cracking for another couple of inches. Many methods have been tried to


reduce throat erosion since smokeless powder became the primary rifl e pro- pellant, including platings and coatings ranging from chromium to ceramics. These can slow down erosion, but the steel underneath still gets hot. Coating bullets with molybdenum disulfide doesn’t slow down erosion much either, since it only reduces bullet friction, a relatively minor source of the heat gen- erated when a rifl e goes bang. One of the problems with an


eroded throat, of course, is that accuracy starts eroding too. Exactly how long this takes depends on the cartridge, the steel, and how long and often the barrel is shot hot. Much also depends on the shooter’s defi nition of accuracy. A benchrest shooter often considers a barrel shot out in fewer than 1,000 rounds, but I’ve known varmint hunters who’ve gone far longer before replacing the barrel. My old friend Chub Eastman, who


worked for Leupold and then Nosler for decades and turned gun writer in his semiretirement, once had a prairie dog rifl e chambered for the 223 Rem- ington. Chub kept pretty close track of the number of rounds shot through the rifl e, and the barrel fi nally quit shooting minute-of-prairie-dog at around 20,000. Chub then had the rifl e rebarreled – and the original barrel cut in half lengthwise – to see what remained inside. The an- swer was “not much”: The rifl ing was completely gone for six inches in front of the chamber. Now that’s a long throat! For decades the common belief


has been that throat erosion can be compensated for by seating bullets out farther (though it would have been hard to seat a 50-grain Ballistic Tip far enough out in Chub’s barrel). This often helps accuracy, but several of the lab ballisti- cians I’ve ever talked to have noted that peak pressure rises and becomes erratic as a throat fi rst starts to erode. At first this increased pressure


is because of increased bullet friction in the cracked throat, but can become much worse when steel starts chunking, probably because the diameter of the throat grows enough that thin-jacketed, lead-cored bullets actually “bump up” in diameter as they enter the worn throat. The bullet then must be squeezed down again as it enters the rifl ing, in-


www.varminthunter.org Page 115


The fl iers disappeared from the 221’s targets after the throat was smoothed with 15 shots of 220-grit fi re-lapping compound.


creasing the peak pressure. One solution to throat erosion is to


cut off a couple of inches of the rear of the barrel, then refi t and rechamber the


shortened barrel, eliminating the eroded section. Depending on the contour and length of the barrel, this sometimes can be done two or three times.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192  |  Page 193  |  Page 194  |  Page 195  |  Page 196  |  Page 197  |  Page 198  |  Page 199  |  Page 200  |  Page 201  |  Page 202  |  Page 203  |  Page 204  |  Page 205  |  Page 206  |  Page 207  |  Page 208  |  Page 209  |  Page 210  |  Page 211  |  Page 212