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Old 10-21-2019, 09:16 PM   #1
musubi
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Cuttled Barrel Ballasting

I'm planning to build a 120 cm cuttled carbon barrel invert roller, but I'm having trouble in my thoughts on how to ballast it correctly. Everything is in pieces still and wanted to plan this out. I'd like it to be negative/neutral with the shaft and positive buoyancy after the shot. I've built straight carbon barrelled guns, but this cuttle shape is throwing me off as I'm expecting this to be more buoyant. Additionally, I won't be having a reel (and line) like my other pipe guns.

I've adjusted the the gun ballast in the past by using lead shot pellets in the muzzle or handle. I'm thinking this may not be enough and may need to screw lead pieces on somehow.

I've been trying to work out the buoyancy mathematically, but I'm not sure if I'm over-thinking this. I just don't want to set the barrel plugs and regret not setting it deeper or shallower. I see that some cuttled barrels come foam filled. Mine isn't, but is that something that would be recommended?

Anyway, if any of you have some thoughts on this, I'd appreciate it.
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Old 10-21-2019, 10:34 PM   #2
popgun pete
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Re: Cuttled Barrel Ballasting

Check the barrel’s water displacement with its ends sealed in a tub. Prod it so that it goes right under and the raised level in the tub is how much water it displaces. Mark the water level, take the barrel out and then fill the tub up to that level with extra water. The water you add and its weight is the buoyant upthrust you get from the barrel minus the barrel's dry weight in air. If you don't measure the water you added then you can siphon it out to reach the original level in the tub and then weigh the filled container with the water and then without to obtain the weight of the water.
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Old 10-22-2019, 02:01 AM   #3
Andrew Makely
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Re: Cuttled Barrel Ballasting

Any thoughts on foam filling as opposed to plugging the barrel? Advantages and disadvantages?
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Old 10-22-2019, 07:57 AM   #4
popgun pete
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Re: Cuttled Barrel Ballasting

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Any thoughts on foam filling as opposed to plugging the barrel? Advantages and disadvantages?
With foam there are no leaks, although foam can be compressed by pressure if you use the wrong type. Air filled barrels give the lightest result, however water is always a possibility of getting in. Originally corks were hammered into the ends of alloy tube barrels and then "O" ring seals were used as the smooth metal tube lent itself to sealing. As carbon barrels may not be so smooth inside I think foam is the best bet there. Under pressure end plugs can move slightly inwards and you need a dynamic seal as the plugs get squeezed by going deep say down to a hundred feet or 3 atmospheres of extra pressure (4 atmospheres absolute).

Last edited by popgun pete; 10-23-2019 at 04:10 PM. Reason: fixed the typos
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Old 10-22-2019, 10:37 AM   #5
Mikel_24
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Re: Cuttled Barrel Ballasting

Even if the barrel is cuttled... the ends are going to be cilindrical for sure (to be able to attach a muzzle and handle). I know for a fact that there are manufacturers that sell rubber stoppers designed for the different ID of the tubes used in spearguns.

You can also buy lengths of solid rubber cilindrical profile and sand to shape (belt sander or even angle grinder with flap disc). Then insert to the right place (keep them in boiling water a couple minutes to soften them a little and ease insertion). If you want to be double sure you could use some SIKAFLEX (construction sealant) or the US equivalent.

You stated that you will not be using a reel, but just inc ase you change your mind, allow some extra room in the handle end, so you don't drill into the sealed volume if you decided to attach a reel.

This is the spanish site I would be buying from if I needed any.
https://www.clipcarbono.com/225-tapo...producto-tapon


Regarding the bouayancy... well, aim for positive and then balast as required. If you have enough room in the tube (between the stoppers and the muzzle/handle) you could use pellets, but they are going to rattle. If you don't care much about looks, then you could use stick on lead weights. The same used to balance alloy rims in cars. You could also persuade to curve a little and stick them on the INSIDE of the barrel (given you have some spare room)

Mikel
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Old 10-22-2019, 01:30 PM   #6
musubi
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Re: Cuttled Barrel Ballasting

Thanks everyone for your replies and thoughts. Really appreciate it. I really didn't have a container or tub long enough to do the barrel displacement, so I math-ed it out with some help with CAD and creativity. For the odd shaped components like the handle and muzzle (and pulleys) I used a small container and measured incrementally. Pete, I like your idea of the siphoning the water out and measuring the removed water. I'll have to keep that in mind.

