Lower SD and ES but larger group size at 100 yards

[boisepaw]

Rank amateur here with a question. I'm shooting a McCree rifle, Vortex PST scope with a Benchmark barrel and an Atlas bipod in 6mm CM. EVERY bullet I shoot (Hornady Amax 105 gr., Nosler RDF 105 gr., SMK...both 107 and 110 gr., Berger Hybrid 105gr.) when loaded over 42 grains (+/- .1 grain) of H4350 shoots extremely well.

But the very best SD (under 5) and ES (under 10) 5 shot strings that I shoot do NOT always translate into the smallest groups at 100 yards.

Logically I would think that the lowest SD and ES are going to give me the tightest groups at 100 yards and continue out to 1000 yards and beyond. But I'm not seeing that in my shooting.

Particularly, the Hornady Amax 105 consistently gives the lowest SD and ES. But the Berger Hybrid 105...while usually (but not always) giving nice low SD and ES, is ALWAYS the most accurate of all the bullets that I load.

Any suggestions about how I should be thinking about this?

I'd like to find a place and time to be consistently shooting 500-1000+ yards but I want to have the best possible load to do that.

 

[canezach]

A couple of things come to mind:

First, you said you're a rank amateur, so it's possible you have poor fundamentals resulting in bad groups

Second, if you haven't tried a seating depths test, you haven't tightened up your groups at all.

 

[Dogtown]

But the very best SD (under 5) and ES (under 10) 5 shot strings that I shoot do NOT always translate into the smallest groups at 100 yards.

That's just reality.

The low SD and ES just means the bullets are leaving the barrel at a consistent velocity. But that's only one piece of the puzzle; you want the bullets leaving the barrel at a consistent velocity AND in a harmonic node when the amplitude of the vibration racing through the barrel is at a local minimum.

Low ES translates to bullets landing relatively close as you increase distance. Higher ES means there will be more vertical separation over that distance. That's why you want low ES and a small group for ELR shooting.

 

[boisepaw]

A couple of things come to mind:

First, you said you're a rank amateur, so it's possible you have poor fundamentals resulting in bad groups

Second, if you haven't tried a seating depths test, you haven't tightened up your groups at all.

Thanks for the input. I appreciate it.

I normally go through a two step process when working on a new load. I start with Scott Satterlee's method to narrow down the bullet, powder and charge weight that works well. When I find that "node" that seems to have roughly the same velocity within a range of roughly a half grain of powder, then I will start fiddling with the seating depth.

I don't know if anyone else has had the same experience but, unlike my experience loading for 308, 243 or 6.5 Creedmoor, I am AMAZED at how forgiving is the 6mm Creedmoor. Each of the four bullets I mentioned shoot great at 41.9 to 42.2 grains of H4350. And they all seem to like the same seating depth...right around 2.12 inches to the ogive.

Out of 65 five shot groups with that rifle at 100 yards with the different loads in different weather conditions, only 4 groups were OVER 1" center to center. 18 of the 65 groups were 1/2" or better center to center. Even in my old hands and with my old eyes.

It just strikes me as an incredibly forgiving caliber.

 

[boisepaw]

That's just reality.

The low SD and ES just means the bullets are leaving the barrel at a consistent velocity. But that's only one piece of the puzzle; you want the bullets leaving the barrel at a consistent velocity AND in a harmonic node when the amplitude of the vibration racing through the barrel is at a local minimum.

Low ES translates to bullets landing relatively close as you increase distance. Higher ES means there will be more vertical separation over that distance. That's why you want low ES and a small group for ELR shooting.

I think I'm tracking with you but let me see if I've got it right...

The low SD and ES are all well and good but each bullet will set up its own (different) harmonics in the same barrel. So low SD and ES are critical to long range shooting but then you need to find the bullet that, as seen by the group size, seems to be favored by that barrel in terms of the harmonics.

And would it then be true that any load that has an SD of under 10 and an ES of under 20 is going to shoot well out to 1000 yards? As long as the barrel "likes" that particular bullet?

 

[badassgunworks]

Low Sd is obtained threw powder volumes and some brass prep included anneal. Accuracy is obtained threw seating debth and brass prep. Also the use of a tuner helps with accuracy fine tuning.

 

[Dogtown]

Sort of.

Low ES is critical to long range because even if you were getting super tight groups at 100 yards, the difference in velocity at the muzzle from a large ES results in a vertical dispersion (ex the faster bullets hit high and the slower ones hit lower). When the distances are relatively short, an ES of 75fps won't make much of a difference, but at 1500 yards that's a huge difference in vertical drop. Plug a load into JBM Ballistics and look at the drop at 1500 yards. Then run it again 75fps slower. Notice the difference between the drop of the first and second bullet. At 400 yards it's not a whole lot, but at 1500 it should be significant.

