Tag Archives: 7.62/.308

Does an M14 Really Turn Cover Into Concealment?

By Andrew Betts


If you spend enough time at an outdoor range, especially on the weekdays when the retirees are there in force, you are certain to hear someone opine that they prefer the M14 to the AR/M16/M4 because it “turns cover into concealment”. This is usually in conjunction with their opinion that the DoD made a terrible error in moving to the 5.56x45mm, rather than the much more manly 7.62x51mm. No one can claim that the 7.62mm NATO does not have more power. The cartridge contains significantly more powder and it launches a heavier bullet at only moderately lower velocity. Is that extra power actually useful for penetrating cover, though? Does it really “turn cover into concealment”?

To answer that, we took a look at a few real world objects of varying composition. The question is not whether the 7.62mm penetrates more deeply than the 5.56mm. It is widely known that 7.62mm will penetrate more deeply in some materials such as wood, while 5.56mm can often penetrate steel plate at close range better. M193 55 gr FMJ can even defeat Level III armor plates that are rated for multiple 7.62x51mm M80 147 gr FMJ (https://youtu.be/QrWtgyFQ8LU). The claim that the old guys are making is that the M14 can kill a man who is hiding behind an object that would stop a 5.56mm. In other words, does a small difference in penetration depth really translate to a difference in whether a specific object will act as cover or not? If the cartridges are compared in terms of go/no-go, will the M14 really “turn cover into concealment”?

For the first test, we will consider concrete barriers. There are a variety of concrete walls, block walls, and other concrete barriers in the urban landscape that a person might take cover behind. The concrete varies somewhat in the ratios of the ingredients but all are composed of cement, sand, and sometimes larger aggregate. Regardless of the recipe, concrete has high compressive strength and low tensile strength. That means that it works very well for applications such as load bearing walls, but not so well for a second story floor. It resists being crushed but when bent, it cracks easily. That also means that it works pretty well to stop a bullet, but it is destroyed in the process. We tested two kinds of concrete. The first is a concrete block common to privacy fences, with lots of small aggregate and air voids.

The second is a concrete paver. While not as sturdy as a poured concrete wall, the paver is made from mostly cement and sand, with little aggregate and no air voids.

In both tests, neither round was completely stopped by the concrete barrier. While the 7.62mm did look more impressive, the 5.56mm also made it through and neither cartridge seemed to retain much ability to wound on the other side of the wall. That is to say, both would likely cause a painful wound but neither were likely to penetrate deeply enough to have a high probability of causing incapacitation. A bad guy on the other side of either of those barriers would have an awfully bad day to be sure, but he would likely have the opportunity to make your own day much shorter. To sum up, it is a very close race with little practical difference between the two cartridges.

Of course, an 8” thick, poured concrete wall with rebar reinforcement is likely to stop both rounds cold, but it is also outside our ability to test. There are almost infinite variations on the thickness and composition of concrete structures and some will certainly stop both cartridges while others will not stop either cartridge, as seen in the above tests. It would take substantial resources to conclusively identify exactly what sort of barriers could be penetrated by which cartridge and at what distance. For our more general and limited testing, the conclusion is that both cartridges can penetrate some concrete barriers. There may very well be a special Goldilocks barrier that is just thick enough to stop the 5.56mm but not the 7.62mm. From what we can see of this testing, it seems likely that such a barrier would also bleed so much energy from the 7.62mm as to render it nearly harmless, though. Both cartridges failed to fully penetrate a single water jug in this test so if the thickness of the concrete were increased to that magical point where 5.56mm was stopped but 7.62mm passed through, the 7.62mm would be even less energetic than was seen in this testing, which means a very minor wound.

