APTA-tude adjustment

I haven't used my bigshot since getting an APTA.

I keep it for back-up.

I'm generally aiming for 60-100+', either for a high TIP or a shot up and over a tree's top, depending on the day.
 
I’ve been working with Nick and Luke to get “tighter groups” with the APTA. This vid shows my latest configuration.

It isn’t a product, you can’t buy it and it’s not even a good idea for a product because it’s so customized to me personally. Nevertheless, I’m absolutely convinced that these “projectile” systems will be the wave of the future. For years, I’ve been proud that I’m getting better every year with my slingshot --- then I realized that THAT’S THE PROBLEM!

Go with a projectile system and you can be deadly (professional) on the first day you pick it up.



parental alert: popcorn, 2 beers



OF
 
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What a great video and exhaustive look at the APTA.

Is tree stuff going to adopt your innovations?

BTW I think u could've one-timed that crotch with my bigshot ;)
 
Thanks for the comment, Tree. I really don't know what TS is going to do ... there's way more work to do to turn this into a real product. And it's not clear what the market really wants to buy. Make yourself heard ... !

If your comment was to suggest hitting that branch was an easy target, let me go you one better: if you CAN’T hit that branch with either an APTA or a BigShot, you should consider re-assigning yourself to helping out around the chipper. Or worse, spending your time making YouTube videos!

That shot was not to hit the branch but to demo the precision of the shooting groups. I called the target to be six inches right of the trunk. I’m guessing it was wide right by eight inches or so.

If anyone could come up with a tool that a new user could put a bag through a hula hoop consistently, I’m guessing we’d all say that’s pretty awesome. There's still a lot of work to do here.

Tom
 
oldfart said:
Thanks for the comment, Tree. I really don't know what TS is going to do ... there's way more work to do to turn this into a real product. And it's not clear what the market really wants to buy. Make yourself heard ... !

If your comment was to suggest hitting that branch was an easy target, let me go you one better: if you CAN’T hit that branch with either an APTA or a BigShot, you should consider re-assigning yourself to helping out around the chipper. Or worse, spending your time making YouTube videos!

That shot was not to hit the branch but to demo the precision of the shooting groups. I called the target to be six inches right of the trunk. I’m guessing it was wide right by eight inches or so.

If anyone could come up with a tool that a new user could put a bag through a hula hoop consistently, I’m guessing we’d all say that’s pretty awesome. There's still a lot of work to do here.

Tom
Click to expand...
Tom, thanks for your detailed video of the OF air cannon. It was very informative and I like the idea of the red dot and mortar position since the trees I must shoot at are Ponderosa pines that are over 100' and are dense enough that I must shoot up at a steep angle.

I had some questions about the volume of the air chamber. According to my calcs the area of a cross section of a 1" pipe is approx. .79 sq. in. whereas the 1-1/2" area is 1.77 sq. in. So a 50% increase in diameter causes the area to more than double, I show the volume of 2' of 1.5" pipe to be just over 42 cu. in. To equal that the OF model's pressure chamber would have to be around 52" long.

I am guessing your models performance has alot to do with your use of CO2 cartridges. If I use compressed air what length of 1" do you recommend? Thanks.
 
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Great comment. Calcs are correct.

The "sweet spot" of my pressure chamber is 31 cuin or 36" x 1" Scd40 aluminum, pumped to 130 psi or one 12g cartridge. I got to that number by starting with a 72" chamber and lopping off 6-12" at a time and running shot tests. Here's what I learned:

1. You get different results depending on whether your using a bike pump or a cartridge. With the pump, you fill the device to a target pressure you see on the dial. With the cartridge, you fill from a fixed volume on gas.

2. Beyond a certain length, a bigger pressure chamber doesn't get you much. It adds size and weight and actually degrades shot performance, but in different ways.

3. On a pump, bigger volume means more time/strokes/effort to fill a big chamber to a target pressure. BUT you don't get any benefit for your extra work because, depending on barrel length and bag weight, the bag gets out of the muzzle before the exta energy can get on the bag. The oversize chamber doesn't hurt, it just makes you work harder.

