6.5G vs. 5.56 For a Long Range Scoped AR15 Course

[jeff556]

Folks,

I'm looking at taking a Scoped AR course this year. The course would cover targets from 0 - 700 yards.

My first thought was to use my 16" Grendel. My wife has a 16" 5.56 rifle that she would use.

I started looking around for loads for each rifle and it looks like the Black Hills 5.56 77 grain TMK is a real game changer. The 5.56 load offers better drop performance than the Hornady 123gr ELB at 700 yards - 6.1 mil vs. 7.1 mil. The Grendel has a small edge in wind deflection at that range - 1.9 mil vs 2.2 mil.

I used the manufacturers data on BC and MV at JBM Ballistics to come up with these numbers. Hornady used a 24 inch barrel and Black Hills used a 20 inch barrel. To try to normalize the numbers I knocked 100 fps off of the Hornady MV to try and account for the shorter barrel.

I'm having second thoughts about using a Grendel for this course. I'm thinking that the flatter shooting offsets the small advantage of the G round in wind deflection.

Thought? Which would you choose and why?

[cb4017]

That would be a tough one. I think for me it would come down to which rifle was more accurate with the ammunition you plan on using and cost. All things being equal I believe the 5.56.

[LR1955]

Folks,

I'm looking at taking a Scoped AR course this year. The course would cover targets from 0 - 700 yards.

My first thought was to use my 16" Grendel. My wife has a 16" 5.56 rifle that she would use.

I started looking around for loads for each rifle and it looks like the Black Hills 5.56 77 grain TMK is a real game changer. The 5.56 load offers better drop performance than the Hornady 123gr ELB at 700 yards - 6.1 mil vs. 7.1 mil. The Grendel has a small edge in wind deflection at that range - 1.9 mil vs 2.2 mil.

I used the manufacturers data on BC and MV at JBM Ballistics to come up with these numbers. Hornady used a 24 inch barrel and Black Hills used a 20 inch barrel. To try to normalize the numbers I knocked 100 fps off of the Hornady MV to try and account for the shorter barrel.

I'm having second thoughts about using a Grendel for this course. I'm thinking that the flatter shooting offsets the small advantage of the G round in wind deflection.

Thought? Which would you choose and why?

Jeff:

Use the one that gives you the most confidence.

LR55

[Texas]

I agree with LR55, confidence is a big part of accuracy.
Before the Grendel, if I thought I might get a shot past 400 yards, I always took a 7.62X51 or 30/06. As time progressed, I had more confidence in the 7.62X51 and the 30/06 stayed in the safe.
Now after successful hunting past 500 yards with the Grendel, the 7.62X51 spends most of the time in the safe.

[jeff556]

I've had some pretty good instructors and at this point I'm pretty confident with either 5.56 or 6.5G on steel silhouette targets at 700 yards. That out to be a piece of cake compared to the stuff LR1955 and Co. had us shooting at Boomershoot. :-)

I'm very grateful for that.

I know I still have a lot to learn, so I'm interested hearing what the horde has to say about the tradeoff between drop and wind drift.

[kmon]

At known distances elevation is more of a constant correction than wind call to me, I would go with the Grendel since it does a little better in the wind if equally familiar and comfortable with both.

Wind seems to be the ever changing factor in long range shooting and the ability to judge it is an artform.

[biodsl]

I'm thinking that the flatter shooting offsets the small advantage of the G round in wind deflection.

Just playing devil's advocate here. Will you be shooting known distances? Is wind a consideration for the training facility/range you'll be at? Gravity doesn't change, wind does. With a rangefinder and ballistic app, I find it easier to compensate for distance than wind. But LR55's advice seems pretty sound.

A second thought is you mentioned your better half will be there with a 5.56. It might be a good idea to level the playing field. ; )

[JASmith]

...I used the manufacturers data on BC and MV at JBM Ballistics to come up with these numbers. Hornady used a 24 inch barrel and Black Hills used a 20 inch barrel. To try to normalize the numbers I knocked 100 fps off of the Hornady MV to try and account for the shorter barrel...

That arbitrary 100 fps can make a difference -- it is more like 30-50 fps for the 2 inch difference in barrel length for the Grendel.

You really want to use the velocities that the 16" barrels produce to do a good comparison, and even then you should shoot both at distance in the same weather conditions.

Run both over a chronograph in the mean time. You'l get a far more definitive comparison of the muzzle velocities.

If you don't have or can't borrow or buy a chronograph, use this link and a good guess for the powder weight along with the manufacturers claimed velocity and barrel length to get an estimate: http://shootersnotes.com/calculator/velocity-estimator/

There's lots of load data in the manual and at Ammoguide.com even for 16 inch barrels and the velocity estimator will help minimize guessing with respect to barrel length differences.

