155gr Amax twist rate

brijohn · October 6, 2013, 07:32 PM

I am new to the forum, tons of info so hopefully this hasn't been covered. I will be loading for a Ruger M77 Mark II, 22 inch barrel, 1 in 12" twist chambered in .308 Win. I want to use 155gr Hornady Amax in front of Varget. The box says 1 in 12" twist or faster which mine is, will it stabilize or is a 1 in 12" borderline?

precision_shooter · October 6, 2013, 07:43 PM

1:12 should be fine and may be optimal for that bullet. Im loading 155 amax with varget but I have 1:10 twist. They work fine as long as your muzzle velocity is sufficient.

hodaka · October 6, 2013, 08:06 PM

Only one way to find out if your rifle likes that bullet. Load some up and try. Most of my 30's like the Sierra 155's.

brijohn · October 7, 2013, 09:28 PM

Thanks for the info, time to experiment.

Bart B. · October 8, 2013, 08:05 AM

As the .308 Winchester is the offspring of the 7.62 NATO which was developed with a 22 inch 1:12 twist barrel for bullets about 145 to 172 grains in weight, if your rifle doesn't shoot 155's very accurate, it's not the twist that is the problem.

snolden · October 9, 2013, 08:38 PM

The 155 AMAX really likes about 2800 fps so try to get there and see if it works in your rifle.

Bart B. · October 10, 2013, 07:34 AM

With due respect to snolden's suggestion you try to get 2800 fps with that bullet, attempting to reach a given velocity in your barrel may not be a good idea. We don't know its internal dimensions and if they're on the big side of specs, you'll need to load powder charges way over maximum to do that.

Besides, bullets have no nervous system and therefore can not "like" any speed they fly at. They don't know how fast the leave the muzzle nor how fast they spin. There is an rpm spin rate each bullet shoots most accurately. It changes with twist and muzzle velocity. Any combination of twist and velocity that spins it best will produce the best accuracy.

Your 1:12 twist barrel will shoot that bullet somewhere between 2700 and 2900 fps with max loads and it'll do just fine.

old roper · October 10, 2013, 08:40 AM

Most of the suggestion on velocity for 308 with the 155gr AMAX @ 2800fps come from this

http://www.hornady.com/store/308-Win-155-gr-Match/

as noted velocity is from 24" long barrel

Bart B. · October 10, 2013, 10:03 AM

From the "Scrapbook" page in the above link:

Quote:

Nobody could have imagined the accuracy of a 155 gr projectile at 700 and 800 meters. Firing in 9 o'clock and 3 o'clock winds of 10-15 km/h, from 800 meters, we were able to score groups as small as 6" while firing from the prone.

6" at 800 metres (875 yards) is excellent for any factory ammo. Too bad we don't know what the larger groups were.

Other 155-gr. 30 caliber bullets have been doing that well and better since 1991; first Sierras then a few years later, Bergers.

I wonder what twist Hornady uses in their .308 Win. test barrels for the 155 AMAX.

**Unclenick** · October 10, 2013, 01:36 PM

And don't forget the Lapua Scenar 155.

Brijohn, Here is a link to a stability calculator. You need bullet total length, plastic tip length, bullet weight, bullet diameter, bullet muzzle velocity, atmospheric conditions (though you can use standard defaults) and barrel twist. The calculation output is an estimate of the gyroscopic stability factor you will have. For hunting, Sierra recommends that gyroscopic stability factor fall between 1.3 and 3.0 for adequate accuracy, and for match shooting that you try to get it between 1.4 and 1.7. Not always possible, and many modern match bullets are made well enough to shoot well with the higher side hunting numbers, but those ranges are the ballpark to shoot for.

brijohn · October 10, 2013, 05:54 PM

More excellent info. According to the calculator with the conditions today it figures out to 2.049, will load some up and give them a try.

tobnpr · October 12, 2013, 07:45 PM

That JBM calculator is a great tool...
When I ordered the barrel for my 7-08 I was told that a 9.5 twist wasn't fast enough for the 162 Amax by many forum "pundits"- and the calculator said otherwise.

The calculator was correct.

Bart B. · October 13, 2013, 08:30 AM

I was told a 1:13 twist .300 Win Mag barrel would not shoot 180-gr. boattail bullets smaller than 2 foot groups at 600 or 3 foot ones at 1000 yards when I had it built as a longer range hunting rifle. Sierra's 180's went into 1 MOA at both ranges when checking it out. JBM's calculations put those bullets at 1.485 stability factor; at the low end but good enough.

October 6, 2013, 07:32 PM	#1
brijohn Junior Member Join Date: October 5, 2013 Posts: 7	155gr Amax twist rate I am new to the forum, tons of info so hopefully this hasn't been covered. I will be loading for a Ruger M77 Mark II, 22 inch barrel, 1 in 12" twist chambered in .308 Win. I want to use 155gr Hornady Amax in front of Varget. The box says 1 in 12" twist or faster which mine is, will it stabilize or is a 1 in 12" borderline?

