6mm Bullet Weights that Will Stabilize in a 13.5-twist Barrel

[South Pender]

I have a new 6PPC rifle coming that has a 13.5-twist Krieger barrel and Dakota Varminter action (pics below). It's not a benchrest rifle--more like a super-accurate (I hope) varmint rifle (or maybe just a range toy). In any case, I gather that 6mm bullets in the 60-gr.-68-gr. range will stabilize in this barrel, but I'd like to be able to use some varmint bullets that are slightly heavier--maybe 70-75 gr.. Does anyone here have experience with heavier 6mm bullets in slow-twist barrels, like 13.5" or 14"?

 

[guntech]

It is said a 13.5" twist for bullets up to 70 grain but so much depends on the shape of a particular bullet when you stretch the limits with slow twists. Who wants to shoot a 75 grain round nose (probably the only shape that may stabilize) I would try a 69 grain Sierra as fast as you can get it going... forget about heavier.

 

[DEZ]

68 gr bergers will do fine but probably nothing over 70 68 plenty of weight for coyotes lol

 

[Jefferson]

just use the Berger column and be done with it
if you look on the usa barrel websites they give you the approximate weights to use with a certain twist

buy a box of heavier buckets and try then, some work not bad but it depends on,the group size and distance that will
make the day at the range worthwhile

 

[b72471]

6PPC 1in 14= 68gr.

 

[South Pender]

just use the Berger column and be done with it.

Yup. I've picked up some of those--64 gr.

 

[laker415]

The 68 grain Berger flat base are awesome as well. I use them in a faster twist 6br and the groups are ridiculous

 

[coleman1495]

Maybe try the “Killer Bees” from Stinger Ballistics? I have no experience with them but they are in your weight range and look interesting.

 

[Potashminer]

I have no experience among 6 mm bullets for what you want to try. However, reading on-line - it appears that twist rate and bullet stabilization is about bullet LENGTH, not necessarily bullet weight. I have examples here of 130 grain Norma "Golden Target" bullets that are significantly longer than Round Nose 160 grain Hornady, both are 6.5 mm diameter bullets - see picture below.

I got interested in this, because I ended up with a Husqvarna 4100 which is 1-12" twist in 7x57. Old school standard German and Spanish 7x57 used much tighter twist - like 1-8.66" or so (one turn in 220 mm or so?) - old school was 173-175 grain round nose bullets. I ended up with a pile of Woodleigh 140 grain PP SN, because they were the shortest 140 grain bullets that I was able to find to buy of that weight. Is no doubt that within same brand and same style - like, say, Nosler Partition 140 grain versus 150 grain versus 160 grain in 7mm (.284") or for .277", that the heavier bullet is also longer - but I do not think that carries across - always - when comparing one brand and weight to another brand or style. Looking at various "stabilization" formulas - most seem to want to know bullet length, not so much bullet weight - to calculate a required minimum twist rate in the barrel. Although bullet weight might get "snuck it there" because most formula's also want bullet velocity - and is typical that same cartridge will drive lighter bullet at higher velocity than heavier bullets, at similar breech pressure.

 

[South Pender]

Maybe try the “Killer Bees” from Stinger Ballistics? I have no experience with them but they are in your weight range and look interesting.

Right. I've been to the Stinger Ballistics web page and see two 6mm. bullets that are definitely worth trying in this rifle—the 64-gr. Killer Bees FB and 68-gr. BT.

I have no experience among 6 mm bullets for what you want to try. However, reading on-line - it appears that twist rate and bullet stabilization is about bullet LENGTH, not necessarily bullet weight.

That's right--it is length, not weight per se, that factors into stability calculations. I stated the question in terms of weight because at that weight-range of 6mm target and varmint bullets, length and weight correlate almost perfectly. These calculations are made easy with two JBM Ballistics web pages, one giving the lengths of most available bullets (http://www.jbmballistics.com/ballistics/lengths/lengths.shtml#Hornady) and the other giving a stability estimate for a combination of length, caliber, weight, twist rate, and MV (http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi).

 

[mikeelliot]

Oh man beautiful rifle. If it shoots as good as it looks don't bother with the heavier bullets. Stay in the ppc wheel house of the mid 60s range and punch tiny holes.

Look forward to a shooting report!

 

[naktabar72]

Oh yes: Heavier = Keyhole....

 

[I Dont Care About You]

I have a new 6PPC rifle coming that has a 13.5-twist Krieger barrel and Dakota Varminter action (pics below). It's not a benchrest rifle--more like a super-accurate (I hope) varmint rifle (or maybe just a range toy). In any case, I gather that 6mm bullets in the 60-gr.-68-gr. range will stabilize in this barrel, but I'd like to be able to use some varmint bullets that are slightly heavier--maybe 70-75 gr.. Does anyone here have experience with heavier 6mm bullets in slow-twist barrels, like 13.5" or 14"?

I think yer gonna find there is a downside to slow twist barrel for varmint use. Years go I built a 221 Fireball on a slow twist barrel specifically to use the really light 35 - 45gr varmint bullets. The problem rears its head terminally. The slow twist rate reduces the explosive action of light skinned varmint bullets, which it turns out rely on spin forces to come apart inside the target. I was never happy with the terminal effects of my rifle, even using the most explosive of varmint bullets.

