Range Report 77smk as sd round

[ubet]

I have a really good load worked up for one of my ars, with 77gr smk. I got a new ar pistol with 11.5” barrel yesterday and went to zero it today. That being said I used the loads I had already. The 77s were averaging 2280fps. Is that going to be fast enough to fragment as keep them loaded as a sd round? It’sa really stable load in my 16” and would prefer to keep uniformity across my ammunition. It did this today at 100 yards with magpul buis pros. So the gun accuracy wise likes the load. Just wondering about terminal performance to 200-300 yards.

 

[USGILT]

The 77 SMK is not a great close range, urban, or combat load and it was never designed to be. But, the longer the range, the better the performance.

A reasonable velocity for a 16” barrel for the 77gr would be around 2650fps...ish.

Quickload
77 grain SMK, 24.5 grains Varget, 2777 fps, 20 inch barrel
77 grain SMK, 24.5 grains Varget, 2638 fps, 16 inch barrel
77 grain SMK, 24.5 grains Varget, 2334fps, 11.5inch barrel

Speer 64 grain Gold Dot is my go to SHTF ammo and in my personal opinion should be yours too. Adequate penetration in gelatin and good intermediate barrier penetration as well.

 

[clcustom1911]

The 77 SMK is not a great close range, urban, or combat load and it was never designed to be. But, the longer the range, the better the performance.

Can you explain why the longer the range (and therefore the slower velocity) the 77 SMK would work better? I'm lost because that goes against all terminal ballistics research.

I do agree the Gold Dot is a great bullet.

 

[fdkay]

Welcome to the world of SBR 5.56.
As you have discovered, once you drop below 16", velocity plummets quickly.
The cartridge is not a very efficient one, but tests that were run with black hills showed a velocity from an 11.5" barrel at 2400 +-
I would prefer to get as much velocity as I could.
Your velocities seem a bit low, what is your load data?

 

[clcustom1911]

I have a really good load worked up for one of my ars, with 77gr smk. I got a new ar pistol with 11.5” barrel yesterday and went to zero it today. That being said I used the loads I had already. The 77s were averaging 2280fps. Is that going to be fast enough to fragment as keep them loaded as a sd round? It’sa really stable load in my 16” and would prefer to keep uniformity across my ammunition. It did this today at 100 yards with magpul buis pros. So the gun accuracy wise likes the load. Just wondering about terminal performance to 200-300 yards.

OP, what is your velocity with the 77 out of your 16"? That grouping looks pretty good, but muzzle velocity may need to get bumped up to 2400 out of that 11.5" to get reliable expansion at 300. The 77 tends to have significant expansion within the first 6 inches of ballistic gel

 

[clcustom1911]

FWIW....

This may not be a "study", but was texting one of my buddies from overseas the other day and he had some direct feedback with the 77SMK and 77TMK out of Mk18's (10.3")...

 

[LRShooter101]

Can you explain why the longer the range (and therefore the slower velocity) the 77 SMK would work better? I'm lost because that goes against all terminal ballistics research.

The "Works Better" at longer ranges has nothing to do with terminal ballistics, it has to do with getting the bullet accurately on the target at longer ranges (beating the wind).

With a .223/5.56 AR load, you pretty much build your load for terminal performance or long range accuracy, it is not real practical to try and do both at the same time.

You also need to consider what is the reality for the "engagement"?
- Rounds that do well with intermediate barriers, don't perform the best when it comes to terminal ballistics or long range accuracy.
- Rounds that are optimal in terms of terminal ballistics, don't perform the best when it comes to intermediate barriers or long range accuracy.
- Rounds that do well with long range accuracy, don't perform the best when it comes to intermediate barriers or terminal ballistics.
So which of the 3 factors are most likely to be the most significant for your typical engagement?

The military needs the ability to engage targets at longer ranges, so they went with the 77 grain bullets which have great performance in the wind. If you hit a target at longer ranges you have done your job. For closer ranges, you make up for the poor terminal performance with shot placement and number of rounds dumped into the target.

