30 replies to this topic

[CaptainSlug]

This was inevitable. 2-inch ID plunger tube with 6-1/4" plunger stroke.

 

I'm starting to hate the 2-inch ID tubing though. The last two orders I received were quite varied in tolerances. If you intend to use this tubing for anything DO NOT GLUE YOUR PLUNGER HEAD PARTS TOGETHER.

You will have to take them apart several times and sand them down in order to get a good fit with the o-ring.

[Hunty Bunches Of Oats]

Has the smaller stock on your pump action variant been an issue in terms of comfort?

[CaptainSlug]

Even for someone as bony as me, nope. It's wide enough to feel fine. If you want it wider or more padded you can slide some pipe insulation over it.

[CaptainSlug]

I'm completely satisfied with how this performed at APOC. I used it for a third of the rounds and didn't have any issues. It's much lighter than any other homemade I've ever built, extremely easy to take apart, and I don't have to worry about it sitting in a car on a hot day (I can't say the same for my hoppers though).

 

I don't think there's anything I can change to the design. The only quirk to mention is that the screws at the front of the plunger tube that hold the bushing in need to be backed out a little before you can install a barrel because they stick inside the fitting just a hair when they're fully tightened down. With the pump-grip installed the phandle piece could also be much smaller than normal. It hit me in the face once or twice while I tried to use the iron sights.

[KaneTheMediocre]

Have you considered halving the draw for the 2" ID version?  I've had good results (=reliable consistent hopper performance) with 3-4 inches on 2" ID tubes.  The volume per length is almost exactly a factor of two greater so I use that as a guide.  I just don't imagine that the extra volume is helping you unless you have a 3' barrel and really want to put holes in people.

Oddly enough, despite the pressure per spring force being halved due to the larger tube cross section, I seem to get close to the same power with the same spring force, though I don't have rigorous measurements of either.  There may be some efficiency bonus related to the functional doubling of plunger speed.

[CaptainSlug]

The normal plunger stroke on the "2-11" style plunger tube is just over 4-1/2 inches. The stroke on the normal +bow plunger tube is 6-1/4 inches.

I came to the same conclusion you did when I was initially developing the 2-11. The extra volume meant that a longer stroke was excessive and I ended up cutting the spring shorter and shortening the stroke. I also got more predictable results using rubber washers than I did with o-rings.

 

However the tolerances on the 2-inch ID polycarbonate tube have gotten wider since then so I haven't been particularly pleased with that and it's something to be aware of. You WILL get a smooth surface and it will be perfectly round, but the ID is +- 0.050" for part number 8585K46. There's an alternate part number (9176T9) that doesn't list tolerances but I haven't ordered enough of it to evaluate it.

 

The 6-1/4" stroke 2-11 was a one-off thing for Gears. In a 1-to-1 comparison with a +bow plunger tube using a 10-inch barrel that one-off blaster was shooting an extra 10 or 15 feet. It obviously could use a much longer barrel, though I'm not sure what kind of pneumatic flow restriction limits may factor into performance.

 

Picking a larger plunger tube in order to obtain a shorter stroke length would be useful in certain design requirements. Say for instance wanting to ad a much stronger spring, then priming it with a 2-to-1 mechanical advantage gun tackle pulley. Or simply wanting a much shorter over-all blaster length.

 

A homemade Ultimator would be fucking awesome.