75 gr. boolets in 9 twist ?? 223

[acemisser]

I keep hearing how some are getting outstanding accuracy with
Hornady 75 gr boolets..I have to wonder as I have tried several
powders and oal,etc and the best I ever had was maybe 3 inchs
at 300 yards. I know it's MOA,but not like the 1 to 1/2 inch others
claim to be getting.Now with my 69 grain SMK I can get 1 inch
or less easy..I have so many 75 gr on hand..Gotta use them..LOL
I also hear these guys are also using 55 gr and getting fantastic
groups.But NEVER seen it..:confused:

[upSLIDEdown]

75gr A-max's don't usually stabilize out of a 9 twist from what I've been told.

[Texas10]

I couldn't get the 75's to stabilize in my 9 twist, not hand loads, not factory loads, not even super performance factory loads. 69's yes, like yours, all day long.

You'll need to screw a 7 or 8 twist barrel on to shoot the heavies. My 8 twist likes the 77 grain tipped match kings. 80's not so much. A bit too long and the SG is too low.

Go here for calculating bullet stability..http://www.bergerbullets.com/twist-rate-calculator/

[gbflyer]

My Predator Hunter was an honest .75 MOA with 69gr Nosler bthp match. Couldn't hit the target with 75gr AMAX. No BS.

[Steelhead]

I have a carbine AR with a 1-9 that shoots 75/77 well even at distance.
It can happen.

[scope eye]

I have also had success with 75gr, and 77gr bullets out of a 9 twist 223, but most shooters will not feel comfortable loading the way they need to be to achieve those results, and this is by no means a slam against shooters who don't or will not load hotter than the provided factory data. it is just what needs to be done to get the desired results, good bad or indifferent.

Dean

[handirifle]

I have loaded some 75gr Amax and got about 1.25 at 100. That when I would get .75" from 55 gr.

[Texas10]

My 12 BVSS would shoot the 75 grain SMK's into tiny groups only when temps were over 100F and high humidity. When the hot summer temps moderated in the fall, groups became more like patterns. Some bullets wouldn't even hit the paper at 200 yds.

Altitude and temperature (air density) play a significant role in group size when you're on the edge of bullet stability. If you're shooting at 9000 ft and 90F you could probably stabilize a broom stick in a 9 twist, although I don't think I would ever try it....LOL

[Texas10]

A thought just occurred to me.......oh ohhhhh:bolt:

You's guys who have success with the 75's and 77's in a 9 twist, if you would log onto the Berger Stability calculator listed in post #3 and enter your data, then post the SG for your particular load as well as your shooting conditions (bullet part-number, temp, altitude, velocity) , we may arrive at a reliable threshold of SG for the 75 SMK and 77's.

Might make for some interesting comparisons.

[SavageShooter]

Great idea Texas10.

http://i63.tinypic.com/35b9mkp.jpg

http://i66.tinypic.com/iypsbb.jpg

The top box of 70 grain TSX bullets has a sticker on it that says 1 in 8 twist is required. The bottom box of Swift's has that statement right on the bullet label.

http://i65.tinypic.com/2qdbazq.jpg

http://i68.tinypic.com/nvb0qh.jpg

The box of 62 grain TSX bullets says a 1 in 9 twist is required.

According to the bullet makers, the dividing line between needing a 1 in 9 and a 1 in 8 twist barrel is somewhere between 62 and 70 grains. As you are all aware, rotational velocity in a given barrel twist varies directly with the linear velocity, so those with a 1 in 9 barrel who are shooting at maximum velocity MAY be able to stabilize a 70 grain bullet. If your linear velocity isn't high enough to impart the required rotational velocity, you may not be able to. In any given barrel twist rate, the SG will vary with your bullet linear velocity is another, maybe simpler way of saying that.

I'm shooting a 1 in 8 Shilen barrel and having no problems shooting 75 grain bullets very accurately. I don't want to be dependent on having to shoot at high velocity to stablize the heavier bullets. I tried to get a 1 in 7 Shilen barrel, but they said it would be a three month wait. They had the 1 in 8 hand lapped, air gaged barrel in stock, so I took it. So far, it is working fine, but 75 grains is the heaviest bullet I've tried in it. They show no signs of losing stability all the way out to 300 yards which is as far as I have tested it.

[scope eye]

One says Recommended they other says Required.

