I'm worried: 32 gr VMax

[Wrangler John]

Wrangler

What measurement are you looking for?
Tip to base or base to ogive?

Overall bullet length tip to base.

.6395
.6395
.6405
.6395
.6390

As noted by others. Base to tip not of much consequence unless your figuring twist rates.
I'm actually pretty impressed they were that close.

Thanks that's just what I needed. I'll post again as soon as I do the math.

[FireBallGuy]

Bowshot.....never heard of anyone have 32 grainers keyholing! You got a strange one there my friend!

[Wrangler John]

Okay, ran the numbers. The 1:12" standard twist rate shows marginal stability for the Hornady 32 grain V-Max. At 3,600 fps the Stability Factor (SF) is 1.228, while at 4,200 fps the SF is 1.292. The entire range of SF is in the "yellow zone" or marginally stable at the muzzle in a 1:12" twist.

With a BC of .210 when they start off at 4,000 fps at the muzzle they are down to 3,465 fps at 100 yards, 2992 fps at 200 yards and 2,566 fps at 300 yards. They are going toward the unstable side of the equation as they slow.

They never go completely stable in a 1:12" twist.

In the 1:11 twist they go stable, in the "green zone", at 3,900 fps and above muzzle velocity with a SF of 1.501.

A 1:10" twist runs them in the "green zone" at all velocities. 3,600 fps produces a SF of 1.768, while 4,100 fps gives a SF of 1.846.

With the 1:8.5" twist they are at the high end of stability or a SF of 2.447 at 3,600 fps and 2.555 at 4,100 fps. I prefer anything over 2.0 SF.

I will be experimenting with the 1:8.5" twist in about a month when the barrel arrives. Given my experience with .224" and .243" bullets, I believe that the twist rates of factory rifles were set way too low for the new lead free bullets and the .204 in both lead core and lead free. If your rifle is key-holing these bullets there may be nothing you can do about it, it's most likely the relationship between the twist rate, barrel characteristics and the bullet dynamics. The polymer tips seem to add to the problem with a large cavity internal to the core, versus a lead core and tip. Nothing is ever easy.

[kenbrofox]

Hi,
After reading Wrangler Johns' post,i need to ask,are there different degrees of stability? quote " at the high end of stability"

[bow shot]

FBG, I did hear of that once (32g pills tumbling) I fergit where... but it surely is a rare thing. I'll see if I can find the thread.

I'll keep going!

[bow shot]

Aye, aint that the truth!!! but as 'ol Will Primos once said, "...but it sure is FUN!"

Wragler, your info makes me wonder, is there a merit to the slow twist rate?

[FireBallGuy]

Find it beyond comprehension that 32's are not stable.....40's yes.....WIERD!

[Wrangler John]

Hi,
After reading Wrangler Johns' post,i need to ask,are there different degrees of stability? quote " at the high end of stability"

That's open to interpretation and empirical experience. Stability in the Miller Formula is considered a Stability Factor of 1.5 and higher. This is the threshold used by the military. A Stability Factor of 1.2 produces stability, but is less stable than 1.5 and above. It's the same as a top that spins plumb at high rpm when it starts off, then begins to wobble as it slows, eventually falling over.

The empirical part is that I have found a 1:14 barrel produces complete instability with a long (0.974") 62 grain Varmint Grenade at 3,100 fps (S.F. 0.609). These bullets are launched tumbling, unable to hit a target at 100 yards. The same barrel shoots .3" groups with 70 grain Sierra MK lead core bullets.

Change the twist to 1:10" and groups drop to .5" to .75" at the same velocity with several unaccountable flyers per 10 shot group (S.F. 1.193). The 1:10" barrel is producing marginal stability under a S.F. of 1.5.

Now we take a 1:8" twist barrel and the S.F. changes to 1.865, or nearing the magic (to me anyway 2.0). If we chamber a cartridge capable of driving these same bullets to 3,600 fps, the S.F. changes to 1.960. With the 1:8" all signs of instability disappear at 100 yards with no flyers and groups averaging .3" with consistent performance.

I have had the same experience with .224 bullets, finding a 1:9" twist barrel vs. a 1:10" twist, is similar in performance with the 50 grain Varmint Grenade. For the .204 bullets in the .204 Ruger the 1:12" twist that shoots the 26 grain Varmint Grenade acceptably at 100 yards, will not group any of the polymer tipped lead free bullets. Hence the idea to test the 1:8.5" twist. If lead tipped .204 bullets are available, they may preform better in a given barrel.

Bullets at the "high end of stability", before spin drift becomes a factor, are more accurate over a longer ranges in theory, and so far in practice. Also, if the S.F. is not at or above 1.5 at the lowest practical velocity in a given twist rate, increasing velocity to compensate will not produce desired results. This may be due to the low B.C. of these bullets and their shedding velocity quickly.

My experience is that the Miller Formula is spot on with what occurs at the target.

[bow shot]

Agreed. Other wierd things:

1) After all my griping, the 32gr VMaxs did really well: 0.024" @100y, and 0.8X" @ 300y. 3 shot groups though, I'm sure they'd open up quite a bit if I kept shooting to 5-10 shot groups.

I called Sierra, they recommend seating to COAL and giving it another (careful) check. I'll be doing that this evening if I can get out of here at a good time and the rain holds back...

[Wrangler John]

Agreed. Other wierd things:

1) After all my griping, the 32gr VMaxs did really well: 0.024" @100y, and 0.8X" @ 300y. 3 shot groups though, I'm sure they'd open up quite a bit if I kept shooting to 5-10 shot groups.

I called Sierra, they recommend seating to COAL and giving it another (careful) check. I'll be doing that this evening if I can get out of here at a good time and the rain holds back...

Yes, that's the other factor. None of the bullets I used liked being seated out much past the listed OAL. In the .257 Roberts A.I. the 80 grain Tipped TSX wouldn't shoot until .050" off the lands, no more - no less. Same with the Varmint Grenades - they needed a lot of jump. Once I work up a load, I live in fear they'll change something.

[Glen]

In the rare occasions I've read where the 32gr V-Max won't shoot worth a hoot the 32gr BK's for whatever reason would. Having said that I firmly believe the 204 shines with the 35-39/40gr'ers. But that's just my simple opinion.

[FireBallGuy]

Share your opinion john.....the caliber shines with heavier bullets!

[bow shot]

Thanks kindly, Wrangler!

[bow shot]

For the visually oriented...

[bow shot]

100y:


300y: