But it says 10"twist or faster !

[Ironworker]

Sierra 60 gr TMK on the box it says 10"twist or faster . My 22/250 has a 12"twist bbl and its a Tac Driver ,especially when shooting those Sierra's at 5,000 FT elevation . I've made center hits on gongs at 400 yds here in Reno NV . But prairie dogs out in Crow Indian land outside Billings the elevation is under 3,000 FT . Will they still stabilize ?

 

[GLShooter]

With the extra speed you will be fine.

Greg

 

[Ironworker]

Dang it ,I just used the Berger Twist calculator . It says at 5,000 ft I'm marginally stable,but at 2,800 I'm not and to expect poor accuracy .

 

[GLShooter]

Based on your program results it should be
educational. I've not always had the results that it comes up with but then I'm not shooting Enfield rifled barrels. Polygonal rifling is a bit different. I have no idea why but can only look at the results. I lay it at the feet of less engraving resistance.

Greg

 

[Ned Ludd]

What were the specific Sg outputs given by the program at the two different elevations? Berger uses the term "marginal stability" in their output for Sg values ranging from 1.0 to 1.5. IMO, this can be very misleading. Typically, bullets with Sg values ranging from maybe 1.25-1.30 or so, up to just barely under 1.50 should not exhibit any major or noticeable loss of precision/accuracy. They simply behave as though their BC is a little lower than the true/actual value. The other consideration for your specific case is that the TMK has a plastic tip, something Berger's calculator doesn't take into account. You might want to try using JBM's stability calculator, which allows you to input the plastic tip length:

JBM - Calculations - Stability

www.jbmballistics.com

 

[Ironworker]

26" muller works cut rifled bbl 12" twist. Well I've only loaded up 12 rounds ,the rest will be 55 gr bullets .

What were the specific Sg outputs given by the program at the two different elevations? Berger uses the term "marginal stability" in their output for Sg values ranging from 1.0 to 1.5. IMO, this can be very misleading. Typically, bullets with Sg values ranging from maybe 1.25-1.30 or so, up to just barely under 1.50 should not exhibit any major or noticeable loss of precision/accuracy. They simply behave as though their BC is a little lower than the true/actual value. The other consideration for your specific case is that the TMK has a plastic tip, something Berger's calculator doesn't take into account. You might want to try using JBM's stability calculator, which allows you to input the plastic tip length:

JBM - Calculations - Stability

www.jbmballistics.com

1.138 very interesting thanks

 

[DiffEQ]

Stability calculations are a very useful 'rule of thumb', but don't absolutely predict behavior. I have some mono rounds that are slow and calculate as unstable on Berger, marginal on JBM, but are phenomenally accurate out to 200 and make me think I might just have some skill at shooting.

 

[JohnKielly]

Distance is the killer when stability is marginal, but it shouldn't be an issue in this instance.

 

[Ned Ludd]

26" muller works cut rifled bbl 12" twist. Well I've only loaded up 12 rounds ,the rest will be 55 gr bullets .

1.138 very interesting thanks

An Sg of 1.138 is getting pretty low to where it could well cause problems. Once the Sg gets down to the 1.0 to 1.1 range, oblong holes in the target or even keyholing may become evident. Hopefully, switching to the shorter 55s will solve any issues you may have.

 

[Ledd Slinger]

Using the recommended twist of a bullet is best, but speed and high elevation can make up for that in a slower twist barrel to an extent. Just keep em running hot and you’ll probably be ok

 

[CJ6]

My friend runs a 10 tw. Kreiger in 240 Weatherby and uses 108 Bergers. They run straight and true out to 880 yds. ( his MAX distance of the range) at his home range winter and summer. Elev is 1342' at the airport. So I take things with a grain of salt so to speak.

 

[pdhntr]

26" muller works cut rifled bbl 12" twist. Well I've only loaded up 12 rounds ,the rest will be 55 gr bullets .

1.138 very interesting thanks

I am interested in the values you entered to get the SG.

I am developing a load for a 22-250 and the SG that I came up with is just over 1.2.

I am still breaking in the barrel but the last two 60 TMK went on top of each other. I am going to test further, going up in powder and then run it over the chronograph. This rifle may see some use on called coyotes in Montana, and I need to get the numbers correct.

Thanks.

Jim