Spiral fluting is recommended for 5R barrels.
The Uni-Throater concept was developed by Dave Kiff to enable gunsmiths to perform precise, repeatable operations quickly with a simple hand tool. The tool features a removable pilot which guides a 6-flute HSS (high-speed steel) cutter. What sets the Uni-Throater apart from ordinary reamers is its unique method of controlling depth of cut.
The straight portion of the cutter passes through a sliding bushing with a tapered shoulder at the front end. The bushing is precisely honed so that the cutter can rotate or move axially with ease, but lateral movement is virtually zero. Behind the bushing, the cutter shank is threaded with micrometer threads (40 TPI). A brass adjustment nut, backed by a knurled lock nut, controls precisely how far into the throat the cutter can reach. The adjustment nut features five equidistant grooves around its circumference each groove corresponds to .005" (.13mm) of axial adjustment. Adjustments as small as .001" (.025mm) can be made with confidence.
To set up the Uni-Throater, gently insert the cutter into a "control" chamber (or a dummy chamber cut to the correct dimensions), turning in the "backward" (non-cutting) direction, until the cutter contacts the rifling lands in the barrel. Zero the adjustment nut against the sliding bushing for a rough adjustment, then tighten a little more (forcing the cutter slightly back out of the chamber) and lock the nuts. Now cut a throat in a new chamber and measure the result. To increase the throat depth of cut, carefully back off the adjustment nut, lock in place, and cut again. Repeat this process until you achieve the required throat dimension. You now have a tool set up to cut the exact same throat dimension every time!
The Uni-Throater can be used conventionally, in a lathe. It also is threaded for attachment on our Uni-Throater T-Handle. With the T-Handle, you can perform throating operations in barrels while they are assembled to the action/stock. There is also a threaded Shank Extension available, which converts the Uni-Throater to a 3/8" (.375" / 9.5mm) square drive. This drive is compatible with our Chamber Reamer T-Handle and common square-drive implements. This Premium Uni-Throater Kit includes both a Uni-Throater T-Handle and threaded Shank Extension at a discount from their individual prices.
The standard shoulder angle for the Sliding Bushing is 30 degrees. In the chamber, this shoulder will contact HIGH on lesser shoulder angles (e.g. the .270 Winchester family of cartridges), and contact LOW on greater shoulder angles (e.g. 40-Degree Ackley Improved cartridges). Usually, this limited contact is adequate to control depth of cut while maintaining concentricity, but a little more care must be taken in the setup to avoid overcutting the chamber. Pacific Tool and Gauge sells replacement Sliding Bushings, and for an extra charge we will manufacture your Sliding Bushing with a custom shoulder angle. Refer to the Sliding Bushing product page for more information.
Uni-Throaters are available for most SAAMI cartridge specifications. The exceptions are shoulderless cartridges (e.g. .30 Carbine or .44 Remington Magnum).
NOTE: All PTG Reamers and Cutting Tools are designed to work with petroleum-based lubricant. Water-based lubricant can give acceptable results, however the life of the tool will be reduced. For best results use petroleum-based lubricant.