October 6, 2013, 07:43 PM	#2
precision_shooter Senior Member Join Date: September 8, 2007 Location: DFW, Texas Posts: 2,475	1:12 should be fine and may be optimal for that bullet. Im loading 155 amax with varget but I have 1:10 twist. They work fine as long as your muzzle velocity is sufficient. __________________ "Laws that forbid the carrying of arms...disarm only those who are neither inclined nor determined to commit crimes...Such laws make things worse for the assaulted and better for the assailants; they serve rather to encourage than to prevent homicides, for an unarmed man may be attacked with greater confidence than an armed man." - Thomas Jefferson, 1776

October 10, 2013, 08:40 AM	#8
old roper Senior Member Join Date: June 11, 2007 Posts: 2,155	Most of the suggestion on velocity for 308 with the 155gr AMAX @ 2800fps come from this http://www.hornady.com/store/308-Win-155-gr-Match/ as noted velocity is from 24" long barrel __________________ Semper Fi Vietnam 1965 VFW Life member NRA Life Member

October 10, 2013, 01:36 PM	#10
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	And don't forget the Lapua Scenar 155. Brijohn, Here is a link to a stability calculator. You need bullet total length, plastic tip length, bullet weight, bullet diameter, bullet muzzle velocity, atmospheric conditions (though you can use standard defaults) and barrel twist. The calculation output is an estimate of the gyroscopic stability factor you will have. For hunting, Sierra recommends that gyroscopic stability factor fall between 1.3 and 3.0 for adequate accuracy, and for match shooting that you try to get it between 1.4 and 1.7. Not always possible, and many modern match bullets are made well enough to shoot well with the higher side hunting numbers, but those ranges are the ballpark to shoot for. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle Last edited by Unclenick; October 10, 2013 at 08:59 PM. Reason: typo fix

October 12, 2013, 07:45 PM	#12
tobnpr Senior Member Join Date: August 1, 2010 Location: Tampa Bay Posts: 4,556	That JBM calculator is a great tool... When I ordered the barrel for my 7-08 I was told that a 9.5 twist wasn't fast enough for the 162 Amax by many forum "pundits"- and the calculator said otherwise. The calculator was correct. __________________ Remington 700/Savage Rebarreling /Action Blueprinting 07 FFL /Mosin-Nagant Custom Shop/Bent Bolts Genuine Cerakote Applicator www.biggorillagunworks.com

October 6, 2013, 08:06 PM	#3
hodaka Senior Member Join Date: April 23, 2006 Location: South Texas Posts: 2,010	Only one way to find out if your rifle likes that bullet. Load some up and try. Most of my 30's like the Sierra 155's.

October 7, 2013, 09:28 PM	#4
brijohn Junior Member Join Date: October 5, 2013 Posts: 7	Thanks for the info, time to experiment.

October 8, 2013, 08:05 AM	#5
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	As the .308 Winchester is the offspring of the 7.62 NATO which was developed with a 22 inch 1:12 twist barrel for bullets about 145 to 172 grains in weight, if your rifle doesn't shoot 155's very accurate, it's not the twist that is the problem.

October 9, 2013, 08:38 PM	#6
snolden Senior Member Join Date: January 25, 2006 Location: N. E. AZ Posts: 387	The 155 AMAX really likes about 2800 fps so try to get there and see if it works in your rifle.

October 10, 2013, 07:34 AM	#7
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	With due respect to snolden's suggestion you try to get 2800 fps with that bullet, attempting to reach a given velocity in your barrel may not be a good idea. We don't know its internal dimensions and if they're on the big side of specs, you'll need to load powder charges way over maximum to do that. Besides, bullets have no nervous system and therefore can not "like" any speed they fly at. They don't know how fast the leave the muzzle nor how fast they spin. There is an rpm spin rate each bullet shoots most accurately. It changes with twist and muzzle velocity. Any combination of twist and velocity that spins it best will produce the best accuracy. Your 1:12 twist barrel will shoot that bullet somewhere between 2700 and 2900 fps with max loads and it'll do just fine.

October 10, 2013, 05:54 PM	#11
brijohn Junior Member Join Date: October 5, 2013 Posts: 7	More excellent info. According to the calculator with the conditions today it figures out to 2.049, will load some up and give them a try.

October 13, 2013, 08:30 AM	#13
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	I was told a 1:13 twist .300 Win Mag barrel would not shoot 180-gr. boattail bullets smaller than 2 foot groups at 600 or 3 foot ones at 1000 yards when I had it built as a longer range hunting rifle. Sierra's 180's went into 1 MOA at both ranges when checking it out. JBM's calculations put those bullets at 1.485 stability factor; at the low end but good enough.