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Thread: COL after pressing bullet variance

  1. #1

    COL after pressing bullet variance

    Hi All,

    I am still relatively new to reloading, and I am having kittens over COL and the inaccuracy when bullet seating. If I sneak up on every one of the loads, I can get "close" to the right COL and sometimes bang on. But unless I reset every time I get a wild variance.

    I have done the following:

    3 presses, Lyman all american, Lyman T-Mag and a mates press, all still showing the variance ( I have also shimmed any movement out of the turret on my t-Mag and All american)
    Various bullets, Sierra Matchking in 77grn 69grn, PPU 62grn (these have been weighed and grouped to, thinking it may be manufacturing tolerances)
    2 types of case, Federal and Lapua match (weighed these and graded them to, in case
    Trimmed all brass to length, cleaned and uniformed primer pockets etc.

    Am I worrying to much or is there an answer I am missing here? IS there something else I can do in this quest for accuracy?

    Thanks to anyone that takes time to read my rantings.

    Chris

  2. #2
    It's most likely the variation in dimensions of the bullet tips that I causing this. Set your seater for the length you need and forget about it. The important part is that the ogive/curved part of the bullet will be seated at the same length each time, and in turn it's distance from the rifling will be the same.

  3. #3
    I had the same worries on my first reloads!
    I think the important factor is not going below the recommended minimum COAL for calibre (causing overpressure), going over is not so much of a problem as long as you don't jam the lands, go over mag length or have the bullet hanging out the case!

    The most reliable way I have found is to measure to the ogive of the bullet in your chamber using a comparator like this
    Hornady Manufacturing Company :: Reloading :: Metallic Reloading :: Tools Gauges :: Lock-N-Load Gauges-Formerly Stoney Point :: Bullet Comparators :: Bullet Comparator Kits :: Lock-N-Load® .224-.308 Comparator Set With 6 Bullet Inserts
    (they are readily available in a couple of different types)
    average half a dozen measurements then back off by 20thou of an inch.
    make up a dummy round to that measurement and check it cycles in your rifle and mag happily, then seat your bullets to this and forget about differences to the tip of the bullet, as said above these change quite dramatically, the important constant is the point the ogive touches the rifling, not the tip. I know a lot of the target shooters play around with this distance to get things spot on, but between 15-30thou off seems to be an acceptable safe starting point.
    Thats just my thoughts of course, worth checking everything twice with your rifle!
    Last edited by andychas; 24-01-2016 at 21:03. Reason: omitted a key word!

  4. #4
    Do not waste time with the comparator faff, what they don't tell you (or understand) is that the ogive varies as well - and that there is no magic 'off the lands' dimension.
    Stick to book COL and get loading.
    You obviously can measure the bullets to calculate the tip to tail variance and work out your seating depth which is more relevant.
    A young man who isn't a socialist hasn't got a heart; an old man who is a socialist hasn't got a head.
    I have summat for sale; here's the M̶i̶d̶w̶a̶y̶ Brownells UK price... effin jokers.
    "The .30-'06 is unstable at close range" - Ahahahahhahh!


  5. #5
    The Hornady/Stoney Point comparators are easy to use and very accurate. An alternative and simple approach is to deprime and size a cartridge case. Sit a bullet of the type you will be using into the case mouth, insert into your rifle and close the bolt, which may take a bit of effort. You will then have a cartridge with the bullet seated at the depth where it is touching the rifling lands. This can cause potentially dangerous high pressure on firing, so adjust seating depth to push the bullet into the case by another 0.020" which you can measure from the bullet tip to the case base. This will give you a safe COAL setting for your seating die which should be reasonably accurate, you can then experiment with SMALL variations to establish what works best. Once you decide on this measurement, you can make a gauge cartridge as described, and use it to setup your seating die for each bullet type you are using. Don't get too hung up on COAL, this will vary a lot between individual bullets from the same box. The measurement of the bullet ogive to the rifling lands is far more consistent and important than the overall length of the cartridge. Find what suits your individual rifle and use that. Also, get a hardback A4 notebook, and use it to keep a detailed record of seating depths, powder loads etc, and keep grouping test targets in it as well. It will over time become a valuable record of what you did, what worked and what did not.

  6. #6
    Buy the Hornady (Stoneypoint) or other manufacturers bullet comparator & use it to measure from the ogive to case head. It's easy to do this and will show much more accurate OAL from where it matters - the ogive. You will then be much more assured of the continuity of seating depth you've elected to use.
    Blaser K95 Luxus Kipplaufbüchse .25-06Rem. Zeiss 8x56, 110gn Nosler Accubond = Game Over!