Next, we will consider one of the few components on a motor vehicle that actually has a good chance of stopping a bullet: a brake rotor. Other than the drive train, the brake rotors (or drums) are one of a very few places where there is actually enough thick metal to have a reasonably good chance of stopping a bullet. Frame rails will usually stop handgun rounds but are unlikely to stop any rifle round and it is common knowledge that the body does next to nothing to stop a bullet. Conversely, the engine and transmission should stop nearly any man portable weapon short of an AT-4. Will the brake rotor be just thick enough to stop one cartridge, but not the other?

In this case, several rounds of both the 5.56mm and the 7.62mm were stopped. It is true that the 7.62mm looked to be a bit closer to getting through, based on the slight cracks on the back side of the disc, but the bottom line is that a person hiding behind that object would not have acquired any extra face holes from either cartridge.

Wood is one of the materials which 7.62mm is said to penetrate much more deeply than 5.56mm so we compared the two cartridges’ ability to penetrate a modest sized log.

On the one hand, the 7.62mm penetrated almost twice as much wood as the 5.56mm. On the other hand, both were stopped and you would need to find a log that was more than 2 ½” thick but less than 4” thick to be able to stop the 5.56mm but not the 7.62mm. Aside from the obvious problem that few people would consider a 4” stick to be “cover”, the difference here underscores something we have long suspected. It is true that 7.62mm can penetrate more deeply, but the difference is unlikely to make any substantive real world difference. That is to say, there are very few objects that are just thick enough to stop a 5.56mm but not thick enough to stop a 7.62mm. Most objects are either thick enough to stop both or thin enough to stop neither.

We did find one material that was soft enough to underscore the difference in a very definitive way: water. This is a test using a 55 gallon plastic drum filled with water as the barrier.

Finally, here is an object that very clearly stopped one bullet but not the other. If your target is taking cover behind a 55 gallon plastic drum full of water, 7.62x51mm can punch through it, while 5.56mm will probably be stopped. In the high speed video, it seems that the 7.62mm was not really moving along that quickly after passing through the barrel, though. It is possible that it would not be capable of doing much wounding after getting through the barrel, but we did not test for that, so the nod has to go to the 7.62mm for getting through.

It is also worth noting here that projectile construction could make a significant difference in any of these tests. If the rounds were changed to bonded soft points, it is possible that both rounds would have made it through the water. If the 7.62mm were a Hornady 155 gr AMAX, it is unlikely it would get through the barrel. There are a wide variety of bullet weights and designs available for both cartridges and some of them will substantially change the performance on these objects. We chose M80 and M855 because they are the commonly issued FMJ ammunition for their respective rifles. We chose a 16” barreled AR15 because it is a good compromise length and we did not have the time to test 11.5”, 14.5”, and 20” barrels. We also did not test at greater distance, where the 7.62mm is likely to have a larger advantage because hauling the test materials 200 yards down range is difficult, bothersome, and disruptive to other shooters. There are a variety of conditions that were not tested and those conditions could give more of an edge to one or the other cartridge.

Overall, most of the tests showed very little difference between the two cartridges. In every test but the water barrel, either both penetrated the test object or both were stopped. Ultimately, it does not appear that there is any evidence to support the unilateral claim that 7.62x51mm “turns cover into concealment”. There may be some very specific circumstances where this is true, but they appear to be the exception, rather than the rule. To be sure, this concept deserves quite a lot more testing. It would be nice to see the differences at range and through a variety of other materials such as live wood and poured concrete. Some day we may continue testing. It seems that the M14 is likely to develop a real, substantive advantage as range
increases because the greater mass and higher ballistic coefficient can carry more energy further down range. On the other hand, this sort of testing only compares a single round of one cartridge to a single round of the other but 7.62mm weighs twice as much and that means a person is likely to have twice as much 5.56mm. In that light, one round of 5.56mm may be just about as good as one round of 7.62mm but two rounds of 5.56mm are far better than one round of 7.62 in nearly any circumstance. The real take-away here is that nothing in the world of firearms and projectiles is nearly as simple as “A is better than B” and it appears that the statement “The M14 turns cover into concealment,” is more often false than it is true.

