Faster or slower powder to flatten trajectory

[abunaitoo]

I'm trying to work a load, for a .308 with a 160gr boolet, that will shoot point of aim at 50yds and 100yds.
I get the best accuracy with Unique so far.
I have to raise the sight to go from 50yds to 100yds.
I've tried Blue dot, 2400, 700x before.
700x is faster and Blue dot , 2400 slower.
Any ideas on whether a faster or slower powder would flatted out the trajectory????
Condom bullets can be pushed fast enough to use the same sight setting at 50yds and 100yds.
Is it to much to ask a cast boolet to do the same?????

[Wayne Smith]

For close range/longer range it's more knowing where the boolit crosses the line of sight going up and where it crosses the line of sight going down. For a lot of rounds the first is around 25 yards and the second is around 100 yards. If you truly want to flatten trajectory you have to increase velocity. Check your load books to see what options you have.

[tsubaki]

Out of curiosity, what length barrel we talking about?
It probably won't make much difference in rifle length barrels.
If you were talking about Contender length barrels then it might be different.

[JSnover]

How high do you have to go to get back on zero at 100 and what is your max expected range? It seems more practical to zero @ 100 and get to know your trajectory from 25 to 125, 150, etc.
Iron sights are generally so close to the bore centerline that with a 50 yard zero you might need a lot more speed to get it to 100 before gravity starts laughing at you.

[Whitespider]

Boolit velocity is the only thing that will change trajectory (assuming everything else remains constant)... the burning rate of the propellent won't.
Projectile trajectory begins the instant the boolit exits the muzzle... what happens inside the barrel is not part of the equation.
*

[JonB_in_Glencoe]

SNIP...

Condom bullets can be pushed fast enough to use the same sight setting at 50yds and 100yds.
Is it to much to ask a cast boolet to do the same?????

Have you read Veral's book, "JACKETED PERFORMANCE WITH CAST BULLETS"

SNIP...
Faster or slower powder to flatten trajectory

The short answer is a slower powder.

[Petrol & Powder]

boolit velocity is the only thing that will change trajectory (assuming everything else remains constant)... The burning rate of the propellent won't.
Projectile trajectory begins the instant the boolit exits the muzzle... What happens inside the barrel is not part of the equation.
*

/\ this /\

[Larry Gibson]

What happens inside the barrel is indeed part of the equation.

To flatten he trajectory from 50 to 100 yards you have to, as mentioned, increase velocity. Increasing the velocity by increasing the charge of Unique probably isn't gong to gain you much as the time/pressure curve will be rather sharp. I suggest using 2400, 4227 or 4198 with a dacron filler and look for a velocity of 1950 - 2000 fps......maybe a bit higher if your 308W has a 12" twist instead of a 10" twist barrel.

Given a scope height of 1.5" above the bore, 2000 fps and zeroed at 100 yards the center of a 50 yard group will hit .52" above the point of aim. Zeroed at 50 yards the enter of the group will hit 1.05" low at 100 yards. If you don't want to change the zero hen a better zero would be 75 yards with the 50 yard point of impact being .12" high ad the 100 yard point of impact being .8" low.

Larry Gibson

[abunaitoo]

It's a 2A enfield. Barrel is 25".
Have to move the site on whole number up from 50yds to 100yds.
Zero at 100dys and aim low at 50yds will not work. Need to aim almost one target down.
Forgot to post that the hits at 50yds are dead on center, at 100yds they are 3" to the left.
Always wanted a copy of "JACKETED PERFORMANCE WITH CAST BULLETS", could never find one for a reasonable price.
I'll try IMR4198 and see what happens.

[osteodoc08]

Just need higher velocity for flatter trajectory. Using a slower powder GENERALLY will yield higher velocity, but it's all relative. Too slow a powder will not burn completely and will yield lower velocity.

You cant have your cake and eat it too with velocity, trajectory and recoil.

[Petrol & Powder]

Larry, I must disagree.

