Question for the Mad Scientists here

[MJP]

Whatta... why use m14 threads then? Now I'm confused. Just adding complexity and machining cost to make these things.
So it's m14 and then it opens up to 16mm, then back to m14 again? Did they bother to radius the corners?
M18x1 and O-ring after the thread would make much more easier to manufacture and you could use readily awailable tubing.
Marko

[rsterne]

Yep, 14mm up to 16, back to 14..... Moving the O-ring inboard of the threads would have cost length, and therefore volume inside.... Since the O-ring is at the outer end, outboard of the threads (which are under pressure), they didn't want to cut into the wall by using 18mm threads in a 16mm ID tube.... I think the current arrangement is shorter overall, for a given internal volume, which is why they used it....

Radius?.... I doubt it, since the inside looks like it was cut in a single pass with a dull tool bit.... you have NO idea how rough it looks.... 

Bob

[MJP]

Well there is 6 threads on those now, it doesn't take so much more room to make it the other way around, 1mm lip before the o-ring to keep it in place when cart is empty, and the thread can start just about 1mm after the o-ring.
And converting to different valve design you don't need the tube, just a stem.
Darn, now I think I hafto make one or two of those carts to test.
Marko

[Privateer]

https://patents.google.com/patent/US20150013656A1/en

[MJP]

Thanks Jeff.
Well that is revealing, not much room for air is there... What was the moment in time they decided to go with this design. The cutaway tells it all, not much to do here but use the outer dimensions and forget the internals if you want any power out of it.
This'll be a long build for sure, and couple of projects before this.

[Privateer]

Part # 31 is not correct for the actual carts.

I'll see if I can draw the proper image of the current parts.

[rsterne]

Correct, Part #31 has the O-ring in contact with the transfer tube (54) AND the inside surface of the front end (45-46), which is flat on the back, flush with the inside of the threads, not recessed.... The actual #31 is a brass disc, 1/8" thick, with a lip around the outer edge to contain the O-ring, which is slightly proud of the end of said disc.... The O-ring used is a # 010, which is 1/4" ID x 0.070" (3/8" OD), and seals in the inner corner, where the transfer tube slides through the front end housing.... it is a dynamic (sliding) seal.... The O-ring is held in contact with the front end by the valve spring, and air pressure....

Bob

[Privateer]

Another part that may not be correct is the transfer tube part  #54
I have 2 different versions.

The best version has the larger 4 holes and some what beveled on the edges.

[Privateer]

I need to do some checking on the cart and how much space is there to work with but here's another Village Idiot question.
 

Say I could add a washer to kind of extend the cart?
I can add the same washer thickness to the barrel to allow for a proper fit.
That would increase the inside volume a tad.
Say I cut the Delrin seal back to add volume also.
A slip fit spacer to keep the pressure for what I remove.
If the Delrin proves to weak? I have Peek 1000
So something like this.

[rsterne]

You have created another leak path between the front housing and the washer, the O-ring will now seal between the washer and the main body tube.... You might be able to do it by using a thinner O-ring gland so that the O-ring squashed out wider and could seal both gaps.... but the clearance between the washer and housing would have to be less than 0.003" or the O-ring will extrude into it and fail....

Yes, you could shorten the Delrin seal, providing you can still create a seal between it and the transfer tube it threads onto.... However, you are only talking maybe a percent increase in volume....I doubt your Chrony could consistently measure the gain....

Bob

[MJP]

One thing you can do, turn down part 59 to spring od and taper the delrin to the same dimension leavin a constant radius to the sealing surface. It should increase flow.

Marko

[rsterne]

Yep, I noticed that when I first saw the cartridge.... It might reduce turbulence at that point, but would do nothing for the flow at the other end of the poppet (Delrin).... Basically, it couldn't hurt....

Bob

[oenomaker]

Has anybody tried going to the manufacturer with this information yet and asking for an explanation?  My "couple" of questions would be:

-Why do you publish such a high fps for a given weight bullet, when real world tests are not corroborating?
-Why is there so much leading in the breech end of the barrel?  Bullets getting "shaved" definitely increases the drag on the bullet as it passes through the barrel and could definitely affect performance.
-Why are their two different designs of the cartridge?  One has a shorter spring, a groove, and smaller transfer ports south of the delrin seal, while the other has a full length spring. 
-Which cartridge is the "current version" that is being sold to customers, and are the two versions marked different in your inventory so that you know what you are sending people?
-Why are there no videos showing a live chronograph test with common pellets (say JSB .35's or the nosler ballistic tips)?  This may dispel rumors about how underpowered the gun may be.
-Why is the transfer pin so rough on the inside?  Do you manufacture in house or do you outsource some of your parts?  If the transfer pin was chrome plated I would imagine that the inside was as well, so it should have been smooth.  (This doesn't surprise me though as a Hatsan owner my 135 in .22 had a significant amount of factory negligence when it came to the finish of many of the components.  When I pulled the piston seal off it had flecks of metal embedded in the plastic!)

I don't think anybody would get anywhere asking questions about the design and why they went that way rather than another.  If they have the time/effort/money to patent the cartridge then it had been in the design and prototyping phase for a long time and they are obviously heavily invested in their "invention."  It would be like questioning somebody why they chose to raise their children they way they did lol.   
 

[MJP]

Well their invention is not theirs to begin with, they just made it bigger and used the most inefficient way to do it.
Those aircartridges go way back to old English patent around 1872 so it's nothing new. That is why I have been wondering why that design, and not something a bit more modern?
Legal issues, easy manufacturing and more profit?
I'm not bound by any of those so let's see what can be had with some time.

[oenomaker]

Its a shame they didn't spend more time in R&D before launching the product.  Talking to David Priestly the owner/inventor on the phone made me realize that he really thinks those MAC cartridges are the best thing since sliced bread.  I doubt they would have a significant overhaul of the cartridge ever.  And the fact that they didn't put a safety on the gun is just plain negligence in my mind...  If I were ever to take that gun into a hunting situation I would want it to be ready to go at a moments notice, and I don't like the idea of walking around with a loaded gun ready to go off without the option of a safety.  I mean c'mon how hard would it be to engineer a safety into that thing!