Home Forums Hunting & Shooting AR and Tactical Rifles 6.8 Ballistic puzzle

I have a 6.8spc upper with a Wilson barrel. It wears a Zeiss Victory 1.5-6 in an LT-104 Mount. I am shooting 95 grain TTSX over 30 grains of Benchmark out of this 16 inch barrel. The barrel and load are zeroed at 50 yards. The first round out of a cold barrel can hit a pecan on top of a fence post, it appears to be consistent day after day shooting 1 round into the same target over weeks and months in the same spot. After about the 3rd round it opens up to about 2 inches for 5 or more when shooting off the bags at 100 yards., but once zeroed i just check zero over the season on the same target. I shot at a buck at 163 yards today and put the cross wire on his shoulder about 4 inches below his spine resting the rifle on the magazine on the padded shooting rail. Buck ran, no blood, no deer. I went back to my truck and got a gallon bottle of water with a blue label in the center of the jug put it at the spot the deer was and climbed back into the stand and fired one round. The bullet I hit the bottle about 4-5 inches above my point of aim. Took the top of the jug off. The ballistic table says the bullet should be about 2 inches low at that point? The only difference is that on the stand I am shooting off the magazine and on the bench rest I am putting the KMR rail on the bag and putting my head down on the stock! I went ahead and made a negative 4 cm adjustment in the scope, but I have no idea what is going on except maybe the rest is different. Anyone got any ideas??

well, I guess I am the only one that has had a POI change with a different shooting position or rest! Let's see I was shooting left handed out of the stand while I normally shoot right handed off the bags, so left eye vs right eye for zeroing the scope, the scope's parallax is set to 109 yards, distance was a lasered 163.5 yards..

Trying to solve problems on the net is guesswork at best.

Guess #1, rail hitting gas block under pressure.

Guess #2, your ballistic table wasn't confirmed and maybe off.

Sounds like you hit the deer too high for the lungs & too low for the spine. I know that's anatomically impossible, but I've seen a lot of deer hit in that area run & evade recovery. I guess it just doesn't do enough damage to the lungs.

Or maybe you hit a twig. The POI change is a possibility too.

This^^^^^^^^^^^

You didn't confirm POI by shooting at any ranges longer than 50; the shot on the jug was 5" high; you were planning for 2"+ of drop; some amount of down angle................it's conceivable you shot over it's back.

Just guessing of course.................

MM

Best place to solve this puzzle is at the range.

Test you POI from a rest, then off the magazine. I'd do it at a variety of distances, and shoot some groups at 150 to 200 yards with this rig. Find out what you really have.

Yup. Yet another example why some of us keep saying not to rely on a near zero, you gotta confirm it at distance. Most prefer to ignore that advice though, with results as shown in the OP.

If you want to use a near and far zero, then zero your rifle at the far zero, and figure out where your near zero is from there. Plenty of people do it the other way around, but that is the lazy way and has a lot of potential for error.

Almost a dead solid certainty for a significant error using a near zero & shooting long w/o confirming & resetting zero at the longer range.

MM

I had a KMR rail that was touching the gas block and I think he has one as well. Being the KMR doesn't have much room and flexes awful easy, that was my first guess.

But I've seen many times when someone was off maybe a 1/4" at 50 and nowhere near on at 200 with a 5.56.

I shoot 1 round at 50 almost every time I go to the property, however the rifle is zeroed at 100. Its consistent in how it behaves. The bullets hit in almost the same place at 50 and 100 within my margin of error. I am wondering how big a difference shooting off the magazine makes now. Perhaps it is just me, as I was shooting left handed resting the magazine on a padded rail.

The plot thickens, eh?......................

And truthfully, I think you have too many variables (all negative) going on that it's not possible to say what happened with any kind of certainty.


MM

Several years ago I watched a hunting partner shoot a buck at 200 yards. I was in a stand about 300 yards from him, and saw the impact of the bullet, as well as hearing it hit. The buck took off and ran into the woods. He thought he missed, and wasn't even going to look for sign of a hit. I kept insisting that I knew the deer was hit, even though we found no blood, and the deer had run a long ways across a field.

To make a long story short, we found the buck just inside the woods. He never left a drop of blood that we could find. Could your der have done the same? Maybe, maybe not, who knows. I have had misses that I could never explain, and even after shooting the rifle off the bench, couldn't find anything wrong with it. Strange things can sometimes happen.

If you can't tell the difference in POI between 50 and 100 yards, you sure can't count on a 50 yard zero being correct at longer distance. The error in your zero doesn't add up, it multiplies at distance.

the ballistic chart says 0.1 inches I think difference at 100 and 50 with a 1.7 inch high scope mount, and this is within the margin of error that I see.

