How does a load/rifle go from 1 MOA to 1/2 MOA by INCREASING distance?!

[LocoGringo]

The Rifle:
Bergara B14 Ridge, 7mm-08, 22" factory barrel
Tract Toric 4-20x50
Banish 30 suppressor in 7" configuration

The Load:
Hornady 139 grain SPBT
Remington brass
42 grains Varget
CCI lrp
MV measured at 2700 fps on the dot

Shooting off of a front rest and rear bag, I wanted to get some chronograph numbers for the load with the new suppressor and test the ballistics calculator results with actual distance shooting at 200 yards. I shot 2 5-shot groups at 100 yards and the groups were 1.110" and .872" respectively. I'm relatively happy with those results as this is going to be a deer hunting rifle. I got the numbers from the chronograph, went on to the Hornady ballistics calculator website, plugged them in and got the drop for the scope at 200 yards. I shot 1 5-shot group at 200 yards. This was my first time trying 200 yards for this rifle and the group measured .881". There was a light, consistent breeze, but nothing that I thought strong enough to push the bullet during flight. Well, I had to be wrong about that because while the groups at 100 were about an inch to the left of bullseye, the group at 200 was 3-3.5 inches to the left of bullseye.

Same shooter, same ammo, same day, same conditions. I understand it's a small sample size, but how does the gun (or shooter) go from 1 MOA at 100 to 1/2 MOA at 200? Oh, just so I'm clear, I'm NOT complaining, but puzzled.

 

[JeffG]

In some load/rifle combinations, I have experienced this. My theory is, the bullet "goes to sleep" and reaches a stasis of spin that is more consistent than when first fired. In the same token, at 300 yards, some of the loads revert back and show the more expected group sizes, or larger.

 

[LocoGringo]

In some load/rifle combinations, I have experienced this. My theory is, the bullet "goes to sleep" and reaches a stasis of spin that is more consistent than when first fired. In the same token, at 300 yards, some of the loads revert back and show the more expected group sizes, or larger.

Can that happen over longer ranges...going in and out? For example, it may shoot great at 300, but get to 400 and it's not as good, but improves at 500...talking about long range shooting with a .308 custom rifle and load, not this hunting rifle.

 

[Blue68f100]

Normally the first couple of 100 yrds a bullets is trying to stabilize from being disrupted when it left the end of the barrel. Flat base bullets will stabilize quicker at shorter distances. BT bullets can take several 100 yrds to stabilize. It's my under standing is once it stabilized it's good till its disrupted. This can be going to sub sonic, or even a different wind current. Higher the BC on the bullet the more likely it's going to resist disturbances.

As far as wind, that's one thing you really need to know all the way to the target. It can be different directions and velocity many times before reaching the target. One way may help you the other hurt you. Those that can read wind have a big advantage when it gets to shooting long range. Just like shooting up or down hill the drop is going to be different at the same range.

 

[AJC1]

I think the key is in the amount of left. You should run a ballistics calculator to see if that is a change in wind, I think it is. Otherwise your scope and bore may be off axis.

 

[AJC1]

Hornaday calculator says 10 mph wind with data provided was .8 at 100 and 3.2 for 200 so that matches. With 139 Interlock at 2700.

 

[z7]

Bullets don’t “go to sleep” but shooter’s relax and just shoot, and often better

When you see your group developing, many folks, myself included, start thinking about how it’s shaping up, and that causes us to do certain things for better or worse

Sounds like a nice rifle and a good load though.

For the op, did you see the group at 200 while shooting it and think “that is really small”?

I wager you saw the group but didn’t really think about it much, and just shot

 

[JeffG]

Can that happen over longer ranges...going in and out? For example, it may shoot great at 300, but get to 400 and it's not as good, but improves at 500...talking about long range shooting with a .308 custom rifle and load, not this hunting rifle.

There are a lot of factors at play, your suppressor axis, wind, barrel harmonics and rate of twist to the bullet used. The best test may be to shoot at those ranges, suppressor off and on, and look at the groups.

 

[JeffG]

Bullets don’t “go to sleep” but shooter’s relax and just shoot, and often better

An old school term referring to bullets stabilizing some distance to the muzzle.

 

[LocoGringo]

For the op, did you see the group at 200 while shooting it and think “that is really small”?

I wager you saw the group but didn’t really think about it much, and just shot

Actually, no, I didn't see the group. It was way left and I wasn't expecting it there. I figured the holes were too small to see at 200 and just shot, let the shots land where they may, and I'd see when I was finished. I also wasn't sure if the ballistic calculator was correct with the elevation, so I wasn't sure where to look...if I was shooting high, low or wherever. The ballistics calculator was dead on for elevation and I was pleasantly surprised by that. I'll edit with the photos of the targets at 100 and 200.

