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308 Win chamber?

 
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  #1  
Old 05-08-2012, 06:10 PM
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308 Win chamber?

I'm converting a Browning A bolt 243 Win into a 308 Win to run as a compact 20" suppressed hunting rifle capable of making consistent sub MOA hits at 1000 yards. I don't plan to take game that far out, but I want the accuracy capability as this rifle will see a lot of range time.

I have a maximum magazine length of 2.815" and I prefer to keep it as a repeater.

I'm planning to run 175 - 200 grain bullets with a 1 in 10 twist.

How have you guys been setting up your 308 chambers to suit this type of shooting? Is a Saami spec chamber versatile enough to perform well in this application?

What are your recommendations for a tack driving 308?
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  #2  
Old 05-09-2012, 08:40 AM
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Re: 308 Win chamber?

Quote:
Originally Posted by brentc View Post
I'm converting a Browning A bolt 243 Win into a 308 Win to run as a compact 20" suppressed hunting rifle capable of making consistent sub MOA hits at 1000 yards. I don't plan to take game that far out, but I want the accuracy capability as this rifle will see a lot of range time.

I have a maximum magazine length of 2.815" and I prefer to keep it as a repeater.

I'm planning to run 175 - 200 grain bullets with a 1 in 10 twist.

How have you guys been setting up your 308 chambers to suit this type of shooting? Is a Saami spec chamber versatile enough to perform well in this application?

What are your recommendations for a tack driving 308?

The 308 is a fine 1000 yard target rifle but on deer size game it should be held to 600 yards Max.

The other thing is that if you look at the ballistics of the175 to 200 grain bullets you will find that
the velocity is very slow and any advantage to using the heavy bullets is lost at extended ranges
because of time of flight in windy conditions.

The 150 and 168 match bullets are about optimum for all round performance,plus the 1 1n 10
may not work with the heavy, slow bullets.

Having competed in matches to 1200 yards for many years the best bullets for the 308 in my
opinion were the 168 gr SMKs and the 160 Accubonds should be a great hunting bullet in the 308.

As far as changing the 243 to the 308 it is an easy change .the barrel simply has to be replaced
and no changes to the action are nessary.

J E CUSTOM
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Last edited by J E Custom; 05-09-2012 at 11:16 AM.
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  #3  
Old 05-09-2012, 11:28 AM
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Re: 308 Win chamber?

Quote:
Originally Posted by J E Custom View Post
The 308 is a fine 1000 yard target rifle but on deer size game it should be held to 600 yards Max.

The other thing is that if you look at the ballistics of the175 to 200 grain bullets you will find that
the velocity is very slow and any advantage to using the heavy bullets is lost at extended ranges
because of time of flight in windy conditions.

The 150 and 168 match bullets are about optimum for all round performance,plus the 1 1n 10
may not work with the heavy, slow bullets.

Having competed in matches to 1200 yards for many years the best bullets for the 308 in my
opinion were the 168 gr SMKs and the 160 Accubonds should be a great hunting bullet in the 308.

J E CUSTOM
Thanks for the input. Every ballistic calculator I can find shows a sizeable ballistic advantage pushing 175-185 class bullets at 2600-2650 fps and 200 grainers at 2500-2550 over the faster 150-168s. There are powders capable of achieving this velocity and then some in a 20" barrel. I am highly considering 185 grain Berger Hybrid tacticals with a.560 BC at around 2600+ fps for hunting and 178 Amax's at 2650 fps for target. I may drop down to the 168 Amax for the increased fps in my target load. This is not intended to take game past 600 yards, but it has to be capable of making sub MOA hits to 1000 with lots of range time.

How is everyone setting up their 308 builds to deliver solid sub MOA performance given the requirements I stated above? The whole design of this build is to have a compact, easy to carry package with an 8" suppressor attached.

Last edited by brentc; 05-09-2012 at 12:18 PM.
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  #4  
Old 05-09-2012, 02:33 PM
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Location: Allen, TX
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Re: 308 Win chamber?

Have you considered leaving it as a 243 or 243AI and putting on a 1:7.5" twist barrel to run the 115 DTAC bullets?

I developed a 308 load for a friend using Berger 175 OTMs fed from the AICS magazine. He has a suppressed 1:10" twist, 20" barrel. Groups are excellent.

He hasn't taken it past 500 yds yet. The 175's appear to have a slight edge at long distance according to the ballistics calculator. ...at least for targets. I don't have JE's experience. So, I'm not sure if that translates to the real world. But, we'll see soon enough.

