Bullet weight and rifle twist

[KJQ6945]

The 55 has a tangent ogive, which is the part that curves from the full diameter down to the tip. The 77 has more of a secant ogive, which is more of a straight line than a curve. So when loaded they will look smaller, even though you can see the real difference from that picture.

The MK262 is an OTM. I bought a box of the polymer tipped, because that was all cabelas had.
What you're saying appears more pronounced with the tipped ammo.

Trigger Time, if you can, post that picture I just sent you. My Photobucket doesn't work.

 

[KJQ6945]

You reloaders and your fancy lingo.

 

[ChristianPatriot]

You reloaders and your fancy lingo.

 

[bcd007]

Here's the magic formula for spin stabilization (The Miller Twist Rule Formula):

(30*M)/(T^2*D^3*L*(1+L^2)) = S

M=bullet mass in grains
T=twist rate in calibers per turn
D=bullet diameter (in inches)
L=bullet length in calibers per inch

S= Stability Factor

S is just a number, what you are looking for is to be as close to 1.4 as you can. This stuff is all available on the interwebs, but it's cool to know how spin stabilization is done. And why some bullets are better than others for weights/barrel spin.

 

[ChristianPatriot]

Here's the magic formula for spin stabilization (The Miller Twist Rule Formula):

(30*M)/(T^2*D^3*L*(1+L^2)) = S

M=bullet mass in grains
T=twist rate in calibers per turn
D=bullet diameter (in inches)
L=bullet length in calibers per inch

S= Stability Factor

S is just a number, what you are looking for is to be as close to 1.4 as you can. This stuff is all available on the interwebs, but it's cool to know how spin stabilization is done. And why some bullets are better than others for weights/barrel spin.

A calculator for those, like me, who are too lazy to do the math.

Twist Rate Stability Calculator | Berger Bullets

 

[Rookie]

How far away is the target?

100 yards.

It is not uncommon for lighter bullets in fast twist barrels to be less accurate. I'm not sure why, maybe too many RPM for a shorter bullet, possibly causing some yaw. That's just a guess, but generally lighter should have slower twist, heavy should be faster.

Try some 62 or 69 grainers and see how they do.

I would still recommend trying heavier ammo. You've got to find what ammo the gun likes, but it will most likely be a heavier bullet from what little I've read about it.

text me if you've still got my info

I have about 500 rounds of 55 grain so I'd like to fit the barrel to the bullet.

 

[Trigger Time]

The MK262 is an OTM. I bought a box of the polymer tipped, because that was all cabelas had.
What you're saying appears more pronounced with the tipped ammo.

Trigger Time, if you can, post that picture I just sent you. My Photobucket doesn't work.

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[Woobie]

The "hybrid" bullets are both. Secant up by the meplat for better ballistics and tangent up at the caliber so it's less sensitive to seating depth.

And those hybrids are supposed to be very good. Berger has really hit a home run with that design. Thanks Brian Litz.

 

[Woobie]

100 yards.





I have about 500 rounds of 55 grain so I'd like to fit the barrel to the bullet.

1:9 should work. It's hard to find a 1:12 for an AR anymore, and if you did, 55 would be the max weight.

 

[ChristianPatriot]

And those hybrids are supposed to be very good. Berger has really hit a home run with that design. Thanks Brian Litz.

Amen

 

[bcd007]

A calculator for those, like me, who are too lazy to do the math.

Twist Rate Stability Calculator | Berger Bullets

Exactly!!

 

[sloughfoot]

3 inch group at 100 yards with 55 FMJBT is not bad. It is within the capability of the ammo. Plenty good enough for coyotes or for self defense. Any match or varmint bullet from 52 grain on up to 77 grain at magazine length will shoot better with your 1X7 twist barrel.

The longer, heavier bullets are deeper inside the case so that they can be magazine length. One reason why powder charge is reduced for them, amongst other reasons.

Don't sweat the barrel twist, no matter the internet wisdom. 1X7 will shoot every bullet weight just fine. I wish every AR I owned was 1X7.

 

[Leo]

The man that said the bullet quality is the 1st key is right. I shot many 52 grain Sierra MatchKings through a 7, 7.7 and 8 twist barrels twist will excellent results. To quantify excellent we are talking a 200-14x score on an MR-31 target during registered competition. That X ring is .75", the 10 ring is 1.75"

The other variable is that none of my experience was with pistol length barrels shooting rifle calibers, my rifles were all high quality 20 inch barrels.

 

[avboiler11]

55gr FMJBT are garbage plinking bullets; if your rifle shoots them well, then be thankful you have a tolerant barrel.

If you want good groups, shoot good bullets...as mentioned upthread, you don't have to run 77s to get good groups with a 1:7 barrel. And if I believed what I read on the internet a 1:9 would make 77s pattern like a shotgun, but 3/4MOA groups tell a different tale...

 

[Woobie]

The man that said the bullet quality is the 1st key is right. I shot many 52 grain Sierra MatchKings through a 7, 7.7 and 8 twist barrels twist will excellent results. To quantify excellent we are talking a 200-14x score on an MR-31 target during registered competition. That X ring is .75", the 10 ring is 1.75"

The other variable is that none of my experience was with pistol length barrels shooting rifle calibers, my rifles were all high quality 20 inch barrels.

Those 52 gn SMK's are great bullets. They're a bit longer, IIRC, than standard 55 gn FMJ's, which if true would help them deal with a tight twist a little better. I haven't used them, as I have concentrated more on the .308 game. But my brother had amazing results with them in his 22-250.

It seems like to me longer barrels can be more forgiving on twist, to a point. I know people shooting shorter barrels often have to go to tighter twists. It's what makes me think it's an RPM thing. The bullet out of the shorter barrel is moving more slowly, and thus has lower RPM. Just throwing stuff out here to see what sticks. I have no real verification for any of this.

 

[Rookie]

I changed barrels and tried again. If it wasn't for the top shot, I'd be happy. Of course, I could just call my flyers and say I'm less than one inch MOA.

The grids are one inch square, so 2 MOA. I'd like one MOA, but I'll try different ammo before changing barrels again. I was using Winchester super x varmint, does anyone have suggestions for 55 grain varmint rounds? I have Hornady V-max that I can try...

 

[Tyler-The-Piker]

Liberty Silverado