Bottom line, nothing beats getting you and your wife on the 700 yard range and shooting together. Even swap guns for some strings to eliminate shooter technique and skill differences.

Afterwords, you'll know which one you feel better about taking to the course regardless of calculated results.

[jeff556]

That arbitrary 100 fps can make a difference -- it is more like 30-50 fps for the 2 inch difference in barrel length for the Grendel.

The 100 fps wasn't completely arbitrary - I based it on a thread on this forum that estimated the velocity loss at 25 - 50 fps per inch. :-)

Your suggestions are excellent. I'll order up some of the ammo and try them over a chrono and see how they group.

[biodsl]

The 100 fps wasn't completely arbitrary - I based it on a thread on this forum that estimated the velocity loss at 25 - 50 fps per inch. :-)

Your suggestions are excellent. I'll order up some of the ammo and try them over a chrono and see how they group.

And report back, please!

[FW Conch]

What is the twist rate on Your 5.56 barrels? Are You sure they can stabilize a 77grn pill?

[LR1955]

I've had some pretty good instructors and at this point I'm pretty confident with either 5.56 or 6.5G on steel silhouette targets at 700 yards. That out to be a piece of cake compared to the stuff LR1955 and Co. had us shooting at Boomershoot. :-)

I'm very grateful for that.

I know I still have a lot to learn, so I'm interested hearing what the horde has to say about the tradeoff between drop and wind drift.

Jeff:

I doubt there is enough of a ballistic difference between the two to give you a distinct edge.

However, understand the nature of shooting steel for score. The people who are scoring you may not be too good at spotting trace or may not even try. They probably have a mediocre or poor optic trained on the steel and are looking for splash and listening for the ping. Could be 'thunk' if they are using thick steel. If it is windy, the wind can also blow the sound away and make it harder to see splash. Could also be that you must knock down the steel.

In the above situations, a bigger bullet gives an edge. A person can read the trace easier, see splash easier, bigger bullets make more noise when they hit the steel and they increase the chances of knocking down the steel.

You may want to find out how this thing will be scored and go from there.

LR55

[Bigs28]

I personally would take the gun i plan on using after the course. I hunt so i would take the grendel to build confidence in it since i would take game at range with it over the 556.

[JASmith]

The 100 fps wasn't completely arbitrary - I based it on a thread on this forum that estimated the velocity loss at 25 - 50 fps per inch. :-)...

Try this thread: http://www.65grendel.com/forum/showt...+barrel+length

It was bult using the Velocity Estimator referenced earlier. It, in turn, used AA test data for different barrel lengths as part of the calibration.

[LRRPF52]

Folks,

I'm looking at taking a Scoped AR course this year. The course would cover targets from 0 - 700 yards.

My first thought was to use my 16" Grendel. My wife has a 16" 5.56 rifle that she would use.

I started looking around for loads for each rifle and it looks like the Black Hills 5.56 77 grain TMK is a real game changer. The 5.56 load offers better drop performance than the Hornady 123gr ELB at 700 yards - 6.1 mil vs. 7.1 mil. The Grendel has a small edge in wind deflection at that range - 1.9 mil vs 2.2 mil.

I used the manufacturers data on BC and MV at JBM Ballistics to come up with these numbers. Hornady used a 24 inch barrel and Black Hills used a 20 inch barrel. To try to normalize the numbers I knocked 100 fps off of the Hornady MV to try and account for the shorter barrel.

I'm having second thoughts about using a Grendel for this course. I'm thinking that the flatter shooting offsets the small advantage of the G round in wind deflection.

Thought? Which would you choose and why?

.3 Mils is not small when you look through the scope. At 700yds, it's about 8".

The other thing is retained energy. You can actually hear the Grendel hit at 700yds, whereas even with a little wind, it is extremely difficult to register the impact of even 77gr 5.56.

Since you will be holding or dialing for trajectory no matter what, and will likely know the range to the targets, there is no practical trajectory advantage to 5.56 77gr. You really have to single-load the 90gr Bergers to make 5.56 a game-changer, and then you basically duplicate mag-fed ballistics of the 123gr Scenar from the Grendel.

For those of us that shoot precision rifle a lot, the main performance parameter we look at first is wind deflection. Wind deflection is what drives the selection of chamberings and bullets, which is why 6mm and 6.5mm are the kings in PRS. BC drives wind deflection.

5.56 is very anemic on steel at 700yds, as you will see. In no-wind conditions, it's fun and very easy to make hits on sils. With any amount of wind, your hit probability starts to spiral downwards very quickly.

Take both and see.