If you need a "mix" of capabilities, you can:
- Load certain mags with certain types of ammo. The challenge is getting as close to a common zero as you can for all of them. You also have to keep up with the different mags.
- "Candy Stripe" your mags when you load them. That is alternate 2 different types of rounds in the mag, so 1 terminal ballistics, 1 long range accuracy, and repeat. When you do this, you will fire multiple rounds on the target (at least 2 or optimally 4), this will ensure that at least 1-2 of the rounds is doing what you want it to. If you do this, typically you zero and run dope for the long range round. You check the terminal performance round to ensure that is "close enough", but given that is will be used for close in work, it doesn't have to be a perfect zero.

It would be great if 1 bullet could do it all, but that is pretty much impossible. As such:
- You need multiple loads that will be masters of each application
- You run a single load that is going to be a jack of all applications
- You pick the one application that matters the most, and use the single load that will be a master

Best of Luck!

 

[W54/XM-388]

The IMI 77gr rounds get out about 2550 ish from the 12.5" barrels, so you could probably go up a bit on velocity.

But for close range, consider that you can push a 40gr vmax to around 3k which in the 100 yard range is pretty effective.

 

[ubet]

I have to go look at the velocity for the other upper. But when I originally built it I remember the velocity nowhere matched what ab said it was at. I trued my velocity with their app and just rolled with it. My chronograph is a Caldwell pro chrony and honestly I’ve never truly trusted what it has said.

ab says it’ll be doing 1750 at 300.

I’m using 24.1 cfe 223, cci#41 mix brass.

 

[SonoranPrecision]

Our guys have been smoking dudes with mk262 out of short barrels for years. If that’s all you have, it will do fine.

 

[ubet]

Our guys have been smoking dudes with mk262 out of short barrels for years. If that’s all you have, it will do fine.

I have bigger caliber, in a bolt action. But not in ar

 

[fdkay]

Our guys have been smoking dudes with mk262 out of short barrels for years. If that’s all you have, it will do fine.

It's been my experience that those guys mostly shoot green tip.

 

[clcustom1911]

It's been my experience that those guys mostly shoot green tip.

In standard units, yes. In units and teams I have experience with, the Mk262 mod 0 and Mod 1 have been go-to rounds. See my screen shot of my text string above.

 

[Deleted member 113831]

Can you explain why the longer the range (and therefore the slower velocity) the 77 SMK would work better? I'm lost because that goes against all terminal ballistics research.

I do agree the Gold Dot is a great bullet.

The 77 grain bullet, as it slows down, becomes much more susceptible to the overturning moment (yawing, tumbling) in a denser medium (flesh).

 

[SonoranPrecision]

I have bigger caliber, in a bolt action. But not in ar

That’s what I mean. 77gr 5.56 is more than adequate for self defense out of a short barreled AR platform.

 

[SonoranPrecision]

The 77 grain bullet, as it slows down, becomes much more susceptible to the overturning moment (yawing, tumbling) in a denser medium (flesh).

However higher velocity promotes fragmentation and explosive energy transfer.

 

[clcustom1911]

The 77 grain bullet, as it slows down, becomes much more susceptible to the overturning moment (yawing, tumbling) in a denser medium (flesh).

So, based in your logic which loosely translated into "slower is a bit better" for terminal ballistics, then the 77smk would be a good choice out of an SBR


I was hoping @USGILT was going to answer.

 

[Deleted member 113831]

However higher velocity promotes fragmentation and explosive energy transfer.

Of course. If fragmentation is the desired effect, then velocity only helps.

 

[Deleted member 113831]

So, based in your logic which loosely translated into "slower is a bit better" for terminal ballistics, then the 77smk would be a good choice out of an SBR


I was hoping @USGILT was going to answer.

Not always, there are no absolutes. Each bullet and rifle combo needs to be evaluated individually. Things like barrel twist and bullet design interact in different ways.

 

[fdkay]

In standard units, yes. In units and teams I have experience with, the Mk262 mod 0 and Mod 1 have been go-to rounds. See my screen shot of my text string above.

