New Army (rifle) marksmanship manual

[frostfire]

https://rdl.train.army.mil/catalog-ws/view/100.ATSC/492701D5-25E9-40A7-9498-74C22831F268-1463059585416/TCx3-22.9.pdf

Very robust and light years beyond the previous manual.
It only takes several decades to adopt tried-n-true techniques from competitive disciplines.
If you've shot PRS, 2 gun, 3 gun, high power, long range, tactical,USASOC matches, etc. nothing new there, but I am glad to see big army catching on. Let's see how the pistol manual looks like and if it's up to TS standard! ;)


Still, no mag on the ground :rolleyes:

[Papa Zero Three]

https://rdl.train.army.mil/catalog-ws/view/100.ATSC/492701D5-25E9-40A7-9498-74C22831F268-1463059585416/TCx3-22.9.pdf


Still, no mag on the ground :rolleyes:


Check page 6-24, the NOTE on the bottom of the page says you can place the magazine on the ground when prone unsupported.

[Team Sergeant]

Check page 6-24, the NOTE on the bottom of the page says you can place the magazine on the ground when prone unsupported.

Very, very bad idea.

A barrel is like a tuning fork and makes the same vibrations every time it's fired. And like a tuning fork if it struck while touching something else it does not have the same tune (vibration).

Besides that if you're placing pressure on the mag while firing you're asking for a jammed weapon.

But what do I know..... ;)

[frostfire]

Check page 6-24, the NOTE on the bottom of the page says you can place the magazine on the ground when prone unsupported.

thank you for the correction :o

[Papa Zero Three]

Very, very bad idea.

A barrel is like a tuning fork and makes the same vibrations every time it's fired. And like a tuning fork if it struck while touching something else it does not have the same tune (vibration).

Besides that if you're placing pressure on the mag while firing you're asking for a jammed weapon.

But what do I know..... ;)


Barrel harmonics are not affected by placing the magazine on the ground. I know it's an old rule of thumb about mags on the ground but the facts are that placing the magazine on the ground doesn't induce malfunctions...but that still doesn't keep some people from repeating that old wives tale. ;) This I know. :)

[Leozinho]

Barrel harmonics aside (don't know enough to comment), I recently had the displeasure of watching young Marines trying to zero with iron sights at 25y. Shooting unsupported prone, none of them could shoot a group tight enough to even begin to know what adjustments to make.

Had they placed the mag on the ground, their groups would have tightened up enough to at least enough to make adjustments with some degree of accuracy.

(Better support from the mag on the ground would have greatly outweighed any issues with barrel harmonics.)

[JJ_BPK]

Barrel harmonics are not affected by placing the magazine on the ground. I know it's an old rule of thumb about mags on the ground but the facts are that placing the magazine on the ground doesn't induce malfunctions.. but that still doesn't keep some people from repeating that old wives tale. ;) This I know. :)

Maybe,, maybe not.. Some of that old wives tail has has do with lazy GI's not seating their mag completely and/or using poor aiming & mounting..

When my platoon was on the firebase (not to often :( ), We would have mad minutes. We would fire into the wood line using as many mags a possible.. Afterwards, I can remember partial mags laying around because they were "misfits" and "bent"..

Not really, the kids would half/a$$ insert the mag,, get a jam,, and move on to the next one.. They also would be shooting from inside bunkers,, using the window sills (usually a stack of rock hard sand bags) as a steady point,, being to lazy to use a proper shoulder mount.. They were counseled,, but kids??

AND this was with the old 20rd mags..

Had one kid, who would insist on using an AK-47, with 50rd mags. I wouldn't let him take outside the wire. He was always cursing and screaming, because the commie mags were bad,, it was his poor handling. I think he still has a SIZE problem?? I see his name in the paper every so often.. :D

By the By,, outside the wire, without window frames,, no problemo..