Related  further reading of 762 penetration


Observations from the range

I have started to see some of the S&W M&P 10 .308 AR rifles.  In it’s stock form it seems ok and functions fine.  However in almost every case I have see where people have tried to trick out their rifles they have ended up with serious function issues.  If you are planning to buy a S&W .308 AR, you have to keep in mind that the .308 does not have complete parts interchangeability with the 5.56/.223 rifles.  Slapping on an AR15 receiver extension and using an AR15 buffer and buffer spring will NOT work.

I saw a person attempting to use a cheap optic mounted on the carry handle of an Olympic 9mm carbine.  Not to mention the problems of working with cheap optics mounted so high over the bore, the carry handle scope mount was a polymer unit made by Tapco.  This scope rail could flex under finger pressure.  It is complete junk, I stick to my statements of that the Tapco G2 AK trigger is the only thing they make that is good.

DPMS AR15s and steel cased ammunition is a poor combination.  While many claim it is the lacquer on Wolf cases that is the problem, it is not.  Just as many polymer or zinc coated steel cases get cemented stuck in DPMS AR15 chambers due to the carbon build up.

I got to fire a couple of rounds out of the “pistol” PPS43-C.

I.O.Inc PPS43-C


This “pistol” chambered in 7.62×25 had more recoil then I expected(I think its do to reciprocating mass, my TT33 doesn’t recoil like that).  Other than that, I liked the sights, the trigger was great for a cheap pistol caliber carbine.  The owner intends to SBR it and I think that would be a very fun little carbine.  He also said that it can very easily be changed to 9mm.  This one was purchased for $300.  If I see one locally for that price I think I will buy it.

LaRue 7.62 PredatOBRs are shipping


According to the LaRue newsletter, the long awaited PredatOBR are starting to ship.  It is cool to see the LaRue take down rifle ship, however I know some people who pre-ordered the PredatOBR wanting the PredaTAR handguard and the OBR barrel and have expressed that they don’t want the take down rifle.  Hopefully LaRue will offer both options.

One more reason I don’t recommend DPMS.

On a quality AR15 or its variations the bolt is cut in a way that the cam pin can only be inserted in one direction, the proper one needed for the rifle to function correctly.

In the case of this DPMS .308, it was not cut that way.  The owner of it dutifully took apart and cleaned his bolt carrier group after each range session, and finally accidentally installed the bolt in turned 180 degrees.  When he fired the first shot, the rifle attempted to eject the case into the side of the upper receiver and the rifle jammed.  In this particular case, I had an awkward time getting that spent case out of his rifle.

DPMS fail backwards bolt
Backwards Bolt


And on a side note, use quality ammunition.  Poor quality reloads or defective/damaged rounds can cause catastrophic results.

.50 BMG

Your .50 BMG rounds should not do this when fired.

A year with the Colt 901

Colt 901 Nightforce NXS

I  received on Monday the Colt 901 AR15 upper adapter.  This really lets me start to use the 901 in the modular capability I was really looking forward too when it was first announced.  Don’t get me wrong, if the 901 was limited to only being a .308 AR I would still find it the best .308 AR for me, but it sure is nice to be able to use it with standard AR15 uppers too.



Since getting the 901, I have made a few changes.  I dropped in a Geissele SSA trigger, replaced the stock with a CTR.  I keep a Nightforce 2.5-10×24 scope on it, but sometimes I take that off and play around a bit with an Aimpoint PRO.  For me, the CTR is a more comfortable and better stock for how I use the 901.  The SSA is just a nice upgrade.  The Nightforce makes it a nice package as the 2.5x setting is still reasonably fast up close, and 10x is enough magnification for me to do some good shooting, with out slowing me down or letting me fool my self into thinking I am running a pure precision rifle.  One ergonomic change that made a bigger effect than I expected was adding Tango Down SCAR panels.  The 901 quad rail is tall and narrow.  I considered adding some rail panels to the side to help make the handguard feel a little more round.  Normally I would use KAC rail panels as I have many of them laying around, but the 901 lacks the notches required for the KAC panels to lock into.  So I picked up some TD SCAR panels and have found that I really like having them on the 901.

