Why??

[RussC]

Why??

what are the reasons someone would choose a 7.62x51 over a 308win? I mean...... knowing the defference now I would have choose to buy a 308win lower. Am I missing somthing? 

[BLKSHEEP]

Why??

what are the reasons someone would choose a 7.62x51 over a 308win? I mean...... knowing the defference now I would have choose to buy a 308win lower. Am I missing somthing?

I believe 7.62 is Military spec. as far as lowers go you could use a lower stamped 7.62 on a upper chambered for.308, it makes no difference.

[RussC]

But what are the reasons for choosing a 762 over a 308 winchester upper?

[survivalshop]

Its all about chamber dimensions & unless you really have a tight 308 chamber (some DPMS ) some milspec from other countries may be tight in the chamber , but it doesn't mean a hill of beans . The commercial 308 in some cases is loaded to a higher chamber pressure , but all modern barrel steels will take the small chamber pressure difference, be it 308 Or 7.62x51 .

I put only 7.62 chambered barrels on my AR 308's & they shoot sub moa with out a problem . I was just out today & all who shot my 20" couldn't believe how accurate it was .( with my hand loads , of course )

[Cabinetman]

Why?  In my case it was a matter of ammo availability.  I've stocked up on 7.62 x 51 for years and would prefer not to have to pay for retail .308 at the prices they are demanding today.  That's my  reason. 

Rome

[mrraley]

Firearms  chambered for 7.62 cartridges will fire all standardized U.S. military 7.62X51 mm cartridges and all factory loaded cartridges in .308 Winchester caliber, but a .308 chambered firearm will not fire 7.62 cartridges.

[Retired JM]

Firearms  chambered for 7.62 cartridges will fire all standardized U.S. military 7.62X51 mm cartridges and all factory loaded cartridges in .308 Winchester caliber, but a .308 chambered firearm will not fire 7.62 cartridges.

I think it's the other way around, bro. All .308 Win chambers will handle 7.62 NATO, but not all 7.62 chambers will handle .308 Win. It's the exact opposite for 5.56 NATO/.223 Rem.

And I concur with SS, the small differences in pressure bewtween 7.62 and .308 is really a moot point, given modern barrel steels.

[Matt.Cross]

Here's a link to a really good article on this issue:

http://www.fulton-armory.com/%5Cfaqs%5CM14-FAQs%5C308.htm

[mrraley]

The difference between .308 and 7.62 is chamber size, slight pressure differences due to powder burn rates, not external case size. Both cases will have the same external dimensions while the .308 has a slightly higher pressure 60Kish vice 50-55 CUP psi for NATO**.

NOTE: This is OPPOSITE from the 5.56/.223 rule of thumb. The NATO chambers have greater tolerances to help with reliable functioning of military ammo. The NATO chamber is ever so slightly longer at .013". This is significant in that for reloading purposes, 308 brass will stretch more in a military chamber upon firing, thereby reducing the life of the brass and possibly promoting case head separation. But that additional chamber length will allow a round to chamber in an incredibly dirty weapon, which is a requirement for military applications. Also be aware this is why mil NATO brass is thicker vice 308 commercial brass. You will also see this "thicker brass fact" posted about 5.56/.223 brass which is a fallacy.

**As a side note the reason the pressure issue is confusing is becuase the military measured 7.62 NATO chamber pressure (PSI) via CUP (in the 40s) vice the normal commercial rating of PSI measured (now) with electronic means. You will see many cling to the 50-55K PSI figure for 7.62 Nato becuase that is what the old Army TMs have in them. Since there is no conversion for the CUP measurement to the newer electronic measured PSI, they are two different numbers i.e no direct comparison. Many people will assume the CUP PSI is the same as SAAMI/Commercial PSI. It is not. Commercial PSI is derived from the direct pressure in the chamber through electronic means (piezo transducer or strain gauges). CUP is a crush measurement of a copper slug that has been fired, again not the same test.

