I posted this on the M14 forum but wanted to post this here as well for anyone who can contribute. I'll probably post this over at accurate shooter too for input....

So as I sit here over-analyzing variables that contribute to accuracy or lack thereof (something I un-nececessarily do a lot of), I spent a lot of time thinking about the different types of chambers that are available to the M14/M1A owner/builder. (bolt-gun guys can chime in too)

The intended purpose of this thread is the help people understand what ammo they should buy or load to get satisfactory results out of their rifles and which ammo or loads to avoid considering their chamber.

I thought it might be helpful to list the common chamber types available for our rifles and give a summary of what specific purpose chamber was designed for. Also list what bullet weights work well with specific chambers. I don't think there's a need to get into the mind-boggling discussions of throat dimensions and freebore, but the data could still be useful to some people.

It's common for new rifle owners to know nothing about chamber options. Most people think that the rifle is simply chambered in 308, and know nothing of the other chamber options available.

So I guess I'll list the common types of chambers, but what I'd need help with are filling in the blanks below that would help someone pick the right chamber for them. Please provide links, if you can, to commentaries or articles that highlight information for the specific chambers listed. I'm excluding the Palma chambers, but if you think they should be listed, I can add them.

.308 Winchester
Intended use: General purpose/hunting

Bullet weights that work well with this chamber: 125gr through 168gr bullets

Bullet weights that don't work well with this chamber:

Benefits/Advantages:

Draw-Backs/Disadvantages:

Additional info/commentary:

7.62 NATO
Intended use: General purpose/hunting

Bullet weights that work well with this chamber:

Bullet weights that don't work well with this chamber:

Benefits/Advantages:Looser tolerances and headspace which reduce chamber pressure and allow the rifle to safely shoot a wide range of military and commercial ammunition.

Draw-Backs/Disadvantages:Looser chamber dimensions allow for more case stretch which reduces brass life for hand-loaders.

Additional info/commentary:

308 Match
Intended use:

Bullet weights that work well with this chamber:

Bullet weights that don't work well with this chamber:

Additional info/commentary:

M852 Chamber
Intended use: General purpose/Hunting/Match Shooting

Bullet weights that work well with this chamber: 168gr SMK

Bullet weights that don't work well with this chamber:

Benefits/Advantages:

Draw-Backs/Disadvantages:

Additional info/commentary:

M118LR Chamber
Intended use: Long Rage Military/Match Shooting/Hunting

Bullet weights that work well with this chamber: 175gr SMK

Bullet weights that don't work well with this chamber:

Benefits/Advantages:

Draw-Backs/Disadvantages:

Additional info/commentary:

Obermeyer Chamber
Intended use: Long Range/Match Shooting/Hunting

Bullet weights that work well with this chamber:

Bullet weights that don't work well with this chamber:

Benefits/Advantages:

Draw-Backs/Disadvantages:

Additional info/commentary:

Jon Wolfe Chamber
Intended use: Long Range/Match Shooting/Hunting

Bullet weights that work well with this chamber: 168gr SMK/175gr SMK

Bullet weights that don't work well with this chamber:

Benefits/Advantages:

Draw-Backs/Disadvantages:

Additional info/commentary:


Please add your knowledge! What's your favorite 308 chamber reamer, and why?

Tony.

Thought I would add this photo (from G&A) that dramatically demonstrates the difference between 7.62x51 chamber on the L, .308 W chamber on the R fired cases. Same load for both:



One thing to read chamber specs; whole other to see the difference. I load for both, in three different chambers, and some 7.62x51 fired rounds are even more dramatic, i.e. cases fired from an Indian made Ishapore 2A are much more swollen, but headspace is OK. Yep, headspace is OK, but the chamber, as in many British rifles is very generous.

I STRONGLY suggest in my experience using only 7.62x51 brass in 7.62x51 chambers if you reload. The thicker, heavier brass, esp in the head area is a nice safety margin, compared to a lot of commercial .308W cases.

I do not have the proper gauges to measure but I have shot a variety of ammo types through my M1A Loaded.

Here is some information similar to what I worked with just to satisfy safety questions:
" I would not shoot commercial .308 ammunition in a bone stock Chinese M14 or a Federal Ordnance M14 with Chinese barrel unless I knew the headspace reading. Springfield Armory, Inc. does headspace M1A rifles in the range of 1.631 " to 1.633 ". Smith Enterprise, Inc. M14 rifles typically headspace at 1.633 ". Armorer built M1A/M14 type match rifles in the 1970s were headspaced at 1.6355 ". SAAMI NO GO is 1.634 " for .308 Winchester. IIRC Fulton Armory has a FAQ article on their web site that says you're okay with commercial .308 up to 1.636 ". Past that, use 7.62x51 mm NATO ammunition up to 1.6405 " which is NATO NO GO. Beyond that you need to see a M14 gunsmith." LINK

I have not tired to push any great accuracy at long distances with mine. I just seek 100 to 200 yard results. I, too, would like to learn more about your topic.

