stable bullet

[guidom]

will a 1-12 twist barrel in .22-250, stablize a 69gr. sierra hpbt match bullet?

 

[Phil]

Unfortunately you just have to try and see.......

I have a friend that shot those bullets from a 12 twist 22BR and they worked fine, but every barrel is it`s own animal.....


Phil.

 

[dabibbee]

My 12 twist will not shoot a 60 grain accurately much less than a 69 grain bullet. My 9 twist will work all day long with a 69 grain but will not shoot a 77 grain bullet with accuracy.

 

[nastynatesfish]

My rifle shot the Sierra match kings ok but wouldn't shoot he noslers. It shot the Hornady 68s pretty well too. Didn't do enough load work to see what would shoot better the 68 or 69. I was using TAC

 

[LawrenceHanson]

In my experience the answer is yes. I recently tested the Sierra 69 grain Match King in the 22/250 at 200 yards.





This particular rifle will perform slightly better with 52 grain match grade bullets. The rifle is a Remington model 722 with a Lilja barrel. This barrel is a three groove design with 1:12” twist rifling. I measured the twist rate several times to confirm.

In the past I had a Savage 22/250 rifle with a 1:12” barrel that also performed well with the Sierra 69 grain Match King bullet. At one time I owned a Remington 22/250 varmint rifle with the factory 1:14” twist barrel and discovered it shot surprisingly well with the Speer 70 grain semi-spitzer bullet. I believe the bullet manufacturers tend to be a bit conservative with their twist rate recommendations. As has been said, you never know until you try.

 

[Laurie]

It shouldn't work if it's a true 1-12" twist. That's not to say it won't, but when you get as marginal in this, you can get acceptable results at one venue and not another, on one day or season and not another as you're in the hands of air pressure, altitude, temperature etc. It'd almost certainly work at Raton 7,500ft ASL in summer for instance.

There are two other issues. One is the real twist in the barrel if it's a factory job - the actual rate can be a half to three quarters inch different from the quoted nominal one.

The other factor is that getting round holes and an acceptable group at short range is not the be all and end all of this story. There was an article in Precision Shooting magazine, later republished in the GB Target Shooter online magazine by Michael Courtney (who is a Forum member) looking at the effect of Sg (coefficient of stability) value on BC using .222 Rem over a large range of velocities to vary the spin rate and hence Sg in this cartridge's slow twist barrels. The conclusion was that Sg values under 1.26 saw a BIG reduction in actual BC and that this should be the minimum value to be achieved when considering bullet and barrel specifications.

However, it's not as simple as that as an earlier research project by Mr Courtney showed that the Miller Formula and others overestimated the twist rate needed for many HPBT match bullets because of the internal airspace above the lead core up to the tip. So you oftentimes get away with a lower Sg value than is deemed desirable or essential.

See:

http://forum.accurateshooter.com/index.php?topic=3834705.0

FWIW, I tested a newly introduced Cz527 .223 Varminter for a magazine many years back, one of the very first produced by the Czech factory and loaded up 68gn Hornady HPBTMs and the slightly shorter 69gn SMKs with fairly mild starting loads. The rifle should have had a 1-9" barrel. The 69gn SMKs would hit the black of a 200 yard NRA target but scored rather poorly. The longer Hornady bullets wouldn't even hit the target frame reliably. It turned out that due to some cock-up the first 100 examples had been given 1-12 rate barrels.

the 69gn 0.224" SMK is nominally 0.900" long. At 3,000 fps you get an Sg of 0.99 in 1-12" at 80-deg and standard sea level atmospheric pressure - that's unstable as 1.000 is the minimum theoretical value giving stability.But, Michael Courtney's findings on such bullets apply so it'll actually be a little higher. (Go up to 3,300 fps and the Sg only increases to a nominal 1.03 as velocity is much less important than either the rifling twist rate or the bullet length to calibre ratio.)

So, as with Lawrence Hanson's reply, you'll likely find that the 69gn SMK WILL stabilise in a 12 inch twist barrel, but the effect on the BC and longer range bullet performance may be the killer here depending on the distances you plan to shoot over.


Don Miller's Twist Rule


Caliber 0.224 Inches
Bullet Weight 69 Grains
Bullet Length 0.9 Inches
Barrel Twist 12 Inches/turn
muzzle velocity 3000 fps
Temperature 80 degrees Fahrenheit (59 is standard)
Pressure 29.92 inches of mercury (29.92 is standard)

Sg = 0.99

Sg shouldn't be less than 1.4. If Sg is greater than about 2.0, you may
gain some accuracy by going to a slower twist barrel.