Monday, May 11, 2009

80 grain Sierras at 200 yards.

 A three inch group with R11 and a four inch group with Betsy.  The target is a 25 yard pistol bulls-eye.

  Just an excuse to post a photo.  Two groups with two different rifles, both shot out of a rifle rest at 200 yards with a Leupold 16X target scope.  I didn't try to put the groups in the middle, just tried to keep them on the paper.  I held inside the 1 1/2 inch X ring at 200 without any problem.  I estimate holding a 3/4 inch group at 200 yards which would be 3/8 MOA. (Minute of Angle)  I don't hold this well with iron sights, my own eyes and a sling.

  The hold and trigger break were very good on each shot.

  A three inch group at 200 will be a six inch group at 400 and about a eight inch group at 600- minimum.  Environmental effects will factor in to open it up.  The bullet slowing down will open it up.  Any little variance in bullet weight, powder load, case capacity, et, et will open it up.


Anonymous said...

The only way I can get 100 yard accuracy with a scope is to back off the scopes power and use a small orange center (like about 1 inch)then you can cover the orange dot with the crosshairs and you know when your hold is drifting off of dead center (you start to see orange dot instead of black crosshairs).

You also have to be very, very conscious of canting the rifle especially with an AR where the carry handle mount has the scope centered about 4-1/2 inches above the barrel. That alone is very bad for accuracy.

As for the targets in the picture, you should be able to beat that group size with iron sights. Try it to confirm if its the bullets.

Keep in mind that some contend 80 grain bullets do not stabilize any closer than 200 yards from the muzzle. If they did some would probably shoot them from standing.

Old NFO said...

Sigh- EVERYTHING opens up groups, nothing closes them down... story of my life :-)

OrangeNeckInNY said...

You're shooting 80 grain bullets from an AR (15?)? What's caliber and rate of twist?

Random York said...

Hi Robert!
My cousin, Brad Simmons, sent this link to me involving car skeet shooting... you may have seen it.
Have a great day!- Randy

Random York said...

and now for our program....

Robert Langham said...

I've hear that about 80 grain Sierra...but can't figure out how it makes sense. Bullets aren't going to come out unstabilized and get more stabilized past the barrel...even with aerodynamic pressure...not to go to the same place.

Anonymous said...

When thinking about 80 grain bullets, think of a perfectly thrown football (Roger Staubach, hail Mary, the early years). At first it may wobble a bit on its axis but then it 'goes to sleep' it stabilizes and just spins all the rest of the way to the target. That's what 80's are alleged to do. Especially in a 1 in 8 twist barrel. Those that have done the math say that the minimum twist to fully stabilize an 80 is 1 turn in 7.7, Like the Kreiger barrels. 1 in 8 just barely will stabilize an 80 grain Sierra but it takes it some distance to settle all the way down and 'go to sleep'. That is the story at least.

Not sure if anyone other than Norma could tell for sure with their bullet tracking radar. You might take into consideration that Lapua doesnt even make an 80 grain bullet and they'll make almost anything if the money is there, no offense intended. The heaviest they offer is the 77 for about 29 cents each.

Also consider the flash photography pictures of a bullet exiting the barrel. The blast gases exit before and around the emerging bullet which is then still accelerating out of a moving, vibrating barrel and hitting the cooler air outside the barrel. Now do you really think it comes out completely stabilized? One of the reasons for boat-tails on bullets is to slip out of the suction of the gas storm it has to fly thru as it leaves the barrel and retain more of its velocity. It is the perfectly tapered flat smooth base on a matchking bullet not the rough tipped hollow point that is the key to their accuracy. They are going twice the speed of sound you know and then some. Oh yeah and revolving around their axis about 2600 times a second or more. To quote Garth Brooks, "its the dance."

aughtSix said...

Anon, as to the wobble... you might want to read this article:

It's written by Bryan Litz, palma trophy champion, and former air-to-air missile engineer. Basically, with the aid of a 6 DOF ballistic program, he comes to the conclusion that a wobble large enough to create the "going to sleep" phenomenon would result in really big dispersion at all ranges.

Also, 80 grain .223s really aren't near the ragged edge at all. Almost all serious HP competitors shooting the .223 use them at the 600 yard line. (The current NTI champion being a notable exception)