stability question

DsrtRat

DsrtRat

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OK, here is the scenario. I have a REM700 12 twist .223. I am trying the new 53gr VMAX's out. According to JBM, I have a stability factor of .8-.9 depeding on the temperature. I have never measured my twist to see if it could be slightly faster than 12 so am using the assumption that it is close.

Here is the question.: When does the bullet become unstable or tumble if not spinning fast enough? According to a couple of ballistic calculators I should not be able to shoot these bullets. I have tried 12 loads so far and my worst group is 1.2, my best is .187 with an average of about .6. Every bullet hole is perfectly round. The only odd thing is the last 6 groups that were shot on 2 different days in sets of 3, had a horizontal stringing to them. Not much wind either day and none of the lower powder groups had that issue.

What I am wondering is if the bullets are appear stable and grouping at 100 yards, can I assume they will be good for longer shots such as 200-400 on coyotes? Could they be wobbling a bit 100 and tip over downrange?
 
You're fine. Most 1:12 twist .224 barrels can handle up to 55gr. bullets with ease. Some, have had luck with some 60gr. bullets as well.

At longer ranges, it's not stability your concerend with, it's wind drift. I would think 400 yds. would be close to max. distance with this bullet as far as accuracy goes.

Your horizontal stringing was either the wind or point of impact shift from you pulling the rifle when squeezing the trigger. That's a technique issue that only you can change.
 
If JBM is indicating a stability factor of 0.8 or 0.9, you've most likely made a data entry error somewhere (most likely the bullet's length)

A 12-twist .223 will easily stabilize 53 grain bullets, as your shooting demonstrates.

If a bullet is not stabilized, the effect is *NOT* subtle. We're not talking about group size increasing a bit; we're taking about going from shooting good groups at 100, to not being able to *hit* the target at 100.

A stability factor of less than 1.0 indicates that a bullet is unstable, and greater than 1.0 is stable. However, these various stability calculations are engineering approximations; the "Sg" factors they give are decent-approximations, rather than the gospel truth. For that reason, you'll often see people saying "you need Sg > 1.4 for stability". What they are doing is applying a 40% fudge factor, to make sure that the bullet really is stable.

If you are not looking for guarantees but rather a best guess, it is likely (but not guaranteed) that a bullet with Sg>1.0 will in fact be stable. If you have the rifle and the bullets, it could be worth loading up some ammo and trying it out.
 
Thanks. Because the bullet is so new, they do not have LITZ data or any data for that matter. What I did was measure 10 of them and came up with an avergae of .835". They are a long sleek bullet (for 53gr) and are recommended for 12 twist or better. I have read that a lot of the 22-250 14 twists are tumbling them but as I mentioned, mine threw them into nice little round holes every time.
 
If the hole is round it is stable. As the bullet goes down range, it gains stability, so range is not an issue.

Usually it only takes 3 shots to determine if your load is stable. If the bullets go in sideaways and the group is more like a pattern, it is unstable.
 
I get decent groups with them out of my TC Encore in .223.

They'll shoot MOA at 200 yards no problem. 53gr VMax is all I buy for my .223.
 
Instability does not necessarily mean a keyhole at 100, although should that happen, its a show stopper. If your 100 yard groups are slightly elongated or egged bullet holes, you'll find accuracy and terminal performance at longer range suffers. Bullet length, not weight is the issue, as an example I observed instability and poor accuracy with 53 gr TSXs in a 1:12 .22-250.
 
I find that for 1 in 12... 45 to 52 gr will be about ideal, while reloading for my Ruger 77 Mk11 ( 1 in 12 ), keyholding was seen with some 55 gr, my pet load for that rifle utilize 52 gr Amax out of the 26 in tube, on the other hand, i have a cheap Superlight 223 nef rifle with 1 in 12 and it wont be accurate with nothing over 45 gr... JP.
 
rnbra-shooter said:
If JBM is indicating a stability factor of 0.8 or 0.9, you've most likely made a data entry error somewhere (most likely the bullet's length)
Click to expand...

Well I need to take that back. Using a bullet length of 0.835" that @DsrtRat has provided, I am also getting Sg~0.9 in standard atmospheric conditions and mv=3000fps using JBM's calculator which I think uses the "Miller Stability Formula" http://www.jbmballistics.com/cgi-bin/jbmtraj_drift-5.1.cgi

I'm a bit surprised to see this much error in the "Miller" results, but there you have it.
 
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