Short Actions L46 222 Remington Magnum seating depth aka free bore

Discussion in 'Sako Short Actions' started by BruceHB, Feb 21, 2021.

  1. BruceHB

    BruceHB Active Member

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    Looking to get a relative CBTO measurement on my father’s Sako L46 222 Remington Magnum with Sierra 22 Cal Bench-Rest 53 gr .224 Hollow Points using a Sinclair Seating Depth Gage, it appears the “Free Bore” is approximately .188 assuming the Hodgdon COAL of 2.275 is accurate.

    In the picture with my measurements using the Sinclair Seating Depth Gage using a fired case with the primer left in and measuring one of the sorted Sierra 53 gr bullets, you can see those measurements in column “B.” The neck length is for comparison references only. The Sinclair COAL (cartridge overall length) is 2.463. This COAL measurement then is the relative measurement whereby this bullet in this case is touching the lands. I took three measurements for the measurement in line 5 and had an ES (extreme spread) of .002.

    I then took the same case and bullet and seated the bullet to a COAL of 2.463 and using a Hornady Bullet Comparator and Hornady anvil, measured the CBTO of 2.100 as a relative measurement.

    Using the Hodgdon COAL figure of 2.275 for a 53 gr hollow point bullet, the difference between my OAL Measurements in Column “B” to the Hodgdon COAL indicate a jump to the lands or Free Bore of .188 or a calculated CBTO of 1.91.

    In looking at the Hodgdon seated depth of .264 and an estimated neck length of .225, it appears the Hodgdon COAL has the base of the bullet approximately .039 into the case below the shoulder. I don’t have the bullet profile specs but guesstimating the bearing surface to be roughly .246. This is really a rough estimate as I measured the bullet base to ogive using the Hornady bullet comparator whose ID measured .210 with using a caliper which is faulty in itself, then using a caliper eyeballed the length of the boat tail at .062 and came up with a bearing surface of .246.

    While I’m just starting load development and will first conduct a ladder test, it appears I’ll be limited in what “free bore” range I’ll have available. The free bore assuming Hodgdon’s COAL of .188 seems huge and I’m wondering what others are finding shooting 53 gr bullets in their 222 Remington Magnums?


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