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Use a lighter piston. There is absolutely no need for an aluminum bodied piston. SHS 14T 7 hole piston is the best general purpose piston. Use a lighter piston head, a POM one such as Prometheus or Lonex. Avoid metal ones, avoid mushroom style "silent" ones. AoE is good, but it is not critical. I've never seen an AoE related failure aside from it being over "corrected", so that is likely not your cause of failure.
Your setup likely failed due to piston pre-engagement, which is caused by feeding issues. Use a pie shaped sector delayer with the SHS gear set, and short stroke from the release side to prevent tappet plate pre-engagement. 2 teeth if you are sub 40 RPS, 3 teeth if you are above 40 RPS.
As far as shimming goes, shim bevel-pinion. Do not use the internet guides that tell you to start from the spur gear, also avoid the guides that instruct you to shim using the top (right) half of the gearbox. That will result in the bevel gear being shimmed too far away from the pinion.
When you shim, make sure every gear is as tight as possible without inducing friction. That means you should be able to wiggle each gear shaft slightly, ideally <0.1mm. As far as spacing between the gears, sector-spur doesn't matter a whole lot, those only strip from piston pre-engagement and if you have D-Boys guns lol. Give a good amount of contact, but leave enough clearance to be 100% sure they are not rubbing. People often shim them as tightly as possible and the result is not pretty. Bevel-spur spacing is important. If you shim too far away, the bevel is more likely to strip.
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