[Team Sergeant]

Barrel harmonics are not affected by placing the magazine on the ground. I know it's an old rule of thumb about mags on the ground but the facts are that placing the magazine on the ground doesn't induce malfunctions...but that still doesn't keep some people from repeating that old wives tale. ;) This I know. :)

Barrel harmonics aside (don't know enough to comment), I recently had the displeasure of watching young Marines trying to zero with iron sights at 25y. Shooting unsupported prone, none of them could shoot a group tight enough to even begin to know what adjustments to make.

Had they placed the mag on the ground, their groups would have tightened up enough to at least enough to make adjustments with some degree of accuracy.

(Better support from the mag on the ground would have greatly outweighed any issues with barrel harmonics.)

This was discussed before, science and all. But we can go back to placing butter on burns too.

Riddle me this, why oh why do we have "heavy barrels?"

http://www.stocks-rifle.com/harmonics.htm Just one of many harmonics/vibration discussions.

I'm guessing you both are SF snipers and 18B's? :D

[Papa Zero Three]

This was discussed before, science and all. But we can go back to placing butter on burns too.

Riddle me this, why oh why do we have "heavy barrels?"

http://www.stocks-rifle.com/harmonics.htm Just one of many harmonics/vibration discussions.

I'm guessing you both are SF snipers and 18B's? :D


I must have missed something somewhere. I don't understand why we are discussing barrel harmonics when the topic is placing the magazine of an M4 on the ground when firing prone unsupported. Did I miss a post or something here?

[Leozinho]

I think my point was missed. Even IF placing the magazine on the ground effects barrel harmonics (I'll let you guys argue that), the benefits of a stable position that comes from the mag on the ground will far outweigh the negatives of any harmonics issue (if there are any.)

I personally think the 'mags on ground induces failures' is not true, based on my personal experience and the opinion of others that I trust. I don't doubt it was once based on some truth, but I don't know what happened in Vietnam, and none of my mags are from that era. I inspect them religiously and consider them expendable. (I also crush them when the lips start to spread or crack. You can write "bad" or draw a big X on them and throw them away, but some dumbass will fish them out of the trash and put them back in rotation).

[Papa Zero Three]

I think my point was missed. Even IF placing the magazine on the ground effects barrel harmonics (I'll let you guys argue that), the benefits of a stable position that comes from the mag on the ground will far outweigh the negatives of any harmonics issue (if there are any.)

I personally think the 'mags on ground induces failures' is not true, based on my personal experience and the opinion of others that I trust. I don't doubt it was once based on some truth, but I don't know what happened in Vietnam, and none of my mags are from that era. I inspect them religiously and consider them expendable. (I also crush them when the lips start to spread or crack. You can write "bad" or draw a big X on them and throw them away, but some dumbass will fish them out of the trash and put them back in rotation).

No, your point is not missed and you are correct in your statement. The unit I am in conducted an extensive assessment of this and actually at one point in time did MTTs to conventional units, teaching this as part of the course. I too grew up with the urban myth that it induced malfunctions but after seeing it proven wrong so extensively over time and circumstances, have changed my opinion on it and now am a strong advocate of it. It works, it doesn't cause issues and it increases the shooters performance/groups at the target. The bullet doesn't lie.

[Team Sergeant]

An M-4 mag catch assembly was not designed to hold the weight of a firing M-4. It's an already flimsy catch that barely holds in the magazine. With a 20 rd mag holding the weight of the M-4 might not be bad a 30rd mag will rock back and forth and as was pointed out might start to bend/crack parts that were never intended to hold weight. I'd sure like to examine the mag catches on those that have been firing with mag touching the ground and view the wear. Especially compared to those that have not used the mag as a firing platform.

Also, as a sniper, I cringe at the idea of using the mag as a firing platform and then attempting to double tap, or acquire the sight with speed as my weapon jumps off the hard ground from the first round.

I fairly certain we already had this discussion concerning harmonics ie the weapon touching something hard like a rock, or a mag resting on a rock and then fired as opposed to firing with a hand in between the stock (or mag) and the rock.

There's a reason we have "free floating" barrels and heavy barrels. And while I know the M-4 is not a free floating barrel the whole idea is not to touch anything hard that might affect barrel harmonics.

