Running .308 rounds in a 7.62x51 NATO chamber

[ukrifleman]

Military 7.62x51 ammo is loaded to an average pressure of 50,000 psi and proofed to an average of 67,000psi.
Some commercial .308 ammo can be loaded up to 62,000 psi and proofed to an average of 83,000 psi.

As you can see, using some commercial ammo in a military 7.62x51 rifle, means you will be shooting at proof pressures, not a good idea! Particularly from a weak action such as a converted Mauser 93/95.

Military brass generally has thicker walls than commercial resulting in reduced case volume, this must be born in mind when using commercial .308Win load data when reloading, as the reduced volume will lead to increased pressures.

To quote from an article by Mark Trope on the Surplusrifle .com forum;" entitled `.308 Winchester VS 7.62 Nato, Quote, "Here at Surplusrifle.com, we recommend in the strongest possible terms, that you do not fire factory .308 Winchester ammunition in any Mil-Surp rifle chambered for the 7.62 Nato round, Un-quote"

A similar article on the .303british.com forum says much the same thing.

I have 2, 7.62 Enfield No.4 conversions and think this is good advice.

ukrifleman.

[Dougan]

I've read some horror stories where headspace has been blamed and as a relatively newcomer to the sport, I just want to be safe.

I wouldn't call it a 'horror story', but have had an incident with this issue - I had an TR converted Enfield that shot NATO 7.62 (black dot, green dot etc.) nicely...then when the NRA changed to .308 Win for TR, I tried some .308 PPU ammo...the bolt wasn't closing properly, and on the second try when I pulled the trigger there was a click, and then nothing...I followed the usual procedure, and after 30 seconds attempted to operate the bolt...as soon as I touched it, it went off ( ) - the bullet hit the mantel, so no harm done, but I did worry me...

...I took it to a gunsmith who changed the bolt-head, increasing the head-space by about 6 thou, and the rifle was then fine for chambering .308...though I still wasn't convinced the action was suitable for higher pressure ammo.

[Steve E]

Be aware that any .308W or 7.62x51 rifle when sent to either of the UK Proof Houses will be proofed as if it were .308W. They will both have the same proof of 20Ton or equivalent. Most No4 and Mauser conversions will pass the proof with ease.

[Charlotte the flyer]

How does an 7.62 SLR with a .308 barrel fit in? I'm assuming that it's .308 as the barrel will also incorporate the chamber won't it? I'm not sure but I think that the bolt is 7.62 original other than having bits removed to stop it from being semi automatic. Confused!

[HALODIN]

Thanks for the links!

[huntervixen]

My Suffolk Rifles SP L1A1 is also London proof house marked for dual .308 and 7.62x51mm, GGG works 99% of the time with no issues, but commercial .308 is a nightmare regarding extraction!

What's the extraction like in the M14?

[HALODIN]

I've been running some tests and speaking to every man and his dog about this, but I'm curious if anyone can offer an explanation for this.

I've been advised the LDT-M14 was proofed at the Belgian proof house in Liege before delivery and is safe to shoot .308 as tested in Visier Magazine "Visier N°6...LuxDefTec M14 US Klassiker-Jetzt neu aus Luxembourg" (see pages 36-43)

There is part of the article here http://issuu.com/vsmedien/docs/visier_06_2013_leseprobe

1 (Good) to 7 (Bad)
147grs RWS Cineshot HP, .................................2
147grs Sellier & Bellot FMJ, .............................4
150grs Tulammo FMJ, ......................................7
155grs Hornady TAP FPD, ................................ 1 (5 shot group 1.9cm IIRC)
168grs RWS Target Elite HP-BT..........................6
168grs Sellier & Bellot HP-King M' King...........3
168grs Remington HP-BT M'King......................5

So it seems like it should be OK, however we downsized a .308 round from 62,000 PSI (.308) to 50,000 PSI (7.62x51 NATO) and 2 of the 3 test shots caused the primer to stand proud out of the back of the brass (see example pic below). I don't believe the brass was new and whilst I don't know very much about self loading yet, could case trimming have caused this? i.e. with new .308 commercial brass would this problem disappear?

[HALODIN]

My Sabre Defense Imbel FAL is marked 7.62 on the receiver, but is proofed .308 and it loves Hornady match ammo, shoots very accurately with NO extraction issues at all. If I use GGG 7.62x51 NATO in the FAL, after about the 6th round when the chamber heats up, they stick and the extraction is horrible, making the rifle unusable. Thankfully the M14 is perfect with GGG, I've never had a single shot even slightly bind with the chamber, it's a pleasure to use. The downsized .308 Lapua rounds were perfect as well.

My Suffolk Rifles SP L1A1 is also London proof house marked for dual .308 and 7.62x51mm, GGG works 99% of the time with no issues, but commercial .308 is a nightmare regarding extraction!

What's the extraction like in the M14?

[huntervixen]

How does an 7.62 SLR with a .308 barrel fit in? I'm assuming that it's .308 as the barrel will also incorporate the chamber won't it? I'm not sure but I think that the bolt is 7.62 original other than having bits removed to stop it from being semi automatic. Confused!

Hi Charlotte,

If your L1 is one of the Anglo Custom examples, the bolt is of a totally different design to the original. The carrier is also modified with a very strange pin mounted on the front that fits into a drilled hole into the forward receiver, just below the piston aperture.

Can't see a good reason for the pin....it would prevent the carrier being used in a semi auto L1A1, but don't really see why you would do that anyway?

These small pins can shear off in fact, I have seen this on a friends Anglo rifle.....now if this prevented the tilting bolt from fully locking or dropped into the chamber it could potentially be very dangerous.

[HALODIN]

Thanks for the info, much appreciated.

To quote from an article by Mark Trope on the Surplusrifle .com forum;" entitled `.308 Winchester VS 7.62 Nato, Quote, "Here at Surplusrifle.com, we recommend in the strongest possible terms, that you do not fire factory .308 Winchester ammunition in any Mil-Surp rifle chambered for the 7.62 Nato round, Un-quote"

ukrifleman.

Holy s***! I bet you had to change your y-fronts after that.

I wouldn't call it a 'horror story', but have had an incident with this issue - I had an TR converted Enfield that shot NATO 7.62 (black dot, green dot etc.) nicely...then when the NRA changed to .308 Win for TR, I tried some .308 PPU ammo...the bolt wasn't closing properly, and on the second try when I pulled the trigger there was a click, and then nothing...I followed the usual procedure, and after 30 seconds attempted to operate the bolt...as soon as I touched it, it went off ( ) - the bullet hit the mantel, so no harm done, but I did worry me...

Yes that makes sense, thanks for the info.

Be aware that any .308W or 7.62x51 rifle when sent to either of the UK Proof Houses will be proofed as if it were .308W. They will both have the same proof of 20Ton or equivalent. Most No4 and Mauser conversions will pass the proof with ease.

I think the .308 aspect is only really specific to the chambering, but I may be wrong.

How does an 7.62 SLR with a .308 barrel fit in? I'm assuming that it's .308 as the barrel will also incorporate the chamber won't it? I'm not sure but I think that the bolt is 7.62 original other than having bits removed to stop it from being semi automatic. Confused!