From say, 25-100 yds, how much difference is there between these three cartridges from 16-18 inch barrels using 123 gr-150 gr FMJ, JHP, or JSP bullets for penetrating common automobiles?
It’s just a performance metric i like to have the capability of and while i already have a .308 rifle I’m wondering if one of the other cartridges could perform about as well in a lighter package.
With the right bullet, I would think the smaller two options would do well enough. Probably even in pistol barrel lengths.
.308 / 7.62X51 NATO is in a different league. There’s a reason it has a strong track record in general purpose machine guns. Performance on soft skinned vehicles being a big one.
I wonder what 6mm ARC can do in this context.
Of the three listed, .308 has a healthy advantage, and 7.62x39 penetrates autos and similar barriers better than .300 BLK.
How much of that is an extra 150 fps (123 gr M43 vs 125 gr .300 blk) or a bi-metal 7.62x39 jacket / core?
Perhaps a copper .300 blk bullet can make up the difference?
I should add i wouldn’t stock any steel-case 7.62x39 ammo, preferring the reliability of brass.
What part of the automobile? A simple door? They will all wiz through a car door. Things like windshields and engine blocks are a different story and more load dependent.
The driver and passengers.
I agree with Will on the auto glass. .308 will be way better at minimizing deflection.
Assuming they are in the car, same deal.
Even under 100 yds? I’d expect common fmj to come apart more at first impact at the higher velocities.
I suppose each cartridge would perform better the harder the bullet.
I’ve seen what 7.62 out of a M240 can do to a car/truck.
You are correct it wont penetrait the engine block, but it will stop the engine with 200-250 yds the only thing not penetraited might be the engine block, but it’s not going anywhere with holes in all of the rest of the engine.
Auto Glass doors and fenders are toast. I’ve seen tire rims shot until they were unserviceable.
From what I’ve seen the FMJ starts to open up but not until it was in the Cab of the vehicle.
I believe that’s mostly a 5.56 issue and dependent on barrel length and bullet type. Some of the barrier blind 5.56 does a good job of retaining mas after passing through a variety of stuff, but basic 5.56 FMJ goes through car doors easily, and usually leave an exit hole on the other side. It’s only in the movies where a car door makes for good cover. Windshields on the other hand are a different matter. It’s my understanding windshields not nearly as thick and tough as they used to be.
I remember a video from 10 yrs ago or more of some journalist approaching a Russian checkpoint (Chechnya, perhaps?) and their little car absorbing what i guess was 100 or more rounds from the front perhaps 50M away as they cowered inside screaming.
As the Russians approached, one could see the had AK74’s. The people in the car were hurt but not killed.
I recall another, more recent video of an American Policemen cowering in his cruiser as a man within 25 yds fired from the front with an AKM 7.62x39. It seemed like every round went through the cabin. The Officer managed to get out of the would-be coffin & engaged and though gravely wounded survived.
In my own experiences playing around i was amazed how much steel, even kind of thick but cheap steel, 7.62x39 could penetrate even out to 200 yds with Russian ball.
I wonder if .300 blk copper solids could do that?
Yeah, even 50BMG won’t punch all the way through an engine block. It will turn the engine to scrap, but it’s not like you are going to shoot some goblin hiding behind it. Does make for dead stops on approaching vehicle threats though. 
It will also punch all the way through a vehicle and woe be to anyone on the back side.
308 punches through sheet metal and windshields with ease. Sure there may be some deviation to the trajectory and maybe the bullet is damaged or separated but it’s still effective. Shooting into vehicles is not a precision event. It also does well in quartering shots. Like you know the guy is hiding behind the rear fender. So you punch through the trunk lid and out the fender.
x39 and 300 are less effective with an edge to x39. 5.56 can punch through, but quartering shots are low probability. It’s all a bit of a crap shoot though. There are variations in how the structure of the car is constructed. Hit some of that hidden inner structure and you go from 1 or 2 layers of steel to 3 or 4.
Guys who knows what they are doing when using a vehicle for cover don’t try to hide behind a door. They try to put as much of that vehicle between themselves and the threat as possible.
M240’s slinging 147gr ball ammo are devastating on soft skinned vehicles under 100 yards.
I’ve seen plenty of examples first hand in Iraq.
You’re over thinking this. Muzzle velocity has a proven track record in increasing penetration of non expanding projectiles.
Well, my .308 is a Tavor 16 in. I like it but if I’m keeping a .308 I think I’d like a longer barrel. Particularly an 18 in M1A.
Don’t 7.62 x 39 and super sonic 300blk have very similar weight and velocity. 300blk being the modern hotness, lots of choices for projectiles I’d expect.
Will, yep they seem virtually identical. I can’t explain the difference. There are a few 300 loads that do better at barrier penetration. 110 TAC is supposed to do pretty well.
Supposedly SIG makes the Rattler in x39 only because it was highly requested. Anecdotally for the improved barrier penetration of x39 over 300. I take that with a grain of salt but it is what I have heard.
Desert Tech WLVRN might be worth a look. I think they offer a 20” bbl .308 and 6.5CM for that bullpup.