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Old 02-05-2018, 10:27 PM   #1
Straits
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Aimrite King Venom 100cm setup questions

Hi all, long time lurker, recently joined the board, and just approved to post.

I've had an Aimrite KV-100 for 5 years now and love it. Unfortunately, not knowing much about gun set up and replacing perishable parts over the years, it's accuracy has declined and it's become unreliable and frustrating. After devouring the posts on this site I think I've got a better understanding of where I've gone wrong in the past and looking to correct it. Below are the issues I can find so far.

Shooting line. Comes stock with mono single wrap. I bought a huge roll of 2.2mm mono when it first needed replacing and have been using it since. Unfortunately this thickness has meant it is a little tight getting the spear into the mechanism and I suspect has contributed to the issues of accuracy. I've replaced with 1.8mm mono, and it is now clear of the sides when loading the spear.

Spear. Comes stock with a 7.5mm Rob Allen spear, 140cm length (though the mechanism safely takes a 7mm). I felt it was a little heavy in the nose, and changed to a 7mm spear, which hasn't changed the slightly heavy feeling nose. Accuracy has been worse since sadly. I'm going back to the 7.5mm spear. Would anyone suggest reducing length to 130cm to reduce the nose end weight? What would this do to accuracy? Would it alter the recommended band lengths?

Trigger. No changes. Well maintained. Love it. The safety feels natural in my hand and it's one of the reasons I got this gun.

Bands. Comes stock with 2 x 16mm rubbers. Band eye to notch is (A) 85cm and (B) 95cm, with band lengths come stock at (A) 55cm=309% stretch and (B) 60cm=317% stretch. I have previously gotten pre-made rubbers sent from Aimrite, though over the years the rubber feels older and less robust, and not knowing the source and age of them I am now keen to do my own. I've bought 14mm small ID rubber. I've read 340%-360% stretch to start is wise, and can cut shorter accordingly. As such I'm planning to use the following to get the desired length:
(A) (85x2)/3.5=48.5cm for a 350% stretch (knot to knot)
(B) (95x2)/3.5=54cm for a 350% stretch (knot to knot)
Any pitfalls or suggestions to the above plan?

I reef spear with this gun, mostly coral trout, tusk fish, jacks, an crayfish, and used to be able to shoot the eye out of most fish. I want to get this gun back to that accuracy and figure I'll get a better understanding of gun physics along the way. All and any help is appreciated.

Thanks
Straits
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Old 02-06-2018, 12:44 AM   #2
2fishin2
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Re: Aimrite King Venom 100cm setup questions

Change to a 130cm 7mm shaft. It will take the "nose heaviness" away guaranteed. 2 14mm bands at 350%
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Old 02-06-2018, 03:50 AM   #3
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Re: Aimrite King Venom 100cm setup questions

Thanks for the reply 2fishin2,

How much does reducing the spear 'hang' affect accuracy and the band width/length equations?

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Old 02-06-2018, 08:06 AM   #4
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Re: Aimrite King Venom 100cm setup questions

Quote:
Originally Posted by 2fishin2 View Post
Change to a 130cm 7mm shaft. It will take the "nose heaviness" away guaranteed. 2 14mm bands at 350%
Good advise
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Old 02-06-2018, 10:45 AM   #5
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Re: Aimrite King Venom 100cm setup questions

reduce shaft to maybe 120 or 130cm.
16mm bands
get a plastic bottle for testing in the ocean or lake
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Old 02-07-2018, 05:24 AM   #6
Straits
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Re: Aimrite King Venom 100cm setup questions

How much does changing shaft length and diameter affect the other variables?

A 7.5mm x 1400mm shaft has volume of 67,725 cubic mm (1400x(pi R squared)) where R is 3.75.
A 7.0mm x 1400mm shaft has volume of 53,851 cubic mm (R is 3.5) which is 20% less volume and therefore mass. Is this correct?

A 7.5mm x 1300mm shaft has volume of 57,403 cubic mm which is 15% less volume that the 1400mm same diameter.
A 7.0mm x 1300mm shaft has volume 50,004 cubic mm which is 25% less volume than the original 7.5 x 1400mm spear.

Please correct me if this maths is wrong (not my strong point). If correct then these are big mass changes. Would it still be recommended to use the same band width and stretch regardless of these changes?
I feel like there should be some adjustment made, just not sure where?
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Old 02-07-2018, 07:37 PM   #7
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Re: Aimrite King Venom 100cm setup questions

A shorter shaft would give you higher shots. Your brain will correct it overtime. Take some pool practice and you will master it.

I would cut the bands to 300-320% to start. Everybody talks about 380%, then you see them either missing shots or farting to load them...

You can always cut some more if needed.
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Old 02-08-2018, 12:15 AM   #8
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Re: Aimrite King Venom 100cm setup questions

farting to load...

for my guns, i've done the 14mm small id bands at 350% which is somewhat in the middle of recommendations. You could do 300 and then cut again, but it 350 is pretty common and a lot people have success with it. I'm also lazy and would rather not want to cut and tie them up again.
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Old 02-08-2018, 07:52 AM   #9
2fishin2
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Re: Aimrite King Venom 100cm setup questions

Farting to load... That's a classic ha

I'm 30cm overhang is perfect for all pipe guns and wood guns also. Any less you struggle to get a good aiming point. 40cm is industry standard for rail guns. Problem with that length is nose weight in short guns like yours and in longer guns both weight and shift whip. Your perfect setup is a 30cm overhang with 14.5 or 14 mm bands cut at a starting length of 350%. After they stretch out you can cut down and use for a longer time. With a short gun like that, you won't be taking long shots so perfect performance and tuning won't be as critical as shooting longer guns and larger fish
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Old 02-08-2018, 10:36 AM   #10
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Re: Aimrite King Venom 100cm setup questions

I know that I really liked going from a 180cm 7mm shaft to a 170cm 8mm shaft on my 140 railgun. That way the gun was more maneuverable; with a stiffer shaft that was less likely to bend and had about the same stopping power.
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Old 02-09-2018, 09:01 PM   #11
Straits
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Re: Aimrite King Venom 100cm setup questions

Thanks for all the replies.
130cm shaft is in the mail and on it's way.

I've tied the bands at 350% as calculated above. First time I've ever tied bands. Used spectra loop at each end, with a solid double granny/overhand knot. Fiddly to get into the small ID hole, but silicone spray helped and needle nose pliers did the job. Double constrictor knot next, which was easier than I thought it would be. Then used dyneema for the wishbone section, and can lengthen or shorten a few centimetres for tuning.

No pool and dirty ocean water out the front from recent rains means I can't test it yet, but very keen to see how these changes go.

I'll try figure out uploading pics, though it's nothing special to look at compared to the gun porn on here.
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