TWO QUESTIONS

[SchuetzenDave]

Caliber 0.459 Inches
Bullet Weight 560 Grains
Bullet Length 1.52 Inches
Barrel Twist 17 Inches/turn
muzzle velocity 1342 fps
Temperature 50 degrees Fahrenheit (59 is standard)
Pressure 29.92 inches of mercury (29.92 is standard)

Sg = 2.46 So a bit more over spin with a bit tighter twist.

Paul:

After the Electro Cardio Conversion at the end of August my Ejection Fraction was 25.

With the heart stabilized my ultrasound on Friday indicated my EF has increased to 35.

Moved from Stage 3 Heart Failure back to Stage 2.

Dave

[DeadEye]

That is fantastic news, thank you for that. I'm sure you're just as pleased, maybe even more so (tic). Things weren't looking good there for a while. Christmas came early for you this year. All our best, Paul and Spot

[Coltsmoke]

Dave, a bullet at 1.520 in length would need more spin like a 1-16 twist barrel, so wouldn't a 1-18 twist be under spinning the bullet, not over spinning the bullet? You know more about this than I do, either I have it all backwards or you just miss spoke on your previous post.

[SchuetzenDave]

The tighter the twist the more it will spin a bullet.

So a 18:1 twist that is already spinning a bullet fairly fast will spin it faster in 17:1 twist and even faster in a 16:1 twist.

But the spin is also dependent on the length of the bullet.

So if your bullet is too short for that twist it will spin too fast and have an Sg greater than 2.0.

But if you use a heavier longer bullet your spin will be less and you can then bring your Sg below 2.0.

Your gyroscopic spin rating is dependent on BOTH barrel twist and bullet length.

In this case the bullet is too short and would do better without so much twist; or else use a longer bullet that is more suited to the tight twist of the barrel.

[SchuetzenDave]

So for this 1.520" long bullet that is travelling at 1,342 fps and weighs 560 grains the gyroscopic spin (Sg) would be for the following twists:

15:1 3.16
16:1 2.77
17:1 2.46
18:1 2.19
19:1 1.97
20:1 1.78
21:1 1.61
22:1 1.47

[desert deuce]

I understand the math and understand the theory.....don't necessarily accept that math & theory always agree with reality at the target.
And, the only way to resolve the question is to read the target. That will over rule the theory & Math every time if they don't agree.

[martinibelgian]

I prefer by far to overspin a bullet than the other way round: It will still be quite accurate, whereas too slow a twist will tumble a bullet every time.... Also, that 2.0 constant for BP already has proven to be iffy at longer ranges.