some advice for rob allen 120 carbon gun plz

[maxma]

I used to have a rob allen 90 aluminum for 2 years, very accure and powerful enough. but I lost it after a dive(my friend take the gun and fish from me, he put the fish in the car and left the gun on the ground:head). I thought everying in the car then drive all the way back to home. Now I am using a BEUCHAT Arka Comp 90 with 6-mm shaft and 16-mm rubber. they are perfect and powerful enough for shoot most of fish I am hunting. I found they are more accure than my old rob allen but not as strong as it. last week I got a change brought a rob allen 120 carbon with 7-mm shaft and 20-mm rubber for a good deal. I know this gun is litter big for the fish I am hunting, but since I never use a 120 gun and rob allen carbon is so famous, I still very happy I got it, but I bring the gun for a dive, man~:vangryI found it is sooo hard for me to load the gun, once I load it, it me very long time keep my heart rate back to usuall. average I load about 10 times for hunting in my area.

so, here is my question. can I just change rob allen single 20-mm rubber to a rob allen single 16-mm ruber? once again the sharf is 7mm. is it going to have much effect on accure? is it has more power than my beuchat 90?

o yeah, one more question, how U guys feel load a 20mm rubber gun?

many thanks

 

[foxfish]

Loading 20mm bands at 2.5-3 x stretch is hard but not so bad once you get a good technique!
However you can use slightly longer 20mm or same length 18mm or 16mm bands - you could use 2 x 16mm for easy loading but more time consuming!
You could even shorten your gun to 110!

 

[maxma]

oh, nice!!! suprise I have so many options!! I do not want to shorten my gun since I just got it and I am thinking collect guns from 50 to 130 if I am not loosing my gun anymore. i am sure I am going to use double 16mm when I change a new shaft. since the shaft come with the gun only have one notch. the area I am diving do not have big fish, the biggest fish so far I shoot is about 80cm blue moki. that is the only time my spear did not go though the fish. I belive the reason is my shaft is not sharp, not the rubber. I do fire a lots sometimes and the spear hit the rock. so I still want to try put a 16mm rob allen brand rubber on my 120 gun. so how long the rubber you think I should use?
many thx

 

[foxfish]

35cm should be about right or 2.5 - 3 x stretch.
A single 16mm on a 120 with 7mm spear is not ideal though - good luck.

 

[maxma]

so, how about I keep 16mm rubber as 35cm length, but change a 6.5mm spear, would be batter?

yeah, use a 7mm spear to shoot fish size between 35cm to 55cm is also not a good idear

 

[hteas]

According to Rob Allen, for a 120 gun:
65 cm band length for a 16 mm band
75 cm for a 19 mm band
remember a loop band is twice the length of a band for a euro style muzzle.
The 7 mm shaft won't reach out as far with a 16 mm band, but for smaller fish it should work fine. Accuracy should also be fine with the smaller band, maybe even better.

 

[stingaree]

Yes a single 16mm/65cm long band combined with a 7 mm/170cm long shaft for 120cm gun is the way to go for the best speed, punch and acuraccy (and dist. range for a single loop mono) and it will get fish ranging between 30 and 100cm as good. Why? Becasuse it works. How do I know? Because I have tried all other alternatives, shorter shafts, longer shafts, shorter rubbers, longer rubbers and the formula above WORKS THE BEST. you can also put 2x 75cm, which is easier to load but will become more clumsy. Also, there is nothing wrong with a single notched shafts (as long as a single rubber is used:hmm). 6.5mm shafts (with a slightly longer rubber) will be a bit more faster, but they won't punch through a spine of let's say a "small" kingfish as easy as 7mm which are just heavier. Forget 18mm or 20 mm untill you become a superloading machine, they're not necessary. If you start targeting fish above 15Kg, then thicker shafts and more power will come into play. This is where I have to disagree with saying; "the best is to keep guns as they come from manufactures." You get one off the shelf and can't either load it or hit a thing with it because they are overpowered and fitted with short shafts (not to mention proper balance). Obviously, this doesn't apply to all manufactures.

 

[maxma]

thanks guys,really appreciate your helps. I am going to do some shooting practice tomorrow with 20mm rubber, hange some empty buttle under my flaot.(got a few in my gardon). hope my order can arrive on monday then I can change to 16mm rubber compaire the difference by myself. I will tell u gus what i think next week.

the a single 16mm/65cm long band combined with a 7 mm/170cm long shaft for 120cm gun sound like a sweat combination for me. one thing I want to make it clear is how you guys work out the rubber length?
for 16mm 120/2+5=65
for 18mm 120/2+10=75
is my fomula right?

 

[foxfish]

If you are using screw in bands you would need a pair of band 30-35 cm long if you are using one loop band you would need 65-70cm band.
The loop band will give a tiny bit more power but screw in bands offer a more direct pull on the spear & can sometimes offer better accuracy - however better to go with stingaree as he seems to know the gun in question.

 

[hteas]

Length is calculated by measuring the length of pull from where the band goes through teh muzzle to the notch in the shaft. With a 20 mm band you should look at a 3 to 1 stretch. With a 16 mm band go to 3.5 to 1. I use 3.25 for the17.5 band on my RA 90.
Less than 3 to 1 gives up the power, while going over 3.5 to 1 stretches the band too far, and again you lose power.
Knowing the length of stretch (about 120 cm), you double the length of band needed, because it goes along both sides of the gun. Then divide by 3.5 (for 16 mm band) or 3 (for 20 mm band) to get the final length. Add a little extra length when you cut the band because the length calculated is between the knots keeping the wishbone in place, and you need a little bit of rubber beyond the knot at each end.

 

[stingaree]

Here is a chart which basically reflects all of the above (courtesy of SpearOZ forum). Good tip with stretch ratio, yeah there are some variations between rubbers quality as well and you can also take in account wearing off, so you can start with a slightly longer rubber and in a couple of months cut it a fraction shorter, the same goes for loading on the first notch initially and on second after while. I add 1.5cm on each side for the overhang behind constrictor knot.