rufous
Well-Known Member
I have been learning some about throat types and dimensions lately. Apparently most if not all factory rifles are chambered with a tapered throat. On a 300 Win Mag the diameter of the throat would be 0.3150" just in front of the end of the neck portion of the chamber. It would then taper down to bore diameter 0.2976" in front of neck (according to the reamer drawing I got from Clymer). A parallel throat should be 0.3085" in diameter and would be however long the gunsmith made it. Some chambering reamers are designed to cut no throat at all and the throat is then cut to whatever length the customer wants with a separate throating reamer. Other parallel-throated reamers have 0.100" or 0.200" or more throat length before the lead.
Anyway my 300 Win Mag was cut with a parallel throat 0.300" long. It was longer than I wanted. I had sent a dummy round to the gunsmith, requesting that he throat it so that the dummy round was just touching the lands. He cut it 0.100" longer than I wanted. The magazine box is 3.600" long and most bullets are touching the lands at a length longer than my magazine box will hold.
I have heard just recently that guns whose chambers are cut with a parallel throat will generally shoot very well with lots of bullet jump to the lands. I did not know this when I got my 300 Win Mag back from the gunsmith and I did not know that it had a parallel throat. So I went about load development under the assumption that the gun would shoot best with the bullets touching the lands or out to about 0.030" off. I got the 220 Sierra Matchking shooting very well at 0.010" off and the 200 Nosler Partition shooting very well at 0.030" off the lands, but both of those loads are too long to fit in my magazine box. I tried many other bullets too including the Barnes 165, 168 and 180 and the Swift 180 Scirocco. None of those shot well at the seating depths I tried but perhaps I should have kept seating deeper and deeper due to the parallel throat.
I have been thinking about having the back side of the action milled out to increase the length of the magazine well. That way I could install a longer magazine box to accommodate the long OAL of my cartridge. But I wonder if I should bother with that, which would cost $150 plus shipping, or if I should just shoot the gun more, trying deeper seating depths. Both options will cost money. Trying deeper seating depths will wear on the throat more. Basically I am wondering if many of you have found that your rifles will shoot tight groups with 0.100" and more bullet jump to the lands if your chamber was cut with a parallel throat or if I should get the action altered for a longer box so I can load long and have minimal jump? Thanks for any advice and experience you can offer, Rufous.
Anyway my 300 Win Mag was cut with a parallel throat 0.300" long. It was longer than I wanted. I had sent a dummy round to the gunsmith, requesting that he throat it so that the dummy round was just touching the lands. He cut it 0.100" longer than I wanted. The magazine box is 3.600" long and most bullets are touching the lands at a length longer than my magazine box will hold.
I have heard just recently that guns whose chambers are cut with a parallel throat will generally shoot very well with lots of bullet jump to the lands. I did not know this when I got my 300 Win Mag back from the gunsmith and I did not know that it had a parallel throat. So I went about load development under the assumption that the gun would shoot best with the bullets touching the lands or out to about 0.030" off. I got the 220 Sierra Matchking shooting very well at 0.010" off and the 200 Nosler Partition shooting very well at 0.030" off the lands, but both of those loads are too long to fit in my magazine box. I tried many other bullets too including the Barnes 165, 168 and 180 and the Swift 180 Scirocco. None of those shot well at the seating depths I tried but perhaps I should have kept seating deeper and deeper due to the parallel throat.
I have been thinking about having the back side of the action milled out to increase the length of the magazine well. That way I could install a longer magazine box to accommodate the long OAL of my cartridge. But I wonder if I should bother with that, which would cost $150 plus shipping, or if I should just shoot the gun more, trying deeper seating depths. Both options will cost money. Trying deeper seating depths will wear on the throat more. Basically I am wondering if many of you have found that your rifles will shoot tight groups with 0.100" and more bullet jump to the lands if your chamber was cut with a parallel throat or if I should get the action altered for a longer box so I can load long and have minimal jump? Thanks for any advice and experience you can offer, Rufous.
