Running several 80% builds: one jig, many receivers

The cost curve on 80% building bends after the first receiver, because the tooling is the expensive part and it is reusable. Here is how to plan a run of builds.

Buy the tooling once per family

One PF940C jig finishes every PF940C you will ever own. One G150 jig finishes every G150. Changing family is the only thing that forces a second kit purchase.

Batch the same cuts

Set the drill and the vise once, then run all the pin holes across every receiver before changing setup. Fewer setups means fewer errors and a faster session.

Consumables

End mills dull, and a dull mill tears polymer instead of cutting it. Keep a spare 9 mm end mill and a spare 3 mm bit per five receivers, and use cutting oil throughout.

Label as you go

Receivers look identical half-finished. Mark each one and keep its parts in a labelled bag, or you will spend the evening matching rails to frames.

Know the legal limits

Federal law does not cap how many unfinished receivers you may buy, but several states restrict possession of unserialized receivers, and building for anyone other than yourself is a different legal question entirely. Build for yourself, and check your state before ordering a pack.

Storage

Unfinished polymer receivers are stable, but store them flat and out of heat. A frame left in a hot car develops a warp that no amount of filing fixes.

This is general information, not legal advice. Laws on unfinished frames and receivers vary by state and city and change often. Check the current law where you live before ordering.