308 Brass vs. 7.62 brass

[RedneckFur]

I'm kinda new to reloading. So far, the only calibers I have loaded are .38 special and 357 magnum. I bought a .308 Remington 700sps a few weeks ago, and I intend to reload for it too. I'm suposed to recive my dies in a few days.

I found a good deal on some winchester 7.62 ammo. I know it will work in a .308 winchester, but I'm not sure how i'll be able to reload it. Its new manufacture ammo.

Are the primers different? Will I have to modify the brass in any way?

I've heard that the brass is thicker and heavier. Will I be able to use .308 load data with this brass, or will that be dangerous? Can I use 7.62 load data with .308 stamped brass?

I'm new to the game and trying to avoid mistakes. Please share your wisdom!

[rn22723]

Reload away! You may have crimped primer pocket to deal with? But you are set.

[Qtiphky]

You say that it will work in a .308. I'm assuming that means it is 7.62x51 (Nato), which is 308 Winchester. However, if it is 7.62x39 or 7.62x54, they won't work in a .308 as they are not Nato but are Russian cartridges.

[Loader9]

The 308 and the 7.62x 51 are not perfectly identical cases and they operate at different pressures. 7.62x 51 operates at 50,000 max and the 308 at 62000 max. Because you have a 308, everything is fine. Reload those Winchester cases just like any other 308. If you find MILITARY 7.62x 51, the brass will be slightly heavier meaning the interior of the case will be slighly smaller causing higher pressures using 308 data.

[wogpotter]

Things you will need to do with MilSpec (7.62) brass in addition to normal reloading.
Getting the crimped-in primer out is harder than with uncrimped commercial (.308) brass. You might want to get a "decapping die" to make life easier on your sizing die.
You will have to remove the crimp. Hand tools work, but are slow. Maybe invest in a die attachment for the press to speed up this step.
Because of internal volume differences caused by the thicker brass you'll need to vary the powder charge to compensate. Reducing by 1.5 gr to go from commercial to military & vice-versa is a good starting point.
You may find that more case trimming is needed,especially with once-fired military ammo. It's frequently used in machine guns & so stretches more.
Other than that go for it.

A note on "pressure differences".
The same bullet, driven at the same velocity from the same rifle will have the same pressure, it's simple math. You're compenstaing for the differences by reducing the powder gharge. You WILL have pressure differences if you use the same powder charge for both.

[Sam06]

Wogpotter is right on. You will find that less powder will achieve more velocity out of Military brass Due to the smaller volume of the case. If you have a Chronograph you can see this. Also the pressure will be more with less powder same reason.

I like the Lee Universal De-primer to knock out those tough, crimped in Primers. to get rid of the crimp around the primer there are several methods. The best is to get a toll for that. RCBS, Lee and Dillon make them. The RCBS kit is the most affordable and will work. It will take a little longer than the Dillon machine but it works. You can also use your Case neck de-burring tool and "Scrape" away the crimp. Be Careful doing this because you don't want to ruin the brass. Military Brass will reload as many times as Civilian Brass maybe more. I usually Anneal the case necks after 8-10 reloadings(But I neck size for my bolt guns).

You are lucky in that the brass will be 1st time fired in your gun. Most 7.62 was shot out of MGs with generous chambers and needs to be FL sized and trimmed before it is usable...............Sam

[FALPhil]

Loader9 wrote:
7.62x 51 operates at 50,000 max and the 308 at 62000 max.

WRONG!!!

See my article at:

http://thefiringline.com/forums/showthread.php?t=326877

[Loader9]

Here are the military specs for 7.62 x 51 ammo. I'm not sure what moron wrote the article you posted but he posted an opinion, not facts.
http://www.inetres.com/gp/military/i...62mm_ammo.html

The military ammo is not governed by the case design and construction as expounded in the above article but on the requirements of the rifle and action. If you look close enough, you'll see 7.62 x 51 ammo loaded far beyond that of the 308. It is expressly for use in the M60 only, not a service rifle like an M14. Using ammo that exceeds the 50000 psi limit will shorten op rod life tremendously. If you had any experience with the M14 rifles, you would have known that. I think something some of you may have missed, the OP is buying Winchester ammo 7.62 x 51, not military. It's not the same thing. In basisc, it's commercial 308 brass with a 7.62 headstamp and sized for the 7.62 chamber and limits the pressure to 50000psi. It works just fine in a 308 rifle. I wonder what Winchester knows that the writer of the article doesn't know?

[The Lovemaster]

I recommend the Dillon Super Swager for removing the primer crimps, it is unparalleled. A little spendy, but worth it.

[wogpotter]

Loader 9
If this is accurate, please explain to me how I've sucesfully done exactly this in an M1a, a Remington 700, and an Imbel FAL since 1973 without any issues at all?
The op-rod of my M1a was never damaged in the slightest, the Remington 700 fired both 7.62mm NATO and .308 winchester, again without problems, the Imbel FAL is sstill firing both without any problems at all.

[FALPhil]

Loader9, I'm the "moron". I did the research. It is not an opinion and it has been reviewed by at least one PhD.

It looks like (a) you don't know how to read, or (b) you don't know how to check out sources on the internet or a library, or (c) all of the above.

