Is 7.62 NATO the same as 308W

[sortwell]

Hi, I have tried looking on other sites, but am still confused.

I am thinking of buying an Omark 308W but it has a Maddco 7.62 NATO barrel. I have been led to believe that you need to be careful as 308W cartridges can be a problem in a 7.62 NATO gun - is it the action that needs to be 308W specific, the barrel or both?

[Rich4]

7.62 NATO is a chamber spec, roomier than a 308win chamber, also loaded to a lower pressure in thicker brass, for your application it's a non event, where it becomes sticky is in OOld converted military actions, at the end of the day load carefully and the case and primary extraction will be your limiting factor.

[PeteFox]

If it is specced as 7.62 NATO, it is not the chamber that will be an issue it will be the bore dimensions. It will be a tight barrel .307" or tighter, with most likely a 14 twist, to suit the 144gn FMJ bullet. May not be suitable for F class pills.
Pete

[johno]

Ring Maddco, would that make sense???

[MattyG]

Omarks were made to shoot L2A2 or F4 7.62mm Ball ammunition. They can cope with hotter loads but have little to no primary extraction and the locking lugs of some barrels and adaptors are softer than others. Even the current ADI manufactured 155 grain target ammunition is a bit hotter than what these rifles were designed for. As mentioned above, the barrel was made specifically for a 144 grain projectile and often made tight to suit Australian military ammunition. At best you would likely need to replace the barrel.

[Frank Green]

If it is specced as 7.62 NATO, it is not the chamber that will be an issue it will be the bore dimensions. It will be a tight barrel .307" or tighter, with most likely a 14 twist, to suit the 144gn FMJ bullet. May not be suitable for F class pills.
Pete

I'll say this only partially correct.

The spec as written since Nov. 30th, 1959 (oldest dated test barrel drawing that I have) is as follows.

.3000" x .3080" bore and groove with a +.0005" tolerance on each. Groove width is .167" +.010", 4 groove and 1-12 twist. Chamber is spec'd as the 7.62 Nato chamber. This is still the standard spec. to this day and is called out on all test barrel drawings that I have seen. Doesn't matter if it's a test barrel drawing from the U.S. Gov't, or from places like Europe, Israel etc...

The above spec has not been changed. There are at least 6 different test barrel drawings I have. All list that spec.

Has the spec' been altered at times for specific/different testing? Yes. We've been asked to make different barrels with that rifling spec. but with a different chamber spec. Or we've been asked to use a Nato chamber but do some barrels with 5R rifling spec. or changed the twist rates etc...

But that spec. I listed above is still standard. We are making 70 more pressure test barrels for the Gov't as I type this that are due to ship in two months.

Now this doesn't mean that a given country and I'll say more 3 world countries who don't necessarily follow the spec. and or what they hold the barrels to for manufacturing tolerances. Same holds true for ammo being made by other countries as well.

Where some of the tight bore barrels came into being I'll say goes back to Creighton Audette. He was a long time U.S. Palma shooter and gunsmith. He was the first person that I know of that asked Obermeyer to make a tight bore/tight groove barrel due to having to shoot at times ball ammo. They found that depending on the maker of ball ammo the bullets where running as small as .3065" in diameter. I believe Obermeyer first made the tight bore barrels back in the early to mid 70's for the Palma shooters.

Later, Frank
Bartlein Barrels

[PeteFox]

Frank
I was referring specificaly to Maddco barrels made as a target barrel to shoot the 7.62 ADF round with 144gn pills. 14 twist was common.
These barrels were made tighter than spec as it was thought to improve accuracy, I'm talking around 1990 here.
Pete

[Frank Green]

My apologies Pete! I misinterpreted your post.

Radway Green was the same way. Bullets where undersize from what I remember.

Obermeyer started making tight bore barrels like I said back in the 70's sometime. I know Krieger started making tight bore 30cal barrels in the mid to late 80's as well. My first palma rifle when I worked at Krieger I put on a .298" x .3075", 12 twist barrel. I wanted the option to shoot the 175gr bullets if I wasn't regulated to shooting 155's.

When we started up here we tooled up for all 30cal barrels. We are tooled for....

.298, .2985", .299" and .3000 bore barrels.

We are also tooled for 7.5x55 Swiss barrels. Those original spec's are .2968" x .3059" plus the tolerance. Talk about tight bore! I measured a mint K31 that I have and if I recall correctly it is .297" x .306". I have shot 175SMK thru it with no issues. Reduced loads of course.