To make a long story short, I was able to estimate the volume of all of the components, and also weigh them. I found the buoyant force and the total weights of the gun (with and without a shaft). My findings are the following:

Without Shaft: Net buoyancy of 1.695 lbs.
With Shaft: Net buoyancy of 0.664 lbs.

Meaning, it'll float with the shaft in, which is what I was expecting. So, I'm going to need to find a way to weigh this down more. I was thinking of utilizing the space inside the barrel to fill it with something before I plug it. Filling it with enough weight to get me on the edge of negative buoyancy WITH the shaft, then ballast it heavier to my liking with the shot pellets at the front and rear. Just my thoughts at the moment, but don't know what to fill it with yet.

As for the plugging of the ends, I usually use rubber plugs from the hardware store and 3M's 5200 Marine Adhesive Sealant. The barrel opening is 26.5 mm or about an inch in diameter. The plug I use is slightly larger at 1-1/4" and conforms around any irregularities in the barrel, with the help of the sealant too.

My calcs were based on setting the plugs at 3" from each end, which should provide ample space for weights or any attachments, should I need something. The MVD handle that I plan to use has space on the trigger guard for a reel (their reel), which is nice and gets me longer band stretch for my invert rubbers.

For the foam, I'm guessing that would help with density and adding more weight to the gun. I'm likely not going to pursue filling this barrel with foam unless I know it would workout, weight wise, for my situation.

I currently have pellets in another pipe gun I use and I do actually like that it makes a rattling noise underwater. It's more tightly packed than loose, so it really only rattles when I twist the gun side to side. A couple fish I target here tend to get curious and attracted to the sound and commotion.

Even though I've got some baseline numbers, I still wouldn't mind hearing more thoughts if anyone has them.
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Old 10-22-2019, 04:02 PM   #7
popgun pete
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Re: Cuttled Barrel Ballasting

A gun builder I know uses stick-on weights as an adjustment, such as those wheel balance weights which you can cut to length, then replaces them later inside the stock. However if opening up the gun is not an option for such post-build installation then you could stay with the stick-on weights. If the gun floats with the shaft it is best to trim the gun nose down for safety reasons. Some guns float butt down without a shaft, you don't want an air launch missile situation or a shaft discharging towards the surface if something lets go and you are not controlling the gun.
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Old 10-22-2019, 04:53 PM   #8
musubi
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Re: Cuttled Barrel Ballasting

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Originally Posted by popgun pete View Post
A gun builder I know uses stick-on weights as an adjustment, such as those wheel balance weights which you can cut to length, then replaces them later inside the stock. However if opening up the gun is not an option for such post-build installation then you could stay with the stick-on weights. If the gun floats with the shaft it is best to trim the gun nose down for safety reasons. Some guns float butt down without a shaft, you don't want an air launch missile situation or a shaft discharging towards the surface if something lets go and you are not controlling the gun.
I may use stick on weights if I end up needing more weight. It's tough trying to plan this one since I feel like I have one shot to get a good ballasting starting point, because once the plugs go in, it's not coming back out. In the end, probably better to be too buoyant than not. I'll do my best to ballast this gun evenly.
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Old 10-23-2019, 05:06 AM   #9
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Re: Cuttled Barrel Ballasting