Looks to me like I'm not the moron. Care to perform some introspection? If you don't know what that word means, you can look it up on http://www.yourdictionary.com

Or maybe you are smarter than anyone else in the world, and you can explain how a cartridge at 52K PSI can launch a 150 grain projectile at the same speed as a cartridge with the same exterior dimensions, using the same powder, as a cartridge at 62K PSI.


I'm listening...

[noyes]

FALPhil

What the heck it's just a bomb right in front of one's face. Their new screen name could be .....

Face less

This guy was lucky



http://www.youtube.com/watch?v=tWygoxV_ApM

[Sam06]

7.62X51 NATO is not loaded for the M60 MG only. It is used in ALL 7.62 guns in NATO. Just like 9MM and 5.56. The 7.62 can be shot out of any military weapon chambered for it from a US Army M134 Minigun to a Italian BM 59.

Loader9 wrote

The military ammo is not governed by the case design and construction as expounded in the above article but on the requirements of the rifle and action. If you look close enough, you'll see 7.62 x 51 ammo loaded far beyond that of the 308. It is expressly for use in the M60 only, not a service rifle like an M14.

This is incorrect!

Commercial ammo runs about 55,000 PSI

Where Military ammo runs about 60,000PSI

The military measures in CUP where Civilian measure in PSI. The outer dimensions are the same but Military brass is heavier 157gr VS 195gr so the internal dimensions are different. You CAN Interchange them in strong well made guns. But when reloading ANY Military brass you have to know about the difference in dimensions and take that into mind when re-loading them.

=1 to the Lovemaster the Dillon is the Bomb!

[wogpotter]

To add to the explaination on pressure "differences" it's both the unit of measure being (mis)qouted, and the method uded to obtain the numbers.
The total crushing forceof the discharge is used to arrive at the CUP method, and then a table is used to convert the difference to the pellet size into a numeric value.
The alternate method uses a pressure sensor to graph the curve of the force & that is measured (IIRC) above half-peak.
It's rather like saying that water has more than one freezing point (all else being equal) 0 degrees Centigrade or 32 degrees farenheit.

[Unclenick]

Correct. If you read FALPhil's article carefully you will realize the table posted by Loader9 uses the old terminology from when PSI was still given to mean what we now call CUP, since they originally didn't know there was a significant difference. I have a number of older (80's and thereabouts) military tech manuals that make the same error. AFAIK, the whole issue wasn't even seriously sorted out in the laboratory until the DuPont sponsored U. of Michigan study of the '06 with round nose bullets in 1965, Absolute Chamber Pressure in Center-Fire Rifles, that determined absolute pressure by strain gauges. You can download a PDF version here, but the salient plot, page 43, was apparently cut off in scanning the PDF version. I have a hard copy I will scan if I remember to? What is missing is the top portion showing that when absolute pressure was 100,000 PSI in their test gun, the copper crusher reading was only 67,000 PSI. This was the start, I believe, of copper crusher numbers ultimately losing the right to be called PSI, and coming to be called CUP instead. The copper crusher was good enough at black powder cartridge pressures and makes a good way to match pressures for different loads, but that's it. It only took 30 years for this correction to get into military documentation. They were still calling CUP PSI until then.

Originally Posted by wogpotter

A note on "pressure differences".
The same bullet, driven at the same velocity from the same rifle will have the same pressure, it's simple math. You're compensating for the differences by reducing the powder charge. You WILL have pressure differences if you use the same powder charge for both.

Not correct the way most people think of pressure. What you said is true for the average accelerating force provided by the average pressure in the barrel during the time of the bullet travels in it (the barrel time), but it is not true for the peak pressure in the chamber which can be varied somewhat independently of average pressure by changing the powder you are using to one with a different burning rate.

An example:

IMI case with 56.2 grains water capacity in gun with tight chamber and 22" barrel firing the Hornady 150 grain BTFMJ seated to 2.780" col:

IMR 4198, 38.5 grains, 58,600 psi peak chamber pressure, 2,750 fps MV
Muzzle pressure 6,880 psi

IMR 4895, 44.8 grains, 49,700 psi peak chamber pressure, 2,750 fps MV
Muzzle pressure, 8,360 psi

Average accelerating force produced by the two loads will be the same.


Case capacity also has an effect even if you are using the same powder to reach the same peak pressure, just because you can fit more powder in a larger case, which makes more gas, which sustains higher pressure longer past the peak. That increases the average pressure applied at the base of the bullet during its barrel time.

An example:

Loading the Hornady 150 BTFMJ to 52,000 PSI with IMR 4895 in a 22" barrel at 2.780" COL:

Winchester case, 59.7 gr water capacity
47.1 grains 4895, 52,000 PSI peak chamber pressure, 2,837 fps MV
muzzle pressure at bullet exit: 8,850 psi

IMI case, 56.2 grains water capacity
45.0 grains 4895, 52,000 PSI peak chamber pressure, 2,788 fps MV
muzzle pressure at bullet exit: 8,450 psi

Same peak chamber pressures, but about 50 fps MV difference because the larger quantity of powder in the bigger case sustained pressure longer.

Nick

[wogpotter]

Good point.
I guess thats why the plotted curve via a transducer is a better data recorder than a copper crusher, because it takes the pressure curve into effect.