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Thread: Correct C.O.A.L won't fit in the mag..

  1. #1
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    Correct C.O.A.L won't fit in the mag..

    So I've just started load development on an old .308 I've had for a while. Got some Sierra 155gr TMK's which are the ideal weight for the gun.

    First thing I do after setting the proper head space is make up a "loose neck" round to determine the distance to the OGIVE for said rifle, whereby allowing the lands to push back the bullet when the round is chambered. Always used this method with excellent consistency. This time was no exception, I chambered 5 rounds and they were all within .0005" of each other.

    Problem is when I set the bullet .015" from the lands the C.O.A.L is 2.960"! Cartridge is too long to fit in the mag. Unsurprisingly really given the max C.O.A.L for .308 is 2.800".

    Anyway it's left me thinking 3 things:

    1. The start of the rifling in this particular rifle is set unusually far forward?
    2. My magazine is on the short side?
    3. The profile of the Sierra bullet has a shallow taper and therefor protrudes further from the case before contacting the lands, which leads me on to thinking I might need to try a different bullet?

    If I set the C.O.A.L to the recommended length (and so the round fits in the mag) the bullet is going to have a massive .175" jump to the lands, which I'm not happy about at all.

    Anyone else come across this problem before?

    Cheers
    Greg

  2. #2
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    What make of mag? I had an after market howa mag conversion that would not let me load to saami length, 2.812 rather than 2.825. Careful filing opened it up and now it's fine!
    Thanks for looking

  3. #3
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    Quite normal I believe, 3 of my magazine rifles are similar. I just make sure I know which rounds I load to mag length.
    Pistol & Rifle Shooting in the Highlands with Strathpeffer Rifle & Pistol Club. <StrathRPC at yahoo.com> or google it.
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  4. #4
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    Several of mine end up with a COAL over 2.900" if I seat a bullet to the rifling. I have one .308 Win with a throat so long, a bullet will generally fall out the case before it can touch the rifling - it still groups well with mag-length cartridges.

    My understanding is many factory rifles are given a long throat to accommodate a wide variety of bullets, including heavy round-nose designs.

  5. #5
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    Thanks for the replies chaps.

    Talking to a few guys at the club yesterday it seems pretty common, though it is the first time I have experienced it.

    One thing that still does worry me is the bullet won't have full contact with the entire length of the neck, it'll just be seated a partial way down. Might not be such an issue but I bet it'll leave a visible band on the outside of the cartridge, and this I haven't seen before.

    Cheers
    Greg

  6. #6
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    Quote Originally Posted by Thegreg View Post
    Thanks for the replies chaps.

    Talking to a few guys at the club yesterday it seems pretty common, though it is the first time I have experienced it.

    One thing that still does worry me is the bullet won't have full contact with the entire length of the neck, it'll just be seated a partial way down. Might not be such an issue but I bet it'll leave a visible band on the outside of the cartridge, and this I haven't seen before.

    Cheers
    Greg
    It is usually suggested that the diameter of the bullets seated in the neck is a good starting point ie 308 should be at least 308 thou in the case or better still start at the recommended COL of 2.800 as in your 308 using the OCW or Satterlee method to test.

    Personally I have never been able to get my head around the concept of seating the bullet 20 thou or less unless it happens to be a bench rest rifle. Most rifles have as many as four sweet spots, granted the first may well be less than 40 thou but that may be the obvious node to find - against it are two points to consider - will it fit the magazine and now with this long bullet balancing at the end of the case neck you are creating quite an air gap above the powder which can delay ignition by a nano second especially as that air pocket will creep back towards the primer as usually rounds are fired on the horizontal.

    I must confess to having a little chuckle when you mentioned 'a massive 175 thou jump' - a chuckle only because my 20 Tac with a custom barrel is 223 back and will group sub .2, my 22.250 at 220 thou and 6.5 at 180 thou - both well less than .5"

    Tried to put a couple of scans of other people's rifles I reload for showing these 'massive jumps' but I'm not technical enough to achieve this.

    Peter

  7. #7
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    Quote Originally Posted by dicehorn View Post
    It is usually suggested that the diameter of the bullets seated in the neck is a good starting point ie 308 should be at least 308 thou in the case or better still start at the recommended COL of 2.800 as in your 308 using the OCW or Satterlee method to test.

    Personally I have never been able to get my head around the concept of seating the bullet 20 thou or less unless it happens to be a bench rest rifle. Most rifles have as many as four sweet spots, granted the first may well be less than 40 thou but that may be the obvious node to find - against it are two points to consider - will it fit the magazine and now with this long bullet balancing at the end of the case neck you are creating quite an air gap above the powder which can delay ignition by a nano second especially as that air pocket will creep back towards the primer as usually rounds are fired on the horizontal.

    I must confess to having a little chuckle when you mentioned 'a massive 175 thou jump' - a chuckle only because my 20 Tac with a custom barrel is 223 back and will group sub .2, my 22.250 at 220 thou and 6.5 at 180 thou - both well less than .5"

    Tried to put a couple of scans of other people's rifles I reload for showing these 'massive jumps' but I'm not technical enough to achieve this.

