BAND STRETCH /spear

[doyenofcastle]

HI ,
I have finished few different wood guns (110cm roller/130cm classic)and now I have to decide which spear/band will be fine ,befor I have read many articles but it make me confused ,the fish around from 3kg to 20 kg ,7mm spring steel is perfect for the classic but for roller no idea ,now for band I have to choose between 2*16 *315%or 2*14.5 *360% //roller 16.5*350% ,my concern to not overpowered the spear or lower than the required ,I have a discussion with rail gun manufacturer usually he used a band stretch 2*16mm* 315% for 16mm and1*18mm* 290 % ,any advices will be appreciated ,
last Q why if u use double 16 at 315% and want to use single 18mm instead ,u have to use 290% ?

 

[Pinniped72]

The lower stretch on the 18mm may have been suggested by the railgun manufacturer for ease of use and loading, an 18mm band is noticeably harder to pull than a 16mm. There is a massive power difference between double 16mm at 315% and a single 18mm at 290% so to keep everything in balance, the spear size would probably need to be different. 6.5 or 6.3mm is a common size with a single 18mm band whilst double 16mm would probably over power them and require a 7mm spear. A 7mm and single 18mm band would be ok at short ranges but I noticed that your guns are 110 or 130cm. Just a few thoughts, whichever way you go, enjoy the guns and dive safe

 

[doyenofcastle]

actually he recommended 18*7 mm ,I did few calculation by primeline formula ,18 mm at 290% will give 158 Ib and 2*16 at 315% will give 289 Ib ,I can't understand the results !
if we need to give general rules for spear size
6mm powered range 155 to 160 Ib
6.5mm powered range ??
7mm powered range 185 to 300Ib
7.5mm powered range 189 to 350 Ib
8mm powered range 250 to 380 Ib

if yu can get the range we can get easily theoretical band stretch as start for our experiment