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All About Guns What's your weapon of choice, and why? Discuss the beloved speargun here! |
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02-21-2018, 07:50 PM | #1 |
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Join Date: Sep 2016
Posts: 9
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Roller gun setup
I need some advice on how to correctly set up a roller gun. It is a 1m Rabitech with an MVD roller head. It came new with a 7.5 x 140 shaft and 16mm rubbers with no pretension at about 300% stretch. I never liked using it because it felt very muzzle heavy and I wasn't very accurate with it. Since then I have just used a different gun and normally run a 120 Pathos with the small ID bands. The only reason I am interested tinkering with it is because I recently took a friend out spearfishing and she was extremely recoil sensitive with the classic guns. I figure the low felt recoil of a roller gun would be perfect for her and I have one laying around anyway.
I have acquired a 7 x 130 spear which should help with a lot of the muzzle heaviness. My main question is how to power the spear, particularly pre-tension. Requirements: Power a 7 x 130 spear effectively to the end of one wrap. Single action loading without a load assist. My current plan is to use the 14mm small ID rubber. There is about 200cm of length between the notch and the band anchor. Aiming for a total stretch of 330% will need a 61cm band on each side with the bands being at 164% stretch at rest. I think this will be easy enough to load but will it be enough power? Just chasing some opinions from people who have had experience setting these kind of guns up. Thanks in advance. Last edited by theslothh; 02-22-2018 at 08:30 AM. |
02-28-2018, 04:32 PM | #2 |
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Join Date: May 2016
Location: Point Loma, SD, CA
Posts: 45
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Re: Roller gun setup
First, I have only been playing around with rollers guns for the past year. But it sounds like the "lighter setup" is much better for the gun itself. Only suggestion would be to minimize spear overhang at the end. When you say not accurate, where is it shooting? Low, High? Where the gun is shooting can point to the problem. I found it incredibly useful to get a target and shoot. I had a problem with my roller gun shooting low until I decreased the hight of the "wishbone catchers" at the end of the gun.
Hope this helps |
03-03-2018, 12:14 PM | #3 |
Spearo-doc
Join Date: Jul 2007
Location: Gainesville, FL
Age: 39
Posts: 249
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Roller gun setup
Hi there,
Since you are using a lighter shaft, then my suggestion is to use thinner bands. Go w/ 14mm Small ID bands. You’ll have several options w/ how short or long you cut your bands, and not to get things too complicated, but basically you will want to optimize your band stretch to ~350-380% Now you can have shorter bands w/little pretension which means they will be very stiffs toward the end (as you load them) but very easy to pull off the muzzle, or then the opposite: longer bands but it means you may not achieve the effective stretch ratio unless their pretension is pretty tight, which makes it much harder to pull at the muzzle to almost impossible without a load assist. Either way, you want to make sure you are achieving a stretch ratio of the bands of at least over 320% and that you have some tension left at the end of the roller, otherwise you haven’t achieved any benefits by converting your conventional gun into a roller (if any, you degraded the original performance!!!( I hope the above makes sense? Anyhow, a good compromise is to go middle ground. I’ll share an article that Chris Coates wrote not too far ago and it explains this in detail and the pretension to stretch ratio http://spearguns.blogspot.com/2016/0...t-and.html?m=1 Rollers are really good, but lots of folks give up on them as they don’t set them up properly.... To give you an insight on this, I’ve a rob Allen carbon, 110cm w mannysub roller head, 16mm small id bands pretensionned all the way to the handle (Can’t be loaded without a load assist), but stretch ratio of 380%, and coupled w a 140cm 8mm shaft. Super accurate, takes more than 2loops of line and pull the reel. Excellent choice in dirty deep water where we frequently encounter by game fish too (up to 100lbs!!!), and extremely manageable recoil. I hope that’s helpful Sent from my iPhone using Tapatalk
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" The sea, once it casts its spell, holds one in its net of wonders forever" --- Jacques Yves Cousteau |
03-06-2018, 07:45 PM | #4 |
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Join Date: Aug 2013
Location: Cambridge, MA
Posts: 184
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Re: Roller gun setup
I was about to get rid of my roller too until I rerigged the gun and now it's amazing! Super accurate and no recoil, absolutely sold on roller guns!
I then converted a traditional mako into a roller with the mvd roller head. With 350% stretch small ID bands, you'll be able to load without a load assist and it'll take out a double wrap (I'd recommend you double wrap instead of single wrap). As far as the anchors for the bands, you should be able to get them right in front of handle where there's screws. Measure from there, to the roller, and then roller to farthest back notch/fin on the shaft when it's in the mech. Take that total distance and divide by 3.5 (for 350%) stretch and then you'll need 2 rubbers that length. You can than tie up those bands and when you're ready to use the gun, you stretch them to the anchors to get the pretension. This is what worked for me, other can comment also. Let me know if you want some pictures of how I did it! |
03-07-2018, 02:10 AM | #5 |
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Join Date: Sep 2016
Posts: 9
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Re: Roller gun setup
The band anchors are right at the handle, replaced the screws that were holding the handle to the barrel. I like the idea of using bands that stretch from band anchor all the way to the notch. My main concern was that to achieve the 350% ratio with the long bands would require a lot of pre tension and I wasn't sure if it could be loaded without a load assist. Thanks for all the insight.
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03-07-2018, 06:24 AM | #6 | |
Spearo-doc
Join Date: Jul 2007
Location: Gainesville, FL
Age: 39
Posts: 249
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Re: Roller gun setup
Quote:
Great advise. I recommend the above too. Just a minor thing though, w the above calculation of bandstretch, you are likely not getting 350% but more so 320-330% depending on how long are your wishbones (you have two wishbones at each end of the bands). there’s a different calculation formula where you can subtract non stretchable parts but it can also get too complicated. Good luck. Sent from my iPhone using Tapatalk
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" The sea, once it casts its spell, holds one in its net of wonders forever" --- Jacques Yves Cousteau |
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