Help on sighting in

Your riflings aren't quite right for your bullets. Try something lighter.

 

I believe 45 grain is the lightest.

 

You can buy any weight from 40-80 grain bullets for 223. Most of them you have to reload but it will help you.

 

1:8 twist is pretty fast and you should, be able to stabilize bullets up to a weight of 80 grains. American Eagle isn't exactly target ammo. I'd try something in a quality 68gr match or hunting load. The 1:8 twist barrels I've used always seem to like 68 grainers.

Black Hills 68 Gr Heavy Match loads in their "blue box" reloads are usually very accurate, but kind of pricey. Federal hunting loads have worked well also, as well as Winchester Power Points in 64gr.

 

My bad I read 1:6 riflings. Ya heavier bullets are alot better for them grooves.

 

Also if you zero at 50 yds, you should be about an inch and a half high at 100yds, close to 2 inches high at 150 yds, and about three quarters of an inch high at 200 yds and at 250 yds you would be at about an inch and a half low. (Using 55gr FMJ)

If you are using a carbine barrel you may see a bit more drop because of lost velocity, when compared to a 20" barrel.

 

1:6 is even faster. Most AR barrels come in 1:12, or 1:9, 1:8, 1:7, or 1:7.7. Some 1:10 twists and other odd balls out there as well. Original twist rate when the M-16 was being developed was the very slow twist rate of 1:14.

 

Ribbs,

First of all if you are zeroed at 100 yards with the 55 gr. American Eagle rounds FMJs you should automatically have about 2.7-3.0 inch drop at 200 yards. I am going to continue but understand that my thoughts are not to challenge your ability at all but to try to dissect the problem.
First have you benched the rifle and used bags or a support to sight it in from the rest at 100. Your rifle should be able to get at least 1.5 MOA (Inch) groups at 100 yards with the American Eagle ammunition. Of course if the group is an inch and a half spread at 100 it will be magnified at 200 way more than twice the spread. As far as 5 inches off at 200 lets think about the WIND! That realy effects the 223 round. If you have a 10 mile an hour full value (Cross wind at 90 Degrees) it will move the round off to the opposite side of the wind around 2 to 2 1/2 inches at 100 yards. So imagine what the effects of the wind at 200. 5 inches as you mentioned is nothing if you consider the wind mentioned. That might put that to rest? As far as the 8 inches low unfortunately that is not the fact that your rifle has the 1 in 8 twist. It would not effect it that much. In fact a 1 in 8 although they like slightly heavier rounds best seemingly would not have a drop of 8 inches. I would suggest you bench or support the rifle on a solid surface and bags at 200 to check and do it on a calm day. Things like trigger pull, breathing and a slight flinch could cause drastic results at 200. You will know if you bench it and practice good trigger pull and do not breathe when pulling the trigger. If the rifle is shooting great at 100 there is no problem with the ammunition or your rifle. Oh by the way are you using a scope or optic that could have some parallax problems. The delayed breathing technique when pulling the trigger to shoot is called the natural pause! Just suggestions and good luck.
All the above information is pending the good performance at 100 yards!
03

 

how did you zero? 100 yards? 50? 25?

are your rounds keyholing?

 

Ribs...lots of good thoughts here. One other, how experienced are you? Shooting 250+ yards is an order of magnitude harder than 100-150. As stated, every minor error you make on trigger pull, breathing, sighting, etc is really magnified at higher ranges. Wind and bullet weight become important as well.

 

As Doc posted zero 2"+ AT 100 YDS. This will give you a point blank to 250 yds. When you zero at 100 yards all rounds will fall below the parabolic line of trajectory beyond the 100 yd. mark. The line of sight should be high at 100 yds.

 

This is very true. Or you can zero at 50 yards which will keep you within 2.5" of POA from 0 to about 250 yards.

 

First, I'd get some good factory ammunition and see how your groups look, and then worry about sighting in. I doubt there's anything wrong with your barrel, and 1:8 should be fine with 55 grain ammo.