

Well, DO they need to be exact measurments? because I took it apart about an hour ago for cleaning and thorough lubing, the spring is about 6 inches long, around an inch diameter, the wire looked to be a little over 2mm's and Im not sure what you mean about compression... Its a strong spring to be sure, I could push it down only about half an inch with my thumb when puting the stopper at the back into position again.

I don't know the velocity, I do not have a chrony (could be a song it rhymes so well...) and I'm a little apprehensive of the hang time system, firing straight into the air goes against everything I have learned about gun safety.
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Unread postAuthor: Ragnarok » Fri Jan 23, 2009 6:20 pm

sputnick wrote:Well, DO they need to be exact measurments?

It's nothing that has to be done, but knowing that kind of thing makes it easier to guestimate how much power can be squeezed out of the rifle.

However, yes, if it's being done, it does need to be pretty precise, particularly the wire diameter measurement - which because in the formula it's used to the 4th power, a 10% error in it results in a 46% mistake in the end result.

I'm not sure what you mean about compression.

Compression is both the preload on the spring when in an "uncocked" position (relative to it's totally unloaded length), and the further compression applied on cocking - both distances, not forces.

I don't know the velocity, I do not have a chrony, and I'm a little apprehensive of the hang time system, firing straight into the air goes against everything I have learned about gun safety.

No need to use the hang time method. Much better choice is to get some kind of recording device, set it to record in the middle of your range, fire at something that makes a noise, then take the resulting audio file, open it in something like Audacity, measure time from firing to impact, divide the distance by that number, and you'll get a reasonable estimate.

Then work out the kinetic energy from the velocity and pellet mass.
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Unread postAuthor: jor2daje » Fri Jan 23, 2009 8:51 pm

I know exactly what you mean with wanting to keep a gun you got for free, my friend gave me his old $200.00 gun for 20 bucks. The only thing I would do was get a new scope, and maybe refinish your stock.
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Unread postAuthor: sputnick » Fri Jan 23, 2009 8:56 pm

Yea, this weekend I'm probably going to get some balck spraypaint, and redo it mall ninja style :lol: It's either that ot woodland camo, but I really dont want to dump the money on all the paint I won't use ever,

Also I want to build a bipod (more function than looks) and some form of ammo reserve in the stock, if I can find a way to make it looks decent. any suggestions woul be great :wink:
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Unread postAuthor: jor2daje » Fri Jan 23, 2009 10:00 pm

I would suggest against a bipod unless you can make it sturdy but very light weight. I built one but it seemed more of a hindrance than an advantage, bipods get in the way when your breaking the barrel. And if your firing prone then you either have to roll over or get up to cock and reload, and that gets pretty obnoxious.

And on the stock why dont you just sand down and re varnish i think the wood look is pretty cool.
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Unread postAuthor: Ragnarok » Fri Jan 23, 2009 10:13 pm

I'd suggest against a bipod full stop. Springers don't like them because of the spring vibration on firing. Add in a bipod and that vibration has now got a hard surface to jar against and disturb your aim.
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Unread postAuthor: sputnick » Fri Jan 23, 2009 10:16 pm

I almost never fire from prone, I find the breakbarrel alone a great hinderance, for any accurate shooting it's usually me on my deck, on the bbq lid with a towel over my arm for extra control, with that I can shoot the penny at over 60 feet, I want to be able to shoot from anywhere steadily, and the jarring is pretty much the same no matter what you shoot from, and after the pellet has left, I don't care what happens, I take upwards of a minute for each shot when making precise shots.
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Unread postAuthor: jor2daje » Fri Jan 23, 2009 10:43 pm

You could build a bipod with springs that would absorb the shock, maybe some stiff rc car shocks, they are light weight and have good shock absorbtion you could extend them with something light like aluminum. And if you used some springs you could make it lock up against the barrel if you wanted.
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Unread postAuthor: Ragnarok » Fri Jan 23, 2009 10:47 pm

sputnick wrote:I want to be able to shoot from anywhere steadily, and the jarring is pretty much the same no matter what you shoot from, and after the pellet has left, I don't care what happens, I take upwards of a minute for each shot when making precise shots.

No, you're misunderstanding. This vibration happens before the pellet has even left the barrel, and with a bipod it has an outlet to disturb your aim and thus POI unpredictably.
Using a bipod will almost always destroy a springer's accuracy, and the effect is particularly prevalent on older or lesser quality springers.

My TX might just be able to get away with it (although I don't try). It's a good example of a good make, and I've got anti-torque and damping adjustments in it.

Your Gamo doesn't have these things on its side.
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Unread postAuthor: sputnick » Fri Jan 23, 2009 10:49 pm

When I make the bipod, I will probably use CPVC, cheap, strong, and thick. I'll just start with 3/4 up near the gun, with 2 springs in it, then 1/2 against the springs inside the 3/4, and bolted but on slides so they can move, then I have to make them fold , Rag, if I chose the right springs, do you think it will work alright to dampen a bit? haha I have a long weekend ahead of me, I will keep everyone updated!
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