Now if you want to sling lead downrange then have at it. Hell I saw a video of a police shooting the other day where the police officer was employing the "gangster hold" on his pistol.

And while I appreciate your unit conducting testing, I'd rather see an weapons engineer from say "Colt" conduct those same "tests" and see what they have to say. ;)

[DJ Urbanovsky]

Another thing: In the event of a case head failure, the design of the M4/M16/AR family of rifles funnels the force of the explosion down the mag well and out the bottom of the magazine. This blows the floor plate of the magazine off and spews the contents of the magazine all over the place. If the the magazine is being used as a mono-pod, that practically turns the magazine into a grenade...

This happened to me about 15 years ago. Twisted the bolt carrier in the upper receiver, bulged the sides of the upper and lower receivers, split the bottom of the bolt carrier, and vented all of those hot gasses down and out the bottom of the magazine. Magazine body was bulged out almost like a soda can, and blew the floorplate, spring, follower, and remaining rounds out the bottom of the magazine. I got a scrape and bruise on the inside of my support forearm as magazine contents made their exit, but that was the worst of it.

Tried mortaring the gun to clear it, and ripped off the end of the charging handle for my efforts. Actually had to remove the barrel nut to get the gun apart. Upper and guts were toast, but aside from bulged magwell, lower was fine. Squeezed the sides back together in a vice, slapped a fresh upper on it, and the gun ran fine. I probably have pics, if not that old trashed bolt carrier, still around here somewhere.

[frostfire]

The unit I am in conducted an extensive assessment of this and actually at one point in time did MTTs to conventional units, teaching this as part of the course. I too grew up with the urban myth that it induced malfunctions but after seeing it proven wrong so extensively over time and circumstances, have changed my opinion on it and now am a strong advocate of it. It works, it doesn't cause issues and it increases the shooters performance/groups at the target. The bullet doesn't lie.

I just got done with an MTT mission. Had a pvt who couldn't group worth a damn. Shot 17/40 paper qual for the warm-up qual. I changed his position, got his L hand off the heat guard & sand bag and placed it at the mag well for both supported and non-supported. Likewise, I showed him a kneeling technique where you put the mag on your knee (2:22 https://www.youtube.com/watch?v=gOH7NrZNvdM) He shot 30/40. The MTT unit I'm with did a test with sandbag vs. sling vs. hand. Using guys who know how to shoot (they shoot ragged group at 25 w issue M4/M16) and same point of aim, we got different point of impact with each position. Conclusion: that non free-floated system is crappy enough that having a sand bag vs no sandbag is enough to cause zero shift at 25m! So effect of position/hold/rifle-surface contact on barrel harmonics is definitely there. Mag on the ground and holding at the mag well create a consistent, improvised "free float." It does require a degree of flexibility though.

FWIW, I have experienced malfunction (double feed) with resting mag on the ground. Marked that magazine, tossed it away, and I never experienced another malfunction using "well maintained and inspected" mags.


An M-4 mag catch assembly was not designed to hold the weight of a firing M-4. It's an already flimsy catch that barely holds in the magazine. With a 20 rd mag holding the weight of the M-4 might not be bad a 30rd mag will rock back and forth and as was pointed out might start to bend/crack parts that were never intended to hold weight. I'd sure like to examine the mag catches on those that have been firing with mag touching the ground and view the wear. Especially compared to those that have not used the mag as a firing platform.