I understand what you're talking about. I'm not saying that it was never used.
I managed the ammunition account for NSWU 3 for 1 year out of KNB.
I managed ammo going from Kuwait to Iraq and Afghanistan.
In my time, NO ONE ever requested MK262. It was always green tip.
I had stocks of 55 grain and MK262 which were never ordered.
I even encouraged the use of MK 262.

 

[LRShooter101]

APPLICATION!
Try putting MK 262 through an intermediate barrier and see how much luck you have consistently hitting and killing the target!
Try consistently hitting a small target past 300 meters with M193 or M855 and see how much luck you have!

The key with bullet performance is CONSISTENCY!
- Is it going to tumble consistently every time?
- Is it going to expand consistently every time?
- Is it going to fragment consistently every time?
- Is it going to penetrate barriers consistently every time?
- It is going to travel accurately to a long range target every time?
NO bullet can answer yes to all of those questions all of the time. As such, you need to figure out which one of those questions is the most important and find the bullet that can answer yes to it the most consistently.

"Our guys have been smoking dudes with mk262 out of short barrels for years"
Define "smoking dudes"?
- Was it one round and down or were they simply wounded?
- Did they hit them with 1-2 rounds or dump 2-5 rounds into them?
- Was it optimal shot placement or did they just get a round inside center mass?
- Was it at CQB distances or beyond 300 meters?
- Was the engagement in open air or behind intermediate barriers?
As the blood trails indicate, plenty of combatants have also been hit with Mk262 and lived to fight another day because it is not the magic bullet that some people like to make it out to be! Is it a good combination of performance characteristics, yes! Is it the "Master" of all performance characteristics, no!

If you take a realistic look at:
- Environment: Distance, Open Air or Barriers
- Bullet: Design & Performance
- Rifle & Load: Resulting Velocity, Twist Rate
You can figure out what is really going to work best for your application.

If you just want to do whatever other people are doing, best of luck, you had better pray that everything that they are doing will be the exact same as what you are doing!

 

[SonoranPrecision]

APPLICATION!
Try putting MK 262 through an intermediate barrier and see how much luck you have consistently hitting and killing the target!
Try consistently hitting a small target past 300 meters with M193 or M855 and see how much luck you have!

The key with bullet performance is CONSISTENCY!
- Is it going to tumble consistently every time?
- Is it going to expand consistently every time?
- Is it going to fragment consistently every time?
- Is it going to penetrate barriers consistently every time?
- It is going to travel accurately to a long range target every time?
NO bullet can answer yes to all of those questions all of the time. As such, you need to figure out which one of those questions is the most important and find the bullet that can answer yes to it the most consistently.

"Our guys have been smoking dudes with mk262 out of short barrels for years"
Define "smoking dudes"?
- Was it one round and down or were they simply wounded?
- Did they hit them with 1-2 rounds or dump 2-5 rounds into them?
- Was it optimal shot placement or did they just get a round inside center mass?
- Was it at CQB distances or beyond 300 meters?
- Was the engagement in open air or behind intermediate barriers?
As the blood trails indicate, plenty of combatants have also been hit with Mk262 and lived to fight another day because it is not the magic bullet that some people like to make it out to be! Is it a good combination of performance characteristics, yes! Is it the "Master" of all performance characteristics, no!

If you take a realistic look at:
- Environment: Distance, Open Air or Barriers
- Bullet: Design & Performance
- Rifle & Load: Resulting Velocity, Twist Rate
You can figure out what is really going to work best for your application.

If you just want to do whatever other people are doing, best of luck, you had better pray that everything that they are doing will be the exact same as what you are doing!

Clint Smith once said, “pistols put hole in people, rifles put holes through people, shotguns (with the right load, at the right range) will remove a chunk off your opponent and throw it on the floor”.

As far as I’m concerned, (God forbid) if I ever have to shoot someone to save the life of myself or any other person, they’re getting shot to the floor regardless of what firearm, caliber, or load I’m shooting.

Could you do better than mk262? Definitely. Could you do worse? Oh hell yeah.
I try not to get too caught up in the “this one is 2.03% more effective than that one” crap.