In for the notifications.

benny,

I read in another thread that bullet weight was not as important as the type of bullet.

What, to you, would the bullet weight have to do with a chamber size as far as accuracy? As far as the chamber, if it is safe, then maybe the question is, "Does it really matter?"

I know from pistols, for instance, that different powders, loadings and bullets make a difference on how a given pistol works for me. Some chambers are tight and others are more loose for a given cartridge. But, with the same brass, XTPs and others seem to fly well at longer distances compared to others.

I have heard for years that certain bullet weights are best at certain distances with rifles but what if that is not as important as finding the right powder, load and bullet for a given rifle - no matter the rifle's name?

When I talk about bullet weights I'm talking about chambers being designed with certain bullets in mind.

Here's a post with exactly what I was looking for...

My .02 cents worth anyway, and list my opinion in reamer order.

.308 Winchester

Generous freebore and leade angle. 125-180grn bullets @ 2.80 COAL and although some 180's many fit deep into the case hampering the M/V the original barrels 1/12 rate of twist are the real reason for most inaccuracy.

7.62 Nato 147-155 bullets

This is really a loose compromise chamber generous everywhere, one never knows when a rifle is going too be cleaned next or fired under what conditions, one never knows where there going too get ammo so its a comfortable feeling knowing your allies have ammo that will fit in your rifle and hopefully it will still work? With that in mind the freebore length is kept long too stay out of pressure issues just incase some allied ammo is loaded hotter.

.308 Match 150-180 bullets.

This is just a min spec .308 Winchester chambering with a snugger neck, the freebore and leade angle are better shaped too fit the 168SMK nose.

Obermeyer Match.

This is a older reamer that works really well with almost everything. Way back in the day when M118NM ammo was issued, it was fired is std. NATO chambered rifles. Not really the best for optimum accuracy. Long story short the Obermeyer is a NATO body and the freebore and leade is adjusted too better fit the USGI 173 bullet profile.


M852

The Military likes acronyms and M852 sounds cool, its really just a 7.62 NATO body and the freebore and leade adjusted too fit the 168SMK for less Evil Kinevel jump into the rifling.

M118LR

Almost the same as the Obermeyer but its cut too fit the profile of the 175SMK bullet better.

Wolfe Chamber.

Its my understanding this was a much needed/updated Obermeyer, a page was taken from Bill Wylde's book. The neck diameter was snugged up and still give the bullet reliable release while maintaining good chamber/case aberration then the freebore and leade are encapsulated in there own diameter so the bullet is held center/true into the throat, the leade angle was also laid back a smidge so the bullets jacket and core distortion are minimized as much as possible when the bullet swages into the rifling(throat).

Me, being a 2 dimensional thinker. Nez or Jon can give you the big picture thinking and the why's behind the changes done.

Tony.

Well benny,

After seeing your build thread, I can see why you are asking the chamber question.

Frankly, my M1A has fired everything I've fed it in .308 and 7.62x51. My accuracy at 100 yards has been less than an inch at 100 yards.

Because of this thread, I've been reading various articles. Many say that finding the correct chamber does increase accuracy.

But, I have never tried to get the most accuracy possible. I have thought of mine as a functional firearm for me at less than the rifle's capability.

In fact, I have used my M1A Loaded in Three Gun for the fun of it and have been told I get the "He Man" award for sound and fury - and that without even ripping my pants. Blowing targets over may be close to a procedural. There's nothing like 7.62 at 10 yards. Ha.

I did find this article about measuring one's chamber with Cerrosafe. How To Measure Your Rifle Chamber This is just something I have never done. I am not sure why the chamber would affect the accuracy out to say 200 yards but that seems to be more your bailiwick, for sure.

IMO, there isn't a whole lot of point to this discussion.

Once you begin discussing REAMERS, and having things chambered by a smith, all bets are off. Any decent smith, even a half-hack-in-his-garage, can use a throating reamer to make whatever bullet you want work with whatever chamber you want.

does this guy know what he is talking about ?
http://how-i-did-it.org/762vs308/

quote:

Originally posted by bendable:
does this guy know what he is talking about ?
http://how-i-did-it.org/762vs308/

To an extent. I only skimmed that site, but one thing that stuck out as wrong was the warning to not shoot 308 out of a 7.62 chamber due to headspace and brass flow issues. There are plenty of 150ish weight loads on 308 brass that work well out of the various 308 semi auto rifle that are currently available.