Ar15 5.56 77smk going transonic

[B Man]

Rifle is shooting 77gr SMK’s at 2783 fps muzzle, I am at sea level. My ballistic app says between 750-800 yards it was going transonic and I guess it didn’t lie. I shot earlier at 790 yards and noticed my 1/2-3/4 moa rifle was struggling to consistently hit a 1.5 moa plate. I kinda thought the 77 SMK would handle the transition better but maybe not. Any other experience especially at sea level? will the 77 gr TMK handle it any better? i noticed it would only gain me about 75 yards at the same velocity.

 

[TonyTheTiger]

Do you have zero wind where you live? In my area a 1.5 moa plate with a .5 moa rifle beyond 600 yards would be a struggle no matter what, just because the wind is always present but never consistent.

 

[B Man]

Do you have zero wind where you live? In my area a 1.5 moa plate with a .5 moa rifle beyond 600 yards would be a struggle no matter what, just because the wind is always present but never consistent.

Wind was practically dead and I was inside a stand of pine timber that shields it even more. I have flags on my target and they were down or just barely trying to move.

This rifle is holding 1/2-3/4 MOA consistently at 500 yards not 100 yds. I just got the chance today to push it farther since I’ve been extending the range and had next to no wind to test it.

 

[alamo5000]

Rifle is shooting 77gr SMK’s at 2783 fps muzzle, I am at sea level. My ballistic app says between 750-800 yards it was going transonic and I guess it didn’t lie. I shot earlier at 790 yards and noticed my 1/2-3/4 moa rifle was struggling to consistently hit a 1.5 moa plate. I kinda thought the 77 SMK would handle the transition better but maybe not. Any other experience especially at sea level? will the 77 gr TMK handle it any better? i noticed it would only gain me about 75 yards at the same velocity.

You are making huge assumptions (and mistakes). At that distance there are dozens of factors involved, but that doesn't mean the rifle shoots any worse.

Your mistake is that you automatically assigned the blame on one thing.

 

[B Man]

You are making huge assumptions (and mistakes). At that distance there are dozens of factors involved, but that doesn't mean the rifle shoots any worse.

Your mistake is that you automatically assigned the blame on one thing.

Not assigning or assuming. I’m pretty sure I asked.

 

[alamo5000]

At that distance and velocity your bullet travels about 18 feet above the ground at max ordinance. Depending on the terrain, almost 20 feet above the ground can have big differences in wind vs on ground level in the shooter's position. Terrain and how the vegetation is can cause a substantial variation. Likewise if you are shooting upwards (even some) you can get 'unseen' wind doing all sorts of things as it snakes around high and low areas.

Trees can also be a thing. One of the places I shoot at has a tree line that is fairly high on one side, but about 400 yards out it stops and the ground starts to slope upwards. Trying to read flags there is a problem all it's own. One flag is dead still, one is pointing straight up, but the next two point in different directions.

 

[Charger442]

What barrel length?

Is that a Chrono confirmation on the MV or just assumed from load data?

Also, what was the outside temperature? No matter what, the calculation for the speed of sound is always temperature dependant.

 

[alamo5000]

Not assigning or assuming. I’m pretty sure I asked.

My bad then. It "sounded like" you were saying the bullet is the main problem, or at least what you thought it might be. I was merely responding to say don't jump to that conclusion so quickly.

The bullet might be a thing but in my opinion it would be way down on the list of things to suspect.

 

[B Man]

At that distance and velocity your bullet travels about 18 feet above the ground at max ordinance. Depending on the terrain, almost 20 feet above the ground can have big differences in wind vs on ground level in the shooter's position. Terrain and how the vegetation is can cause a substantial variation. Likewise if you are shooting upwards (even some) you can get 'unseen' wind doing all sorts of things as it snakes around high and low areas.

Trees can also be a thing. One of the places I shoot at has a tree line that is fairly high on one side, but about 400 yards out it stops and the ground starts to slope upwards. Trying to read flags there is a problem all it's own. One flag is dead still, one is pointing straight up, but the next two point in different directions.

flat level ground here. But, you bring up a valid point about height and trees. This is in a stand of timber & the vegetation is heavier at ground level with me than it is where the bullet will travel so you might have a good point of it hitting a wind change I’m not aware of. Not looking to just throw blame but being this is where it said the bullet goes transonic I was curious if it just didn’t handle it well and was showing it today. I have never pushed this load this far.

 

[B Man]

What barrel length?

Is that a Chrono confirmation on the MV or just assumed from load data?

Also, what was the outside temperature? No matter what, the calculation for the speed of sound is always temperature dependant.

