Anyone else have doubts about the tables...
I am shooting a 139 grain SST from my Ruger #1 in 280 at 3000 fps. The BC of the bullet is listed by Hornady at .486, according to the Sierra manual- a BC of .48 at 3000 fps is listed as the following:
Zeroed at 200
6.6 inches drop at 300
19.? drop at 400
Here is the deal- with my setup with a 200 yard zero- a buddy and I were shooting today at a 100LB propane cylinder CAP- just the 6 x 3 inch cap that protects the valve. I have it hanging from a chain and we put it on the fence at 350 yards (laser range finder). I was holding over by 1/2 a cap- or about 3 inches- and was hitting it right in the middle- about 6 inches below my aiming point. According to the Sierra manual- I should have been holding over by about 12 inches. I realize the numerous variables involved- but I don't feel that I will need to raise another 13 inches to cover the last 50 yards from 350 to 400.
I will be doing a lot of 400 to 500 yard shooting- but not for another month- when spring finally gets here, and was wondering if anyone else has done testing like this.

I have had similar results myself but found out what I believe is at least somewhat of an explination.
I was just reading about Swift Siroccos shooting flatter than ballistic tables say they should. In studying these tables you find out that the actual shape of the ogive will drastically change the result. There may be a lot more to it than I could ever begin to relay in a message posting format. The drag coefficient is critical.

My thoughts were the same- better the BC than the computers can project accurately. It will just take some real world shooting at longer ranges to determine my rate of drop. I knew others had looked at this data and were questioning it.

Was your load at 3000fps chronoed or quoted from the book? gj.

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www.moaammo.com

Well, you have hit upon exactly why a guy needs to take his gun out and test it at different ranges rather than believe printed data from Sierra or anyone else.

There are SO many variables involved. Are you really getting 3000 fps, did you chronograph the load? What elevation are you shooting at? Maybe the new SST bullets are really better than they say. Look at some of Rick Jaminson's writings in Shooting Times, he finds a lot of variance in Ballistic Coefficient of the same bullets when fired in different rifles.

I CAN tell you that my buddy and I have checked Sierra's data against several of our rifles at measured ranges out to 500 meters and found them to be VERY close to what we experienced. We used to compete in what was called a Varmint Silhoutte match from 200 to 500 meters with our 22-250's and 6mm's. We found that Sierra's data was very, very close to what we were seeing at those ranges.

Just keep testing and record what you are getting so you know what to expect in the field.

R Flowers

Yes the load was cronographed- 15 shots averaged about 3015 fps.
I live in the middle of the lower pennisula here in Michigan. I believe the elevation is about 755 feet.
I firmly believe in recording my own data and then comparing it to the manuals. I looked up the data in my Speer manual and it also is very close to the Sierra data. Real world testing will commence when the weather breaks, and I'm not freezing after a couple hours.

I found the article I was thinking of when I posted earlier. It was Rick Jamesons' in Shooting Times, April of this year. His reasoning was backed up by balistitions (sp?) at two different companies. The ogive shape used for the ballistic tables is actually quite a bit blunter than the modern design of say the SST, Nosler BT , or Sicroccos. Drop needs to be checked by actually shooting the load at the max distance you plan to shoot. I even noticed a slight variance in the results of shooting 140gr. GameKings out of my 7mm to what the tables indicated they would do. Just thought you might like to read the article as it shows in detail his comparisons to books in actual shooting.

I would suggest that you go to the JMB website. http://www.cybermesa.com/~jbm/ballistics/traj/traj.html It will allow you to imput all the variables, air temp, barometric pressure, altitude, windspeed, ect. I have found that most bullets are pretty close to what the published data states once all the weather has been accounted for. Matter of fact I found their numbers (BC) for the 135MK in 27cal to be spot on, usind the JBM program, out to 900yds. Took down the numbers for the area I was shooting in and made three different charts for different temps and the elevation was dead on. Windage was a little off but then I was only guestimating on actual windspeed.

[This message has been edited by txhunter (edited 03-27-2002).]

I have fround that the serria tables to be very close. Good enough to get you with in inches of where you should be minor ajustment for each rifle is common.

Jamison's article also states that most programs do not use the proper drag coefficient for VLD projectiles. Dr.280 go back to your "SSts not as accutrate" post and look at the shadow graph I linked to from antoher post on long range ballistics ...shows the affect of a cannelure..which may be beneficial who knows.