GTA
General Discussion To Gateway To Airguns => The Shop => : tjk September 18, 2009, 12:11:11 AM
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Here's a question that I've yet to find a deffinitive answer too. Say you have a Quest 1000 which is .177 caliber,...and a Quest 800 which is a .22 caliber,....Are the exit ports in the compression tubes the same size/diameter? Would making the port holebigger for a larger caliber barrel have any significant or detrimental difference with speed and power? Just thought I'd toss out this "trial-balloon" to see what the general concence's is. Thanks,tjk
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They port diameters are the same in both rifles. You'd gain only a few FPS by enlarging the transfer port.
I've done it on 3 or 4 different Quests and the effect was always the same. I believe the bit I used was 1/8 inch. Pretty much just slightly bigger than the port itself. I also chamfered the port on both side. The front was easy, but for inside the tube I had to make a tool to hold my countersink bit.
You don't want to go any larger than 1/8 ince or you'll end up loosing velocity.
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Here's a good link on transfer ports.
http://www.pyramydair.com/blog/2008/10/air-transfer-port-part-2.html
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I've messed with them also, did some B3's awhile back and as mentioned there's only a slight gain and past that it go's downhill.:( Ed
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My thinking is they are the same size , looking at the beeman rs two barrel rifles one in 22 and one in 177 they use the same power plant and just change the barrels using a set screw so they have to be the same I don't think crossman would do anytthing different why have to do a mch. change when you don't need to . Howie
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I agree with Howie. Doubt that the time would be taken to machine different diameters for .22 and .177 calibers. Primarily because it would involve extra steps. Therefore time. And time = money.
Also I have the dual barreled Beeman, with the .177 and .22 calibers and the powerplant works just fine for the two. Using the same port.
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We discussed this on the Diana Werke. Seems like the 34's, etc, use the same transfer port. From what I've read (in the link, above), you have to be really careful in tinkering with these. Not just increasing diameter but the configuration of the hole, front and back, as well. Kind of like reconfiguring a vortex. Some shapes are better than others.
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Thanks for the replies fellas. I thought about this from a rifle originally chamberred for .177 converted over to a .25 caliber barrel. Seems to me that the smaller port might not provide enough compressed air' impact' ( too much resistance in port size) on a much larger and heavier .25 cal pellet. Almost like shooting a 28 grainned .177 pellet through a Quest/Gamo, and the damage it could do to a main spring. Does this change the equation in my original question,...or is it still just a matter of the pellet/barrel ratio?!? tjk
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My thinking is and I could be wrong is the exit port is not that critical and by this I don't think we as layman we can't make a whole lot of difference to the rifle by changing the exit size I've tried this with a b3 a long while ago and it did make a little difference but I'm not sure it was worth the effort. The difference in fps from 22 cal to 177 or any other cal is mostly the weight of the pellet that controls the speed since you have to overcome the weight to get the pellet moving and then also to keep it moving so that is why the speed is lower in a 22 cal than a 177 but you make up for it on the other end with the ft.lbs. in energy. I've have tried the calculators and it doesn't work out so their must be a log. type scale. howie PS a 1/8 inch hole worked best on the B3 .