Was going to post something on this a while back, but the method with JBM calculator seemed too convoluted. The other day, cayugad posted a link to this calculator: http://www.handloads.com/calc/index.html


What's great about this one is that it has a total drop calculation. Total drop is the drop from the bore-line. The bore line is determined by where you sights are set and it is line the bullet would travel if there were no gravity. When the muzzle velocity is slower, then the drop is greater, because it takes longer to get to a given range.

Below is load I'm considering for Elk using 410 BB HP. GOAL, be able to keep all my bullets in a 8 " circle at 150 yards.

Let's assume my sighting precision is 2.0 MOAwith open sights.

Let's assume that bullet instability is 1.5 MOA (this is rifle/powder/bullet combination's natural spread with zero velocity distribution) It would be like a machine rest spread where all the muzzle velocities were identical. Bullet instability MOA is a function of range so one can't just keep protracting it out forever.

Lets add them together, 2.0 + 1.5 = 3.5 MOA. So at 150 yards I might expect to keep all my shots in a (3.5 x 1.5) 5.25" inch circle, PROVIDED, my velocity distribution is zero (all my MV's identical)

Of course they won't all be. What is clear, I must keep the velocity component of the spread to less than 2.75" or I won't meet the goal of keeping all the shots in a 8" circle. From the tables below, if I chrono my MV's between 1300 fps and 1375 fps, then the total drop will range from 29.53 and 32.54, a difference of 3.01"or about 2 MOA at 150 yards.The vertical distribution component is range dependent,meaning that the further one goes out, the greater the MOA of the distribution.

Adding the 3.01 inches to the the 5.25" (8.26"), I find I haven't met my goal. In order to achieve it, I must improve my sighting precision or reduce the velocity spread, which are the only two factors I am able tochange. Assuming all the above assumptions true, in the absence of wind, I would find my distribution to form an elliptical shape which is 5.25" wide and 8.26" tall. From a machine rest the shape would be 2.25" wide and 5.26 in" tall.

For those who remember UC's post of a target using the BS conicals. It had a very narrow width and was somewhat tall. The very narrow width was an indication of very good sighting precision and bullet stability. The somewhat tall portion of the pattern was an indication that the velocity distributions were somewhat broad.

Happy Hunting, Phil

First of all, I would get a solid nose bullet....you don't need expansion, penetration is the key.

What is your load? and are you using a 'wad' under the bullet?

More info please!

Pglasgow I must say, your posts amaze me. They make perfect sence, even though you are talking about some seriously complex principles. I learn so much from them that aids me in my shooting. Granted, I don't think I will ever be able to calculate like you can, but I now know that if my groups are narrow and tall, then I need to make my power weights more accurate.

Thanks for todays lesson, I look forward to more!

BS,

My intent about this post was to give folks an easy way to calculate the velocity contribution to vertical spread of their patterns from their chronys. I actually don't plan to hunt out to 150 yards, although I would take immense pleasure in keeping all my rounds at 150 yards in an 8 in pattern with my open sights. The problem is, I have been measuring velocity distributions greater than I posted, so I know that I probably can't without improving the distribution of MV's.

I did plan to use wads or some other gas seal with the BB 410s when I tested them. Part of the reason I considered them was that I hoped I could narrow the velocity distribution with them. In any event, I am getting advice from"every one I know"regarding what bullet/charge combinations should be usedand yours also is welcome.

Happy Hunting, Phil

OK, starting to under stand

Have you tried a hard heavy seat of the bullet, and then, try a softer, or less seating pressure.

I have a 50 with a 1-30 twist that shoots Maxi's quite good with a charge of 115FF.........the groups really tightened when I started using a wad and opened the front diameter up to thegrove diameter. [on the maxi mold]

You also need to maintain a constant fowling in the bore.....very important! Many different ways, justneed to find one that works for you.

I've been seating hard thinking that it leads to more consistent results. What are you doing?

I've got a maxi-mold, a Lee I think from Cabelas, but I don't know what diameter the top band is. I still have some maxi's I poured many years ago with my Dad's smelter, but they are not pure lead. Did you say that your mold's top band diameter was adjustable? or that you modified it be the diameter of your rifle's groove's diameter?

Happy Hunting, Phil

I made a cutter that can be closed up in my TC aluminum mold, it opens the top band to .512 and the middle to .502.

BS,

If you know, what are are the band diameters of the ordinary Maxi-ball? My groove diameter is .510. Land diameter .501.

Your gas seal arrangements are almost identical to those I planned for the 410 BB, the only difference, rather than buying the sub-bases right off, I was planning to use somerecovered Powerbelt skirts or sabots minuspetals, under the wads to see what benefit the plastic contributed over-all. What benefits over the "wad only results" did you see?

I really like the idea of the plastic-wad combination. Thinking the wad will swab the barrel each loading, and the plastic help to prevent powder contamination. I'm looking forward to trying it.

Happy Hunting, Phil

PA Bow/Flinter,

I failed to mention that there is another way to narrow a vertical spread without narrowing the velocity distribution. Increasing the average muzzle velocity will decrease the vertical spread even when the velocity distributionremains wideand is just one of the reasons light bullets and heavy charges are popular.

Some of us enjoy using moderate charges and heavy bullets. For us,velocity distribution can be a considerable hinderance beyond 120 yards.

Happy Hunting, Phil

And once again, you make an excellent point. But for my circumstances...if I can even make a group with my flintlock past 50 yds, I'm happy.