-- richard
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  #5  
Old 05-09-2012, 02:56 PM
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Re: 308 Win chamber?

Quote:
Originally Posted by rscott5028 View Post
I developed a 308 load for a friend using Berger 175 OTMs fed from the AICS magazine. He has a suppressed 1:10" twist, 20" barrel. Groups are excellent.

He hasn't taken it past 500 yds yet. The 175's appear to have a slight edge at long distance according to the ballistics calculator. ...at least for targets. I don't have JE's experience. So, I'm not sure if that translates to the real world. But, we'll see soon enough.

-- richard
This is exactly the setup I'm going for. Do you know of anything special in your friend's setup? What is the max OAL of the AICS magazine?
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  #6  
Old 05-09-2012, 05:21 PM
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Location: Allen, TX
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Re: 308 Win chamber?

Quote:
Originally Posted by brentc View Post
This is exactly the setup I'm going for. Do you know of anything special in your friend's setup? What is the max OAL of the AICS magazine?
Nothing special.
Rem 700, Shilen barrel, AI Stock, NF scope. Forgot who made the can.

Measured 5 different AICS 5 and 10 round 308 mags at ~2.888"

Seating the 175 OTMs at COAL=2.233" (.035" jump) with plenty of mag clearance.

-- richard
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  #7  
Old 05-14-2012, 01:15 PM
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Posts: 2,114
Re: 308 Win chamber?

Quote:
Originally Posted by brentc View Post
I'm converting a Browning A bolt 243 Win into a 308 Win to run as a compact 20" suppressed hunting rifle capable of making consistent sub MOA hits at 1000 yards.
That'll be hard to do with a 20 inch barrel. There may be powders that'll push your bullet choises out fast enough, but not with a low enough muzzle velocity spread to shoot no worse than 1 MOA from shoulder fired rifles in hunting environments. The rifle and its ammo will have to shoot no worse than 1/2 MOA at 1000 to do that. Note the very best benchrest 1000 yard rifles don't do that well. The record for shoulder fired high power prone shooting with a scope's 1000 yards is 19 out of 20 shots in 1 MOA; with a .300 magnum. Even the top classified folks rarely get more than 12 or 13 shots out of 20 in the 10 inch scoring ring on the long range target. Adding a supressor will degrade accuracy a little bit; a lot if it's a bad one.

Quote:
I have a maximum magazine length of 2.815" and I prefer to keep it as a repeater.
That limits the powder you can put in a case. When the .308 was "the" round for NRA high power competition, 190 and 200 grain bullets were seated out to about 2.9 inch OAL and single loaded. 26 and 28 inch barrels were used shooting the 190's at about 2560 fps and the 200's about 2470 fps.

Quote:
I'm planning to run 175 - 200 grain bullets with a 1 in 10 twist.
That's a good choice for 24 inch or longer barrels, but the 200's may not stabilize to well with the lower velocity a 20 inch barrel will produce with sub MOA accuracy at 36,000 inches down range.

Quote:
How have you guys been setting up your 308 chambers to suit this type of shooting? Is a Saami spec chamber versatile enough to perform well in this application?
SAAMI spec .308 Win. chambers (or virtual copies thereof) with standard .344" necks were used to win virually the matches and set the records from 1963 until recently when the 26 and 24 caliber match bullets finally became competitive.

Quote:
What are your recommendations for a tack driving 308?
I don't know what the Browning action's abilities are and track record is for super accurate rifle shooting. Instead, get a cheap, used Winchester Model 70 (or 670, 770), square the bolt and receiver faces, lap its locking lugs to the receiver, then fit a 26 inch Kreiger 1:11 .2980 x .3075 bored/rifled barrel in a medium-light weight taper. Replace the firing pin spring with a new 26 or 28 pound one. Put in a Jewel trigger with a 1 to 2 pound pull. Epoxy bed only the receiver in a stock of your choice. Attach the scope of your choice.

Next, learn what processes, techniques, tools and components to use for sub MOA acuracy in reloaded ammo. Then go buy, use and test them.

Then you'll have to learn how to hold you sights in an aiming area under 1/2 MOA on that 1000 yard target, dope the wind correctly and finally shoot the rifle well enough to meet your objecdtive. It's been done by others but they usually wear out at least one barrel in the process. Best wishes in your endeavor.
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