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Discussion Starter · #1 ·
GZK-1636 vs DK-1632

I have been enjoying the skinny DanKung 1632 tubing for quite a while now. My tubing bin contains some of the red version as well as the natural amber. I find the 1632 to be excellent for .177" BBs and 1/4" steel ammo. Speeds are very nice and the tubes are dead quiet to shoot.

This week I got my hands on some GZK 1636 to test out. My example is in the bright green color but it also comes in black. The 1636 should fall between 1632 and 2040 for performance. The 1636 has the 3.2 mm OD of the 1632 but the heavier 1.0 mm wall thickness of the 2040. This tube should perform better than the 1632 with heavier ammo and about the same with the BBs and 1/4" steel.

The 1636 was cut to match the 1632 measurements but it stretched a little. The 1632 was already broken in for the test.

Ammo = steel

Testing temperature = 68F

Draw length = 32"

Tube off frame for measurements

DK-1632

Tube measurements = 7 1/2" length, including 2 3/4" loop

Draw weight = 5.0 lb draw

.177" BB = 251 fps

1/4" = 229 fps

5/16" = 194 fps

3/8" = 165 fps

GZK-1636

Tube measurements - 8" length, including 3" loop

Draw weight = 6 lbs, 14 oz

.177" BB = 254 fps

1/4" = 234 fps

5/16" = 211 fps

3/8" = 182 fps

The 1636 is advertised as having "low temperature resistance". I'm now guessing that this means the tube should perform acceptably with temps down to 50F. I learned that this doesn't mean the tube is "anti-freeze" or "anti-cold". The tube failed the freeze test.

Testing at 28F temperature

DK-1632 --- 1/4" = 174 fps

GZK-1636 --- 1/4" = 182 fps

Once the above testing was completed, I shortened up the 1636 a bit and reduced the loop size. The draw weight came down a little and the speeds dropped a few fps.

GZK-1636

Tube measurements - 7 3/4" length, including 2 1/2" loop

Draw weight = 6 lbs, 11.5 oz

.177" BB = 251 fps

1/4" = 230 fps

5/16" = 209 fps

3/8" = 180 fps

My next test could be to reduce the loop size and shorten the 1636 to maybe 5 1/2" (580% stretch). But I'm looking for a tube that will give a long life so I don't think a super stretch will do what I want. A full loop set of 1636 should give nice performance with 3/8" steel but draw weight might be over my desired top limit of 8 pounds. I still might do these tests just for the sake of seeing the numbers. A comparison with Premium DK-2040 would be another interesting test for speed numbers.

It seems that the DK-1632 still rules as the best tube for BBs and 1/4" steel. Too bad it goes wonky in the cold.

The GZK-1636 appears to be a good choice for 5/16" steel. A 7 1/2 to 8 pound draw weight should put the speed over 220 fps with a 32" draw length.
 

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Discussion Starter · #6 ·
I accidentally worded the tubing description wrong. My bad for rushing at 1:30am instead of sleeping.

Brain fart = "The 1636 has the 3.2 mm OD of the 1632 but the heavier 1.0 mm wall thickness of the 2040."

Correct wording = "The 1636 has the same 1.6 mm inside hole diameter as the 1632 but it has a 0.4 mm larger OD (3.6 mm vs 3.2 mm). This results in the same 1.0 mm wall thickness as the popular 2040."
 

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UPDATE- More testing done this morning

I retied the 1636 tubes and tested again. The tube now feels about maxed out with the 50/50 taper and my 32" draw length.

GZK-1636

Tube measurements - 7 1/4" length, including 3 5/8" loop (50/50 taper)

Draw weight = 9.0 lbs

Draw length = 32"

Temperature = 68F

Ammo = steel

5/16" = 236 fps

3/8" = 201 fps
 

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Try some 1636 this weekend and didn't like it. Even though I tie an identical band set as my 1632 and shot 8mm steel frameless style all I did was bruise my finger so in the bin it went
 

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I will be picking up some 1636 soon, hopefully.

I really appreciate all the great info and knowledgeable people on here!!
 
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I was just looking over my results with Precise Yellow flatband and noticed that the 1636 performs very similar with 5/16" steel and similar draw weight. The 1636 was actually a few fps faster.

Precise Yellow Flatband

Band cut = 7/8" x 5/8"

Ammo = 5/16" steel

7 1/2" band length = 224 fps --- 8.75 lb draw weight

7" band length = 234 fps --- 9.25 lb draw weight

6 1/2"band length = 244 fps --- 9.56 lb draw weight

GZK-1636 Tubes

Tube measurements = 7 1/4" length, including 3 5/8" loop (50/50 taper)

Draw weight = 9.0 lbs

Ammo = 5/16" steel

5/16" steel = 236 fps
 

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Help me understand why there are no tests at 9lb draw weight with straight band set?