2 things about that Jimmy:

- If this is on an AR, your scope height is a lot more than 1.7". More like 2.6-2.7" depending on your mount.
- If you're zeroed (truly zeroed) at 100, you should be ~1/2" - 3/4" low at 50 yd depending on the load.

If your ballistic table is predicting 0.1" difference, that's part of your problem because it's way off. Gotta make sure those inputs are right to get somewhat realistic numbers, but even then you can't trust them until you verify with actual shooting.

With that said, ~1.75" low at 163 yards should be about right, but if your "zero" isn't actually zeroed but off by 3/4" at 50 yards, that accounts for several inches difference right there. Combine that with differences in your shooting platform, and errors start to add up fast.

As far as shooting off the magazine, we shot some drills mostly offhand except for the first shot allowed arms on a bench while kneeling at 200 yards, second shot was prone off the magazine at 100, sitting at 75, kneeling at 50 and standing at 25 with 223/5.56 and there was not enough difference across the board to miss the vitals of a deer much less the whole deer.

Something is wrong and as Yondering said, your scope is centered 2.7" above the bore with a LaRue SPR mount. I'd start by sighting in at 200 yards dead on then work your way in noting POI at each distance.

sorry about the sight height, was not thinking when I wrote. The bullet is supposed to be about 2 inches low by 175 yards if zero is 100 either way. I need to shoot the gun at 200 yards off a bag from a bench rest.

For deer, I'd just zero at 200. You should then be point-blank out to 250 or so.

I'm not sure why you tried to spine it. If you had aimed dead center of chest, that gives you about 8-10 inches of error to play with. In your case, being it was shooting high, you would have spined him. If it had been shooting low, you would take out his heart.

It was user error plus maybe some parallax.

Me and my son shooting our AR at the range. same everything. I held the handguarg and rested my hand on the rest. Dead center bout an inch high at 50 yds. He rested the rifle on the rest bout 3 inches high 3 inches right.
at first I thought it was the sight but when I noticed how he was letting the rest hold the handguard I told him to do it my way.
Dead center bout an inch high. So how the rifle is held/rested does affect POI.

Yep and I was shooting left handed as well, as I cannot get turned around far enough in that stand to fire the rifle from my normal side.

I did not read the replies.

I never trust computed data. ONLY trust it how far you've shot it on paper. You owe that to the game, so you don't screw it up like this one.

As to impacts vs rests, again years of shooting will show that positions and tensions on rifles affect impact. Same but actually more so with handguns for us at least.
So if we shoot off bipod, we zero off bipods. If we pull the bipod off(weight) I rezero...

We shoot them left and right handed, and a few times from loose to snug to see if and how impact changes.

With all that said I've done the same once, with a 6/6.8. Perfect rest, chip shot , about 120 or so, everything good, gun was floated and shot very well. Never found deer or blood. Or nipped limb or anything. Did a LOT of looking, no way I should have missed. Went and shot the gun at a feed bag, hit a dime size target very next shot out of the gun. What can I say, I figure I somehow missed. Maybe you didnt' screw the deer up, maybe you just missed for whatever reason.

FWIW for us though, 100 yard zero with an AR to a 160 yard shot would never lead us to aim at the spine like you did. Too much chance of going over, or hitting over the spine, that shot would have been half up the side of the deer for us, and I suspect you'd also have had a dead one.

But get out there and shoot. Thats the ONLY way.

Agreed, and want to add to that - some guys seem to think the spine of a deer is a lot higher than it really is; what seems like a "spine shot" to some is really just hair, skin, and maybe a little meat at the top of the back. jimmyp that's not necessarily directed at you, you might be an expert on deer anatomy for all I know, I've just seen some guys make that mistake in the past.

I was about 4 inches down his shoulder (I thought) at least that is where I was aiming.

4 inches down is about where the CNS spinal cord is, if not even a hair further. Have to remember you have layer of hide and hair, tissue, the full depth of the backstraps, and then the center of the spine. I never attempt to aim for impact more than 1/3 of the way up.

YMMV. I'd rather burn em low, than make nasty burger high to get infected possibly later.

well it was a bad shot one way or the other, I have not had good luck with that 6.8spc, killed a big doe with it and she was right on top of me so naturally I shot lower down into her shoulder than I wanted. Not much time to hunt left this year, so I will be carrying my 257 roberts, with 117 grain hornady's over H4350 it does a good job from near to far.

If you put the shot from the 257 in the same place as the 6.8 you'll have the same. IMHO.

Obviously the point there is know the gun.

When we started out years ago, we didn't really realize that. Now we know. Heck the zeros for our 300/221 sub/suppressed start at 25 and are different every 25 yards out to 200 yards with the 194s. Some are close enough, but still they are different come ups or downs.

Most of the time you make your own luck.

Wishing you the best of good luck!