5.56- 69 SMK VS. 77SMK What am I missing here ?

[Rprecision]

So I am starting to get some plans together for my new 5.56 Precision AR Upper. It’s based on an 18” SPR Noveske 1/7 Barrel. This is an Mk12 type, but not a clone.

I have been toying around with what bullet to start out with. My intended purpose is a 0-600 yard gun, with a maximum of 800 yards. I think that seems reasonable for most conditions for a 5.56.

Through my reading it seems our military has grown quite fond of the Mk262 Ammo. 77 Grain SMK @ 2700-2750 Fps. Seems to be the load of choice for extended ranges and the DMR (Designated Marksmanship Rifle) program.

Prior to this I found the 68-69 Grain Match bullets interesting. I had some pretty positive experiences with Gold Medal Match 69 grain loads. So I tore into the ballistics and found:

(All calculations are made at 8000’, 20% Humidity at 60 degrees. Velocities are based on what I suspect is reasonably attainable for each load.)

A 77 SMK with a .362 BC @ 2700 Fps takes 1.8 Mils to 350 yards, 7.3Mils to get to 800 yards with 2.1Mils of drift at 10 MPH. 353Ft LBS at 800. Stays supersonic to 1200 yards

A 69 SMK with a .301 BC @ 2850 Fps takes 1.2 Mils to 350 Yard, 7.2Mils to get to 800 yards with 2.5Mils of drift at 10 MPH. 272Ft LBS @ 800. Stays supersonic to 1100 yards

They are neck and neck to 800 in drop, Wind is within .5 Mils, and within 80 Ft LBS of energy. To boot the 69 grainer’s have a better midrange trajectory, all-be-it .6 Mils.

Why should I continue to look at the 77-grain loads? Like most things spelling this out on paper doesn’t always translate to the real world. So what am I missing here?

Thanks

 

[Huckleberry75]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

Looks pretty cut and dried right there. Some guys just have to have what the military has or as close as they can get. I personally just worry about what works for my applications.
Based on your post, I would run the 69's. I am sure that someone will come along and "correct me".

 

[Niles Coyote]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

I am making loads with both right now. The rifle will tell me which to continue with.

 

[1lnbrdg]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

I'd say that was a pretty interesting observation.

That wasn't what I see when I run the numbers on JBM ballistics.

It looks like the 69gr bullets at 2850fps goes sub-sonic betwixt 700 & 800 yards on the JBM website.

I have shot the 69's and the 77's both at 600yds and there is a very noticible difference in how they act in the wind though I've shot some good scores at 600yds with the 69's.

 

[tigerfan_9]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

Those velocities are low for the 77. Should be more like 2750 so only and 100 fps difference with the same barrel length this should put the 77 supersonic further and better in the wind once you get way out there.

 

[JoshcBoucher]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

I just got done reading a "study", in one of the Magazines, of 'twist rate and Bullet weight". That's probably going to be the factor on accuracy. The "heavier" bullets want a faster twist rate, Like 1/7, or 1/8. They mentioned some one doing a 1/6.5 "custom", too.Just a thought. Certain guns didn't "like" the heavier bullets. They shot some 90 gr., as the "max", just to see, and they tumbled to the target, in some of the 1/12, and 1/9 rates. Seems a "test" is the answer, when ya get her. 1/7 is your best option, anyway, for the heavier bullets.

 

[1lnbrdg]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

After my experience with 1/8 twist barrels, I'd never use anything less than a 1/7~something twist.

That won't shoot 90gr bullets but it will shoot every match bullet down to 52gr well.

If you're planning on shooting the varmit bullets, 1/9 should do fine, the faster twist will cause some of them to vaporize before reaching the target.

 

[excess]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

I think you are missing some important things here.

The heavier, higher BC bullet (GM223M3 in the plots, from Federal's website) has better velocity retention:

This ends up in higher downrange energy:

Plus, I can use a rangefinder to determine my dope, but figuring out what the wind is doing from me to a long range target is harder, and as you noted the heavier bullet has the edge here:

Take a look at Part 1 Of Litz's Applied Ballistics book - he states a heavier bullet is almost always better for long range shooting.

Sorry for the funny colors - stupid Webshots doesn't handle a png well.

