bigtim6656

I asked a few weeks back about firing a 7.62 in a 308. I though since a .223 rifle with 5.56 was a bad idea, but .223 in a 5.56 was ok.

The general thought HERE was a 7.62 shooting 308 was bad, but a 308 firing a 7.62 is ok.

Checking dpms's site for some info about another subject I found a FAQ page that says the total different then the guys I talked to on here.

Not calling anyone wrong, I will be calling dpms to double check.
I just want to post the info incase someone like me was planning on buying one of the other and wanting to fire both.

THIS IS FROM DMPS ADMIN ON THEIR FORUM
http://dpmsinc.com/forum/posts.aspx?postID=2271

While you can physically fire either 308 or 7.62 NATO from a 308, you
will see reduced accuracy from increased wear in the throat of the
rifling and a higher chance of erratic cycling, including a higher
chance of failures to extract. It is for this reason we recommend using
only commercial 308 in a 308 barrel.

DPMS does not recommend or warranty the use of 7.62x51 ammo in a .308 chamber.

A 7.62x51 chamber can handle both types of ammo. Determine your actual chambering by looking on the underside of your barrel forward of the gas block or front sight base.

The lower receivers of these two rifles are identical and will be stamped 308 even on a 7.62, the lower stamp should not be used to determine actual chambering. FWIW, the .260, .243, .300 SAUM, .308, 7.62x51 and 6.5 Creedmoor all use the same lower receiver.

Nomercy448

So basically what you're saying is that DPMS (not surprisingly) have a disclaimer on their site saying shoot .308 in .308 rifles and shoot 7.62x51mm in 7.62 Nato rifles... And Ruger puts "caution guns are dangerous" barrel stamps on all of it's guns, and McDonald's put's "Caution: Contents are HOT!" on it's coffee cups and lids...

What their lawyers allow them to say and what is real are not necessarily the same thing...

bigtim6656

No, they say a 7.62 can fire both rounds, but a 308 can not

warbirdlover

I thought the .308 and 7.62 were identical in dimensions and loads. So I looked it up and found this...

http://www.303british.com/id36.html

keylargo

If I am not mistaken this is the same issue you find in the .223 vs 5.56mm. The issue is not the size of the cartridge,but the pressue it can be loaded to. The 7.62 and 5.56 Nato are loaded to a higher pressue than the .223 or .308. so rifles chanbered to the nato specs can handle both.

Nomercy448

Actually, the cartridge dimensions for the 5.56x45mm and .223rem are not identical. Specifically, the 5.56x45mm has a thicker case, therefore less powder capacity, and the 5.56 also is rated to higher chamber pressures than the .223rem. Additionally, the chamber throat is longer for the 5.56. So in a .223rem the longer 5.56mm cartridges may actually seat the bullet into the rifling when chambered, which can create a dangerous pressure spike.

So typically, since the 5.56mm NATO is the LONGER and HIGHER PRESSURE of the two, it is safe to fire .223rem from a 5.56mm chambered rifle, but it is not recommended to fire 5.56 NATO rounds from a .223 chamber. However, from my personal experience, the excessive throat jump when firing shorter .223 rem cartridges in 5.56 NATO chambers has a negative effect on accuracy. For the handloader, the .223rem brass can be loaded with the bullets slightly longer in the case to reduce the throat jump and improve accuracy.

THAT SAID, in modern firearms many manufacturers have recognized the danger of consumers mixing up cartridges, and therefore are proofing their .223rem chambers to withstand 5.56 NATO pressures. HOWEVER, the chamber throats are still machined shorter, so excessive pressure from seating the bullet into the rifling still represents danger. Shooters can mark their bullets with magic markers to test to see if the bullet is contacting the rifling when chambered. If so, then the 5.56NATO cartridges should not be used in their rifle, if not, the shooter should set the bullet slightly longer, and test until the COL to reach the rifling is found to determine if the throat jump is safe.

Alternatively, the cartridge dimensions for the 7.62NATO and .308win are minimal with the major difference coming in the pressure rating. However, SAAMI has determined that the two cartridges can be used interchangeably. The real danger is for the handloader who might mistakenly charge a 7.62 NATO case (lower capacity) with a full .308win powder charge, creating excessive chamber pressures.

Based on SAAMI pressure limitations, the .308win should NOT be fired in older 7.62NATO rifles. The .308win max pressure is 24% higher than the 7.62 NATO. However, in modern rifles, the same barrel blanks are used for both rifles, with the same dimensions of steel surrounding each chamber. The steel can withstand the same pressure regarless of the headstamp on the brass, so modern rifles won't notice any difference between the two.