bullets disintegrating mid flight?

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At the range today to test some new loads, afterwards I figured I would use up some old reloads I made a few months ago for a ladder test of 55 grain V-max and tac. In march or so when I made them they had had non-amazing accuracy so I put the rest away. First couple of shots today weren't even on the paper which was kind of alarming, then I noticed I was getting a puff of smoke about 20 feet downrange of me, I shot one more directly into the berm and saw no dirt kick up, leading me to think the bullets were just disintegrating soon after leaving the barrel.

This was happening with 24.5 of TAC and the CCI 41, which was the lowest charge I had tried previously. It seems kind of curious that the heat of today would have such an effect on these bullets, especially since I was testing with an entire grain more powder previously and not seeing this effect.
 
The rifle was a 1:8 twist 26" heavy varmint barrel from white oak. I shot the 55 grain VMAX in this rifle before and they worked out fine, however today it was much hotter, and also the rifle itself was boiling hot from shooting a ladder test of some other stuff.
 
if it's 1:8, that doesn't seem too fast- was there a different crimp on these??
can you access a chrony?
 
With that load and a 26" 8 twist you are close to 300,000 RPM that is a little high for the thin jacketed Vmax's.

Dean
 
I can't say for sure but I have seen a few shooters at cmp with mystery rounds vanishing. You guessed it....all tipped
Vmax and some new Sierra tipped.
Whats funny is it happened to one shooter with both 30-06 and 223.
The Sierra where from a 308. Although funny thing is he would shoot 2-3 shots then a shot would not hit paper. I have not even come close with the Hornady 75 grain A max or Vmax bullets in accuracy vs the 75 BTHP so I stopped trying
 
I don't have a chrony, but I suspect that the extra heat from today might have made the powder ignite faster and spike hte gas pressure maybe giving some extra speed. Its surprising that this happened with 24.5 of TAC whereas in march 25.5 was totally fine.
 
Shooting AR's at 1000 yards I've watched many bullets vanish. Sometimes the jackets get nicked and other times they are just pushed too fast. 7 tenths of a grain was enough to cause a few of my 80 grain sierras to come apart in flight.
 
This is the formula for those inquiring minds, Velocity X 720 Divided by Twist = RPM. In this in this case 3300 X 720 = 2,376,000 Divided by 8 = 297,000 RPM.

Dean
 
The MV X 720/Twist Rate = RPM formula, is a quick or layman's version of the actual true measurement formula which is, MV x (12/twist rate in inches) x 60 = Bullet RPM.

Dean
 
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Here is how I'd figure the long version. Once you have this, you can distill it down to an easier equation.

Assume 1 in 7 inches
Assume 3000 fps.

A bullet going 3000 fps is going to do 1 foot in 1/3000th second.

In that one 1/3000th of a second it will turn 12/7 times. Or 1.714 times. (a 1:7 twist barrel turns once in 7 in. The bullet will travel 12 inches in that time period. So total twists = 12/7)

Since it will turn 1.714 times in 1/3000th of a second, it will turn 5143 times in one second. 1.714 x 3000 = 5143

There are 60 seconds in a minute so it will turn 308,571 times in a minute. (5143 x 60).

RPM = Revolutions per minute = 308,571 RPM

Don
 
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They're spinning apart. There's no question in my mind. That puff of smoke down range is where it happens. Those varmint bullets are designed to be fragile and come apart inside a small critter. They can't stand the RPMs of that 8" twist barrel. Typically such a short twist barrel is intended for long, heavy, very low drag bullets for long range shooting.
 
I've seen it happen multiple times in matches, usually when someone is using a light varmint bullet in a rifle designed for mid to heavy weight target bullets. 55 grains is too light for a 1:8 twist 26" barrel. Even pushing a mid-weight bullet too fast can make it spin apart. You'd probably be better off using something in the 70 grain range.


(Next comment will be from some dude who shoots nothing but Wolf steel 55 grain out of this 1:7 16" carbine at 25 yards and "it works fine." Yeah dude, we know.)
 
I don't have a chrony, but I suspect that the extra heat from today might have made the powder ignite faster and spike hte gas pressure maybe giving some extra speed. Its surprising that this happened with 24.5 of TAC whereas in march 25.5 was totally fine.

I hear TAC is very temperature sensitive. Never tried it myself so that could be range legend.
 
I've seen it happen multiple times in matches, usually when someone is using a light varmint bullet in a rifle designed for mid to heavy weight target bullets. 55 grains is too light for a 1:8 twist 26" barrel. Even pushing a mid-weight bullet too fast can make it spin apart. You'd probably be better off using something in the 70 grain range.


(Next comment will be from some dude who shoots nothing but Wolf steel 55 grain out of this 1:7 16" carbine at 25 yards and "it works fine." Yeah dude, we know.)

The guy who shoots wolf does have a valid point though. The key thing is that a 55 gr military bullet is different from a 55 gr varmint bullet.
 
I hear TAC is very temperature sensitive. Never tried it myself so that could be range legend.

I can't imagine it being enough to make up for a full grain of powder.

I've run as high as 27.2 gr on a 55gr, from a 16" 1:7 AR. That was a hot load, but I didn't have issues with it.

I never got great accuracy with it either...about .6-.7 MOA from my bolt action 223 which shoots 1/3 MOA with Varget or IMR 4166.
 
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The guy who shoots wolf does have a valid point though. The key thing is that a 55 gr military bullet is different from a 55 gr varmint bullet.

Yep They're also going a lot slower out of a short barrel
 
Whats surprising to me is that this exact same load was fine a couple months ago, and even produced some pretty good groups. The rounds I shot last week were not only the same loads but the same batch I made. However it was a much hotter day and my rifle was cooking from shooting some hot 50 grainers before that.

I just loaded up some more 69 SMKs to try, I had good performance out of them before.
 
Whats surprising to me is that this exact same load was fine a couple months ago, and even produced some pretty good groups. The rounds I shot last week were not only the same loads but the same batch I made. However it was a much hotter day and my rifle was cooking from shooting some hot 50 grainers before that.

I just loaded up some more 69 SMKs to try, I had good performance out of them before.

The 69smk just seem to work and work well.... I still have a ton of nosler and hornady 77s 75s. I'm not shooting much at all these days.
I loaded up some 60 grain Nosler Varmint tipped bullets and shot a 198/200/5X at 200 yards shot from a 1/8 twist 20"
Load data said approx 2900 fps?
I have loads by rights should work and they just don't....example I load 8mm mauser cast loads. If I run them slower than 1500fps they suck get into 1650-1900fps and it's 10 ring ??
 
Whats surprising to me is that this exact same load was fine a couple months ago, and even produced some pretty good groups. The rounds I shot last week were not only the same loads but the same batch I made. However it was a much hotter day and my rifle was cooking from shooting some hot 50 grainers before that.

a couple of months ago it was probably 20 degrees cooler out, maybe more
 
Yep They're also going a lot slower out of a short barrel

I can't run any 55 or less varmint bullets in any of my 1:7s without really neutering the velocity to prevent that. Not worth it to me.

If I was going to run varmints I'd run a really slow twist and ramp the speed up as high as possible.
 
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