And while I appreciate your unit conducting testing, I'd rather see an weapons engineer from say "Colt" conduct those same "tests" and see what they have to say. ;)

Not only I rest mag on the ground, with that rocking motion, I jam the mag to the ground then pull it to my R shoulder with both L hand (on the mag well) and R hand creating a solid platform that moves as a single unit with each recoil. It's like opposite of loading the bipod. That rack grade A2 with issue ammo gets an "upgrade" in accuracy with that technique ( visual example at 0:33, also various weapon systems with mag on the ground and no malfunction https://www.youtube.com/watch?v=3rXykqvVHmkO ) . I made a believer of folks at various units after they see the groups at 25, 100, and 200. Still, that "flimsy catch" worth merit to investigate. I admit I never shot thousands of round ( only < 300 in a single session) with that technique and observe wear and tear. Let me ask my contact at Colt and the head armorer at Barrett

In the meantime, some empirical testing (having anti-tilt follower helps)
https://www.youtube.com/watch?v=IcBGtoH_uSc

We need Longrange1947 and Gene Econ to chime in :D

[Papa Zero Three]

An M-4 mag catch assembly was not designed to hold the weight of a firing M-4. It's an already flimsy catch that barely holds in the magazine. With a 20 rd mag holding the weight of the M-4 might not be bad a 30rd mag will rock back and forth and as was pointed out might start to bend/crack parts that were never intended to hold weight. I'd sure like to examine the mag catches on those that have been firing with mag touching the ground and view the wear. Especially compared to those that have not used the mag as a firing platform.

Also, as a sniper, I cringe at the idea of using the mag as a firing platform and then attempting to double tap, or acquire the sight with speed as my weapon jumps off the hard ground from the first round.

I fairly certain we already had this discussion concerning harmonics ie the weapon touching something hard like a rock, or a mag resting on a rock and then fired as opposed to firing with a hand in between the stock (or mag) and the rock.

There's a reason we have "free floating" barrels and heavy barrels. And while I know the M-4 is not a free floating barrel the whole idea is not to touch anything hard that might affect barrel harmonics.

Now if you want to sling lead downrange then have at it. Hell I saw a video of a police shooting the other day where the police officer was employing the "gangster hold" on his pistol.

And while I appreciate your unit conducting testing, I'd rather see an weapons engineer from say "Colt" conduct those same "tests" and see what they have to say. ;)



Jeff, the moment one starts thinking there is nothing new to learn and stops looking at a subject with an open mind is the moment one becomes outdated. If you doubt what has been said here, then go out on the interwebs and google this topic. I can save you some time though and tell you that resting the magazine of the M4 on the ground doesn't have a detrimental effect. As has been mentioned here, the anti tilt followers in todays magazines is probably the biggest reason but even if you have an older one without the anti tilt, chances are you won't experience a malfunction.

This practice has even sparked industry to produce what is called mag-pods. These are placed on the bottom of magazines to help make a more stable platform for using this technique. And as you can see, it's also in the manual now. Not saying that it's right just because its in the manual, as we've all seen wrong things in manuals before. Remember when 6400 mils was in the sniper manual and that higher humidity meant the air was thicker? Both used to be repeated ad nasuem and even taught when I went through SOTIC. Today, no up to date instructor will repeat any of that dogma, as it has been proven to be incorrect. However, even in this "new" manual, they still managed to fuck it up and use 6400 mils in Fig 3-2 when discussing MOA and MILs in chapter 3. So I can see how even now, you might be skeptical of placing a magazine on the ground despite what others have said.

The point being is that you don't have to believe me, the manual or anyone else in the shooting industry. But if you are dead set on not believing what has been presented, then go out and try it for yourself and see how it turns out. In fact, I encourage you to go out and do it and prove the rest of the world wrong. I know what the outcome will be....but what do I know. :)

[Team Sergeant]

I spent 20 years in, infantry and SF and have spent more time with an M16/M4 than most. I've fired the weapon with the mag touching the ground, it bounces and the lesson was learned.

Yeah, you might get a first round hit but subsequent shots from that position will produce nothing but a bouncing weapon. And as I've said that's ok if you're just slinging lead. And if you're holding it so tight as to reduce the bouncing, well you've just defeated the purpose of accurate firing.

As an SF sniper I held the weapon as light as possible while firing and it did the trick, especially for the long shots. And the reason for the very light triggers.

I've never stopped learning, outshoot me and I will watch and learn. But you're not going to outshoot me with a weapon bouncing off the ground.

