I have someone that I know who has a DPMS .308 AR. I am going to be teaching him how to use it. He has a scope on it. I would assume that the come-ups/trajectory would be similar to an M1A or Garand but he has stockpiled 180 grain ammo. Does anyone have any info on this? Specificly if it was zeroed at 25 meters, what would that put you out to? 200 meters like 150 grain ammo or would it be less since it is heavier.
What velocity does he have them loaded at?
The trajectory of a bullet will change with the weight of the bullet and the velocity.
Also twist rate might be an issue, but I think the DPMS stock twist rate is 1:10 with ought to work fine with a 180gr.
If you know the ballistic coefficient of the bullet, muzzle velocity, projectile weight, and the distance from the center of the bore to the center of the scope (sight height) you can find lots of free calculators on the web that will give you the info you're after.
Here's basic info from my calculator for 180gn .308 win You mileage may vary as there are a lot of variable that go into the equation, but at least this should give you an idea:
25m 0
50m +1.11
75m +1.93
100m +2.38
150m +2.06
200m 0
250m -3.97
300m -10.05
350m -18.46
400m -29.46
450m -43.32
500m -60.37
If you've got him zero'ed and shooting well at 25m then back out to 200m and get some real world data.. it should be close. Then you can go to 100, 300, 400, etc make adjustments, take notes and then keep the data with the rifle so you always have it. IMHO, nothing can replace real data for your rifle and your ammo.
HTH
According to iSnipe (an IPhone app)
Winchester 180gr powerpoint has a BC of .248 mv of 2620
using a 2.5" sight height and a 25M zero -
100 yds -4.27MOA
200 yds -2.22 MOA
300 yds +1.37MOA
400 yds +6.18MOA
500 yds +12.39 MOA
Yes. Nothing beat real world data. I just wasn't sure what 180 grain ammo would do out of it and I wanted to get the maximum use out of a day at the range. I am pretty sure of what 150-168 grain would do as I have used those out of my M1A's.
Anyone have a recommended program for calculating trajectories?
Thanks y'all
I have the same iphone app that lprgcfrank has. I'd just picked a different cartridge the data I posted... and I think my sight height was 1.6"
If you have an iPhone, iSnipe is definitely worth the $6 (or so) because you have it in your pocket and take it with you everywhere you go. You can pick from a wide variety of factory loads or input your own data and get calculations (and save them too) I basically use it like you're thinking DwayneH. Just enough knowledge to get me in the ballpark and get real data from there.
I had to actually look up on google what an iphone and an app were. I'd still be using windows 95 if that computer hadn't died last year.
Quote from: DwayneH on December 04, 2009, 06:55:26 PM
I had to actually look up on google what an iphone and an app were. I'd still be using windows 95 if that computer hadn't died last year.
DwayneH - don't feel bad about not knowing what an iphone and an app are - I've been working in the information technology world since 1982 so I'm almost up to what my kids know O0
My home club runs 2 rifle refresher's a month and I use the iSnipe app to help out folks get their rifles zeroed for the distance they intend to shoot - I tell them if you think this is cool - come to an Appleseed and we'll teach you to shoot that rifle now that it's zeroed -
I'm amazed how many rifle owners don't know IMC and how it's like magic to them.....
The velocity would be impacted by what length barrel it has. Those DPMSs come in 16, 18, 20, and 24 inches.
http://www.frfrogspad.com/extbal.htm
I found this this morning and having been eating it up. It has a good explanation of external ballistics