2875fps

2800 fps

HALF A MIL difference from just an ES of 75

As for harmonics, I like to think of it as timing when the bullet leaves the muzzle. The barrel is vibrating as that shockwave is racing up and down the length of the bore. If you look at a sine wave, the peak and trough is where the motion from that vibration is slowing down, hits an inflection point, then speeds back up. The middle of the wave is where the movement of the muzzle is closer to a constant velocity and hitting a maximum speed. Ideally you want to time your bullets so that they leave the muzzle when the vibration amplitude is at its lowest level (at the peak or trough, which are the local max and min values). The vibration pattern varies depending on so many factors, including barrel composition and contour.

Powder change is a coarse adjustment in velocity while seating depth is more of a fine adjustment - at least that's how I've always thought of it. So you find a powder charge that gives you consistent velocity and ideally in the ballpark for where you want POA/POI. Then seating depth adjustments fine tune that load to add/reduce velocity into that sweet spot. Not everyone believes in this philosophy, so don't take it as gospel.

 

[Dogtown]

Stupid diagram time

Black = bore
Blue = amplitude of vibration moving through barrel steel (faster than you'd think)
Red = points where the flex of the barrel is moving fastest
Green = points where the flex of the barrel has slowed and changes direction

 

[b6graham]

your rifle doesn't shoot under 10 for an ES. the same way that the smaller ES/SD bullets wont always have the larger groups. it's just noise and not significant in any way. the same as cherry picking a .1" group to post when in reality the gun shoots 5/8"-3/4" if you took 20 groups and aggregated them together with the same POA

you're likely wasting a lot of time and components trying to find a 'perfect load' before going to distance

once you realize that small sample sizes of chrono data don't mean much you'll enjoy reloading and shooting more

with modern components and reloading gear you really just need to focus on picking a speed you want that's below pressure and go shoot. all the loads are very likely within the same ES/SD/Group size if you shoot enough groups

 

[badassgunworks]

your rifle doesn't shoot under 10 for an ES. the same way that the smaller ES/SD bullets wont always have the larger groups. it's just noise and not significant in any way. the same as cherry picking a .1" group to post when in reality the gun shoots 5/8"-3/4" if you took 20 groups and aggregated them together with the same POA

you're likely wasting a lot of time and components trying to find a 'perfect load' before going to distance

once you realize that small sample sizes of chrono data don't mean much you'll enjoy reloading and shooting more

with modern components and reloading gear you really just need to focus on picking a speed you want that's below pressure and go shoot. all the loads are very likely within the same ES/SD/Group size if you shoot enough groups

True but you can have a large sample size averaging 8- 10 ft per second standard deviation are you can have a large sample size 0-4 ft per second standard deviation. Its all in understanding how to achieve desired end results. just good enough is never good when shooting ELR no amount of quality wind calls solves a problem.

 

[b6graham]

@badassgunworks agreed

but he's shooting a 6CM and mentions 1000y so the definition of ELR isn't quite the same. i'd wager any of his bullet/ES/SD combinations are plenty good enough for what he's doing

this thread would probably be better in the Reloading Depot

 

[badassgunworks]

Agreed and understand. There are so many factors that come into play but these kind of issues one must understand that standard deviation doesn't always equal accuracy and accuracy doesn't always equal quality standard deviation. Who knows the barrel is it even broke in is another Factor. Next question is the barrel even the quality that you can expect the best of both worlds. Sometimes it doesn't always have to do with the manufacturer. I have seen so so companies make phenomenal barrels and I have seen great companies make shity barrels . what quality of thread and chamber job was done. Bedding issues Crown issues. Scope Parallax issues. Shooter fundamentals.

 

[jasent]

What chrono are you using?

 

[babyguppy]

Sort of.

Low ES is critical to long range because even if you were getting super tight groups at 100 yards, the difference in velocity at the muzzle from a large ES results in a vertical dispersion (ex the faster bullets hit high and the slower ones hit lower). When the distances are relatively short, an ES of 75fps won't make much of a difference, but at 1500 yards that's a huge difference in vertical drop. Plug a load into JBM Ballistics and look at the drop at 1500 yards. Then run it again 75fps slower. Notice the difference between the drop of the first and second bullet. At 400 yards it's not a whole lot, but at 1500 it should be significant.

View attachment 7883320
2875fps

View attachment 7883318
2800 fps

HALF A MIL difference from just an ES of 75

As for harmonics, I like to think of it as timing when the bullet leaves the muzzle. The barrel is vibrating as that shockwave is racing up and down the length of the bore. If you look at a sine wave, the peak and trough is where the motion from that vibration is slowing down, hits an inflection point, then speeds back up. The middle of the wave is where the movement of the muzzle is closer to a constant velocity and hitting a maximum speed. Ideally you want to time your bullets so that they leave the muzzle when the vibration amplitude is at its lowest level (at the peak or trough, which are the local max and min values). The vibration pattern varies depending on so many factors, including barrel composition and contour.