4. On a cartridge, the oversize chamber hurts you by reducing the shot pressure. Surprisingly, as you shorten the pressure chamber, performance goes up dramatically, but only up to a point. You can actually hear this when you shoot. The sound goes from a "shoving" sound to a sharper "punching" sound. You start splitting bags.

5. During a shot, the bag inflates like a balloon due to the differential pressure across the bag. Halfway down the barrel, half the bag feels 150 psi while the other half feels atmosphere at zero. Air flows into and out of the bag, but not at the same rate so the bag inflates. This is actually very desirable ... It improves the seal to the barrel wall so you do't leak energy around the bag and it guides the bag better to stabilize it as a projectile. But there's a limit ... The bag rips at the seams. Bags are super strong in their traditional pulling direction with the ring. The inflating force stressed the bag across the seam instead of along the seam.


So what's up with all this?. The stock TS chamber is 22" long or about 1/3 larger than my 31 cuin "sweetspot". After they went with the butterfly valve, I installed the valve and cut 4" off their pressure chamber. Shots on cartridges got dramatically better; and it was faster to pump manually. BUT I didn't like it. My hand position to the valve wasn't as good and it made an Oldfart bend way to much to sight and shoot from the mortar position.

For a one-piece unit used with a pump, I think TS has got it exactly right. If you want cartridge option and/or the mortar position, I like the 36 X 1 chamber.

One very last thing ... And I haven't published this ...
Late last summer I started fooling around with another wrinkle: A 36" barrel. Remember, once you've committed to a 36" chamber, there's really no penalty to trying a longer barrel ... It all goes in the same case. I THINK I was seeing better accuracy or "tighter groups". Maybe. A little. But I didn't have much time with it before the winter came in. If it turns out to be true, the improvement will be marginal, not dramaric.

Hope this is useful. I'exhausted from all the typing and looking for the Pi button on my calculator.

Tom
 
Very informative and really saves the rest of us a lot of heavy lifting... or thinking, as the case may be... I have been thinking about ordering some cartridges, for when I forget the pump or feel too lazy to use it. But, it would seem that I'm probably better off just using the pump with the stock TS device. But, I am interested in knowing... if I assume the 12g cartridges will not perform well, what about the 16g cartridges? With a stock APTA, will the performance be satisfactory? I'm curious as to whether you have tried this.

Again, great post with very informative content.
 
oldfart said:
Great comment. Calcs are correct.

The "sweet spot" of my pressure chamber is 31 cuin or 36" x 1" Scd40 aluminum, pumped to 130 psi or one 12g cartridge. I got to that number by starting with a 72" chamber and lopping off 6-12" at a time and running shot tests. Here's what I learned:

1. You get different results depending on whether your using a bike pump or a cartridge. With the pump, you fill the device to a target pressure you see on the dial. With the cartridge, you fill from a fixed volume on gas.

2. Beyond a certain length, a bigger pressure chamber doesn't get you much. It adds size and weight and actually degrades shot performance, but in different ways.

3. On a pump, bigger volume means more time/strokes/effort to fill a big chamber to a target pressure. BUT you don't get any benefit for your extra work because, depending on barrel length and bag weight, the bag gets out of the muzzle before the exta energy can get on the bag. The oversize chamber doesn't hurt, it just makes you work harder.

4. On a cartridge, the oversize chamber hurts you by reducing the shot pressure. Surprisingly, as you shorten the pressure chamber, performance goes up dramatically, but only up to a point. You can actually hear this when you shoot. The sound goes from a "shoving" sound to a sharper "punching" sound. You start splitting bags.

5. During a shot, the bag inflates like a balloon due to the differential pressure across the bag. Halfway down the barrel, half the bag feels 150 psi while the other half feels atmosphere at zero. Air flows into and out of the bag, but not at the same rate so the bag inflates. This is actually very desirable ... It improves the seal to the barrel wall so you do't leak energy around the bag and it guides the bag better to stabilize it as a projectile. But there's a limit ... The bag rips at the seams. Bags are super strong in their traditional pulling direction with the ring. The inflating force stressed the bag across the seam instead of along the seam.


