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PPA-CF vs PA6-CF?
Does anyone have experience printing PPA-CF and PA6-CF? I had read that "PPA-CF is 48% stronger" than PA6 if you get good layer adhesion, but I'm seeing conflicting info regarding impact resistance. Anyone have input who's printed and used both?
Would PPA-CF be viable for printing a standard AR lower? Compared to modified variants like the Hoffman and Defiance?
No. Tensile strength of 7051 aluminum is still roughly 5X that of PPA-CF and even the much weaker 6061-T6 is still 3X stronger. Stoner would have had to over-design the lower by 3 - 5X (despite having weight reduction as a major goal) for an all-polymer MIL-SPEC lower to be viable (even with injection molding).
I have over 800rds through a PET-CF Defiance lower receiver, with brass inserts for the trigger assembly. They are 100% a viable option, and I've had 0 issues with cracking or breaking of the original I printed. I just wanted a one-piece design. The only part of the lower that gets worked and is prone to breaking is the buffer tube mount. There's 0 "pressure" in an AR lower, to worry about "tensile strength" in that regard.
You may want to look into Middleton's GAP: https://guncadindex.com/detail/Grandmas-Apple-Pie-GAP-v15:6
You buy the metal buffer tower from a parts vendor and print the lower. Comes with an ambi bolt catch and dovetails, as Middleton is wont to do. It's not one-piece, but it slims the lower significantly since it takes force from a more manageable angle.