Yes man this hypereutetic pistons are weak, you need more end gap in first ring as much as 24 posibly, and one thing you must not forget this pistons must be used in an engine with the total timing reduced to 36 or 34 degrees, i have broken 6 of this in diferent aplications so be care, and if posibly run good fuel.
Non-sense!! If you are breaking that many pistons you are not doing something right. Also there is no difference in the timing for KB hyperutectic pistons.
KB pistons are fine BUT, the ring end gap MUST be right. Looking at what your ring gaps were set at I would have to say they are too tight. The link 1bad posted gives you the "ring end gap factor" you multiply that by your bore size for a given application and this is your ring gap.
I have run KB's a ~500HP 385ci SBC and they are still in that engine today, this is after over 7 years of use and abuse.
If you are looking for a different piston and a better piston take a look at Wiseco Pro-Tru Forged pistons. I am running them in my 6" rod, blown 388.
I found the best deal through www.dirttrackthunder.com
they are good people to deal with and have great prices.
For your application you need part number PT020H and the price is $449.00 including hastings moly rings (complete set). They are flat top 2 valve relief forged pistons (complete with pins and locks). Here are the details.
FLAT TOP 2-VALVE RELIEF
ROD LENGTH 6"
COMP HT. 1.125
PIN DIAMETER .9272
Head Vol.-Comp Ratio
Pro-Tru pistons by Wiseco are an excellent option for a forged racing piston. They come complete with Hastings Plasma Moly rings, chrome moly wrist pins and spiro loxs.
Here is a link to the page these pistons are on (top of the page) http://www.parts123.com/PartFrame.as..._Track_Thunder
Hope that helps.
I just noticed you said you want to keep the compression at 10:1. Were you running flat top KB's? If so what size are the chambers on your heads? I don't see how you are getting 10:1 with true flat top pistons. This could be the reason you broke the pistons as well, hyperutectics do not like detonation and that is a sure way to break them.