So what's up with all this?. The stock TS chamber is 22" long or about 1/3 larger than my 31 cuin "sweetspot". After they went with the butterfly valve, I installed the valve and cut 4" off their pressure chamber. Shots on cartridges got dramatically better; and it was faster to pump manually. BUT I didn't like it. My hand position to the valve wasn't as good and it made an Oldfart bend way to much to sight and shoot from the mortar position.

For a one-piece unit used with a pump, I think TS has got it exactly right. If you want cartridge option and/or the mortar position, I like the 36 X 1 chamber.

One very last thing ... And I haven't published this ...
Late last summer I started fooling around with another wrinkle: A 36" barrel. Remember, once you've committed to a 36" chamber, there's really no penalty to trying a longer barrel ... It all goes in the same case. I THINK I was seeing better accuracy or "tighter groups". Maybe. A little. But I didn't have much time with it before the winter came in. If it turns out to be true, the improvement will be marginal, not dramaric.

Hope this is useful. I'exhausted from all the typing and looking for the Pi button on my calculator.

Tom
Click to expand...
Tom, thanks so much for the detailed info. Most helpful.

Regarding the splitting bags. A number of the recreational air cannon users are using plastic grocery bags as wadding. Seems to me that might solve the bag ripping condition. At $15 a pop that could add up quick. How much pressure did you use when the bags ripped or did the seams just weaken with use?

Also, has your red dot held its zeroed in setting or has the recoil moved it off? What make did you use?

Accuracy and bag punching power is probably going to be critical for efficient use with my Ponderosa pines because there are no nice open forks to aim at. The whorls of limbs are typically 12" to 24" apart depending on annual rainfall and the effective openings to target reduce the closer you stand to the trunk. Like the difference in shooting through a ladder from a distance vs. trying to shoot up through one while standing next to the bottom.
 
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JeffGu said:
Very informative and really saves the rest of us a lot of heavy lifting... or thinking, as the case may be... I have been thinking about ordering some cartridges, for when I forget the pump or feel too lazy to use it. But, it would seem that I'm probably better off just using the pump with the stock TS device. But, I am interested in knowing... if I assume the 12g cartridges will not perform well, what about the 16g cartridges? With a stock APTA, will the performance be satisfactory? I'm curious as to whether you have tried this.

Again, great post with very informative content.
Click to expand...
Jeff, a 16g cartridge works fine with a stock APTA. But the $/shot is about double over a 12g. But th Zefal connector is small, cheap and makes perfect sense as a backup.
 
gpick said:
Tom, thanks so much for the detailed info. Most helpful.

Regarding the splitting bags. A number of the recreational air cannon users are using plastic grocery bags as wadding. Seems to me that might solve the bag ripping condition. At $15 a pop that could add up quick. How much pressure did you use when the bags ripped or did the seams just weaken with use?

Also, has your red dot held its zeroed in setting or has the recoil moved it off? What make did you use?

Accuracy and bag punching power is probably going to be critical for efficient use with my Ponderosa pines because there are no nice open forks to aim at. The whorls of limbs are typically 12" to 24" apart depending on annual rainfall and the effective openings to target reduce the closer you stand to the trunk. Like the difference in shooting through a ladder from a distance vs. trying to shoot up through one while standing next to the bottom.
Click to expand...
Gpick, I've tried different waddings from a handful of leaves to some very nice cylinders cut from closed cell foam. Generally, I'm not a fan because 1) they're not needed for normal shots and 2) I don't like chasing the foam disk across the yard on a windy day. But, if you are going for serious height, the wadding lets you crank up the pressure without splitting the bag. It's not exact, but without wadding I would see bags fail after about a dozen shots at 160psi. They would fail after 1-3 shots at 200psi.

