Air Gun Home :: View topic - Advanced concepts in QB-7x/2260 Mods

AdrianM · New Member

I am really new to the world of air rifles but I have a few ideas I would like to bounce off you guys that may make our guns better.

1. Right now barrells are secured by set screws. While it is nice that we can change barrels and calibers is this feature really necessary? I propose barrels be heated shrink fits into the breech. This would be a much more stable and well sealed system. No o-rings would be needed at all.

2. Right now we have a single gas port coming up from the bottom of the barrel. I propose the barrels be larger in diameter with a reduced O.D. behind the pellet (When inserted into the breech this reduced O.D. area allows gasses to flow all the way around the barrel to...3,4,5 or 6 .0625" x .125" oblong holes around the barrel forming a series of gas ports into the barrel. These muitiple gas ports would have much more flow than an enlarged single port and they would never catch and damage pellets like a too big gast port would.

3. What about using a stamped or machnied soft copper gasket instead of ice maker hose to seal the lower cylinder to the breech and barrel? The would need to be replaced every time you disassembled the gun but they would be very consistant in seal and internal dimension.

Let me know what you think?

Alstone · Moderator & Site Supporter

Hi Adrian welcome to the site, I think some of your ideas do have merit, the problem is to increase the number of feeder holes would put extra cost on the product, also the extra holes and associated machining would allow some of the gas to expand before it got behind the pellet, you need as little space as possible beteen the valve and the pellet, now if you could place the valve actualy on the holes things would be different, also slope the holes towards the pellet, then I think you would have a very efficient system, but again at extra cost this applies to shrinking the barrel in and replacing O-rings with copper washers. But good luck with your ideas.

AL

AirGunEric · Site Admin

Hello:

As well as the production cost elements which Al mentioned, there may be more:

1) Most guns nobody changes the barrel size much- certainly not the average buyer, and even in the "hobbyist" crowd- most guns retain their original barrels with some fairly common exceptions- i.e. Crosman 2240s and the like where one of the most common mods is installing a longer barrel. That being said, the easy removal of the barrel may have something to do with warranty expenses to the manufacturer. I'm not sure why this mindset would be applicable to throw-away type guns built these days (most Crosman's and Daisy's for example) where guns are more often replaced outright rather than repaired when under warranty- but in more expensive guns, perhaps to limit the service time barrels are set-up for faster removal rather than ultimate stability and sealing.

2) The idea of better/more efficient gas flow is always good, but on top of what Al had mentioned in respect to design- I'm wondering how much/how many pellets are really damaged by a large gas impact? Is this really a concern (it may be- but you don't hear much about it)?

3) Any method for sealing more effectively is useful. I think the common modification of using freezer/water line plastic is so the average "Joe" has easy access to it without having to be a machinist. And while a copper gasket would be better- depending on how it is used (i.e. set inside the port holes vs. a outer/surrounding seal) it could impede gas flow just as much as the plastic tubing once it is pre-loaded/clamped down. I think the bigger question here is "why do most guns manufactured use an o-ring or "soft" gasket in this application?" Probably back to Al's idea of cost- an o-ring squeezed between two openings is easy to install 'correctly' on a factory floor and is a very simple replacement once it is required.

Undoubtedly, there are all sorts of better ways of doing things- but they all need to be balanced out; part and production costs vs. actual improvement vs. the market the gun is addressing. So, a cheap pistol-type gun like the Crosman 2240- no real economics to it for a $50-75 gun. On a higher-end gun like an AirForce Condor at $800, or a Walther Dominator 1250 (which I believe will be in the same price range when it's available in the US) I would hope such ideas/changes are more readily integrated by the manufacturer.

AdrianM · New Member

Since many guys report a FPS incresed with longer bolt probes (to a point) and this creates more space behind the pellet I dont see how ring of smaller ports with a total flow greater than a single port could be bad.

I am a machinist and I have access to some pretty insane equipment. I guess I will just have to try a few things out to see what happens

Alstone · Moderator & Site Supporter

The problem is that all the extra porting and multiple changes in direction of the gas tends to interfere with the smooth flow, and therefore restricts the efficiency of the gas expansion as applied to Co2, that is why people tend to make the path from the valve to the pellet as smooth as possible, the reason that you get an increase in fps by extending the bolt probe is that the volume behind the pellet was not correct in the first place, but if the volume is to big there will be a pressure drop right at the time when you want everything you can get to move the pellet from its start position.

But certainly have a go no one gets anywhere without exprimenting and if you can get round the problems sucessfully good luck to you, and let us know how you get on.

AL

leadman · Veteran Member

the reason behind probe exstensions in the 22xx series is to get the pellet past the tp instead of sitting right above it