  7. #7
    Quote Originally Posted by Sauer90 View Post
    Do not waste time with the comparator faff, what they don't tell you (or understand) is that the ogive varies as well - and that there is no magic 'off the lands' dimension.
    Stick to book COL and get loading.
    You obviously can measure the bullets to calculate the tip to tail variance and work out your seating depth which is more relevant.
    Pay heed to this advice. It is the most solid reloading advice here.~Muir

  8. #8
    Quote Originally Posted by Sauer90 View Post
    Do not waste time with the comparator faff, what they don't tell you (or understand) is that the ogive varies as well - and that there is no magic 'off the lands' dimension.
    Stick to book COL and get loading.
    You obviously can measure the bullets to calculate the tip to tail variance and work out your seating depth which is more relevant.
    Sauer and Muir
    Interesting and well received thoughts on this, can I just check a couple of things with you, bearing in mind the OP is loading target ammunition in his search for maximum accuracy (sierra matching)?
    I get that the Ogive can vary, surely not as much as the tip though?. In all the measurements Ive made, the ogive hasn't varied anywhere near as much, not is the ogive as liable to damage as the tip?
    Whilst I can see there is no one magic "off the lands dimension" do you not think that each rifle is different (throat lengths) and each rifle will perform more consistently if you do find its best off the land distance with any given bullet?
    As an example with a .243 (max book COL 0f 2.710")
    If I load up a 95gn Sierra Matchking target round (a 1.16" long bullet ) to the book distance, its seating depth is very deep in the case (potential for overpressure?), with a long jump to the lands (in my rifle it would have nearly 2 tenths before it contacted the rifling). I can overcome this by measuring to the ogive and safely seat the bullet nearer to the lands. Overpressure potential of deep seating aside, it makes more sense to me for the bullet to have less distance to be yawing before it gets stabilised by the rifling?
    By measuring the bullet length variances and averaging them out to get a seating depth, aren't you faffing about as much as using a comparator anyway?
    when you say the seating depth is more relevant, what does this give you if not both a safe min/max OL and effectively the distance to the lands?

    I absolutely realise that precision measuring is far less relevant to a home loader who just wants reliable, safe ammunition to stalk at distances under 150yards than it is to a someone who target shoots at greater distances as well and wants to get the max possible accuracy out of his rifle. It would be useful for us newbies to hear more of your thoughts.
    cheers
    Andy

  9. #9
    Is factory match ammunition loaded to a specific 'off the lands' or just to sammi spec? Rhetorical question.

    As to potential for overpressure, well if that is a book col, where is the 'potential'?

    Personally I don't ever worry about jump to lands, paying attention to case prep and assembly will usually result in match grade performance.


    By measuring the bullet length variances and averaging them out to get a seating depth, aren't you faffing about as much as using a comparator anyway?
    I did not say you have to measure, but it costs less than a plastic and aluminium tool, and is a more useful dimension in general.

    As to yawing in the leede you might want to look at a cut chamber and think that through again...
    Last edited by Sauer90; 25-01-2016 at 10:14.
    A young man who isn't a socialist hasn't got a heart; an old man who is a socialist hasn't got a head.
    I have summat for sale; here's the M̶i̶d̶w̶a̶y̶ Brownells UK price... effin jokers.
    "The .30-'06 is unstable at close range" - Ahahahahhahh!


  10. #10
    Sauer,
    thanks for your reply, its interesting to get your thoughts.
    re overpressure, I'd always been told that seating a bullet too deep can (in some loads/circumstances) lead to overpressure. With some newer, longer target bullets, do you not think that could be an issue? would it not be better with a longer nosed bullet to negate that (albeit maybe slight) risk and forego concerns of being slightly longer on OAL. The SAAMI spec on OAL is there to prevent bullets coming into contact with and jamming into the lands (causing overpressure), and obviously takes into account a huge variety of rifle chamber and bullet design, taking the lowest mean figure to be safe. consistent measurement and backing off correctly from the ogive (which is what touches the rifling, not the tip) and in your own rifle gives you that surely?

    I totally agree that proper case prep etc is vital and that distance to lands within reason shouldn't be an issue, but the OP is having a problem with target loads and if he's happy to be weighing cases, bullets etc. then looking at various seating depth methods and OAL's is potentially useful to him?

    I get that measuring bullet variance gives you a useful figure, on its own though Im not sure what you mean. Do you mean that you then just subtract this measurement from the book OAL without any interaction with your rifles specific chamber? or do you mean making up a dummy round and trying in the chamber as in one of the other posts?

    Re the yawing I clearly need to think that through again as Im still not sure what you mean, all i know is that the bullet is mobile and wobbling when its in the leede, its only stable when its held by the rifling. There surely must come a point where allowing too much free travel is detrimental to accuracy?

    Apologies for all the questions, Im not trying to be confrontational with any of this, I know that every person has different ways of doing things, its incredibly useful to hear the thoughts of experienced loaders like yourself so thank you for your responses.

    cheers
    Andy

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