I also have a 6BR varmint rifle, in which I use 70gr Nosler Ballistic Tips and they are simply fantastic. The blow the living daylights out of gophers.

The bullets I'd suggest for your slowish twist 6PPC would be Hornady VMAX in the 58 and 65gr weights. Those have the best chance of good accuracy, high velocity and good terminal effects.

I have tried HP and SP varmint bullets and none of them are anywhere near as good terminally as the polycarbonate tipped varmint bullets.

 

[Andy]

As has been stated, the primary factor concerning stability is bullet length, although its shape is a factor, as is to a lesser extent, muzzle velocity.

You'll be looking at bullets shorter than 0.700", and the heaviest 6mm bullets that length that you're likely to see will weigh about 70 grs.

 

[South Pender]

As has been stated, the primary factor concerning stability is bullet length, although its shape is a factor, as is to a lesser extent, muzzle velocity.

You'll be looking at bullets shorter than 0.700", and the heaviest 6mm bullets that length that you're likely to see will weigh about 70 grs.

I think I can go a little longer than that. Two Berger 6mm. target bullets that I think will work well--the 65-gr. BT and 68-gr. FB--are .833" in length. And the Berger 6mm. 64-gr. column target bullet noted above is .81".

 

[DEZ]

Right. I've been to the Stinger Ballistics web page and see two 6mm. bullets that are definitely worth trying in this rifle—the 64-gr. Killer Bees FB and 68-gr. BT.


That's right--it is length, not weight per se, that factors into stability calculations. I stated the question in terms of weight because at that weight-range of 6mm target and varmint bullets, length and weight correlate almost perfectly. These calculations are made easy with two JBM Ballistics web pages, one giving the lengths of most available bullets (http://www.jbmballistics.com/ballistics/lengths/lengths.shtml#Hornady) and the other giving a stability estimate for a combination of length, caliber, weight, twist rate, and MV (http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi).

I use Killer Bees from stinger Ballistic they are excellent canadian made in Calgary Both in my 6ppc and my 30 br more consistent than berger and much easier to get

 

[Andy]

I think I can go a little longer than that. Two Berger 6mm. target bullets that I think will work well--the 65-gr. BT and 68-gr. FB--are .833" in length. And the Berger 6mm. 64-gr. column target bullet noted above is .81".

Berger (and field performance) will be the best judge of that, but I think that any bullet that long regardless of shape and weight will be very "marginally stable" in a 13.5" twist. Look at Berger's Twist Rate Stability Calculator https://bergerbullets.com/twist-rate-calculator/ and see what happens when you go to even a 14" twist with the same bullet and then a 13", 12" and 11" twist.

The good news is that a bullet that leaves the muzzle stable, tends to remain stable throughout its entire flight, as even though forward velocity reduces quickly, bullet spin reduces much more slowly.

 

[South Pender]

Berger (and field performance) will be the best judge of that, but I think any bullet that long will be "marginally stable" in a 13.5" twist. Look at Berger's Twist Rate Stability Calculator https://bergerbullets.com/twist-rate-calculator/ and see what happens when you go to even a 14" twist with the same bullet.

The good news is that a bullet that leaves the muzzle stable tends to remain stable as even though forward velocity reduces quickly, bullet spin reduces much more slowly.

Yes, you're right. In fact, I did go to the Berger website that gives dimensional details about these three bullets. Minimum twist values given for each bullet are 1:13 for the 65- and 68-gr. bullets and 1:14 for the 64-gr. column target bullet--all .81" or .833". When I enter the length, weight, caliber, MV, and twist values into the JBM Ballistics stability calculator, all three Bergers show low stability (Sg) values between 1.03 and 1.10, indicating "marginal stability" as you note. However, as I understand it, the best accuracy seems to occur in that "marginal stability" region for the 6PPC at least. It seems that many shooters have reported stable results with all three in 1:13.5 and 1:14 barrels, so I'm fairly confident that they will work in my 1:13.5.

 

[South Pender]

I use Killer Bees from stinger Ballistic they are excellent canadian made in Calgary Both in my 6ppc and my 30 br more consistent than berger and much easier to get

Nice to see a Canadian making top-quality bullets. I looked high and low for a Canadian maker of BR bullets, and Stinger Ballistics was the only one I could find. (There may be others, but I couldn't find any.) I'm hoping that the Killer Bees are in the Bart's class (Bart's seem to be winning a lot of BR matches in the US.) Have you shot any Bart's in your 6PPC or 30 BR? And, if so, have the Killer Bees compared favorably with the Bart's?

 

[I Dont Care About You]

I use Killer Bees from stinger Ballistic they are excellent canadian made in Calgary Both in my 6ppc and my 30 br more consistent than berger and much easier to get

I have all the parts necessary to build a 30BR and make ammo. One of these days I've got to put that rifle together.

Hmmmm .... I know Rick Pollock. Awesome guy and a hell of a BR shooter. Apparently I need to check out Stinger Ballistics bullets.