OP asked if a 77gr OTM out of a short barrel AR would be adequate for self defense. I whole heartedly believe the answer to that is yes.

 

[hic28]

Mk262 works great up close. @clcustom1911 is correct.

 

[alamo5000]

The 77 SMK is not a great close range, urban, or combat load and it was never designed to be. But, the longer the range, the better the performance.

A reasonable velocity for a 16” barrel for the 77gr would be around 2650fps...ish.

Quickload
77 grain SMK, 24.5 grains Varget, 2777 fps, 20 inch barrel
77 grain SMK, 24.5 grains Varget, 2638 fps, 16 inch barrel
77 grain SMK, 24.5 grains Varget, 2334fps, 11.5inch barrel

Speer 64 grain Gold Dot is my go to SHTF ammo and in my personal opinion should be yours too. Adequate penetration in gelatin and good intermediate barrier penetration as well.

This first line runs contrary to almost every recognized expert on the subject of terminal ballistics that I've read. That said they are talking SPECIFICALLY out of a short barrel. While I agree that the SMK wasn't designed to be something specific in this regard, but it certainly excels at it in this specific arena.

I agree that a target velocity of around 2600fps (+-25 fps) out of a 16" barrel is about right.

Ammo choice will depend on a lot of factors, barrel length being one of them.

 

[alamo5000]

Can you explain why the longer the range (and therefore the slower velocity) the 77 SMK would work better? I'm lost because that goes against all terminal ballistics research.

Be careful who you listen to on the internet but in this case I think it depends on a whole host of factors. Velocity and mass make up energy on target. Run some comparable tests of say 55 grain ball ammo vs 77 grain ammo and you will see a superiority of energy on target with the 77 grain as you go out. In comparable results basically at 300 yards for example there is roughly 125 to 150 more ft/lbs of energy on target with a 77 grain starting at 2600 fps vs 55 grain starting at 3000 fps.

The differences start to show up almost instantly when you use that one metric however at 200 yards they start to really deviate with the 77 grain winning out on that one metric.

That said, there are definitely more metrics that should be measured before making a final decision. Things like bullet design and terminal performance of the design matters a lot.

 

[alamo5000]

So, based in your logic which loosely translated into "slower is a bit better" for terminal ballistics, then the 77smk would be a good choice out of an SBR


I was hoping @USGILT was going to answer.

Slower is not always a 'bit better', especially for terminal ballistics. We can easily get off in the weeds here but speed isn't everything. Bullets (ie projectiles) have a minimum velocity window where they are effective for both penetration and fragmentation. Those velocities vary widely depending on the exact projectile in question. Regular 55 grain ammo is HEAVILY dependent on velocity to perform in terminal ballistics hence it is a poor choice when shooting it out of short barrels. Add speed though and it creates massive cavitation. Slow it down and you don't get penetration or cavitation (less mass going slower=less penetration).

With a heavier bullet, especially like the SMK or TMK they have thin jackets and are proven to fragment at much slower speeds whereas this is not the case with 55 grain ball.

Don't look at one aspect. Consider the totality of the situation.

 

[Hollywood 6mm]

77s are pretty damn nasty from everything I have seen, but they also suck when you get barriers (especially auto bodies/windshields) involved. Personally, I wouldn't use hand loads for SD/HD, and I prefer a good bonded bullet (namely Gold Dots/Federal Fusion) for my SBR for that role. They still work great at reduced velocities and the bullets work well through barriers if that's a concern.

 

[PracticalTactical]

I learned a few things about how bullets perform way back when Colt came out with the AR15A2 Delta HBar. if you can remember that rifle... At the time it was the cats pajamas.

For guys old enough to remember, that rifle came about after the military fronted millions into any interested rifle company to come up with a proposed replacement for the M16, at that time when they were still running slow twist barrels and 55 grain bullets. That's when they released the first M16A2 with the 1:7 twist. I think it must have been in the 1980s some time.

I hunted Eastern Woodchucks and White Tailed Deer alot in those days, so ballistic test subjects were plentiful.