And I'll happily go head to head with anyone that desires to fire a weapon with the mag resting on the ground for accuracy.

[Joker]

This should be in the Comedy Zone.

[Papa Zero Three]

I spent 20 years in, infantry and SF and have spent more time with an M16/M4 than most. I've fired the weapon with the mag touching the ground, it bounces and the lesson was learned.

Yeah, you might get a first round hit but subsequent shots from that position will produce nothing but a bouncing weapon. And as I've said that's ok if you're just slinging lead. And if you're holding it so tight as to reduce the bouncing, well you've just defeated the purpose of accurate firing.

As an SF sniper I held the weapon as light as possible while firing and it did the trick, especially for the long shots. And the reason for the very light triggers.

I've never stopped learning, outshoot me and I will watch and learn. But you're not going to outshoot me with a weapon bouncing off the ground.

And I'll happily go head to head with anyone that desires to fire a weapon with the mag resting on the ground for accuracy.


Just out of curiosity, did you watch this video at all?

https://youtu.be/IcBGtoH_uSc


You can see how much the weapon moves between rapid fire shots as well as the target he is hitting consistently. I don't know why you keep referencing sniping when we are talking about an M4 and the max distance on a qual range for a soldier is the 300 meter E type/Ivan target. Conventional soldiers are using this technique on the pop up qual ranges and are able to score higher than soldiers who don't do it. When you start them off with the mag on the ground when they zero at 25m, it's not unusual to see groups where all the rounds are touching or will fit under a quarter. This technique helps soldiers out and is effective. As a sniper, you should know that anything that makes the gun and the shooter more stable is a plus.

I challenge you to go out and try it for yourself. Do 1ea 30 round mag prone unsupported, mag not on the ground for 10 shot groups at 25ms. Then do 1ea mag prone unsupported WITH the mag resting on the ground for the same 10 shot groups . I will bet you the 60 rounds of ammo that your groups with the mag on the ground are all tighter than the other groups where you didn't use the magazine for support. And if for some crazy reason that doesn't happen, I will drive over to your apartment and hand you the 60 rounds along with a 12 pack of Guinness, 2ea steaks and a gift certificate for free attendance to the next rifle/carbine course I run. :)

[Team Sergeant]

Just out of curiosity, did you watch this video at all?

https://youtu.be/IcBGtoH_uSc



LOL, first off the mag in that video is "not" on the ground. (I started laughing as soon as I saw him, the gun and the cloth.)

Second we don't have a clue how much cloth it's sitting on or how much straw is under it. When I employed the sniper rifle I always tried to sit it on some sort of cloth, be it a woobie, a hat, a rucksack etc. instead of the ground. The cloth ensured it didn't jump and it stayed in place for the subsequent shots.

We can agree to disagree, but I don't think you're going to find "trained" snipers (and not a 2-3 day police marksmanship course) that would be willing to shoot like the joker in that video. Let's see him do the same thing on a hard ground, say rocks and such or a sidewalk or street, "without the cloth".

He's "busted" no myths, especially shooting myths.

(And I live in a house that I own.....;))

[turboprop]

This should be in the Comedy Zone.

x2

[Peregrino]

Just out of curiosity, did you watch this video at all?

https://youtu.be/IcBGtoH_uSc

----. :)

Concur. The times, they do be a changing. When shooting a carbine (M4/M4gery) not only am I putting the magazine on the ground, I'm loading it just like I would a bipod on my precision rifle. And when I'm out playing silly "gun games" I'm choosing between 20, 30, and 40 round magazines to get maximum advantage (my neck doesn't flex the way it used to when I was 20). And that's to rapidly hit 3 MOA targets out to 300+ (carbine appropriate ranges). I also crush and dispose of bad magazines - believe it or not they're supposed to be expendable/disposable.

Side note - SF's current M4A1s are spec'd to have DD free-float handguards. Barrel harmonics and shifting POI are no longer the problem they used to be. Unfortunately, because Mother Army is still supplying the barrels (P2 vs. P11 money), they have the standard front sight assy which is dorky as hell poking up from the middle of the handguard.

