max bullet weight

[a357lever]

what do you thing the max grain load for 1 in 9" rate for 223 rem?. i have some 69 grs like to go to 77 but i thing that might not work. also what do you think of 190 gr for .308 with 1 in 12"?

[Hobie]

Depends on the bullet LENGTH. You for sure can shoot the Sierra 70 gr. SP but I understand the 77 gr. AMAX is too long. I've shot the Sierra bullet with great success in my OLD SP-1. I bought 1000 of the Winchester 64 gr. SPs for my 1-9" twist gun.

[O.S.O.K.]

Yep - normally 69 grain is fine but not much more.
And the 190 should be fine in the 308

[JohndeFresno]

Here is a link:
http://www.shootingtimes.com/ammunition ... ndex1.html

There are twist rate tables at various places on the Internet and in several reloading manuals, where the specific brand or mold number of a bullet is included (such as "Lyman 311041"). Some tables are pretty extensive.

But essentially the Greenhill Formula still seems to apply, as mentioned in the article referenced above.

T=Twist rate
D=Bullet diameter (caliber)
R=Ratio of Bullet Length to Diameter
(Length/Diameter)
MV is used here as an abbreviation for muzzle velocity.

For MV up to 2800 fps:
T=150*(D/R)

For MV > 2800 fps:
T=180*(D/R)

The article cited above states that it is not always easy to compute the perfect twist rate; and practical testing of the bullet in a particular firearm is the ultimate proof because of various reasons; the formula is not always exact for each firearm. But the formula will put you in the right arena.

Quoting from the article:
"If we were to do the Greenhill Formula on Sierra's .308 168-grain MatchKing, we would come up with an ideal twist rate of 1:11.76. That's close enough to 1:12, which is a common twist rate for .308 and one that does very well with 168-grain bullets.

The numbers on the 175-grain MatchKing, which has a diameter ratio of 4.081 (1.257 inches divided by .308), look like this: T=150 x .308/4.081, which gives us an optimum twist rate of 1:11.32.

That 0.44-inch difference may not seem like a big deal, but it is. As an example, take a look at just about any custom .308 tactical rifle these days, and you are almost certain to see a barrel with a twist rate in the 1:10 to 1:11.25 range. That's because the classic 1:12 twist usually shoots lighter projectiles--155-grain Palma bullets and 168-grain MatchKings--just fine, but that twist rate rarely shoots the more popular 175-grain bullets well at all."

[Hobie]

Thanks John.

[JohndeFresno]

You are welcome, Hobie and all.

I created a spreadsheet that works with Excel 97 forward (including the Vista era version; I believe it's Excel 2007).

It is formatted for up to 25 entries, to keep it small and simple and on one page. The formula fields are locked so that they aren't accidentally altered.

You enter:

MV (Muzzle Velocity)
...so that part of the formula works correctly

Caliber (e.g. .308)

Length (Bullet length)
...measure with calipers to three digits, for accuracy
... e.g. 1.257

Ignore the "Ratio" column - it's the ratio of the diameter to the length.

You'll get an "Inches per twist" answer.

In the example, you see 1:11.320 twist, as in the above cited article.

You can download the file, Greenhill_TwistRate.xls - 21 KB, at least for the time being, by clicking on:
http://drop.io/hidden/wdbs3egku9heut/as ... ZS14bHM%3D

I always mention "for the time being" because I've gotten out of the IT business since I retired this year and don't know how long I'll maintain my website storage; I'm trying to wean myself from the crazy world of bits and bytes.

[a357lever]

thanks guys i think i will go with 168gr .308 and my 223 has a short bbl real short so i think 69 max!, so its best with 55, 62,-64gr in 5.56 thanks for that good info this site is the best.