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Squeaky

Proper .308 twist rate?

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Hi Guys:

I'm going to be getting a heavy barrel made chambered for .308 Winchester for a custom build using a McMillan A-4 stock. I'll be firing Federal GMM 168 gr. SMKs through it. I've always assumed a 1:10 twist rate is needed. However, I've noticed both C&H and GA Precision make M-40 clones with barrels that have a 1:12 twist rate.

My question is why the difference? Am I correct in thinking that a 1:12 twist rate is better for heavier bullets? Would 1:12 be better for 168 gr. SMK bullets?

I will not be firing any bullets lighter than 168 gr. in this barrel.

I just don't want to spend $$$ on a barrel and have an incorrect twist rate for my ammo.

Thanks guys. :-)

 

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I'm trying to make a rifle that's capable of 1,000 yd. shots. That's beyond my capability at the moment only because I don't know where a 1,000 yd. range exists. I want it to definitely be good for 500 - 700 yards.

Will get a 20 moa scope base. Probably a fixed SWFA 16x scope.

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Thanks guys. You've all been a big help. I basically just need to get a barrel and the stock. Then I'm off to my gunsmith to have the action trued.

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On 10/6/2019 at 8:03 AM, patriot said:

You'll want a 1:12 twist so you can run 168-175 Matchkings

Wouldn't a 1-10 be better for that range? I thought 1-12 was more suited for 150-168grn

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On 10/8/2019 at 7:21 PM, gunfun said:

Wouldn't a 1-10 be better for that range? I thought 1-12 was more suited for 150-168grn

You're right. 168s are great on deer though, so that's why I went with 1-12 on my bolt gun, a Savage Tactical in .308. It's a sub-MOA gun out of the box with factory Sierra 168gr Matchkings. Hard to beat for twice the price. Still, 175s are damned good in it. It's hard to beat factory 308 168gr Sierra Matchkings. Most accurate stuff I've ever shot.

Edited by patriot

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I suppose I'll go with 1:12 since that's what the Corps apparently uses (or used). Like I said above, I noticed both C&H and GA Precision use Schneider barrels with 1:12 twist.

To be specific, these are M-40A3 replicas I'm referring to. A gentleman had a GA Precision M-40A3 at my range a couple of summers ago. He graciously let me fire a three shot group. It was first time I'd ever clover-leafed. Of course, it helped having a 16x scope too.

As I recall, heavier bullets need a slower twist.

 

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So ... it's ok if your shots don't go through the same hole after spending $$$$$ on a custom build including trueing the bolt, bedding, and pillars? Whew! I'm glad to hear that.  

I'll take my therapist's phone number off of speed dial.

 

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Getting bullets through the same hole every time is 30% gun 20 % ammo work up and 50% trying to figure it all out .

There are good days and bad days at the range. Just remember why you are there. 

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I have a 308 setup and ready to go also just built a 556. Not ready to get to the range because I need to be in the mood to shoot.

If I am not in the mood no tight groups. I think that is true for most shooters

 

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On 10/9/2019 at 5:21 AM, Doug Hartley said:

Use the calculator below and it will tell you what you want to know.

 

Doug

 

https://bergerbullets.com/twist-rate-calculator/

I usually go with this one, but I have used the berger calculator to double check too. https://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

 

On 10/11/2019 at 3:44 PM, patriot said:

You're right. 168s are great on deer though, so that's why I went with 1-12 on my bolt gun. Still, 175s are damned good in it. It's hard to beat factory 308 168gr Sierra Matchkings. Most accurate stuff I've ever shot.

A lot of 1-10 precision guns use the FGMM 168 match king as their recommended load for factory bench marks. i.e. the LWRC REPR that I was playing with a few years ago. Arguably 168s are "over stabilized" in 1-10, but they seem to shoot well out of pretty much every 308, which is why they are so popular as a standard.  I don't pretend to expertise, but I think of 165-170 in 308 /30-06 as the overlap load which is likely to give good results in a gun chosen at random, since they are right in the middle of the overlap between what the common twist rates are good at. I don't pretend to be a good precision shooter, though I am working to improve. My take on this topic is that for 308, if you are wanting the ability to shoot cheap ball, and also do some precision shooting, potentially using some of the ELD bullets, 1-10 will work well with the long range precision loads (& heavier hunting bullets), and well enough with the cheap stuff too. 