Lots of older "wisdom" that has been rendered obsolete by lessons learned in the last 15 years of continuous combat. I'm just fortunate by the nature of my current job to be able to follow the changes (and adopt the ones I like) as they're being debated, validated, and implemented.

[Papa Zero Three]

LOL, first off the mag in that video is "not" on the ground. (I started laughing as soon as I saw him, the gun and the cloth.)

Second we don't have a clue how much cloth it's sitting on or how much straw is under it. When I employed the sniper rifle I always tried to sit it on some sort of cloth, be it a woobie, a hat, a rucksack etc. instead of the ground. The cloth ensured it didn't jump and it stayed in place for the subsequent shots.

We can agree to disagree, but I don't think you're going to find "trained" snipers (and not a 2-3 day police marksmanship course) that would be willing to shoot like the joker in that video. Let's see him do the same thing on a hard ground, say rocks and such or a sidewalk or street, "without the cloth".

He's "busted" no myths, especially shooting myths.

(And I live in a house that I own.....;))



Are you seriously going to question the cloth and the ground under it? OK, well then, as was posted on page #1, here is another video from the 2015 armed forces skill at arms meeting showing US and foreign soldiers shooting M4s and placing the magazine on the ground. How do you explain this? Did they all miss? If it doesn't work, why are so many of them doing it? You can rationalize all you want, it won't change the facts that this does work.

https://youtu.be/3rXykqvVHmk


I attended SOTIC, I teach precision rifle courses and I shoot my M4 prone unsupported with the magazine on the ground, as do others, because it works, I promise. :)

Congrats on the house. Last time we linked up you were in an Apartment, not counting the BBQ Get together you had at old boys house a while back.

So are you going to accept the 60 round challenge I proposed above? :)

[Team Sergeant]

So are you going to accept the 60 round challenge I proposed above? :)

Sure, we'll fire from a concrete sidewalk, 300m targets and we'll see who engages faster. :munchin

[Papa Zero Three]

Sure, we'll fire from a concrete sidewalk, 300m targets and we'll see who engages faster. :munchin

Wait a second, you were all about accuracy a few posts above, now you are about speed. Which is it? It doesn't matter what surface you choose. You can do it on the concrete pad at the range and then do it in the gravel dirt right in front of the concrete pad, the results will be the same.

But more importantly, this topic is about a person, 1ea, using a technique (placing mag on the ground), that improves THEIR shooting performance, it's not a "versus" or a competition between people. Which is why I challenged you to go out, on your own and try both techniques and see for yourself and come to your own intelligent and facts based conclusion.

[Team Sergeant]

Wait a second, you were all about accuracy a few posts above, now you are about speed.

Sorry, but accuracy and speed are like peanut butter and jelly, they go together. Ever see a three gun guy walking through the course?:munchin

Backing down?
:D

[Team Sergeant]

I've been watching these shooting styles trending the last decade too, you teaching any of them? :D

[Papa Zero Three]

Sorry, but accuracy and speed are like peanut butter and jelly, they go together. Ever see a three gun guy walking through the course?:munchin

Backing down?
:D


No, not at all. But it seems like you are flip flopping on what it is YOUR argument is against mag on the ground.

Lets put this back into perspective a bit. The target audience here is the average, conventional soldier. Using this method, mag on the ground, the "average" conventional soldier is able to engage pop up targets on the standard Army qualification range and achieve higher scores. That in itself is indicative of a valid technique and balance of accuracy and speed. Your argument against it is moot, you are just being obstinate in admitting that the "Old Sarge" urban legend that it causes malfunctions has been proven to be invalid.:)

[Leozinho]

I thought we were discussing whether the mag on the ground caused malfunctions and hurt accuracy by disrupting barrel harmonics.

Now the argument has shifted to mags on the ground is a bad idea because it slows down follow up shots due to recoil hop??? (but apparently only when placed on concrete.)

