For want of better place I'm starting this thread here in the 'smithing' area.
If anyone is thinking about entering the POLYMER 80% lower market, I'll offer some observations.:
1-While you CAN do the gouging on a drill press, it's far better if you invest in an X/Y axis vise for the press. It's slow and requires patience and care but it CAN be done successfully. That said, quite often there will be Dremel handwork involved in producing a working part-again, slow and careful.
2-It's a fairly easy 15 minute job to cut one using an actual router 'jig' and produces a useable product only requiring some clean-up of burring around holes.
3-There are several versions some of which use a separate nut for the pistol grip and some that use a brass insert cast into the polymer. Also some use a captive pin/set screw to hold the bolt catch in place while others use the common roll pin(be darned careful when driving that pin in place). Most/all are designed with a 'closed' trigger guard. One reason for this is strength-the weakest part of the AR lower is the area where the trigger pin and trigger hole cut is located. The 'closed' trigger guard adds strength and rigidity to this somewhat weak area.
4-Quality of the 'cast' is variable (and these are only my observations). JMT seems to be a good product-I found no voids or porosities in the internal cutout areas. Polymer 80 RL556v3 comes in as #2 with only limited porosities and virtually no voids. The Polymer 80 had several issues with porosities, voids, and internal imperfections. These are actual observations of several of each version.
5-Regardless of brand, I found that there's a considerable variation in tolerances and not just any combination of polymer lower will fit with any/all uppers. It's like a big game of mix & match with pairing up combinations that fit. So don't expect to just take home upper and lower and have them fit properly. Just a SWAG that 10 lowers and 5 uppers will result in 5 sets that fit and that might be a bit high. I had to do a LOT of hand fitting on some.
If anyone is thinking about entering the POLYMER 80% lower market, I'll offer some observations.:
1-While you CAN do the gouging on a drill press, it's far better if you invest in an X/Y axis vise for the press. It's slow and requires patience and care but it CAN be done successfully. That said, quite often there will be Dremel handwork involved in producing a working part-again, slow and careful.
2-It's a fairly easy 15 minute job to cut one using an actual router 'jig' and produces a useable product only requiring some clean-up of burring around holes.
3-There are several versions some of which use a separate nut for the pistol grip and some that use a brass insert cast into the polymer. Also some use a captive pin/set screw to hold the bolt catch in place while others use the common roll pin(be darned careful when driving that pin in place). Most/all are designed with a 'closed' trigger guard. One reason for this is strength-the weakest part of the AR lower is the area where the trigger pin and trigger hole cut is located. The 'closed' trigger guard adds strength and rigidity to this somewhat weak area.
4-Quality of the 'cast' is variable (and these are only my observations). JMT seems to be a good product-I found no voids or porosities in the internal cutout areas. Polymer 80 RL556v3 comes in as #2 with only limited porosities and virtually no voids. The Polymer 80 had several issues with porosities, voids, and internal imperfections. These are actual observations of several of each version.
5-Regardless of brand, I found that there's a considerable variation in tolerances and not just any combination of polymer lower will fit with any/all uppers. It's like a big game of mix & match with pairing up combinations that fit. So don't expect to just take home upper and lower and have them fit properly. Just a SWAG that 10 lowers and 5 uppers will result in 5 sets that fit and that might be a bit high. I had to do a LOT of hand fitting on some.