My brother and I were sitting and chatting, and he started to wonder about the feasibility of loading the 123 Gr. Hornady SST or Z-Max in a .308 rifle. Have any of my fellow gunnies tried loading the .310 dia. bullets into a .308 casing and if so, how did they perform? My concern was would the loaded round chamber OK, or would the 2 thou added diameter make too difficult to chamber. My Mossberg Patriot is very snug in the chamber to the extent that the thickness of the neck wall with different brass makes chambering a loaded round needing more force than others to get the bolt to close.
7.62X39 bullets in a .308
- Thread starter LawrenceN
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Reloading is something that should be approached with caution and experimentation while possible, should be within reasonable parameters, using proper load data. The first question is "What are you trying to accomplish with shooting a jacketed bullet that is .002 thousands larger?"
Do you have hundreds of 7.62x39 bullets you are trying to get rid of? If so, perhaps offer someone a trade for 308?
If you like the 123 grain Hornady SST in your x39 rifle have you tried the 125 grain Hornady SST for 308?
Do you believe that you have shot out the bore of your rifle, which you have proven by an inability to shoot consistent groups with any sized 308 bullet and/or you have witnessed bullet tumble on your targets. If so, have you slugged your barrel to confirm? If so, would you consider shooting cast bullets which are often 1 to 2 thou oversized?
Are you hoping that you can gain "efficiency" in using less powder for a similar velocity by forcing through a larger bullet through a tighter bore? Not sure if you want to risk testing that theory, nor would you have proper equipment for load development. You can review existing powers/burn rates to come up with a recipe for 308 bullet combinations that gives you more rounds per pound, to lower the cost of each round.
Finally, have you researched published power/load data to confirm which companies publish such a recipe for shooting 7.62x39 bullet in a 308 rifle? If you have, please share.
As you note hard closing of some of your reloads, have you confirmed your case sizing processes with a case gauge (bumping shoulder back far enough/cam over on press). Have you checked the OAL of your rounds?
In summary, I do not see where the assumed benefits of this experimentation will outweigh the potential costs.
Do you have hundreds of 7.62x39 bullets you are trying to get rid of? If so, perhaps offer someone a trade for 308?
If you like the 123 grain Hornady SST in your x39 rifle have you tried the 125 grain Hornady SST for 308?
Do you believe that you have shot out the bore of your rifle, which you have proven by an inability to shoot consistent groups with any sized 308 bullet and/or you have witnessed bullet tumble on your targets. If so, have you slugged your barrel to confirm? If so, would you consider shooting cast bullets which are often 1 to 2 thou oversized?
Are you hoping that you can gain "efficiency" in using less powder for a similar velocity by forcing through a larger bullet through a tighter bore? Not sure if you want to risk testing that theory, nor would you have proper equipment for load development. You can review existing powers/burn rates to come up with a recipe for 308 bullet combinations that gives you more rounds per pound, to lower the cost of each round.
Finally, have you researched published power/load data to confirm which companies publish such a recipe for shooting 7.62x39 bullet in a 308 rifle? If you have, please share.
As you note hard closing of some of your reloads, have you confirmed your case sizing processes with a case gauge (bumping shoulder back far enough/cam over on press). Have you checked the OAL of your rounds?
In summary, I do not see where the assumed benefits of this experimentation will outweigh the potential costs.
In a general sense, I would say yes, you can do it without issue. Start low, work up a load. Assuming you start low, you should be able to create something that is perfectly safe.
However, you mention that your particular 308 rifle is already tight in the chamber, so that extra little bit of bullet diameter might cause you issues in your particular rifle.
However, you mention that your particular 308 rifle is already tight in the chamber, so that extra little bit of bullet diameter might cause you issues in your particular rifle.
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Seems like you already have a rifle with a defective chamber / throat. Without verifying a few things, ( chamber cast and careful, accurate measurements ) I wouldn't shoot that rifle with normal ammunition, and certainly not with bullets that are two thou over diameter standards. In a .308 rifle with a "normal" chamber, your question would be more reasonably answered that it is OK, but proceed with caution. But it looks like you already have a rifle condition that is driving up pressures. No point in tempting fate.
One "trick" that cast bullet shooters use to determine if sizing cast bullets is necessary or not is to place a bullet by hand into a case fired in your rifle but not resized. . If it slips in easy, it is not too big for the throat. If it has to be forced or does not slip in easily, the bullet is too big and must be resized. At least for cast bullets, if they fit the throat of the chamber being a little big for the bore is of little consequence to pressures. They swage down to bore size on firing. But if the cartridge neck has no room to expand and release the bullet, pressures can spike rather dramatically and that's dangerous.
One "trick" that cast bullet shooters use to determine if sizing cast bullets is necessary or not is to place a bullet by hand into a case fired in your rifle but not resized. . If it slips in easy, it is not too big for the throat. If it has to be forced or does not slip in easily, the bullet is too big and must be resized. At least for cast bullets, if they fit the throat of the chamber being a little big for the bore is of little consequence to pressures. They swage down to bore size on firing. But if the cartridge neck has no room to expand and release the bullet, pressures can spike rather dramatically and that's dangerous.
Well, I have a similar situation. I hand load for the 7.62 x 54r which is also supposed to be the same bore size ss a 7.62 x 39. I found it shot great with .312 speer 180 hotcores. Only later did I slug my bore to find out it was .3085. I will be trying .308 bullets in this Mosin now. I'm sure if you work up a load carefully it can be done, its probably best to shoot proper sized bullets as I'm sure over sized stuff would wear your bore more and be higher risk.
Yes, you can load 123 gr .310" bullets in a 308. The barrel/bullet diameter is close enough not to matter. Just start with the Start load and work up as per normal. I made a 7.62x39 rifle using a .307 dia barrel. No problems.
BUT you say your rifle may have a tight neck. If it does, a fat bullet may make a pipe bomb.
Take a fired case and measure the outside diameter of the neck. This something like your chamber neck diameter.
Then chamber a fat bullet in a sized case and measure the neck diameter. If it is smaller than the fired case, the brass has room to expand to release the bullet and you are GTG.
OP, I use the .310 SSTs regularly in .308 bores.
One thing that can be an issue is pushing them to fast. They're designed to expand properly at 7.62x39 standard velocities and should be loaded accordingly in the 308 Win or 30-06 and others.
I've also used them in an M1 Carbine I have with a custom barrel. They shoot very well in that 1-15 twist bore at Carbine pressures.
If you have to turn the necks of your cases to use these bullets, it may not be worth the effort to you.
One thing that can be an issue is pushing them to fast. They're designed to expand properly at 7.62x39 standard velocities and should be loaded accordingly in the 308 Win or 30-06 and others.
I've also used them in an M1 Carbine I have with a custom barrel. They shoot very well in that 1-15 twist bore at Carbine pressures.
If you have to turn the necks of your cases to use these bullets, it may not be worth the effort to you.
You answered your own question - if it chambers it would likely be fine. The question that needs answering is will it chamber, and you won't get that answer on a forum. Make a dummy cartridge and try.
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