Dean

[SavageShooter]

Yep, That is exactly what they say. And that is the difference between the termonology used by the people at Barnes and the people at Swift. Barnes says RECOMMENDED. Swift says REQUIRED. Either way, shooters have been warned the bullets in those boxes may not shoot well in their rifles if their twist rate is below what is recommended or required.


http://i68.tinypic.com/2ufrmzn.jpg

The 100 grain Speer bullets on the left have no twist label. That is because most 24/6mm caliber rifles have at least a 1 in 10 twist and it will stablize those 100 grain bullets at normal velocities. On the 107 grain SMK bullets, Sierra simply says 8" twist or faster. They don't say recommeded or required. Most shooters get the message however it is stated. We are begining to see these lables on the newer, longer, heavier weight bulltes that are being brought out by the bullet makers in some calibers. These labels are made necessary because many shooters are not aware of the necessary relationship between the bullet length, its linear velocity, and the twist rate of the barrel in order to have good accuracy with those bullets. Read any of the Internet shooting forums and you will see all the complaining and griping posted about how sorry the new heavy bullets of brand XX that were not accurate and what lousy bullets brand XX is making. When anyone goes behind them on that forum and asks the question of what their barrel twist rate is, they almost always come back with the classic " Well, what difference does that make?" They probably don't know what their barrel twist rate is, and for certain, they have no clue to the answer to the question they asked.


So the legal advisors to the bullet companies have advised the bullet makers to warn the purchaser that unless they have the stated barrel twist, the bullets may not shoot accurately. It is unfortunate that they have to do that, but with many of today's public school educated Americans, it becomes necessary. For example, you would think most people would know when you order a cup of coffee at McDonald's, it is going to be hot and they should not spill it in their lap, but you would be wrong if the recent verdict against McDonalds for exactly that means anything. The jury in the case was that stupid too. Apparently there are some people who do not know coffee is usually served hot and they probably didn't take a physics class in school either. And it's a shame our nation has come to that condition. They used to teach basic physics when I was in school. Obviously, from the barrel twist rates now printed on some of the newer bullet boxes, they no longer do.

The Berger web site linked to by Texas 10 in post #3 above tells it all and is easy to use. It is limited to Berger bullets if you only use the selected list, but it can be used for other bullets not made by Berger if you enter the required information for analysis.

[scope eye]

Or if you don't have the recommended or required twist you can just send them faster.

Dean

[SavageShooter]

Yep. And that is exactly what I said in post # 10 above:
As you are all aware, rotational velocity in a given barrel twist varies directly with the linear velocity, so those with a 1 in 9 barrel who are shooting at maximum velocity MAY be able to stabilize a 70 grain bullet. If your linear velocity isn't high enough to impart the required rotational velocity, you may not be able to.

This is not rocket science stuff. If you ever held a gyroscope at one end while it was spinning and tried to move it, you know all about the gyroscopic effect which is what the rotational velocity on a bullet provides. The longer a bullet is, the more gyroscopic effect (the faster it must spin) required to stabilize it. As you say, you can achieve that by increasing the linear velocity since rotational velocity is a direct function of it, but only within the limits of the cartridge case, action, and barrel to contain the increased pressure required to provide that additional level of linear and rotational velocity. It's a lot simpler and safer to just increase the rate of twist in the barrel.

It'sa free country and shooters are at liberty to do it any way they choose.

[TMD11111]

A few weeks ago I picked up a 12 FVC in .223 which is a 26" barrel with a 1/9 twist. I've only taken it out a few times and used some different ammo that I have loaded for one of my Varment AR's, one of them was 75g Hornady BTHP's with 23.8g of Ramshot Tac. This load was getting aroung .75-1.00" groups @ 100 yards. I decieded to measure my chamber and see if I could improve the accuracy with different seating depths. I loaded 6 rounds each at .010, .020, and .030 off the lands to see what each would do. With the load that was .020" off the lands I put all 6 rounds in one little hole that measured .240" from center to center. Needless to say on the way back from the range I stopped by my LGS and picked up 500 more of them (its all they had on the shelf).

[darkker]

And bullet weight has essentially nothing to do with the whole discussion, the "dividing line" is because of LENGTH. The length is what needs a rotational stabilizing force, so as to keep the pointy part facing the target.
That is why, a 77gr SMK is more easily stabilized than the 75gr Amax; the SMK is heavier, but noticeably shorter.