RimfireCentral.com Forums - View Single Post - Inconsistent POI with 17 HMR
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Old 09-19-2019, 02:27 PM
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Feb 2014
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My testing showed that measuring OAL (total cartridge length) was misleading because of the gross variation in the dimension of the plastic tip length. That fact is what guided Steve Boelter to measure the length from the ogive to the base of the rim. That dimension will be a more accurate measurement, and he believed the ogive has more effect on chamber pressure. I just followed his recommendation.
Measuring a box of 50 will give lots that cover a range of .010-.016" variation in ogive length, with a normal bell-shaped distribution. For my rifle, best groups came with ogive lengths that were middle of the pack. Increasing upwards from the optimum length, as the bullets became seated closer to the rifling I saw some extreme fliers. Measuring a box of 50 takes about 15 minutes once you have the rimfire gauge set up to measure the ogive. I tried the quick-and-dirty method of measuring OAL with calipers, but that was disappointing due to the plastic tip variations that I mentioned above.
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