I transitioned from a 1:12 twist Sako 223 running 55 grain soft points to the 1:7 twist AR running 69 grain SMKs. The difference in terminal performance was absolutely astounding. I never believed it was the bullet that made the difference but the spin rate was the reason. There's simply additional rotational energy.

To this point I have always wondered why ballistic gel tests never discuss spin rate. It is a variable after all and I've always felt that faster spin rate of the 1:7 was the reason for the lightening strike performance difference I became so familiar with.

Above it was mentioned how terminal performance can improve at extended range and there may be some factual basis for that. As the bullet slows down in forward movement, the spin rate does not. As a result, the spin rate per linear inch is actually increasing as the bullet travels down range. That will affect how the bullet reacts on impact, despite the velocity loss.

It's really not any different than the performance difference I got between the fast and slow twist rifles I mentioned above.

I didn't catch any mention of the barrel twist rate in above posts, only barrel length. While that will affect velocity, the twist rate can be used to jack up the terminal performance even if there is a velocity loss from the shorter barrel.

I'd be interested to see ballistic gels tests that compared same bullets at different twist rates, to see what difference it would make under test conditions.

I do recall out of curiosity, shooting a few ground hogs even multiple times with SS109s with the 1:7 at close range and they performed miserably. They just poked clean holes with no expansion or tumbling because they were so over stabilized. So, balancing the spin rate to bullet design is a subject I've never seen discussed in forums and it should be. It's relevant to this thread.

So keep this in mind when it comes to barrier penetration. Whats good to pass through a barrier is not good for maximizing damage to flesh.

 

[clcustom1911]

Here's some EXCELLENT info about cloning the Mk262 load.

I watched almost all the videos today. Fantastic empirical data. Use it as you see fit. I know I sure as shit will.

 

[ubet]

This is all great, thank you. And one reason why I asked here. I knew I’d get credible answers from both sides and a good discussion.

I’ve hit coyotes with the 77smk from my 16” and it will fuck their world up. If that’s any indication. I know it’s not apples to apples. I have some 62gr hpbt I’m going to try. If they work I’ll run them in the pistol. Cause the rifle abso-fucking-lutely hates them!!!!

 

[CrabsandFootball]

There are definitely better pure self defense bullets for the .223/5.56, especially with the introduction of quality bonded bullets and "barrier blind" rounds. The Gold Dot, M885A1, Mk316, SOST and a bunch of others.

The 77SMK has been used for almost 20 years as a pretty damn good replacement if you don't need penetration of armor of the M885 for two main reasons. First accuracy. The Mk262 is a much more accurate load in most guns than M885. With a rack M4/M16, you may get 2-3MOA with m885. Switch over to Mk262, and you will tighten that up by half. If you can't hit your target, then nothing matters. The second issue is performance out of short barrels. M885 (and M193) for that matter require a certain velocity in order to reliably fragment in targets. This is what puts people down instead of just putting holes in them. M16 with its increase velocity will fragment at further ranges than an m4. (Roughly 200 yards vs 50/80 yards). With a 12.5" and under barrel, you may not get any fragmentation due to velocity loss.

The 77SMK performs very well out of short barrels. With the thinner jacket you are not only going to get more yaw and less pass through, but more reliable fragmentation.

Is the 77SMK as good as dedicated SD rounds out of a SBR? Probably not. Is it significantly better than issue M885 and the best option for those in uniform? Probally. Is it a suitable load for civilians who have access to it? I say yea, much better than m193 loads 90% of people run in their guns.

 

[Shadow7Hill]

FWIW....

This may not be a "study", but was texting one of my buddies from overseas the other day and he had some direct feedback with the 77SMK and 77TMK out of Mk18's (10.3")...

View attachment 7408396

Many people like a do it all round. That was the genius of “barrier blind”. However the thin jacket if the MK 262 77gr acts almost as a frangible or varmint grenade. If you’re not shooting through glass, walls or anything like armor the MK 262 is a devastating round.

 

[Pusher591]

Why run the SMK when you can run the TMK? Higher ballistic coefficient and it also has a lower terminal threshold for fragmentation then the SMK. From my talks with a few guys at Sierra the fragmentation threshold is around 1900 and has shown to fragment more consistently then the SMK’s.