 

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Well ... I'm on the fence again because the guy who wrote this article built an M-40A3 replica using a Shilen barrel with a 1:10 twist.

He got really good groups with it at 100 yds. However, I'm wanting something that's capable of 1,000 yds. whenever I find a big enough range. I don't doubt a .308 cartridge can go that far, it's my own skill that needs to be developed.

Anyway ... enjoy this article guys:

https://rifleshooter.com/2016/01/building-a-usmc-m40a3-cloning-the-marine-corps-sniper-rifle-from-1999-2009/

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Just go for it and the rest will sort itself out. Remember this is fun right?

No one ever has the perfect gun. They have a lot of less than perfect guns that shoot just fine.

Now ! Get off the fence and build that sucker and we will want pictures.

Have fun you could live in LA

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Cabela's has this: Ashbury Precision Ordnance Saber® M700™ Precision Bolt-Action Rifle

on sale for $850

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On 10/19/2019 at 4:11 PM, jerry52 said:

Just go for it and the rest will sort itself out. Remember this is fun right?

No one ever has the perfect gun. They have a lot of less than perfect guns that shoot just fine.

Now ! Get off the fence and build that sucker and we will want pictures.

Have fun you could live in LA

LA is definitely a place you can perfect your craft. You can make the perfect gun, just apply yourself bro.

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I don't know if anyone is still viewing this post, but I wanted to share how it finally occurred to me to call Sierra Bullets since I'll be standardizing on Federal GMM ammo with 168gr. SMK bullets. 

The guy said 1:12 twist is excellent for their 168 gr. & 175 gr. SMK bullets. He also said that, generally speaking, a rifle gets made with a faster 1:10 twist rate in anticipation of heavier 180 - 200 gr. bullets getting used. A slower 1:12 rate is just fine for the Sierra Match King 168 gr. bullet.

So ... I'll get a barrel made chambered for .308 Winchester with a 1:12 twist rate.

 

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17 hours ago, Squeaky said:

I don't know if anyone is still viewing this post, but I wanted to share how it finally occurred to me to call Sierra Bullets since I'll be standardizing on Federal GMM ammo with 168gr. SMK bullets. 

The guy said 1:12 twist is excellent for their 168 gr. & 175 gr. SMK bullets. He also said that, generally speaking, a rifle gets made with a faster 1:10 twist rate in anticipation of heavier 180 - 200 gr. bullets getting used. A slower 1:12 rate is just fine for the Sierra Match King 168 gr. bullet.

So ... I'll get a barrel made chambered for .308 Winchester with a 1:12 twist rate.

 

Excellent choice.

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Thank you Mr. "Patriot!"

I don't need this rifle. It's just that the M-40s with the McMillan stocks are so cool. I like the A-4 stock. It's a classic. I'm simply trying to learn how to build a custom rifle and eventually have fun at the range. For this much money though, I want to make sure I order proper parts.

I have a Timney 510 trigger, a Badger recoil lug, a clone of the Badger M5 bottom metal (for AICS mags. later), and a Remington 700 SA receiver that I'll get trued. Just need to get a barrel and the stock, cerakote the metal parts, and glass bed the stock. Oh...gotta get a scope too.

As far as the barrel twist rate goes, I figured the Marine Corps knew what they doing. I've heard a rumor the Marines know a little bit about shooting rifles.  :)

 

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I listened to Sierra and .mil as well when I made my choice.

Sierra is a great resource. I've called them with ? a few times. Very helpful.\

Done right, you'll have a hell of a rifle. 

 

What glass are you looking at?

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With my modest means, I'm considering a fixed 16x or 20x SWFA MRAD scope with TPS rings and base. Good enough. I don't like messing with magnification settings. SWFA's are pretty easy to learn how to use. I believe in the K.I.S.S. principle.

The gentleman who let me fire his GA precision M-40A3 clone had a 16x scope (or it was set to 16x) and it really helped with getting a tight group. However, I took a long time to get my natural point of aim set first before firing. I honestly was pleasantly surprised to get a clover-leafed group because I am not a competition shooter.

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SWFA scopes are pretty nice for the money. I know of some pros using them for work.

Check samplelist. There are some good buys on demo optics there.

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Happened to notice the other day that a box of Hornady .30 caliber 168 gr. AMAX bullets says on its label a 1:12 twist rate is suggested.

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