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Old December 9, 2019, 11:33 PM   #38
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Join Date: January 7, 2008
Posts: 3,068
The highest velocity within safe pressure limits

Since I have loaded the 270 for decades, I have learned a little more about it than most other calibers, though there is always more to learn. For quite a while now, I have narrowed the field of bullet weights down to just 3, i.e., 130 grain, 140 grain, and 150 grain. I've shot other weights, but I feel that I lack sufficient experience with those others to have anything to say authoritatively.
That being said, I've shot plenty of ammo in the three most common weights, some factory ammo, but probably 95% handloads. I've carefully danced on that red-line and occasionally put just one foot slightly over to find the limits of safety. The conclusions that I have come to seem to indicate that with optimum propellants, I can expect to achieve the following velocities from my 24" barreled model 70 Winchester:
  • 130 grain bullets ..................3,200 fps.
  • 140 grain bullets ..................3,100 fps.
  • 150 grain bullets ..................3,000 fps.

These would be maximum loads using optimal powders; with sub-optimal powders, excessive pressures would manifest their symptoms before these velocities could be reached. With a 22" barrel, these figures should be reduced by a full 100 fps. My experiments were conducted using a chronograph, which you really don't need if you are willing to stay away from maximum loads. Some rifles will exhibit excess pressures at slower speeds no matter what you try.
I have gone over these figures at times.... Most notable was when I was getting 3,285 fps with 140 grain bullets. All seemed well and good; the cases and primers looked right, no sticky bolt-lift, etc. so I loaded the cases again with the same recipe and apparently the same results,....until I went to load them a third time and found that half of the cases took the fresh primers awfully easy. I found that I could fully seat new primers on several of these cases with my bare hands. The conclusion I reached is that the pressure was way too high and that the first indication was not loose primer pockets, but rather, it was the velocity itself.
Factory ammo is made to be safe in every rifle of that caliber. Thus, it usually only matches their listed velocity in those few rifles with minimum chamber and bore specs. Each rifle is at least a little different than the next. My brother had a 270 with the barrel cut to 20" for a saddle scabbard. His rifle was always around 200 fps faster than my 24" barrel because of minimal chamber dimensions. Loads that were completely safe in my rifle were way over-pressure in his. Factory loads did everything they were supposed to do, in his rifle only, but not mine.
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