Fragmentation was seen fairly well all the way down to 1700 but 1900 was extremely consistent.

 

[Shadow7Hill]

Why run the SMK when you can run the TMK? Higher ballistic coefficient and it also has a lower terminal threshold for fragmentation then the SMK. From my talks with a few guys at Sierra the fragmentation threshold is around 1900 and has shown to fragment more consistently then the SMK’s.

Fragmentation was seen fairly well all the way down to 1700 but 1900 was extremely consistent.

Some complaints I have heard, although I don’t think they are valid largely are; it fragments too fast.

I have seen get tests and people start to freak out when penetration is less than 12-14”.

It all goes back to the round is not barrier blind, anything that fragments that good won’t go through an intermediate barrier well.

Basically if your shooting a living creature, without armor or having to shoot through intermediate objects both the TMK and SMK will get her done. If your shooting an elephant or heavy skinned “Dangerous Animal” then it may not be the ticket.

But, humans aren’t “Dangerous Animals“ largely they are sheep a little humor for effect

 

[Davo308]

Good thread that leads me to a question about the best choice Ive got for sd.

My state does not trust citizens with a regular ar grip and so my primary sd guns are a shotgun and pistols that I can operate as designed.

But I do have a 20 inch 9 twist and 16 inch 8 twist ar. I have m193, m855, various match loads with the 77 grain smk. I have no bonded or soft point rounds.

For self defense, at indoor distances, whats the best choice from the above?

 

[HOOFER]

I understand what you're talking about. I'm not saying that it was never used.
I managed the ammunition account for NSWU 3 for 1 year out of KNB.
I managed ammo going from Kuwait to Iraq and Afghanistan.
In my time, NO ONE ever requested MK262. It was always green tip.
I had stocks of 55 grain and MK262 which were never ordered.
I even encouraged the use of MK 262.

most of those units don’t go through normal procurement procedures and take operational ammunition With them

I have buddies that are in the “army” that only shoot .40 hydra shocks and you won’t find that in a TAMiS account.

 

[Dolomite_Supafly]

I was not active military at the time but when I was in AFG I was issued 62g and 77g Blackhills. I can say that hitting targets at beyond 500 yards seemed more consistent with the 77g than the 62g.

 

[fdkay]

most of those units don’t go through normal procurement procedures and take operational ammunition With them

I have buddies that are in the “army” that only shoot .40 hydra shocks and you won’t find that in a TAMiS account.

Really?
1. There is expanding ammunition available through the supply system
2. They downloaded every time they came out of theater.

 

[db2000]

Here’s some data from my gun.
12.5” BA Govt barrel

76F 26% 29.86mmHg
SMK 77 gr HPBT
LC brass x 1 firing
H4895 23.8 gr
Fed 205M
Ogive 1.843
COL 1.750
Magneto V3
2566, 2603, 2540, 2562, 2579 fps

 

[Shadow7Hill]

Good thread that leads me to a question about the best choice Ive got for sd.

My state does not trust citizens with a regular ar grip and so my primary sd guns are a shotgun and pistols that I can operate as designed.

But I do have a 20 inch 9 twist and 16 inch 8 twist ar. I have m193, m855, various match loads with the 77 grain smk. I have no bonded or soft point rounds.

For self defense, at indoor distances, whats the best choice from the above?

I cant tell you “the best”

I can tell you things I have noticed.

USMC FMJ, SOST/Mk-318 & 77gr SMK W/cann Mk 262 all fed well.

-Mk-262 most accurate and close quarters as long range effects on bad guys .

-Mk-318 less accurate than 262 performed better than FMJ CQB & Distance seemed like a compromise between green tip on penetration of barriers without simply poking 5.56mm holes straight through people.

-FMJ/Green tips. If you are shooting through vehicles or if the person my be wearing issued body armor this is what it was designed for and the only thing it really excels at in my opinion.

LE work we used soft points which have morphed over time. Winchester, Speer and Federal.

