What is the Freebore and throat for a .243 L579? I may have big trouble.

Discussion in 'Sako Medium Actions' started by rchouser, Mar 19, 2015.

  1. rchouser

    rchouser Member

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    I brought home this L579 243 Heavy barrel FI last Sunday. I was getting ready to load some "first rounds" with hopes of finding some fine accuracy.

    As a first step, I pulled my Hornady Comparator and set it up with a .243 win casing and a Fowler 80 gr match bullet. I find that it hits the lands almost 1/8 inch beyond the end of the case mouth. I then selected a Speer 105 gr spritzer. This hit the lands exactly at the end of the case mouth. To the outside of the case mouth.

    What the heck, this is a 1:10 twist barrel, I can't go any bigger bullet. Is this just extreme throat erosion or is this chamber very long throated or long free bored? Is there something everyone else knows about the chambers in late 60's Sako's?

    I really don't have any history on this gun. I have never fired a round. I have confirmed the twist (more or less) with a cleaning rod. I don't see any "smith" stamps for an AI or anything plus an AI chamber should still accept a standard 243 to the shoulder.


    I am stumped. Can anybody shed any light on this. I have been reloading for 40 years and have never seen the like. Maybe I need to tap the comparator into the chamber to fully seat the dummy casing?

    Help if you can.

    thanks rch
     

  2. cmjr

    cmjr Well-Known Member

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    Your going to find all these early rifles are long throated, new or used. Especially if you come from a discipline of seating in the lands for accuracy. These are designed as hunting rifles and they have to fit whatever you feed them. Flip side is they still shoot with some jump. I load my Heavy barrel 243 to fit the mag and that's where I leave it but if I'm after bug holes I'm not shooting a 50yr old factory gun either. I would load to SAAMI spec a bullet in the 80-95gr area and shoot it before I became concerned with jump.
     
  3. sakoluvr

    sakoluvr Active Member

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    Yep, forgetaboutit if you are used to running handloads kissing the lands. Load to magazine constraints and try different bullets/loads that will give you the desired accuracy. With a slow twist you can only go light. I have found Barnes bullets shoot well (they are generally long for caliber) despite a serous leap into the barrel. The rifle that my son is holding in my avatar is a .308 and it loves 130 gr Barnes TTSX's. Best of luck and enjoy the testing.
     
  4. bloorooster

    bloorooster Sako-addicted

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    Rc...save yourself some undue stress and just go shoot it! Mine shot Nosler ballistic tips into the .3''s with the OAL just enough to fit the magwell. 80-95 gainers do best...for me. That gun also shot Federal Power shock 100 grs factory ammo into a half inch pretty consistently.

    If this is your first Sako...you will feel better when you shoot it a bit. That's when it starts.
    Work up a pet load or two and give it a whirl!~Bloorooster
     
  5. rchouser

    rchouser Member

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    Thanks to all who replied. I can now go to sleep without worrying about what is up with my new old Sako throat. I will load of few different bullet types in the morning and then sneak off to a range and see where we are at. While I am not a true bug hole addict, 1 moa at 600 yards is 6+ inches. Not a lot of extra room for a varmint gun to be outside of MOA.

    On the other hand, what a beautiful gun. I love the way it lays up with the heavy barrel for off hand standing. The wood is really pretty in the sun. The bluing is little thin in places and the wood has a few light nicks and dings, but, at 64, so do I. The trigger is amazing... almost too light. I will choose my starting powder in the morning.

    Thanks again for this great forum.
    rch
     
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  6. David_S

    David_S Well-Known Member

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    As other posters have written, just go shoot it! But I think you will find more and more "like cases" if you start shooting the new generation of sleek pointy low BC bullets such as the Berger VLDs and Hornady ELDs.

    For example, a 145gr ELD-X projectile in my Sako 75 270 WSM has a COL of 80.2mm (3.157") when touching the lands but the magazine is barely 75mm in length. So to fit the magazine it has to be seated at least 5mm (0.197") off the lands! I have not yet tested this projectile but the 130gr SST is similar, though not as pronounced, and I have found the SST shoots just fine with a jump of around 4mm.

    Once you have a reasonable load which fits the magazine I suggest you experiment with different seating depths as you may find a more accurate node at an even bigger jump! Something I learned just the other day (from the Berger site I think) is that bullets with a secant ogive - as the SSTs and ELDs - are more sensitive to seating depth than those with a tangent ogive used by older styles of projectile. Seems you pay a price for everything - higher BCs and less drag but more fiddly seating or lower BCs, higher drag and less sensitivity. One thing I am sure of though is that no deer I have shot has ever had the faintest notion what an ogive was! -David
     
  7. Cali

    Cali Well-Known Member

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    I have the L579 sporter in 243 and maybe I was just lucky but my first two handloads shot extremely well. 100 gr Nosler ballistic tip bullets and Speer 70 gr hollow points easily group at .5" to .75".
    Three shot groups in that rifle are always less than one inch.
     
  8. mark garrison

    mark garrison Member

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    [​IMG] My heavy barrel L579 cuts a tight clover at 100. [​IMG] I love this load. Anneal your cases and check for concentricity. I bow to the Forrester.



    Sent from my iPhone using Tapatalk
     
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