5.56 ammo question

[ejfalvo]

New Sig 556, went to the range today with 2 brands of ammo. Generic white box 55g and Olin Penetrator 55g. Shot 100 yards with iron sights on 8in "dirty bird" targets off a bipod. Generic ammo grouped in an orange-sized group. The Olin looked more like I wasnt aiming at all-placement all over the target. I wasn't aware that ammo could be so different. Shot the generic first.

Anyone else have this type of extreme experience with different brands of ammo?

 

[a-sheepdog]

Alot of those types of issues are caused by quality control issues at the ammo factory. Some rifles are finicky, but in my experience, not usually the AR style rifles. Find what yours likes and go that direction. We had alot of issues with the Remington ball ammo out of our rifles. Alot of misfires and fail to fires. Maybe it was just a bad lot, but it is still quality control problems in my opinion.

 

[5whiskey]

I haven't even heard of olin penetrator. I don't know if that's a super premium brand or a super cheap brand. Is generic the name of the company? At any rate, I would size most oranges at 3-4 inches. If you're only holding that @ 100 yards you're behind the power curve. Try some decent ammo for a few rounds. In any somewhat decent AR you should hold 2 moa with decent ammo.

Also, I don't know if the forearm is free floating or not. If it is NOT, you can post some wildly sporadic groups using a bipod because you have upward pressure on the barrel. Otherwise, with no pressure on the barrel or in a "free float" situation, you should be able to hold 2 moa with cheap surplus ammo. At least that's what I've noticed with wolf and brown bear. YMMV.

 

[PMROY]

Are you talking about the 5.56mm(62)FMJ, M855 Penetrator? I know that on the single, 20 round box, the back bottom has OLIN and its address?

 

[Al Thompson]

Oh yeah. It's usually not so extreme, but it happens. I've seen several very accurate rifles fling bullets in patterns when fed chow they didn't like.

5Whisky, 2 MOA groups at 100 yard with iron sights are pretty good.

 

[ejfalvo]

Yes its the Olin 62 Penetrator. The generic stuff is by Pavi (I think). I returned the Olin and dealer gave me more of the generic. Ill run thru this lot and see if I can find quality ammo. I live in way northern NJ and 5.56 is hard to come by.

As far as accuracy, I have no problem believing that with quality ammo this Sig will be very accurate. I was using the BUIS, the little flip down rear site on the Sig and with these old eyes, it was difficult to get a clear sight. I've ordered the Sig diopter as well as the Burris AR-332 - that should really make a big difference.

Thanks for all the advice.

 

[IndianaBoy]

The SS109 bullets used to load 'penetrator' or M855 ammo is known for not being particularly accurate.

It is difficult to assemble the bullet with the steel penetrator perfectly concentric.

My AR groups pretty well with it, but it is probably more an issue of the particular lot of ammo, not your rifle. I have a bunch of '93 production British milsurp from Radway Green.

 

[sohlman]

I am new to THR so please excuse me if I am stepping on anyone’s toes.

I think you would get better accuracy by using a heavier bullet say 69 grain or more when shooting the Sig 556 rifle with 1:7 twist. I think I got the specs right on your Sig.

The reason that I am suggesting that is that the .223 (5.56) rifles usually have 1 of 3 different twist rates. 1:7 Mil-Spec, 1:8 usually Stainless Steel barrels, and 1:9 in commercial barrels. Each bullet has an optimal twist rate based on its length and diameter, To determine the optimal twist rate of a bullet we use the Greenhill formula.
Basically what the formula tells us is that the smaller bullets 60 grains or less will perform better in the 1:9 twist and 69 grains and above work better in the 1:7 twist.
The Olin 62 grain would work better in the 1:8 twist.

Shooting the lighter bullets in a 1:7 twist barrel will cause the bullet to over spin and go wild or centrifugal force will tear the thinner jackets apart .Using a heavy bullet in the 1:9 twist will not spin the bullet fast enough to stabilize it and it will tumble making a key hole shapes in the target or it will just go wild.

 

[no.5enfield]

"Shooting the lighter bullets in a 1:7 twist barrel will cause the bullet to over spin and go wild or centrifugal force will tear the thinner jackets apart .Using a heavy bullet in the 1:9 twist will not spin the bullet fast enough to stabilize it and it will tumble making a key hole shapes in the target or it will just go wild."

I've heard this for a long time from many different sources, but have yet to see an actual shooting test that proves it. Of course every rifle has a bullet it prefers but I don't think accuracy will drop drastically with 15gr difference. have a 1:9 barrel that shoots 55 and 69gr equally well(around 2-3moa with a reddot). My rifle isn't a freak because I've observed other ARs with the same barrel perform similarly. If anyone has a link to an actual comparison of barrel twist to bullet weight please let me know.

BTW Sohlman, Glad to have you here and I'm not ragging on your post, just wondering if this is an old wive's tale that we have all been taken by.

 

[CZguy]

sohlman,

Welcome to the high road. That was a well thought out first post.

 

[sohlman]

Thanks for welcoming me to the discussion

Here is a link that discusses twist rate in more detail.

http://www.loadammo.com/Topics/July01.htm

I started reloading Ammo about 20 years ago and it is amazing how such little things can make a drastic difference of a bullet preformance. even guns from the same manufacturer may have a different bullet that it prefers. you have to keep trying different combinations until you find the perfect round for your gun.

 

[briansmithwins]

Both my 1/7 barreled ARs will hold under 2.5MOA with either PPU 55gr or 55gr XM193. 50gr thin jacked varmint bullets are within 2" of the 55gr POI at 100 yards. They did not disintegrate when I shot them either.

My rifles like the 75gr PPU much better as I get 1.25-1.5MOA when using those.

Buy some samples and go shooting. Figure out what works best for you and then buy a couple thousand rounds. BSW

 

[arizona98tj]

5Whisky, 2 MOA groups at 100 yard with iron sights are pretty good.

Totally agree! And I always thought that the standard rule of thumb for a "rifleman" @ 100 yds was 4MOA. At least that is what the Appleseed course qualifies you at....and not that many folks shoot 4MOA with iron sights. I guess they are all too old and their eyes are all used up.

5Whisy,
While my .223 788 holds sub-MOA groups @ 100 yds, I would be tickled pink if I could keep it @ 2MOA after I removed the optics.

 

[no.5enfield]

"not that many folks shoot 4MOA with iron sights"

Arizona, you must be spending too much time on other gun boards! It seems like I'm always reading about somebody shooting .5moa with their iron sighted .30-30 or mosin!