Colt 901 AImpoint PRO Wilcox

A friend shooting the 901 with an Aimpoint PRO in Wilcox mount.

Colt 901

Colt 901 lower with 5.45 upper.  Using the 901 lower with standard AR15 uppers means I have to carry less stuff with when I go shooting.


When I shoot off the bench I have generally been using a Harris BRMS bipod.  I have also been trying a Grippod on this rifle but I am not sure if it is right for this rifle.  If you end up shooting off a hard surface, those slick feel of the grippod slide way too much when shooting .308.


Soon I will add an AMBI safety and another sling mount.  I find I often use the left side mag release and the right side bolt catch, the ambi-safety will make the rifle fully ambidextrous.

My future goal is to register it as a Short Barreled Rifle so I can run a 10.5 inch 5.56 upper on that lower, and also have the 16in .308 upper.  I really want to have a hard case that will contain the set of a 5.56 SBR upper and the standard 901 upper along with a few optics.  That pair, combined with a small .30 can suppressor that could work on both uppers would do most everything I could want out of an AR.

7.62 NATO, Turning cover into concealment since…. well, not as often as you may think.

Almost anywhere you go on the internet and read about guns used for combat or defense you will find the guys who will tell you that to kill anything bigger then a cat, you need the .308 . Often this is followed up with the smarmy little quip, “308 turning cover into concealment since 1953.”    The problem with this is that it is not exactly true and the 308 is hardly the tank killer its more rabid fans make it out to be.    The war on terror is often used as proof of the 30 cal rifles being better then 556.   What they do not mention or maybe don’t know, is if a 556 wont penetrate a brick wall, a 308 probably won’t either.

I took my 308  out to do some testing after hearing that old chestnut about cover etc. one too many times.  I have shot at a lot of stuff, with a lot of stuff and seldom have seen the performance claimed that a 308 will give.   I set up a little wall of cinder blocks and put a cardboard target behind it and backed off about 75 yards.  Then fired a few 7.62 ball rounds at it to see what got through.


The blocks did not even have all the other things associated with a normal house mixed in.  No pipes, or wiring or paneling or drywall. this would be an advantage for trying to penetrate the wall since it would have nothing else to get in the way. So, according to the 308 boys club, the round should have zipped through and exploded the target like an A-bomb.


The block cracked.  But the round did not go through and destroy the target. It took three rounds to do this.  Nothing that hit the target was even close to lethal. Just a few pieces of block. Keep in mind, this is from not very far away and was block only. None of the other things that make up a wall in a dwelling or some other facility that would have insulation, Wiring and pipes adn who knows what else.    Increase that yardage to 200-300 yards and beyond and the performance would drop even more.  You could turn the cover into some thing less then cover, but it would almost take up your entire mag.

The 308 is an effective round. But, it weighs more. costs more, recoils more. is harder to shoot then 556. Needs longer follow up, the guns are heavier , slower and louder then a 556.  Think long and hard about these things along with what you really need your rifle to do before you buy a 7.62 rifle based on what some will tell you about its magical unicorn stopping power. It is a potent round, but it is not what some make it out to be.

To add to above, I was reminded by Mark Hatfield that the effectiveness of the 308 or any round for that matter on blocks, is lessened even more when the block are set by real masonry.  Blocks standing free will break apart and give the round a more impressive look that does not reflect reality when trying to shoot through a real wall.


The picture above is a small structure  that housed a pump for a well. It was made after the main house was built and was constructed in the exact same manner as the house walls. The holes in the picture are form a 308 shooting M80 ball from less then 30 yards.  Not one of the shots penetrated the blocks.  Hardly the godzilla destroying power internet experts will tell you the 7.62 NATO  has.