If I was building for max height, I would go for:
42 X 1 chamber
Steel, not aluminum
Ball, not butterfly
Pressure relief poppet valve at 225 psi
Closed cell foam wadding


Regarding the alignment on the Reddot, here's what worked for me:

Use a picatinny rail with a curved bottom. The rail will self-align down the barrel to get close enough so you can zero with the wind age/elevation screws built into the Reddot.

I used a tool called a ClampTite to wire the rail to the barrel. Google it. Nice, neat, secure, right through the rail slots. Don't drill into the barrel ... It will abraid the inflating bag.

Once it's mounted, I bore sight with a laser torpedo level. Only takes about 5 minutes in the basement. I re-checked four times last summer because I was taking so many test shots. Dead nuts, never had to make an adjustment. Compared to a shotgun recoil, the Reddot doesn't even know it's been taken out of the box.
 
oldfart said:
....If I was building for max height, I would go for:.....
Click to expand...

Wow, oldfart, you have done a tremendous amount of research and work on the APTA. Thanks! Though I started by using one of Nick's first steel ones, I never delved into it to that degree. But what I did find is that if you are going for maximum height a longer barrel will give more height per psi. A one foot increase in barrel length will make a noticeable difference. That said, though I use a three foot, 1 1/2" chamber, because I had trouble turning the valve with a shorter chamber, I have a two foot barrel on mine and can still shoot a 12oz bag over the top of any tree in Montana with it.
 
Thanks oldfart, "even a blind squirrel finds a chestnut" :sisi:. One time I was taking a shot and my line got wrapped around the handle grip and snapped it right off, narrowly missing my hand. When I first got my apta I was so excited to use it I tied my slip knot backwards and well..as you might guess it flew great :rolleyes: didn't find the bag til spring after the snow melted. Cant wait to upgrade!
Are there any non lead bags that shoot well?
 
oldfart said:
They would fail after 1-3 shots at 200psi.
Click to expand...

What bags have you had fail? I commonly use between 150 minimum and 200psi and have never had an issue. Probably have at least 60-80 shots on my first set of 2 12oz Weaver premium (as recomended). That's still with the old ball valve aluminum version.
 
Sonshine, we've had the same experience. With the ball valve, I used 160-200 and never broke a bag. The valve geometry "ramps up" the pressure and accelerates the bag more gently, but at the cost of reduce range and wider groups. The butterfly shoots higher (and with less variability) so you can/should back off a little on pressure. I dropped the pump to 100-165psi and the cartridge from 16g to 12g. The bags are OK and, additionally, it fits with the lower pressure rating on the butterfly (175psi).

DSMc, you mentioned the 3' barrel ... just by coincidence, the 3' barrel+butterfly+3'x1" chamber seems to set up so that the pressure gauge on the bike pump pretty nearly acts as a height gage in feet (!).

I've used both Weaver and Stein, both about equal for durability. I don't know anything about non-lead shot.

OF
 
Wow, oldfart, this is a really great post, and a great piece of information. Having an APTA set up so that there is an almost direct correlation between psi pumped and height achieved would be really cool, and helpful, too. Combined with one of those hand held tools that allows you to determine the height of a tree would create a system that would allow a climber to achieve the height of throw needed with minimal wasted effort.

Thanks again for this post, and for doing all of the research that went into it.

Tim
 
[QUOTE="TimBr, post: Having an APTA set up so that there is an almost direct correlation between psi pumped and height achieved would be really cool, and helpful, too.

Tim[/QUOTE]

Tim,
Thanks for the good words and the enthusiasm but it's not that accurate ... only a nice guide to get you into the ballpark. All in, the biggest shot variable left with my APTA is the skill/judgement to know how much loft to fire into the shot. You can aim left/right of a branch union to a few inches but you're still aiming 3-5 feet above a branch. The good news is that it's repeatable ... if you aim carefully and see your shot go low by 18", you can pick your next spot 2 feet higher and the next one will zing just over the branch.

OF
 
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