That means any newer weapon will be able to fire 308 Commercial ammo as manfs would not let them out the door if they could not, due to liability. Don't believe me, run the numbers/powders in any internal ballistics calculator and they will all be close to the 60K mark. BTW the proof load for the 308 commercial is 75K PSI, so don't worry about the 60K.

GO GAGE CHAMBER SPEC INFORMATION (TOLERANCES FOR GOOD-TO-GO CHAMBERS)

•AR-10 NATO – 1.633-1.638 (stainless steel, chrome moly, and chrome lined barrels) "

308 Winchester (SAAMI) Headspace

GO - 1.6300"

NOGO - 1.6340"

FIELD - 1.6380"

7.62 NATO (Military) Headspace

GO - 1.6350"

NOGO - 1.6405"

FIELD - 1.6455"

Note that the military chamber would fail a NO GO check with a SAAMI gauge, but pass a FIELD check using the proper military gauges.

[RussC]

Why?  In my case it was a matter of ammo availability.  I've stocked up on 7.62 x 51 for years and would prefer not to have to pay for retail .308 at the prices they are demanding today.  That's my  reason. 

Rome

Every time I ask this question most people will give me the difference between the two but not the reason why they would select one over the other. You have done that. Your reason, which is a good one, is the only one I could come up with for selecting the 762 over the 308win. Are there any others? My reason for selecting a 308win over a 762 is that could use both rounds and not be concerned about the higher pressures in the 308win round. I understand that most folks don't have that concern at all.

Thanks to all

[Slash]

For most intents and purposes .308 vs. 7.62 is a distinction without a difference.

But it does give internet commandos something to argue about . ;)

[fr3db3ar]

I have to say that this must all apply to factory ammo.  I'm shooting LC brass which I'm sure started as 5.56. and loading it with 55 vmax and 69 smk and shooting out of my R-15 and Stevens with no issues what so ever.

[Cabinetman]

I'd like to add that my barrel is marked .308WIN, not 7.62 x 51.  When I bought the rifle, I was not asked what flavor of .308 I wanted.  I just got the "luck of the draw".  This was back when the large caliber platform rifles were on a 6 month backlog. I didn't have to wait.  When I discovered the mark,  I was a bit confusted but, as another poster above states, there's no dimensional difference you have to be concerned about.  More importantly, however, when I was reading through the literature that DPMS put in with my rifle, they clearly say that I'm going to void my warrantee if I shoot ANYTHING except commercial .308 in it that that includes handloads.  Well, I'm not a gambler but I do have a lot of experience with 7.62 x 51 ammo having shot it in just about everything that is cut for that caliber including the MAS 49/56.  I didn't care about the warrantee knowing that the 7.62 x 51 would be just fine in that chamber.  The first five or ten rounds were tight but after that it shot 100% just fine and I've got about 1000 rounds through it over the past few years.  For me the barrel mark is a distinction without a difference except when it comes to DPMS's warrantee on their product.  At the current prices of commercial .308, however, having a rifle that could ONLY handle commercial .308 would be like having a sports car that only handles 93 octane fuel.  You'd end up only driving it on weekends and holidays.  Me?  I want my beauty to go to the range with me every trip I take so surplus it is! 

Rome

[Grunt Medic TXARNG]

The barrel could be marked .308 or 7.62 - as has been pointed out, with new made barrels this is not a problem, as the manufacturers are aware that any barrel marked 7.62 will most likely be used at some point to shoot .308 - and so is built and proofed to take the higher pressures of the civilian specification. 

Where you can run into problems is when you use a surplus military parts kit or barrel to make a firearm, and then fire .308 through it - when those barrels were only made and proofed with 7.62x51 NATO in mind.  This is the case with a G3 parts kit I have, and why I had a new barrel installed on my M14 parts kit when I had it built.

So for the OPs question - in your case it makes no difference which one you 'choose' - as they are essentially the same thing for what you are looking at. 

If that makes me an 'Internet Commando' so be it - although this Internet Commando is also a graduate of the US Army Small Arms Master Gunner School.