 

[wrhunter]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

From personal experience handloading both bullets I determined that in MY rifle (1-8 RRA) I can't get the speed with the 77's to beat the 69's until 600 yards or more.

 

[Bayou1535]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

Great topic OP as I'm just finishing up with a build with the same barrel and was unsure of what to use.

 

[opeagle]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

If lethality is a concern there may be another side.

 

[turbo54]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

You're missing 4 key points:

90gr Berger
80gr Amqx
75gr Amax
75gr hpbt <--- focus attention here, as they fit magazines handily

Also , my 600 yard service rifle load is ~24gr Varget and 80amax. That's about 2850-2900 fps, and 12 moa from 100-600.

 

[Rprecision]

Re: 5.56- 69 SMK VS. 77SMK What am I missing here ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Niles Coyote</div><div class="ubbcode-body">I am making loads with both right now. The rifle will tell me which to continue with.</div></div>

Undoubtedly, I am looking at the external ballistics first, but your right. If she loves the 77’s this was a study of futility. However, given the twist I don’t think is should be hard to find s sub MOA load in either.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 1lnbrdg</div><div class="ubbcode-body">I'd say that was a pretty interesting observation.

That wasn't what I see when I run the numbers on JBM ballistics.

It looks like the 69gr bullets at 2850fps goes sub-sonic betwixt 700 & 800 yards on the JBM website.

I have shot the 69's and the 77's both at 600yds and there is a very noticible difference in how they act in the wind though I've shot some good scores at 600yds with the 69's.</div></div>

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tigerfan9</div><div class="ubbcode-body">Those velocities are low for the 77. Should be more like 2750 so only and 100 fps difference with the same barrel length this should put the 77 supersonic further and better in the wind once you get way out there. </div></div>

You both bring up a valid points, 100 Fps difference is probably more useful. It seemed from my reading most folks running a 77 SMK were on the absolute edge of safety and reliability to get 2750 Fps +

I decided to rework the original values, same conditions using another program with different velocities. Here what I got.

A 77 SMK with a .362 BC @ 2750 Fps takes 1.7 Mils to 350 yards, 6.9 Mils to get to 800 yards with 2.1Mils of drift at 10 MPH. 354Ft LBS at 800. Stays supersonic to 1150 yards

A 69 SMK with a .301 BC @ 2850 Fps takes 1.6 Mils to 350 Yard, 7.1Mils to get to 800 yards with 2.4Mils of drift at 10 MPH. 285Ft LBS @ 800. Stays supersonic to 1050 yards

Results are very similar to using the vortex calculations. Of note, JBM figures supersonic at 1100 Fps, whereas it is closer to 1030-1050 ish at my altitude. I really only brought this up as a measure of comparison anyways.


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tigerfan9</div><div class="ubbcode-body">Those velocities are low for the 77. Should be more like 2750 so only and 100 fps difference with the same barrel length this should put the 77 supersonic further and better in the wind once you get way out there. </div></div> <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: xmark</div><div class="ubbcode-body">From personal experience handloading both bullets I determined that in MY rifle (1-8 RRA) I can't get the speed with the 77's to beat the 69's until 600 yards or more. </div></div>
This is one of my concerns when looking what the potential is with the 77’s

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: opeagle</div><div class="ubbcode-body">If lethality is a concern there may be another side.</div></div>

The 77’s build around 80 Ft LBS more energy at 800 and closer to 100 Ft LBS at the mid range of 350. In terms of effective terminal ballistics, maybe this is where the golden nugget is. While 100 Ft LBS is nothing to shake a stick at its also a between 15% and 7% more energy on target.

 

[Chili656]

Here is a dope card that you can copy & paste to add to the buttstock of your rifle. Condition for creation:

1. 18in barrel is roughly 2800FPS
2. Mk262 Mod 1
3. Elevation 0ft, Temp 59F, 50% Humidity.
4. Sight HOB= 2.685in (ADM Recon Mount)
5. You will need to adjust the Suppressor POI shift, tailor it to your equipment.

 

[mrtoyz]

Here is a dope card that you can copy & paste to add to the buttstock of your rifle. Condition for creation:

1. 18in barrel is roughly 2800FPS
2. Mk262 Mod 1
3. Elevation 0ft, Temp 59F, 50% Humidity.
4. Sight HOB= 2.685in (ADM Recon Mount)
5. You will need to adjust the Suppressor POI shift, tailor it to your equipment.

