Reloading 6.5 Creedmoor

[Fuj']

Fuj', can you explain what 1.3 as calculated is referring to?

The Miller stability calculators used by JBM and others list the stability numbers as 1.3 as the
minimum and 2.0 as maximum. Simply put, under 1.3, you run the risk of key holing and over
2.0, would mean over spinning and possibly blowing bullets up. JBM is a free online calculator.
Very simple to use. I have several I use, but JBM is quick when checking stabilities.

And Mr. Hoback.....Why would I recommend a twist without knowing the bullet and speed you'll
be dealing with. If your ordering up a 1:7.5 twist, that's fine if you did the math.

[charlie b]

For the most part I rely on the bullet mfg to determine twist for stable bullets....BUT....it is not written in stone. The muzzle velocity is a large factor in this. Drive a bullet 100fps faster and the spin rate is that much higher with a higher stability factor.

Keep in mind the Miller stability equation is a simplification of the basic stability equations. The main points are they assume a bullet profile that looks like a football and the velocity range is intended to be near Mach 2.5. The fine points of bullet design can make the calculated number off a bit. It is a good guide, but, again, not definitive.

Working with Sierra 77SMK's in 1:9 twist barrels. Sierra recommends 1:8 or faster but the 1:9 works in many rifles, at least when the velocity is closer to max. Maybe if you use a 16" barrel and subsequent slower velocity then a 1:8 will be necessary, or maybe Sierra is just being conservative and want the bullets to be stable at minimum book loads.

Last, when working 'near the edge' atmospheric conditions can change enough to upset the stability. Much colder or warmer, higher or lower elevation, humidity can all change the stability of the bullet. Some variations of the Miller equation (like JBM) allow input of temp and pressure due to this.

[Ernest T]

The Miller stability calculators used by JBM and others list the stability numbers as 1.3 as the
minimum and 2.0 as maximum. Simply put, under 1.3, you run the risk of key holing and over
2.0, would mean over spinning and possibly blowing bullets up. JBM is a free online calculator.
Very simple to use. I have several I use, but JBM is quick when checking stabilities.

And Mr. Hoback.....Why would I recommend a twist without knowing the bullet and speed you'll
be dealing with. If your ordering up a 1:7.5 twist, that's fine if you did the math.

Thanks, I'll play around with that calculator to see what I can learn.

[Ernest T]

I loaded a few different powders and bullets this week.

This was 42 grains of RL-16 with 140 grain Barnes Match Burner bullets, loaded at seating depths of 2.260, 2.220 and 2.180 in two three shot groups. I was following the advice in the Berger manual for loading VLD bullets. The top left and middle right were loaded to 2.260. The top right and bottom left were loaded at 2.220. Finally, the middle left and bottom right were loaded to 2.180. The first group at 2.180 averaged 2658 FPS with an ES of 17 and SD of 7. The second group averaged 2659 with an ES of 29 and SD of 12. I don't think I've shot a bad group with this powder and bullet. I think I'm going with 2.180 since it will load in a magazine, but the others weren't that bad either.



I used this target for varying loads of H4350 with 140 grain Nosler RDF bullets with a seating depth of 2.298 which is at the lands. I really like that 41.4 grain group. That group averaged 2642 with an ES of 10 and SD of 4. The ES and SD numbers were much smaller with Hogdon 4350 than RL-16 or Winchester 760. Notice I don't have any measurement on the middle right target? I don't know where the third bullet went. I don't think its likely I missed the target entirely, but I can't say it went in one of the other holes either. I only shot two rounds at the bottom left target as I had a misfire with one.




This was Winchester 760 loaded with 140 grain Berger Target VLDs. I extrapolated data from the Hornady manual and Barnes website to come up with the min and max loads for this combo as the Berger data seemed to call for very low loads. The brass didn't show pressure signs at any of these loads. It's an interesting target as the initial impacts were much lower than those with RL-16 or H4350. I adjusted the scope up after the first three groups. I don't have good data for ES and SD because about every other shot failed to record on the chronograph. Velocity varied from just below 2600 to 2665 at the max load today.

[charlie b]

So the top target were all the same except seating depth? And no scope change? So you should overlay each pair of groups to give you 6 round groups. Will give you a better idea of which seat depth is better.

When it boils down to the final 'settings' I shoot a minimum of a 5 round group. The only time I shoot less than 5 rounds is the initial velocity ladder (which is 3rnd each). There are enough data points that I can identify a trend (most of the time).

I only mention because I have had to redo a series. The 3 round groups looked wonderful. But, a 5 round series showed a different preference.

[Ernest T]

So the top target were all the same except seating depth? And no scope change? So you should overlay each pair of groups to give you 6 round groups. Will give you a better idea of which seat depth is better.

When it boils down to the final 'settings' I shoot a minimum of a 5 round group. The only time I shoot less than 5 rounds is the initial velocity ladder (which is 3rnd each). There are enough data points that I can identify a trend (most of the time).

I only mention because I have had to redo a series. The 3 round groups looked wonderful. But, a 5 round series showed a different preference.

I'll start shooting five round groups now that I'm close. I just didn't want to waste the powder, primers and bullets on loads that weren't close.

[charlie b]

Understand. For me it's the kind of thing that a 3rnd bad group will show a bad load, but, a good group may not be a good load.

And then there is the 'me' factor. Sometimes a bad group is just me not shooting well. I tend to get that a lot more than I'd like :)

[Ernest T]

For anyone interested, Graf and Son's had H4350 in 8 lb jugs today.