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Originally Posted by Mikel_24 View Post
......keep them in boiling water a couple minutes to soften them a little and ease insertion). If you want to be double sure you could use some SIKAFLEX (construction sealant) or the US equivalent.
You stated that you will not be using a reel, but just inc ase you change your mind, allow some extra room in the handle end, so you don't drill into the sealed volume if you decided to attach a reel.
This is the spanish site I would be buying from if I needed any.
https://www.clipcarbono.com/225-tapo...producto-tapon
Regarding the bouayancy... well, aim for positive and then balast as required. If you have enough room in the tube (between the stoppers and the muzzle/handle) you could use pellets, but they are going to rattle. If you don't care much about looks, then you could use stick on lead weights. The same used to balance alloy rims in cars. You could also persuade to curve a little and stick them on the INSIDE of the barrel (given you have some spare room)
Mikel
thanks for sharing Mikel
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Old 10-23-2019, 03:25 PM   #10
musubi
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Re: Cuttled Barrel Ballasting

So after thinking about how to weigh the barrel down more, without sticking weights on, I'm planning to fill the barrel with clothes. I'm planning to cut up old clothes and pack it in. I'm aiming for 0.8 lbs to add and adjust after with lead pellets at the muzzle and handle. I calculated I can add another 0.6 lbs of pellets after I stuff the barrel to ballast. I don't think I can add 0.8 lbs of clothes inside, so I'll improvise with something after weighing/measuring halfway.
Anyway, it may sound weird, but I thought I'd update my thread on that thought.
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Old 10-23-2019, 04:17 PM   #11
popgun pete
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Re: Cuttled Barrel Ballasting

One way of checking if a barrel is leaking, besides the change in weight when holding it, is to give it a shake and you can hear the water sloshing around inside. If you use cloth then the weave acts as a sponge and you will not hear water moving around. Just a thought on using something that sucks up water. Closed cell foams don't hold water, but open cell foam does. I remember a gun that used open cell foam, it only stayed buoyant until the foam filled up.
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Old 10-23-2019, 04:47 PM   #12
musubi
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Re: Cuttled Barrel Ballasting

Thanks Pete. That's a good point. So far (knock on wood) I haven't had an issue of leaking barrels. Maybe it's because I use a lot of the 5200 sealant or I've been lucky. With foam, I'm just a little concerned it won't be as heavy as I need it to be. For the closed cell foam, is this a spray application or something you stuff inside?
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Old 10-23-2019, 05:07 PM   #13
kavachi
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Re: Cuttled Barrel Ballasting

Quote:
Originally Posted by musubi View Post
So after thinking about how to weigh the barrel down more, without sticking weights on, I'm planning to fill the barrel with clothes. I'm planning to cut up old clothes and pack it in. I'm aiming for 0.8 lbs to add and adjust after with lead pellets at the muzzle and handle. I calculated I can add another 0.6 lbs of pellets after I stuff the barrel to ballast. I don't think I can add 0.8 lbs of clothes inside, so I'll improvise with something after weighing/measuring halfway.
Anyway, it may sound weird, but I thought I'd update my thread on that thought.
gotta give credit for thinking waaaaay outside the box with ballasting there Musubi! island style
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Old 10-23-2019, 05:14 PM   #14
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Re: Cuttled Barrel Ballasting

one option, which provides perfectly distributed ballast, is going up half a mil in shaft diameter. With invert roller setup recoil from the heavier shaft should not be a problem.....
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Old 10-23-2019, 06:10 PM   #15
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Re: Cuttled Barrel Ballasting

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Thanks Pete. That's a good point. So far (knock on wood) I haven't had an issue of leaking barrels. Maybe it's because I use a lot of the 5200 sealant or I've been lucky. With foam, I'm just a little concerned it won't be as heavy as I need it to be. For the closed cell foam, is this a spray application or something you stuff inside?
There are foams that are two pack stuff which when mixed expand, being self-foaming, but they are not held in high regard due to the way the stuff expands and uniformity of the resultant cellular structure, or lack thereof, and the strength of the final foamed product as in resisting compression. There are cylindrical foam blocks that can be stuffed in sections into constant bore barrels, but that is not much use to filling bulbous barrels. Needs some research as there must be a way to do it.

https://purios.com/en/blog/types-of-...do-they-differ
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