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 Well-Known 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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  2. desperado

    desperado Member

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    Hi BruceHB,
    I'm new to the forum, and came across your post. I also have my Dad's Sako in .222 Rem Mag. Mine's a L469. Like yours, the free bore is excessively long if the goal is to accurize your ammo. I no longer remember the actual number, just that it was hopelessly large.

    Here is the rest of the story on this rifle. Dad's intention was to build a varmint rifle. He never completed it. I became interested in the rifle three decades ago.
    It must have been shipped by Sako as an action-only, as it was fitted with a raw steel barrel in a profile considered heavy for the time, which I assume was installed by the US importer. The barrel has no markings. I have no idea why it was not blued to match the receiver.
    It was accompanied by an unfinished (raw) walnut flat-bottom stock blank which had been inletted to match the barreled action, but the exterior was not shaped.
    I epoxy pillar-bedded the stock and free-floated the barrel using a scraper, then shaped the exterior and applied an oil finish. I cleaned up the exterior of the barrel and blued it. A local gunsmith known for precision rifle work accurized the trigger and reverse-crowned the barrel. I topped it off with a Leupold Vari-X III 6.5-20x mounted in Leupold Sako rings.
    I wish I'd taken pictures before starting the work, to show the transformation. ;/

    It's been some time since I've loaded for or used this rifle, but I still have my reloading notes. I believe we are close to each other in OC and are of similar age. Let me know if you'd like to meet up and compare notes.
     
    Last edited: May 17, 2021
  3. desperado

    desperado Member

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    Following up, I found my old records and see that my recollection about the free bore was incorrect. It looks like I was able to place a 50 grain bullet as close as 0.005 inch to the lands. What I don't have is a record of the COAL and whether I exceeded the magazine length in order to chamber the bullet near the lands, and I don't have any more of those rounds. My three most accurate loads gave 5 shot vertical spreads between .350 inch and .375 inch at 100yds.
     

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