You pull to 9# with the back half single tube but not to 9# with single tube. This seems to be a common approach to testing pseudo tapers and I can not understand why. Is no one willing to pull tubes to maximum elongation unless pseudo tapered?

What happened to following the scientific method?
 

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Discussion Starter · #14 ·
Help me understand why there are no tests at 9lb draw weight with straight band set?

You pull to 9# with the back half single tube but not to 9# with single tube. This seems to be a common approach to testing pseudo tapers and I can not understand why. Is no one willing to pull tubes to maximum elongation unless pseudo tapered?

What happened to following the scientific method?
Your joking, right? The speeds for the flatbands increased 10 fps per half inch decrease in band length? A fairly accurate estimate for the 9 pound Precise Yellows would be 229 fps with 5/16" steel. The Precise Yellow test was done months before the "1632 vs 1636" testing but I thought someone might appreciate seeing the comparison so I posted the old numbers.

I like the speed from pseudo tapered tubes. I had previously tested single 1632 tubes and could not get to my goal of 250fps with .177cal BBs. The heavily stretched singles also broke quickly under the stress. My skinny tube comparison was done to compare the tubes when set up to approx 250 fps with .177cal BBs. I'm guessing that the 1636 could get 250fps with singles but I haven't gone there yet. The testing takes time to set up the tubes, perform tests and document.
 

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Northerner,

I think your testing of the flat bands is flawed. Judging by the draw weights you are stretching the shorter bands more. My experience is the longer the bands the faster the ammo flies if both the shorter and longer bands are both maxed out. Looks to me that you maxed out the shorter bands but did not on the longer one. To get a fair comparison you need to max everything out.
 

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Discussion Starter · #16 ·
Northerner,

I think your testing of the flat bands is flawed. Judging by the draw weights you are stretching the shorter bands more. My experience is the longer the bands the faster the ammo flies if both the shorter and longer bands are both maxed out. Looks to me that you maxed out the shorter bands but did not on the longer one. To get a fair comparison you need to max everything out.
LOL... good one... I'll try to grow my arms longer so I can get more stretch. Seriously though, I do all my testing with a 32" draw length. I'm not a butterfly guy.

There are many ways to test bands. You can set them up for equal draw weights and check speeds. You can set them both up for a certain speed with a certain ammo weight and then check how they perform with other ammo (like above). You can compare tapers to straights with the same draw weights. You can go for max draw and compare speeds and draw weights. Etc... It all takes time.

As was mentioned by others, there is too much variation between bands to get overly serious about numbers. I like numbers so I test for myself and share with those who want to read. There will be variation from tube-to-tube and band-to-band and even when the same color is used. Different lots or ages of the "same" tubing will often draw differently and sometimes measure differently. Too much variation. It's not science. It's just fun.

My neighbor helped me shovel my driveway the other day. He didn't quite do it the way I like but I was grateful and thanked him for his time and thoughtfulness.
 

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Doing all your testing with 32" (any constant) draw length is absolutely the right way to compile meaningful data.

Controlling your experiments to limit variables to one at a time and clearly identify the variable is an ideal pattern. You seem to be attempting to do that. I see above a comparison where tension, tube configuration of size, pseudo taper vs single, (or possibly looped), relaxed length, temperature, shooting with a pull and quick release vs deferred release may all be managed. It appears that introducing pseudo taper into the mix might be somewhat random and not be done as a singular modification.

You should anticipate the bands or tubes to have a short service life when maxed out. The data you are creating is beneficial.

Growing longer arms would be good for all of us when considering only situations where longer arms is a benefit...

Hopefully you do understand that with pseudo tapers you are effectively stretching half your relaxed length to a greater elongation and the looped half is being elongated less. The life expectancy of the configuration is going to be based on the weaker portion of the product which will be the knots, the single tube section or similar areas. The double tube section only acts like it would if you had a full loop and pulled the same tension getting 300-400% elongation.

I have seen numerous discussion where the pseudo taper design is challenged, usually by someone claiming engineering expertise. Then ridiculed, usually by those claiming experience with what works best. I have never seen a discussion where actual valid test data was introduced into the conversation. I thought you might be a person that had the drive to create that data as you are looking for the solutions that data would point to.
 

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Thank you for all the testing you have done. I have a understanding based on your information and have found it very useful.
 

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Glad I revisited this thread and saw the updates. My first order of the 1636 arrived recently and I banded some up today.

I didn't set up the chrony, but my impressions support the numbers you've been getting.

I really appreciate your effort, @Northerner!

I'm shooting 3/8 steel, butterfly (58-inch draw) with singles, and today's aim was to match the point of impact with the 1632, 1636 and 2040.

I got close enough for my purposes. I ended up with:

11-1/4 inches for the 1632

12-1/2 inches for the 1636

14 inches for the 2040.

I haven't checked the draw weights yet.

I'm guessing the speeds are similar, although it seems the draw weight increases with the tube size.

I'll post chrony results when I take the time to set it up. Maybe the next time a cold snap traps me in the basement!
 
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