Powder change is a coarse adjustment in velocity while seating depth is more of a fine adjustment - at least that's how I've always thought of it. So you find a powder charge that gives you consistent velocity and ideally in the ballpark for where you want POA/POI. Then seating depth adjustments fine tune that load to add/reduce velocity into that sweet spot. Not everyone believes in this philosophy, so don't take it as gospel.

reality sucks. This is the stuff that makes me cry.
weird thing is.. I had two bullets (i know, 2 doesn't mean crap, need at least 5 bullets to perform the same way)
anyways.....
I pulled 2 bullets and reseated; and both were within 2 fps of each other. I was wondering if the neck tension was the reason. Anyways,, I still think about this. Dang, next thing, I'll have to buy a neck tension gauge..etc.. to prove my hypothesis. Lube those necks,,, it does help..

 

[boisepaw]

What chrono are you using?

Magnetospeed

 

[jasent]

Magnetospeed

Are you doing accuracy test at the same time as speed tests?
With a few of my barrels I’ve had the magnetospeed affect harmonics and group size. Not just point impact but grouping as well.
I have also seen loads with 25 es where the faster rounds impact low and the slower impact high making for great groups at distance. Test your loads at distance and you may be surprised

 

[boisepaw]

Are you doing accuracy test at the same time as speed tests?
With a few of my barrels I’ve had the magnetospeed affect harmonics and group size. Not just point impact but grouping as well.
I have also seen loads with 25 es where the faster rounds impact low and the slower impact high making for great groups at distance. Test your loads at distance and you may be surprised

Great question. I will check the accuracy with the Magnetospeed and then shoot a group without. General accuracy seems fairly consistent with and without but indeed POI usually changes.

 

[jasent]

Great question. I will check the accuracy with the Magnetospeed and then shoot a group without. General accuracy seems fairly consistent with and without but indeed POI usually changes.

I used to do load work exclusively with my ms on and take the best es I could. But in a few instances that was not the best load in the rifle for elr. First case of this was shooting at 1500 yards with my 243. My great es load was doing ok and as I finished up for the day I decided to shoot the rest of the rounds left over from load work and found the other load that had greater es but same accuracy at 100 as best es load held better at 1500 than the first (5” vertical compared to 10”) further testing of both loads proved to be true

Since then only a few barrels have had this happen so I now just test at distance to decide loads.

Happy shooting

 

[boisepaw]

I used to do load work exclusively with my ms on and take the best es I could. But in a few instances that was not the best load in the rifle for elr. First case of this was shooting at 1500 yards with my 243. My great es load was doing ok and as I finished up for the day I decided to shoot the rest of the rounds left over from load work and found the other load that had greater es but same accuracy at 100 as best es load held better at 1500 than the first (5” vertical compared to 10”) further testing of both loads proved to be true

Since then only a few barrels have had this happen so I now just test at distance to decide loads.

Happy shooting

So my next question…where do I find your 1500 yard range at which to shoot?

 

[jasent]

It’s a private range in central Washington

 

[Rocketmandb]

So my next question…where do I find your 1500 yard range at which to shoot?

Your screen name has Boise in it. If you're in ID, then you should have a large number of options on BLM land.

 

[boisepaw]

Your screen name has Boise in it. If you're in ID, then you should have a large number of options on BLM land.

Yeah...I could find them 20 minutes away in Idaho...straight south of the airport and into the desert. But I'm the numbnuts who moved from Idaho to Maryland. But it was for a good cause...my grandsons!

 

[Rocketmandb]

Yeah...I could find them 20 minutes away in Idaho...straight south of the airport and into the desert. But I'm the numbnuts who moved from Idaho to Maryland. But it was for a good cause...my grandsons!

Yeah, not much near you - I'm originally from the DC area. However, there is a facility in Central Virginia. It's a bit of a haul for you, but...

https://blackbearsc.com/

 

[Dogtown]

If you're concerned about the Magnetospeed affecting your barrel, try not being such a barbarian and move up to an off-barrel mount:

Magnetospeed Archives

Make sure to check out our Magnetospeed at low prices!. Our Magnetospeed are manufactured using cutting-edge technology and materials right here in the USA.

www.mkmachining.com

Chrono Mount PRO

**Display Holder Optional** Building on years of experience and customer feedback, we've taken everything that was loved about our original Chrono Mount, and made it even better! REPEATABLEEvery hand loader and long range marksman knows, repeatability is a MUST. The Chrono Mount Pro isolates...

www.wiserprecision.com

 

[jasent]

If you're concerned about the Magnetospeed affecting your barrel, try not being such a barbarian and move up to an off-barrel mount:

Magnetospeed Archives

Make sure to check out our Magnetospeed at low prices!. Our Magnetospeed are manufactured using cutting-edge technology and materials right here in the USA.

www.mkmachining.com

Chrono Mount PRO

**Display Holder Optional** Building on years of experience and customer feedback, we've taken everything that was loved about our original Chrono Mount, and made it even better! REPEATABLEEvery hand loader and long range marksman knows, repeatability is a MUST. The Chrono Mount Pro isolates...

www.wiserprecision.com

Hey I resemble that comment