[Tuukka]

If talking about shooting fast and accurately, especially from harder surfaces also?

Why do IPSC rifle shooters in the Standard class shoot from a magazine rest vs. mag off the ground?

Gives to a much more stable platform and less recoil.

But what do I know, I am an Open class shooter with bipod.. ;)

( Been on the National IPSC Open rifle team though almost every season since 2009 and seen plenty of Standard shooters also )

[frostfire]

If talking about shooting fast and accurately, especially from harder surfaces also?

Why do IPSC rifle shooters in the Standard class shoot from a magazine rest vs. mag off the ground?

Gives to a much more stable platform and less recoil.

But what do I know, I am an Open class shooter with bipod.. ;)

( Been on the National IPSC Open rifle team though almost every season since 2009 and seen plenty of Standard shooters also )

that's right :D No high speed gear for joes. The manual is geared towards regular joe trying to increase qualification score and being an effective member of fire team. The annual all army small arms championship at Benning has the same purpose. One year, the AMU almost allowed participant to use mag coupler....until some shenanigans showed up with 3 mags coupled together and pretty much shooting from an improvised benchrest! Heck, without strict rule of issue equipment only, I would use this https://www.magpul.com/products/pmag-d60-ar-m4 :D Same rule apply at AFSAM, AASAM, and similar combat matches all around the world.

[Patrin]

I've been fortunate enough to attend some carbine courses at Mr. Howe's CSAT facility.

He's instructed me to shoot with the magazine braced against the forearm, finding natural POA, etc. Not much pressure is on the magazine, but it's very stable and works with or without body armor.

The second picture is my bare bones LW Colt and, using his method, last week, I was hitting chest size steel to 600 yards at the CSAT range with irons.

[SomethingWitty]

I am a little late to the party here. I did get to see some of the process of writing the new manual and the end product probably suffers from having way too many fingers in the pie so everyone can get OR/NCOER bullets.

As far as resting the magazine on the ground; it is definitely the most viable option for 90% of joes. I'm Distinguished Rifleman/Presidents 100 and I do it anytime I have the option to. Anytime you can rest the rifle on something it's going to be easier to shoot. Shooting is 40% trigger control, 40% stable position, and 20% sight picture. Having perfect trigger control or a perfectly stable position allows you to shoot good scores while being bad at one or the other. Sight picture is really you either get it or you don't.

There is more than likely some truth to the old dogma that resting the rifle on the magazine caused malfunctions. It can probably be attributed to the old style feed ramps, bad magazines, and unservicable equipment. I can see how pushing forward on the rifle while resting the magazine would orient rounds so the tips would catch. M4 feed ramps extend further, and continue into the upper receiver. Also the new magazines and pmags are a lot better than the old green follower and black follower mags.

There are some downsides. The rifle does bounce down if you don't put some force on the front. The difference is from putting 100% of the rifle weight on the mag, to 60% or so. But who cares on the Army qual course? You only have one shot per target anyways.

Another thing is that teaching marksmanship is always easiest by building a stable position, and then perfecting trigger control, and sight picture. If you put Joe in a position where it's almost impossible to fuck up: like prone supported with a sandbag under the front and army green sock full of sand under the back, it is almost impossible to fuck up grouping and zeroing. Then it's only a matter of removing the training wheels to learn positional shooting. But 90% of units never get past the grouping and zeroing stages. And chasing a zero all day is not good training for a soldier.

Insofar as barrel harmonics; the only real cardinal rule is to not rest the barrel on anything. And beware of shooting through the sandbag. How you rest the magazine or lower isn't terribly important because the upper more or less floats on top of the lower. Using a sling on a normal M4 is weighting increased stability vs a shifted zero. The amount of shift depends on sling tension, and is at least worth confirming at 25 or 100. It's usually not a lot because Joe isn't going to put 30 pounds of tension on it like a highpower shooter.

There's always pros and cons, but the bottom line is that it's a lot easier to teach Joe ways to be more stable first so he has a foundation to work with and see the effects of good sight picture and trigger control.