Since my hi-vel 30-06 loads prefer 0.314" cast bullets, it seemed logical to give the barral a 0.314" throat. No one has ever tried this before, so it was a wild shot in the dark. Inquiring minds have to know.
For $60 plus $9 shipping, Dave Manson supplied a custom throating reamer. Since Dave seems to claim a 0.0005" tolerance, I specified 0.3135" - 0.3140" freebore and 0.2990" - 0.2995" pilot. I didn't specify the angle, but his standard leade angle is 3°.
The actual dimensions are 0.3133" freebore and 0.2987" pilot. It's hard to measure the angle, but it appears to be at least 3° and maybe more. Since this experiment was just a shot in the dark, the slightly undersize dimensions weren't critical.
It would have been easier and faster for me to unscrew the barrel and put it in the lathe to cut the throat, but I elected to cut the throat by hand to show that it can be done.
An extension is needed. You can buy extensions but I made my own. I cheated and used the lathe to make a coupling. The coupling diameter is a perfect fit in the Remington receiver so it supports and guides the reamer from the rear (alternatively, I could have drilled and reamed the primer hole in a cartridge case, and used that as a guide). With the front of the reamer guided by the pilot and the rear guided by the coupling, it was easy to make a straight cut.
The hard part is cutting to the correct depth. I used the upset slug method to make a chamber impression, and then by eye adjusted the seating depth of the reamer so that enough reamer was sticking out of the coupling to clean up the existing throat. It only took a couple of seconds to make the cut.
Then I made another chamber impression. It looked like I needed to cut just a wee bit deeper, so used calipers to adjust the reamer depth, and made another cut. Yet another chamber impression confirmed that the throat was deep enough. In fact, I may have gone a little farther than necessary, but that\s OK for this experiment.
Cutting took a few seconds. Making the coupling and the several chamber impressions took half a day.
The resulting freebore was 0.3133" - 0.3135" diameter, about the same as the reamer.
After considerable trial and error I ended up with a push-thru sizing die that sized air-cooled WW to 0.3127" - 0.3131". Any bigger, and they would not chamber easily. The bullets were oven treated and lubed with Rooster HVR. These bullets were 1-diameter except for a tiny step on the nose.
I loaded 10 rounds each of several different powders. The bullets were seated out to where the front band nudged the tapered lead. At the range, most rounds chambered with moderate resistance. A couple required some cussing, and a couple chambered with no effort. On the whole, that's better consistency than I was able to achieve with the old 2-diameter bullets in the old tapered throat.
At this time of year our private range is opened to the public for sighting in, and it's very crowded. The only available bench was a wobbly wooden left hander that put the rifle a good six inches higher than my shoulder and the morning sun directly in my eye. It was either that or else wait until next year. In retrospect, I should have waited.
Accuracy with the new throat was 6 - 8 MOA. The uncomfortable bench sure didn't help, but I can't blame it all on the bench. None of the loads even came close to shooting a group. OK, so the 0.313" throat sure didn't improve accuracy. Why, I can't say.
I'm confident that the throat was cut straight, smooth, and concentric. The leade angle may be a little steeper than ideal but I've seen plenty worse. For whatever reason, an oversize 1-diameter throat is not the ticket.
So what is the ticket? I don't know. And since I don't know, I think I should continue using these cheap take-off barrels as guinea pigs for chamber experiments before I shell out big money for a custom barrel and custom reamer.
Plan "B" is to set this barrel back an inch and rechamber it with a tight neck. I think that a tight neck will eliminate the need for the oversize cast bullets, so then I'll be able to focus on the throat length and angle. I'll start out with a throatless chamber, and gradually cut the throat a little at a time. I may be able to salvage my 0.313" throater by regrinding it to 0.309" for the next round of experiments. The rechambering experiment will involve some new (for me) skills and tools so it'll probably take all winter or even longer.
Today's experiments did comfirm that Reloader 19 and Ramshot Hunter are very spikey. Even the usually low-spike WW760 had moderate spikes today -- I don't know if that is due to the different throat or due to the different strain gage. Since the adhesive had failed on the previous gage, a new gage was installed with Devcon "Flex" superglue. Other than the cable coming loose during the RL19 string -- more masking tape fixed the cable -- today's pressures seemed consistent and reasonable. Primary pressures were generally lower than book but so were velocities.
This load with Ramshot Hunter was too hot.
Even WW760 had significant spikes today. Velocities were consistent so I can't explain the noisy pressures.
Very consistent pressures with Ramshot Big Game.
The jacketed validation load -- low pressures but low velocities, too.
