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Thread: N140 Temperature Variation

  1. #1

    N140 Temperature Variation

    I thought I might share this experience to save others some time, and avoid potential injuries.


    I am working on a .223 load which I can use out to 600yds.

    I have two bullets I am testing.
    69grn SMK and 68grn Hornady 2278.

    I opted for N140 as I use it in the .308 with 168grn AMax to very good effect.

    Four days ago I shot a 0.289 moa three shot group at 100yds using the 2278.

    Click image for larger version. 

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    As this looked like it was working I ran another test this morning with a five shot group, and only managed to hit (if I can call it that) the paper target three times.

    Click image for larger version. 

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    The only difference was the temperature was 22 Celsius lower.

    I ran the figures through the various programs I have and it appears the drop is around 50fps, and as this is a long bullet with a 1.9 twist, it is on the edge of stability.


    I guess I should have remembered the effect of temperature on N140 as this was the very reason I used Varget last time I worked on this load (about four years ago).

    Luckily this is not a hot load, and I was working in the right direction.
    Previously I had a load for a 60Grn V Max which I worked up in winter, come summer it started flattening primers.

    All part of the learning curve I guess.

  2. #2
    50fps turned a .2 moa load into a 5-6 MOA load?

    doesn't sound right there even with the 22deg

    I used N140 in .308 at the top end of the load data, granted not a particularly unstable bullet but I never experienced opening up of groups like that with any range of temperature, certainly a good 15+ degrees on the days I can think of

  3. #3
    Quote Originally Posted by Cooter View Post
    I thought I might share this experience to save others some time, and avoid potential injuries.


    I am working on a .223 load which I can use out to 600yds.

    I have two bullets I am testing.
    69grn SMK and 68grn Hornady 2278.

    I opted for N140 as I use it in the .308 with 168grn AMax to very good effect.

    Four days ago I shot a 0.289 moa three shot group at 100yds using the 2278.

    Click image for larger version. 

Name:	68Grn_25_4_20150701.jpg 
Views:	12 
Size:	51.0 KB 
ID:	58808

    As this looked like it was working I ran another test this morning with a five shot group, and only managed to hit (if I can call it that) the paper target three times.

    Click image for larger version. 

Name:	68Grn_25_4_20150705.jpg 
Views:	16 
Size:	136.9 KB 
ID:	58810

    The only difference was the temperature was 22 Celsius lower.

    I ran the figures through the various programs I have and it appears the drop is around 50fps, and as this is a long bullet with a 1.9 twist, it is on the edge of stability.


    I guess I should have remembered the effect of temperature on N140 as this was the very reason I used Varget last time I worked on this load (about four years ago).

    Luckily this is not a hot load, and I was working in the right direction.
    Previously I had a load for a 60Grn V Max which I worked up in winter, come summer it started flattening primers.

    All part of the learning curve I guess.
    What about barometric pressure ? Was it a lower pressure day when it shot well ?
    Bullets on the edge of stability can be one way or another on air pressure alone. Thinner air at lower pressure is better for stability.
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  4. #4
    The first group was late afternoon with high humidity and high temperature, the second was early morning, with crisp almost cold air.

    The 2278 is a long bullet which really requires a 1.8 twist.
    I also ran 69grn SMK and they gave only a slight increase in moa, and that was at 200yds.

    I can get the 2278 to work but I have to run it hot.
    It is a better option than the smk as it stays supersonic out to 750yds, where the smk drops out around 650.


    All good fun.

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