View attachment 7512740

What did you use to make this card?

 

[Chili656]

What did you use to make this card?

ShootersCalculator.com | M855 vs MK 262 vs 300 BLK

They have a free calculator that enables you to plug in the variables/conditions you wish. I hope you find it useful. I also made on for your 14.5in AR, if you're interested. LMK.

 

[Chili656]

ShootersCalculator.com | M855 vs MK 262 vs 300 BLK

They have a free calculator that enables you to plug in the variables/conditions you wish. Then I took the values and made an excel spreadsheet. I hope you find it useful. I also made one for my 14.5in AR, if you're interested. LMK.

 

[mq105]

Have you considered 69TMK? I've found them to handle wind slightly better than the 77SMK. Less drop at 600 also.

 

[Chili656]

Not seriously, YET (emphasis on the "yet). I consider myself a novice when it comes to long-range shooting. As of right now, I am personally in favor of the MK262 (77gr OTM) specifically because it was developed and designed for the mk12 spr rifle. I find confidence in that SOCOM probably factored in many variables including terminal and external ballistics and arrived at the 77gr.

I hope that in the future I am able to devote more "scarce" resources to testing the 69TMK.

 

[briang7511]

midway has 77 tmk and powdervalley has 69 and 77 mk in stock. hope it helps.

 

[Greg Langelius *]

I admit to skipping past much of the topic once having read the part about 8000ft. That's a lot of altitude.

In 2002, I shot at Whittington, which, if I can remember correctly, is at or above 6600ft.

Ending 2004, I had a significant heart attack, and lost considerable amount of heart function (LV ejection factor percentage ca 40%, in conjunction with advanced COPD, I haven't been able to run a step since 2004).

I cannot breath at 8,000ft, let alone shoot there.

Bear with me, because there is a point here.

I can shoot at my current altitude of 4350ft, and would likely do fine at 5000ft. I get a bit wonky in the higher parts of Albuquerque, for instance.

My point is that most folks here don't shoot as high as 8000ft, and that makes a significant difference regarding drop and drift. I would estimate broadly that most shooting gets done at around 1000-2000ft and that there's where I do my generic estimations regarding suitable MR bullets. As a generic statement, I find that from a 24" barrel, a Hornady 75gr HPBT-Match bullet will stabilize (possibly marginally) in a 1:9" twist and be good for at least 600yd, maybe 800yd, before going transsonic. That's what I shot at the Tucson 600yd MR Nationals at Ben Avery, Tucson, which range is sub 2000ft. For reference purposes my load is 23.5gr of Varget. For shorter barrels, I suggest a 1:8" barrel, and prefer a 1:7" for my 16" barrels just to be sure with that bullet, but that's possibly overkill.

The way spin decays so slowly over distance, if a bullet will stabilize out to 100yd, it will only get proportionally more stable as distances increase beyond that. Simplified, if the bullet stabilizes at all, it will go subsonic and strike the earth before it reaches a rotational velocity where it destabilizes.

While the tendency is for heavier bullets to require more twist, the operative factor is length, not weight; it's just coincidental that the two tendencies tend to somewhat linked.

When I do my own calcs, I enter a value of 4350ft ASL which corresponds to approximately 85% the station pressure at sea level. Under the circumstances, I have little use to 175gr 308's or 223's above 75gr. I a very happy with 168's o/o my 308, and don't give much though about the transsonic, as most places I can shoot don't reach that far. A 95gr V-Max out of my 260 should remain supersonic well past 1000yd. These are special cases, but for me, they are a reality.

Hoping this helps;

Greg

FWIW, This is the current version of the rifle I used at the 600MR Nationals. Noting the 24" barrel, I would strongly urge you to consider this barrel length for when you're intending to shoot at 600-800yd and 'normal' altitudes. Yes, it's o/o stock currently, as is common throughout the industry, but that changes frequently.

I would suggest the Upper. That's where all the important stuff is happening. Watch the listing frequently, it comes on and goes off the market frequently. It uses a MilSpec standard BCG and bolt.

Another option is then AR Stoner 24" stainless Heavy Wylde Barrel. I built an Upper for a friend with one, and it shoots very favorably alongside my Stag. It uses a standard MilSpec BCG and bolt and has a rifle length gas system.