Ivan,
Don't feel bad about ur RA trigger. I heard it is a great shooting unit overall. As far as trigger in concerned, if it were to match up say to a Steve Alexander or A Riffe, I bet RA need to retail at an extra US$45.00 each gun just to allow a beefed up trigger unit installed. Anyway the initial design of RA was single rubber and now the maxed out at 16mm x 2, so they said.
You are not the only one ( I read on forums ) with a problem of self-firing at 16mm+20mm rubbers, especially if they are shorter than usual. I hope you did not mess with the trigger sears. I did, twice on a JBL and once on a Scubapro pneumatic. I was
"smoothing" out the friction edges of the sears hoping for a sweet release. One of the JBL worked well and the other was so sweet, it self-fired. The same with the pneumatic.
It is a good thing u point this out and see what RA or the US/Australian rep has to say. As a customer you have the right to point it out. As a possible future buyer/s the rest need to know too. RA doesn't reccomend above 16mmx 2 rubber pressure, but I wonder if they stated that in the manual. If they don't, that means it's not entirely ur fault if the rubber slot can actually take whatever rubber diameter and quantity u can install. You will probably think it is OK to do so, anyone would think the same.
I checked with Riffe once. I wanted to use 5x14mm rubbers on my Standard # 2, cause I already have 4 and with muzzle re-inforcement. I thought I wanted to experiment. The slot won't fit but I know how to make it fit when loading. They told me not to do it because the teak stock won't handle that kind of pressure, even though the trigger will do it easy. So, naturaly I listened to them and buy a thicker teak stock-ed Standard #4.
If I were you I would keep it at 16mm x 2 rubbers max and make sure no one is within ur shooting range if ur gun is loaded. However, if I think of total safety I will not have a piece of mind even with 16mm x 2 because if ur 20mm+16mm can blow a trigger sear, the safety margin is just too little. Anyway I will still get an RA if I sorted out the importation bitches...., need 2 know for myself what kind of pressure will the trigger blow apart at and why are they so "popular"
I would generaly feel comfortable to load a gun to no more than 60-75% of its rated trigger capacity, they wear off u know, not that they get any stronger after each shot.
Plain and simple example will be the SCUBA tank, they deal with lethal air pressure. Ur gun accidentaly shooting ur brother is also lethal. A typical scuba tank is rated at 3000 pis/200 bar. The safety burst disc blow at about +-10% extra pressure. The hydro static testing ( per 3-5 years ) on these tanks are at +-5000 psi. Tank expansion is measured, if it expands beyond "safe" limit, it gets destroyed to prevent further circulation. So the safety margin is quite high. New testing method uses Eddy current device because supposedly an older aluminum alloy 6351 has a weakness inherent in the metal itself called : sustained-load cracking (SLC). Some 0.4 - 1% of total cylinders made with 6351 alloy has this problem. Yes, a few explosion worldwide been reported, some have caused deaths.
Speargun manufacturers do not get regulated like high pressure tank manufacturers. In the US.,Department of Transport will make sure Luxfer or the sort design and build those high pressure tanks properly. Many of these cylinders survived over 20 years of use, thus come to think about it, they are damn robust.
For our trigger case we need to consult with the manufacturer rather than trial and error, IF the speargun manufacturer does not provide enough technical data. The trend is always higher power, more range, more penetration and more accuracy. If any speargun manufacturer does not improve their trigger along with the extra power/rubber option they are selling, you need to be more careful, I would.
Stay Safe and point that speartip away from anyone,
IYA