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?
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.