.308 ballistics question

[BigBore45]

It's the ammo. I have about 500 rounds of freedom munitions left from a Christmas gift and it is junk. Half the time I see bullet setback and it's diry and slow to boot. I hate shooting it. Mine is .223 rem. It sucks I can't wait to be rid of it and reload the brass.

 

[Llama Bob]

What dial is that?

That's a very good question...

 

[RecoilRob]

I think you'd have better luck zero'ing at 200 yds then just accepting whatever it does at 100. The problem is do you know if the bullet is rising or falling at 100? I'd think it should still be rising to then hit somewhere downrange again as having two zero's with an AR is pretty much the way I think they should be set up.

If the bullet is flat at 100...it'll certainly do nothing but drop farther out at 200, but if you set it so the bullet is still rising at 100...then the drops to 200 will likely more closely match what the calculators are saying. Try zero'ing at 200 then see where it is back at 100 and I believe you'll then know what's up.

 

[HRnightmare]

With most 5.56 loads

It is an AR10 in .308 not 5.56

 

[HRnightmare]

I might buy one to get into this long range thing more accurately.

I vote for a lack of velocity as the problem. Do you know any body with a chronograph?

 

[JDGray]

When you say supporting with your weak arm, are you shooting off hand?? 2.5" at 100 yards off hand is great shooting!! I have a Rainier match barrel on my AR10, and it shoots sub moa pretty easy, but thats off a bipod and a rear bag.

 

[No4Mk1*]

When sighting in so close and using a calculator, you need to get the sight height correct. It magnifies downrange error if you enter bad data. Also in my opinion a 100 yard zero is the worst possible zero unless you ONLY shoot at 100. A more distant zero even if only 170 yards vastly improves your downrange "hold over" at very little cost at 100yds.

 

[carpboy]

Another vote for starting over fresh with some 168gr HPBT Match loads. I ran into the same situation when shooting my Savage 308_bolt rifle over the weekend. I was shooting my go-to load of American Eagle 168gr HPBT Match ammo with great results, landing 1.5" high at 100yds.This load runs at 2600fps according to factory specs.I then switched to a 175gr HPBT NATO load from Miwall.I fired 3 rounds and looked thru my spotting scope and could not see where the shots landed.Frustrated,I took another shot and looked again, but could not spot where the shots were landing. When I walked out to my target I could see that the shots were landing 6" below POA on the cardboard. Aha! An underpowered, anemic load I sez!The box this ammo came in did not have any ballistic specs on it so I had to search when I got home.Standard 175gr HPBT loads run at 2550fps.I don't think this load was running near that fast.I wanted to try some Nosler 165gr Accubonds I had stashed, but I decided to call it a day.

 

[Trent]

Actually I am glad you mentioned this because I am curious as well. All I know is that the other guys on the long distance sight in range who at the sound and look of it had been doing this for a while and certainly knew how to "talk the talk" and use the proper terminology were either being polite or seemed at least slightly impressed at my targets.

Given the groupings I described: (soda can circumference grouping at 100yds and 1gal bleach jug circumference at 200yds) what would you say about them? Ok, great, terrible? (I have thick skin). I just have no frame of reference to compare to.

I realize after leaving I did not do so many things I should have. Instead I took an identical target and measured approx. distance with my hand and held high on my next shots. Obviously if I find myself in a tree blind I cannot accurately measure what 6" is as accurate when it is an unfamiliar target. I did not attempt to make adjustments to the scope to see if I could adjust it to be dead on at 200yds because I was nervous and afraid I would not be able to re-zero to 100. I also did not take note of exactly where when aiming high my crosshairs met. Nerves and not thinking on anything other than :should this be happening" got the best of me.

Ok... stop and move back a pace or two.

No one has talked to you about parallax yet, or what a dramatic effect it can have on shot placement at different ranges if your cheek weld is minutely different from one shot to the next.

With optics and most 308 pattern AR rifles on the market today, from the bench, with bags, you should be getting a group that can (roughly) be covered by a silver dollar at 100 yards, if you are doing your part, with good ammo. If you are getting soda-can diameter groups, something is amiss, somewhere.

(Unless you are shooting standing unsupported, then carry on, you're doing great...)

If something is amiss, you have to determine whether it's ammo, optics, or the meat-bag behind the shoulder stock

Ammo is easy to change, and can result in dramatic differences in groups. Make sure to shoot 5 (or better, 10) rounds when testing as 3 doesn't really give you enough data to draw any realistic conclusions from. This is expensive if you are talking premium 308 ammo. (start reloading!)

As far as optics, let's back up a smidge and get back to basics.

Your scope - does it have parallax adjustment? Do you know how to check and adjust parallax?

If you get a sight picture and move your head around slightly (be on bags or a sled for this), if your CROSSHAIRS and TARGET move around separately from one another, your parallax is out of whack. If you are center, and crosshair is center on the target, and you move your head slightly up, down, left, or right and your crosshair moves OFF the center of the target - even MINUTELY - your parallax setting needs adjusted. The crosshair and target should appear on the same visual plane and the crosshair should always be aligned with the target no matter how off kilter you move your eyeball. (Note you'll still want to strive to keep your eye dead center in the scope's visual range with no black arcs visible on the periphery, for best results)

If the target and crosshair do not move together on the same visual plane during this test, then every single time you shoulder the rifle you'll get a different point of impact as your cheek weld is different every time (even if you are REALLY good at shooting.. it happens). WORSE, every time you change shooting position (standing, bench, kneeling, sitting, prone), your group will move to a new spot on the target! Guaranteed!

So parallax - this changes with DISTANCE, so you have to reset it when you move from 50, to 100, to 200, to xxx yards, so that your target is on the same visual plane as the crosshairs.

So, step 1, learn where your parallax adjustment is and how to use it, if your scope does not have one... buy a better scope and trade that one in. Make sure the eye relief matches what is comfortable for YOU for what position(s) you will be shooting. Different positions will almost always require different eye relief distances on optics, so variable power scopes that you can dial different powers on, which will inherently change eye relief, are great for positional shooting (note parallax also changes when you adjust objective power! don't forget to reset it if you dial from 6x to 24x). High quality fixed scopes with a wide eye relief range (distance from lens to eyeball), are pretty valuable and worth the extra cash, as it opens up a wider range of option for you to shoot different positions.

Moving on to step 2 - shooting fundamentals. What position(s) are you shooting from? You mentioned prone is a problem, that's fine, shooting from sitting position with a good 1903 (M1907) loop sling is way more accurate than shooting prone with a goofy bipod anyway.

So step 2, get and learn to use a sling.

Back to the 'drop' at XXX yards question, well, 6" drop for a 308 round from 100-200 yard move is very unusual, which is why I skipped that and went in to parallax / etc.

(worth mentioning; when I give advice I don't know the persons' knowledge or experience, nor that of others who may read it afterwards, so if anything sounds condescending or offensive to your level of knowledge just remember I speak to the lowest common denominator who may read the thread at some future date; not directed specifically at you, and not trying to be rude in any way shape or form)