 

[sparkyv]

If these were my results, I'd most assuredly want more samples before I accept them.

I understand it's a small sample size

 

[JerkyFreak]

Your sample size is a tad small...

Just like normal shooters can shoot a 1/4" 5-shot group and then a 1" group 10 minutes apart. We only hear about the 1/4" group.

Next time load 40 rounds and shoot a 20 round group at each distance. Or 4 5-round groups at each. Then your data might mean something.

There has been a lot if anecdotes about this phenomenon, but it is always small samples and not repeatable. The maths and computer simulations also show that it is not possible. Well, not the last time I read about it at least.

 

[LocoGringo]

Your sample size is a tad small...

Just like normal shooters can shoot a 1/4" 5-shot group and then a 1" group 10 minutes apart. We only hear about the 1/4" group.

Next time load 40 rounds and shoot a 20 round group at each distance. Or 4 5-round groups at each. Then your data might mean something.

There has been a lot if anecdotes about this phenomenon, but it is always small samples and not repeatable. The maths and computer simulations also show that it is not possible. Well, not the last time I read about it at least.

Yeah, I acknowledged it was small.

To do what you suggest, I'm gonna need a lot more brass. I'm waiting on an annealer to change .308 brass to 7mm-08.

 

[Soupy44]

I'm betting human element is the major factor here. Even off bags we can easily mess things up!

 

[JFrank]

Actually, no, I didn't see the group. It was way left and I wasn't expecting it there. I figured the holes were too small to see at 200 and just shot, let the shots land where they may, and I'd see when I was finished. I also wasn't sure if the ballistic calculator was correct with the elevation, so I wasn't sure where to look...if I was shooting high, low or wherever. The ballistics calculator was dead on for elevation and I was pleasantly surprised by that. I'll edit with the photos of the targets at 100 and 200.

Nice shooting, it looks like the wind might have blown your 200 yard group together and perhaps the opposite at 100 yards.
There is no sleeping bullets just wind. tune and table manners.

 

[MarshallDodge]

Another thing to look at is parallax. You may have it adjusted correctly at 200 and not so much at 100.

Bryan Litz, Berger's Head Ballistician, said he will pay the plane ticket if you can come to his place and prove that bullets go to sleep.

 

[Pivot Dr]

Yeah, I acknowledged it was small.

To do what you suggest, I'm gonna need a lot more brass. I'm waiting on an annealer to change .308 brass to 7mm-08.

You don’t need to anneal to form 308 to 7-08, I’ve been forming 7-08, 260, 243, and a one of .224 wildcat with out annealing for nigh on to 60 years. 308 to 7-08 is childs play! Lube them up and run them through your 7-08 sizer, done. Just for S&Gs I’ve formed 22-250 and 22 Br from 308 too. I did anneal some and made special forming dies for those though.

 

[sparkyv]

All this effort chasing down tiny groups is what makes this hobby so interesting and enjoyable, isn't it? ...reminds me of Captain Quint in Jaws...gonna need a bigger boat.

I'm gonna need a lot more brass. I'm waiting on an annealer to change .308 brass to 7mm-08.

 

[WisBorn]

@LocoGringo congratulations on the nice groups.
I have seen that the MOA doesn't always correlate. My 7rm shoots 1 1/4" groups out of its pencil weight barrel. At 200 it is less than 2". I remember reading an article in a gun magazine about 25 years ago where the writer was trying to explain this with a theory about bullets stabilizing. And specifically mentioned that 7mm bullets will take longer to stabilize . It was an interesting theory

 

[Krogen]

I won't try to explain it, because I can't But, with a number of rifles I've found it easier to shoot 1/2 MOA groups at 500 yds than it is at 100 yds. This is comparing apples to apples at both distances; the same rifle and ammo. Not the same conditions, though. Since I've seen this on many different occasions I'll disregard the difference in conditions. With that said, I have some rifles/loads that shoot well at 100 yds, but fall apart at 500 yds.

 

[z7]

An old school term referring to bullets stabilizing some distance to the muzzle.

I am familiar with the term, I have seen a good deal of discussion on the topic and it seems to me that most of the effect we see is often a reduction in shooter error and not improved bullet flight

I may be wrong but i would wager that the op has a pretty accurate combo and happened to lay down an excellent 200 yd group and that the load is probably 3/4 Moa capable but most shooters, a huge majority of shooters are not as accurate as our guns (myself included)