Chronographed. 20” barrel

 

[alamo5000]

Also what is the SD and ES of the ammo? That's a big deal at these distances with that round.

Even if your ES or SD is 20fps, that's enough to move everything 6 inches or more at 800 yards.

When you are talking about a total target of at the most 12" across (1.5 moa at 800) that 6 inches of variation can make a big difference.

 

[B Man]

My bad then. It "sounded like" you were saying the bullet is the main problem, or at least what you thought it might be. I was merely responding to say don't jump to that conclusion so quickly.

The bullet might be a thing but in my opinion it would be way down on the list of things to suspect.

No problem at all man. No I just know it says it’s going transonic at that distance and I haven’t pushed It past 600 yds until today since it was really good conditions to test it out. It was highly inconsistent compared to its usual performance so was curious if maybe this was a reason.

 

[alamo5000]

If I was a gambling man I would make the bet that your ES/SD is enough to cause variation, then add the fact that the farther you go the more pronounced the effects of the wind are.

As stated above, wind 20 feet up can act totally different than a couple of feet off the ground.

If I were going to make a bet, it would be on this. Not one singular issue but rather multiple issues adding up.

 

[B Man]

Also what is the SD and ES of the ammo? That's a big deal at these distances with that round.

Even if your ES or SD is 20fps, that's enough to move everything 6 inches or more at 800 yards.

When you are talking about a total target of at the most 12" across (1.5 moa at 800) that 6 inches of variation can make a big difference.

I don’t have my notes but nothing crazy. It shoots good horizontal spreads out to 500 and 600 yds. My chrony was only a sample of 5 shots also and I let it ride after seeing the groups. It was a plenty liveable number I remember.

. I’ll pull it tonight.

 

[Charger442]

Didn't say what the temperature was . Speed of sound at 80 degrees is 1140fps

 

[B Man]

Didn't say what the temperature was . Speed of sound at 80 degrees is 1140fps

82* best I remember

 

[B Man]

That’s adjusting to 82*

 

[Charger442]

That’s adjusting to 82*

Yes, pretty close. Passing trans sonic between 750 and 800 yards

 

[alamo5000]

I don’t have my notes but nothing crazy. It shoots good horizontal spreads out to 500 and 600 yds.

At 500 yards an ES/SD of 20 (exactly the same as I said above) could induce variations of less than one inch.

Out to 800 though and that number grows with the same information by around 4x to 5x (this is in theory using the exact same ammo in both cases). It's not a linear increase, but rather exponential. The math on that is way above my ability.

Also it's worth noting that BC is not a constant number. The farther you go the more it changes if by nothing else than the effects of more drastic velocity changes. And with that the slower the bullet travels the more influence the wind has on it.

 

[BCP]

Rifle is shooting 77gr SMK’s at 2783 fps muzzle, I am at sea level. My ballistic app says between 750-800 yards it was going transonic and I guess it didn’t lie. I shot earlier at 790 yards and noticed my 1/2-3/4 moa rifle was struggling to consistently hit a 1.5 moa plate. I kinda thought the 77 SMK would handle the transition better but maybe not. Any other experience especially at sea level? will the 77 gr TMK handle it any better? i noticed it would only gain me about 75 yards at the same velocity.

Wind, mirage, bullet velocity, variation in your loads, shooter error, if you think it's because they are transonic try single feeding an 80SMK loaded to 2.38-2.45 and 24-25+ grains of varget.

 

[ma smith]

Rifle is shooting 77gr SMK’s at 2783 fps muzzle, I am at sea level. My ballistic app says between 750-800 yards it was going transonic and I guess it didn’t lie. I shot earlier at 790 yards and noticed my 1/2-3/4 moa rifle was struggling to consistently hit a 1.5 moa plate. I kinda thought the 77 SMK would handle the transition better but maybe not. Any other experience especially at sea level? will the 77 gr TMK handle it any better? i noticed it would only gain me about 75 yards at the same velocity.

This is 99% likely due to MV variation at distance, you need SD below 10 to hold 1MOA at 800 yards. The hard, cold reality is .223 REM or 5.56 NATO is very difficult to load at single-digit SD with speeds in the 2,750 range. You need not only a chrono, but you need to be hand-loading, and using the absolute best components.

 

[B Man]

Wind, mirage, bullet velocity, variation in your loads, shooter error, if you think it's because they are transonic try single feeding an 80SMK loaded to 2.38-2.45 and 24-25+ grains of varget.