    Peter
    Thanks for the reply Peter. It is encouraging to hear that bullets don't necessarily need to be be set just off the lands but it's always a variable I've tried to keep tight control of. It does make sense to me that seating a bullet just off the lands will eliminate a lot of potential misalignment that might occur with a jump. When doing testing on my .223 I recorded noticeable differences when seating between .005" & .020" from the lands, so I believe it is influential.

    I'm going to try some different heads. See if I can get the seating depth I want while still being able to fit in the mag. Using polymer tips doesn't help me with the length issue so am going to look at hollow points instead.

    Point taken about the air gap created by seating further out of the case.

    Cheers
    Greg

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    Greg,
    Is it not simply the case that the TMK projectiles are longer/slimmer at the "sharp end" than, say, the equivalent weight SMK and others?
    I was put off using them in my .308 as the OAL increased to the extent that they wouldn't fit the mag if powder space was to be preserved. Presumably the same would apply to your .308 too. Is it a Remington by any chance? In other words, if you seat the TMKs to mag length you risk losing case volume and having a compressed load.

  9. #9
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    Quote Originally Posted by severnsider View Post
    Greg,
    Is it not simply the case that the TMK projectiles are longer/slimmer at the "sharp end" than, say, the equivalent weight SMK and others?
    I was put off using them in my .308 as the OAL increased to the extent that they wouldn't fit the mag if powder space was to be preserved. Presumably the same would apply to your .308 too. Is it a Remington by any chance? In other words, if you seat the TMKs to mag length you risk losing case volume and having a compressed load.
    That's what I'm hoping. They are a long slender profile and I noticed in the .223 they had a longer C.O.A.L than the equivalent 55gr Hornady AMAX head.

    I'm going to try Lapua Scenar's for starters, which I've heard good things about.

    The rifle is a Krico 640S, not at all common so very unlikely I'd get feedback from anyone else who owns one on here!

    Cheers
    Greg

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    Quote Originally Posted by Thegreg View Post
    That's what I'm hoping. They are a long slender profile and I noticed in the .223 they had a longer C.O.A.L than the equivalent 55gr Hornady AMAX head.

    I'm going to try Lapua Scenar's for starters, which I've heard good things about.

    The rifle is a Krico 640S, not at all common so very unlikely I'd get feedback from anyone else who owns one on here!

    Cheers
    Greg
    The Scenars ought to work, but if you really want to use the TMKs then I think you're going to be stuck with single loading and not using the magazine. As you say, the TMKs will probably give you the same probem in the .223. Good luck!

  11. #11
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    The ogive of TMKs is set further down the shank. My Redding seating die won’t sit .223s deep enough firvnag length loading.

    Roy Wetherby was a great proponent of free bore. He was so convinced of his testing that he was the first manufacturer to guarantee the accuracy of his rifles and all factory offerings had a long leade.

  12. #12
    harry mac's Avatar
    harry mac is offline You can't say muntjack without saying mmmmm
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    Forget how far it has to "jump", see how it shoots when loaded to either book length, or just short enough that it fits the mag. You have to work very hard to make a .308 shoot badly.
    The South of England has 2 good things, the M1 and the A1. Both will take you to Yorkshire.

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    Quote Originally Posted by harry mac View Post
    Forget how far it has to "jump", see how it shoots when loaded to either book length, or just short enough that it fits the mag. You have to work very hard to make a .308 shoot badly.
    I 2nd that if it shoots at 2.800 why bother playing with the length? All you are doing is introducing variables and expending materials and time, of course if you enjoy that then crack on, but IMHO too many people jump straight past the basics and then get into trouble because of the "wisdom of the interweb"
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  14. #14
    Parabuteo is offline My Chrony has bought it a couple of times...
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    I only now shoot mag loaded rifles. The point of loading near or into the landes is more to do with getting a more constant pressure spike/release pressure than relationship with the landes.

    The OAL can be pushed back as well as forward and still get excellent groups, although they groups will be more down to the harmonics/load, with the release point being a factor.

    Many military rifle shooters simply set to standard OAL (SAAMI etc, or copy a service round), then neck crimp (which serves a similar function to loading into the landes but does not need the bullet barely hanging on, this is not ideal when you are loading from a mag via a feed ramp as you may well end up with an eccentric bullet).

    Firm crimping gives a more consistant group in all of my rifles which are all mag loaded fairly rapidly. You do not have to worry about the landes eroding and constantly pushing the OAL forward either.

    You can often get great results simply by factory crimping and changing the load.
    I'm a maggot in another life you know

  15. #15
    Parabuteo is offline My Chrony has bought it a couple of times...
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    Quote Originally Posted by kennyc View Post
    I 2nd that if it shoots at 2.800 why bother playing with the length? All you are doing is introducing variables and expending materials and time, of course if you enjoy that then crack on, but IMHO too many people jump straight past the basics and then get into trouble because of the "wisdom of the interweb"
    Pratting about touching the landes is also more likley to get you into an over pressure situation as well Ken, a good firm crimp or neck tension wont.
    I'm a maggot in another life you know

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