What happens inside the barrel affects the acceleration of the projectile while it's in the barrel. However, once that projectile leaves the barrel that influence is over. After the projectile leaves the barrel the acceleration stops and whatever velocity was imparted to the projectile will be the maximum velocity of the projectile. It will only slow down after that point.
The trajectory of the bullet will be determined by factors in place at that instant in time. The primary factors at that point are: The angle of the barrel relative to the surface of the earth, the velocity of the bullet at that point in time (its initial muzzle velocity), the rate at which the bullet slows (which is determined by several factors such as the density of the air and the ballistic coefficient of the projectile) and whether or not the bullet is acted upon by some other force (strikes something but doesn't come to a stop).

[waksupi]

Look at some trajectory charts. For any appreciable increase in flat trajectory, you need to add 300 fps to your current load.

[JonB_in_Glencoe]

It's a 2A enfield. Barrel is 25".
Have to move the site on whole number up from 50yds to 100yds.
Zero at 100dys and aim low at 50yds will not work. Need to aim almost one target down.
Forgot to post that the hits at 50yds are dead on center, at 100yds they are 3" to the left.
Always wanted a copy of "JACKETED PERFORMANCE WITH CAST BULLETS", could never find one for a reasonable price.
I'll try IMR4198 and see what happens.

While lots of books can be had at garage sale prices, I will acknowledge that this ain't one of them, but $25 that goes directly to Veral, via his LBT website seems reasonable to me.

[JSnover]

OR... Just a thought... try a lower velocity. You'll have to raise your sight for 50 yards and let the boolit drop back to zero at 100.

[JSnover]

If you don't want to change the zero hen a better zero would be 75 yards with the 50 yard point of impact being .12" high ad the 100 yard point of impact being .8" low.

Larry Gibson

I don't know if he's shooting iron or a scope but +.12" and -.8" seems plenty close to 'dead-on' for most purposes.

[abunaitoo]

Is LBT still around????
I checked for the book on the web, and the site came back closed down.
Shooting open sights off the bench.

[Maven]

abunaitoo, Here's an active link: http://www.lbtmolds.com/books.shtml

[Larry Gibson]

Petrol & Powder

Your disagreement is noted. However, I was answering the OP's question; "Any ideas on whether a faster or slower powder would flatted out the trajectory????"

You are correct; "What happens inside the barrel affects the acceleration of the projectile"...... thus to flatten the trajectory the bullet must be accelerated faster. The use of a slower burning powder than Unique to increase the velocity of his 160 gr cast bullet is what the OP needs to use to flatten the trajectory. Because it is only by increasing the velocity can the trajectory be flattened. That answers the OPs question.

The last paragraph of my above post addresses all the issues of trajectory you raise. Additionally that paragraph provides he OP, or others, with useful practical information on better zeroing to realize the OPs objective of having the point of impact being close at 50 and 100 yards.

Larry Gibson

[Petrol & Powder]

Larry, I agree but it is not the faster or slower powder that produces the difference in trajectory but rather the change in velocity that produces that change.
So, going all the way back to the OP's question: "....Any ideas on whether a faster or slower powder would flatted out the trajectory???? "
It isn't the powder that changes the trajectory but rather the velocity. Now, clearly some powders will produce better velocities while staying within acceptable pressures.

If ALL else is equal (barrel, bullet, angle of barrel) and two different powders produce EXACTLY the same muzzle velocity - the trajectories will be similar. Let's say a small charge of a fast powder produces a muzzle velocity of 2000 fps from a 22" barrel and a larger charge of a slower powder produces 2000 fps with the same barrel and bullet - the acceleration within the barrel may be different but the resulting trajectory will be the same. The fast powder may accelerate the bullet to that 2000 fps in the first 16" of the barrel and the slower powder may use the entire 22" of barrel to reach that speed but as long as the same bullet exits the same barrel at the same final velocity; the trajectories will be similar.

[WebMonkey]

The Nikon spot on app is great for mapping trajectory given projectile specs and velocity.