It’s no huge deal, not to single load . I was just curious if anyone has experienced it when it goes transonic. No doubt it’s not the most effective choice at that range and have much better choices, these are just fun to lay behind and cheap considering components now days. Appreciate the suggested load

 

[B Man]

This is 99% likely due to MV variation at distance, you need SD below 10 to hold 1MOA at 800 yards. The hard, cold reality is .223 REM or 5.56 NATO is very difficult to load at single-digit SD with speeds in the 2,750 range. You need not only a chrono, but you need to be hand-loading, and using the absolute best components.

I don’t have my data on hand but it was in the high single digit SD’s (8-9) from a string of 5 shots which i know isn’t a large enough example, but I don’t shoot competitions anymore & the load always held a nice horizontal spread to 600 yds so I have just been enjoying shooting. It is handloads also, Win brass, CCI 400, 77smk, 24.2 gr TAC, 1.860” ogive.
I skipped right over 700 yards as it’s in a dip on the property and until I finish my platform I have to skip 700 yards. I’ll test it out more later at 700 and 750 to see if it’s more consistent. I know the old Sierra 168’s would get erratic on me after 800 yards but the 175’s would keep on pushing. Guys at the range use to tell me the 168’s couldn’t handle going transonic so I thought maybe I was running into that here as well. Appreciate the feed back and constructive advice to other variables from everyone.

 

[ma smith]

I don’t have my data on hand but it was in the high single digit SD’s (8-9) from a string of 5 shots which i know isn’t a large enough example, but I don’t shoot competitions anymore & the load always held a nice horizontal spread to 600 yds so I have just been enjoying shooting. It is handloads also, Win brass, CCI 400, 77smk, 24.2 gr TAC, 1.860” ogive.
I skipped right over 700 yards as it’s in a dip on the property and until I finish my platform I have to skip 700 yards. I’ll test it out more later at 700 and 750 to see if it’s more consistent. I know the old Sierra 168’s would get erratic on me after 800 yards but the 175’s would keep on pushing. Guys at the range use to tell me the 168’s couldn’t handle going transonic so I thought maybe I was running into that here as well. Appreciate the feed back and constructive advice to other variables from everyone.

SMK is a great transonic bullet and will hold 1MOA at 800 yards. The limiting factor with 77SMK is the wind-drift, and the MV variation.

Check out JRLB's mk 262 series on you tube. Here is TAC...its around 10, but you need more like 7-8.

 

[B Man]

SMK is a great transonic bullet and will hold 1MOA at 800 yards. The limiting factor with 77SMK is the wind-drift, and the MV variation.

Check out JRLB's mk 262 series on you tube. Here is TAC...its around 10, but you need more like 7-8.

View attachment 8122304

I watched all his mk262 series a few times and still go back at times. I’m a bit of a research junky when I start getting into new territory.
He had a lower SD around 3-4 fps with TAC also. My SD is like 8-9 fps, I remember it was just lower than 10 fps. With CCI 41’s it shot up in the mid to upper teens with the load it liked.

 

[ma smith]

I watched all his mk262 series a few times and still go back at times. I’m a bit of a research junky when I start getting into new territory.
He had a lower SD around 3-4 fps with TAC also. My SD is like 8-9 fps, I remember it was just lower than 10 fps. With CCI 41’s it shot up in the mid to upper teens with the load it liked.

TAC isn't temp stable, so you can't rule out the MV variation unless you are shooting with a chrono.

 

[B Man]

TAC isn't temp stable, so you can't rule out the MV variation unless you are shooting with a chrono.

Correct, but it flows soooo much better than Varget or even xbr8208, almost 50% price, and easily available today it’s hard for me to not use it. I have the other two powders but only a few pounds of Xbr8208 left so I’ve left it until things normalize a little . But yes, my chrony was not with me on this given day so that can’t be ruled out and I haven’t ran TAC in warm weather since we have shifted into spring even though the load was made in low 70* weather I wouldn’t expect a 10* shift to effect things drastically but no data to know.

 

[wade2big]

At that distance and velocity your bullet travels about 18 feet above the ground at max ordinance. Depending on the terrain, almost 20 feet above the ground can have big differences in wind vs on ground level in the shooter's position. Terrain and how the vegetation is can cause a substantial variation. Likewise if you are shooting upwards (even some) you can get 'unseen' wind doing all sorts of things as it snakes around high and low areas.

Trees can also be a thing. One of the places I shoot at has a tree line that is fairly high on one side, but about 400 yards out it stops and the ground starts to slope upwards. Trying to read flags there is a problem all it's own. One flag is dead still, one is pointing straight up, but the next two point in different directions.

More like 6’ over bore max ordinance at 800 yds. Not even close to 18’. Bullet drop doesn’t mean what you think it does. Set your zero range at 800 yards in your ballistic app and then look at the “bullet drop” section for height over bore at any given range.