Soft points in my opinion are around to eliminate the hollow-point pistol ammunition problem of clogged cavities turning them into slugs. The issue I have with that logic is velocity. Rifle cartridge, unless they have extremely thick jackets are going to expand better the closer the range the faster the bullet is traveling. The issue with soft points in semi auto rifles, especially an AR is exposed lead rams into the extension deforms and slows/retards the cycle of operation sometimes causing a malfunction. Federal has done a pretty good job of fixing the issue by having almost a hybrid soft-point. The lead is nearly even with the front of the jacket and it’s not a cavitated hollow-point.

Personally I like the Mk-262 or a TMK version because my focus is shooting people and not barriers in front of them. It also helps reduce the liabilities of pass through and over-penetration of structures.

But, like I said, those are just my experiences and opinions. I am sure others will have different points of view

 

[BoilerUP]

From a 5.56 SBR... best option for a non-Hague restricted shooter inside 200m is a 55gr GMX/TSX. That provides the best combination of maximized velocity, penetration and terminal effects. Beyond those, the Gold Dot, Fusion, and SOST seem to provide excellent balance of velocity, penetration and terminal effects from stubby barrels.

That being said, the 75gr HPBT and 77gr SMK/CC are excellent "jack of all trades" choices with the TMK being mo'betta.

hashtagNotAnOperator

 

[Dolomite_Supafly]

My house gun, an 11.5” AR, has 40 grain VMax bullets loaded at max. When it leaves the house I swap to 75g HPBT loaded near max. The 75g is just for added weight to defeat barriers better than the 40g.

 

[308pirate]

I have bigger caliber, in a bolt action. But not in ar

Mk 262 is 5.56X45

 

[McCrazy]

In general it takes about 2400-2600 fps to get a projectile to cause cavitation which is what causes massive internal organ damage.

Your 2200ish muzzle velocity puts you below that already. Your stated goal of 200-300 yards will be far below that.

If you don't want the expense of buying ballistics gelatin to test the performance of your load at the ranges you are interested in, I would recommend taking some milk jugs with either colored water or even Jello so there is a bit more resistance. Video the impacts with a camera with a high framerate so you can review the performance and see if you deem it acceptable.

My bet is that it won't be ideal but you might find it good enough. It doesn't take a 155mm Howitzer to stop a threat.

 

[Yoteski]

 

[Shadow7Hill]

Cavitation is an interesting subject.

In older days with less advance fragmenting choices cavitation was needed to cause massive internal trauma.

That’s part of the concept of the old FBI test protocol. Penetration and Cavitation being the main factors for acceptable results.

Modern projectiles have reduced velocity fragmentation capability while still being able to maintain form when fired. They also create trauma by dumping energy internal of the initial penetration.

Leaving fragments inside the wound, especially if they are sharp cause a non clotting wound cavity.

Cavitation is also, believe it or not, how they are trying to weaponize pulse lasers.

 

[Tony6БР]

Poor possum I shot square in the chest with a Black Hills 77gr SMK out of a 10.3 inch barreled AR from about 15-20 ft away in my back yard a few years ago. Was getting mid 2400fps. If you don’t think this is an effective CQB load I don’t know what is.

 

[Chicory01]

I understand what you're talking about. I'm not saying that it was never used.
I managed the ammunition account for NSWU 3 for 1 year out of KNB.
I managed ammo going from Kuwait to Iraq and Afghanistan.
In my time, NO ONE ever requested MK262. It was always green tip.
I had stocks of 55 grain and MK262 which were never ordered.
I even encouraged the use of MK 262.

When you say green tip are you referring to Black Hills 77gr TMK or M855A1?

 

[fdkay]

When you say green tip are you referring to Black Hills 77gr TMK or M855A1?

Green tip m855. The Mk262 load did not and does not have colored tip
This was 2007, before the M855A1

 

[Dolomite_Supafly]

My house gun, an 11.5” AR, has 40 grain VMax bullets loaded at max. When it leaves the house I swap to 75g HPBT loaded near max. The 75g is just for added weight to defeat barriers better than the 40g.

It is now 2023 and I am running 75G out of a 13" rifle. Getting 2,645 fps average.