05-31-2012, 04:54 AM
There is one other factor I recently learned about from Bill A.:
Some barrel makers source the cheapest barrel extensions they can find, which is ok if you're building a 5.56 gun or something with a case diameter of a 5.56.
With larger-base cartridges, you need barrel extensions that don't vary beyond certain specs, especially the inner diameter of the teeth in the extension.
The reason is that during the heat-treating process after the teeth and feed ramps are broached, the extensions warp a bit, and can form an elyptical inner diameter that prevents the extractor from being able to snap over the cartridge, and causing lots of shearing of the brass case walls.
This became a headache with some barrels, even very high-end pipes that were threaded into low-cost extensions.
Some barrel makers source the cheapest barrel extensions they can find, which is ok if you're building a 5.56 gun or something with a case diameter of a 5.56.
With larger-base cartridges, you need barrel extensions that don't vary beyond certain specs, especially the inner diameter of the teeth in the extension.
The reason is that during the heat-treating process after the teeth and feed ramps are broached, the extensions warp a bit, and can form an elyptical inner diameter that prevents the extractor from being able to snap over the cartridge, and causing lots of shearing of the brass case walls.
This became a headache with some barrels, even very high-end pipes that were threaded into low-cost extensions.