I thought 308 win could fire 7.62x51...

[ldlfh7]

I recently received a quantity of 7.62x51 lake city brass and I decided to load them up for my Savage model 11 308 bolt rifle. I resized and took all the steps I do for 308 win brass (and I swaged too). When I went to test fire a round, the bolt on my rifle would not close. It was not the 1 round as I tried 10 of them and the bolt would not close with any of them. How is this possible if I resized using 308 win dies?

 

[steve4102]

You die is most likely not bumping the shoulder back far enough, screw it into the press a little at a time until the cases chamber.

 

[Ret.CWO]

You need to reset your sizing die all the way down until it touches your shell holder. This solves the problem 99.9 % of the time.

 

[Tom488]

Not to state the obvious here, but your resizing die isn't set up correctly. You've probably been "resizing" .308 rounds fired out of your Savage, but have only been neck-sizing them, as the rounds aren't going to expand when fired in your bolt-action.

The 7.62x51 you received was probably once-fired from a MG, meaning it's expanded more, and requires full-length resizing.

Assuming you have a full-length resizing die, and not just a neck sizer, you need to turn your die down a little more (should contact the shell holder, with a light cam-over), to completely resize the brass.

 

[CMC]

When loading lake city brass reduce your hand loads by 10 percent, otherwise you will have overpressure.

 

[ldlfh7]

Thanks for the info. Tom 488, you are correct. These are once fired from MG. That makes sense that they have expanded more than my commercial brass. I will try again and see how it goes. Again, thanks for the input. CMC, I am loading 2 grains under the minimum which is only 5%. I have read so many conflicting posts on how much to decrease these LC loads I don't know what to believe. Ill start 2 grains below minimum and see what happens. Do you have any FACTS supporting the 10%? I am not trying to start an argument, just looking for quality information.

Can't I just measure case volume (308 win and 7.62x51) with water and extrapolate the reduction based on the volume of water held?

 

[CMC]

Hi Man the only facts I have are my own experience the same loads on winchester brass and LC brass properly resized.
When I fired the LC loads the bolt was very difficult to turn, a sign of high pressure.
The Military cases also have less capacity , you can measure it.

Lots of info on this link http://www.6mmbr.com/308Win.html

 

[cfullgraf]

It was not the 1 round as I tried 10 of them and the bolt would not close with any of them. How is this possible if I resized using 308 win dies?

I assume the 7.62x51 cases had been fired in another firearm. Depending on the firearm and how your resizing die is set up, you may not be setting the should back far enough or you may not be sizing the body of case enough.

You can take a magic marker (or machinist's bluing) and mark the shoulder down to the base of an empty, resized case and try to chamber the case. The marker should scrape off and tell you where the interference is. You may need to try and chamber the case a few times.

A case gauge will tell you if the shoulder has been moved back far enough but will not tell you if the body has been sized enough. But, if the shoulder is in the right spot and the case still will not chamber, the body is probably too large.

If you are crimping, the cases may be too long for your crimp die setting and you may be upsetting something in the mouth or shoulder that is preventing chambering. I do not crimp my 308 Winchester even those rounds used in a semi-auto rifle.

If the cases are new, they should chamber. The exterior dimensions between 308 Winchester and 7.62x51 cases is the same.

Hope this helps.

 

[john wall]

Textbook 308 WCF and 7.62X51 NATO are not the same cartridge.

The difference is headspace. The 308 shoulder-to-boltface measurement is 1.630" to 1.634".

The 7.62 NATO headspace starts at 1.634" and runs to 1.638".

The 308 NO-GO gauge is 1.634". Typically, your rifle should NOT close on a NO-GO gauge.

In the real world, almost all 308 rifles have 7.62mm chambers. My Ruger GSR has a 1.635" chamber. This is past the NO-GO dimension. However, this is a good thing.

We want our 308's to chamber and fire all NATO rounds.

Bottom line, they are close enough to interchange. However, an autoloading rifle with a 1.638" chamber may develop issues if fired with 308 commercial ammo.

The manual that comes with many Military Style Semi Automatic Rifles will suggest ammo marked "7.62mm".

I owned a Rem 40-X years ago with a 1.631" chamber. It would not chamber Military Match (M118) ammo. I got rid of it.

 

[ArchAngelCD]

Thanks for the info. Tom 488, you are correct. These are once fired from MG. That makes sense that they have expanded more than my commercial brass. I will try again and see how it goes. Again, thanks for the input. CMC, I am loading 2 grains under the minimum which is only 5%. I have read so many conflicting posts on how much to decrease these LC loads I don't know what to believe. Ill start 2 grains below minimum and see what happens. Do you have any FACTS supporting the 10%? I am not trying to start an argument, just looking for quality information.

Can't I just measure case volume (308 win and 7.62x51) with water and extrapolate the reduction based on the volume of water held?

I would not reduce your charge 2 full grains below the minimum, I would start at the min. Even with military brass it's usually not a good idea to go below starting charge weights.

The new Hornady #9 manual had a 308 Service Rifle section and MOST loads have a starting point the same as commercial 308 load data but stop short on the Max end with most of the powders used. You are safe using the starting load data, just be sure to work up slowly and not to go to the Max when using military 308 brass.

 

[StandingTall]

I regularly use LC brass and much of it is machine gun fired. You will need to full length size them the first time you load them.

If you don't have one already...get a case gauge. I use a Wilson case gauge for .308 Win. If it doesn't fit in the case gauge looking like this, then it's not sized properly:



I load for a Savage Model 12. In my experience, if it fits properly in the gauge it will fit properly in the chamber. After you have fired it once in your bolt gun, then you should be able to neck-size only most of the time for that gun.

Also a note of caution on the LC machine gun fired brass - Check for signs of case-head separation when you are prepping this stuff.

Also, as ArchAngelCD stated, don't start 2 grains below minimum. I personally looked at a mid-range charge and started 1 grain below that and it worked for me.

 

[USSR]

I would not reduce your charge 2 full grains below the minimum, I would start at the min.

Totally agree with ArchAngelCD. While you WILL use less powder in LC brass to reach the same velocity/pressure as most commercial brass, there is no need to start below the minimum charge weight listed for .308 brass. Also, regarding resizing MG-fired 7.62x51 (you poor SOB), do not assume that the reason that your resized brass will not chamber is because the shoulder is not bumped back enough. There are basically two reasons why your brass will not chamber: first is the aforementioned shoulder problem, and the second is the expanded web area problem. In any case (no pun intended), what you need to do is take a black magic marker and color the entire case with it. Then, try agressively chambering a round and extract it to see where the hangup is. There will be scrape marks on either the shoulder area or the web area of the brass. This will tell you that you either need to lower your die more to bump your shoulder back more, or use a small base die to bring the web area of the brass back into specs. Good luck.

Don

 

[ldlfh7]

Gentlemen -

Thanks for all the information. I have loaded 10 rounds at the minimum grains and all functioned flawlessly. I was confused on the little differences between the two cartridges but y'all answered all of my questions and I now have a mountain of usable brass - Which makes me very excited. Thanks again to everyone for the help and information.