Faster or slower powder to flatten trajectory

[Larry Gibson]

"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."

The problem is that big "IF" because "all else" will not be equal. Given the OPs load is with Unique in his .308 boosting the velocity of his 160 gr cast bullet to 2000 fps (to flatten the trajectory....his quest) the time/pressure curve and high psi generated will result in poor accuracy. The slower burning powder is needed with its slower time/pressure curve and probable lower psi to maintain accuracy with the cast bullet. An "equal" trajectory is meaningless if accuracy is lost. Look at the Load data in Lyman's CBH; with a 160cast bullet Unique max's out at 1646 fps. It's not until 4759, 4227, 5744 and 4198 are used that velocities reach 2000 fps. The reason for that is as I have mentioned.

Larry Gibson

[Taterhead]

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

He is, although the domain, "lbtmoulds.com" is not active. LBTmolds.com will get you there. I got a mold from Veral earlier this year.

[Petrol & Powder]

Can we agree that the factor that changes the trajectory is the velocity and not the powder used to obtain that velocity ?

The OP's question was incomplete. The question should have been, "Can a slower powder be used to increase the velocity and flatten the trajectory?" The answer to that is an unequivocal YES.

[Larry Gibson]

Petrol and Powder

"Can we agree that the factor that changes the trajectory is the velocity"

Certainly, we already are in agreement on that. Where it appears you disagree is you concurred with "what happens in the barrel is not part of the equation" . I stated "what happens in the barrel is indeed part of the equation". In the barrel is where the velocity is increased "to flatten the trajectory"..........we can agree we agree on that...yes?

Really, there is no disagreement here, you are saying the same thing I am just using different words and phraseology.

Larry Gibson

[Petrol & Powder]

We can agree on that.

[Whitespider]

Larry, it seems like you're splittin' a non-existent hair here.
Trajectory is a function of exterior ballistics... what happens inside the barrel is interior ballistics.

In my post that you originally responded to I specifically said... "Boolit velocity is the only thing that will change trajectory (assuming everything else remains constant)... the burning rate of the propellent won't."

Everything else remaining constant includes the boolit's velocity at muzzle exit. It wouldn't matter for sour owl squat what the burn rate of the propellant was, or what the rate of boolit acceleration inside the barrel was... trajectory will be the same if exit velocity is the same. You brought up the accuracy thing, and I agree that the propellant burn rate can have an effect on accuracy... but the OP's question was not about accuracy (which is terminal ballistics, a different animal from external or internal).

So let me split a hair...
Technically, it is not boolit velocity that effects trajectory to a given point down range... it is the boolit's time of flight that does. Launch two boolits of equal mass (or, more correctly, sectional density) with different ballistic coefficients at the exact same velocity and the boolit with the more streamlined coefficient will have a flatter trajectory... because it's time of flight is shorter, it arrives on target sooner and with a bit higher retained velocity. Trajectory is the effect of gravity on the boolit over a specific period of time... (technically) it has nothing to do velocity.

This is exactly why I said... "(assuming everything else remains constant)" in my original post.
If... IF... everything else remains constant, the only way to flatten trajectory is to reduce the boolit's time of flight, accomplished by an increase of muzzle velocity (because everything else remains constant). What happens in side the barrel is not part of the trajectory equation... it wouldn't matter for sour owl squat if I used Bullseye, 2400, 4831, or FFG if the (same) boolit exits the muzzle at the same velocity, trajectory will be the same.
*

[abunaitoo]

Thanks for the link.
I had the old link bookmarked, and it didn't show.
New address works.
I'll order the book from him.

He is, although the domain, "lbtmoulds.com" is not active. LBTmolds.com will get you there. I got a mold from Veral earlier this year.

[abunaitoo]

That's what I should have asked.
Just didn't know how to say it.
I'll try some slower, slower powder than I've already tried.

Can we agree that the factor that changes the trajectory is the velocity and not the powder used to obtain that velocity ?

The OP's question was incomplete. The question should have been, "Can a slower powder be used to increase the velocity and flatten the trajectory?" The answer to that is an unequivocal YES.

[Larry Gibson]

Larry, it seems like you're splittin' a non-existent hair here.
Trajectory is a function of exterior ballistics... what happens inside the barrel is interior ballistics*

Keep in mind that while I did disagree with you the substance of my post was answering the OPs question.

Not splitting any hair at all. I just disagreed with your statement that what happens inside the barrel isn't part of the equation. What happens inside the barrel is part of he equation as I explained in post #8 and, more importantly, is pertinent to the OPs question. I'm sure some will find your dissertation on exterior ballistics enlightening. However, since we obviously all agree the way to flatten the trajectory is to increase velocity let us ponder where that increase in velocity actually happens. So if you would please answer one simple question for us; Where is it do we increase the velocity, inside the barrel (interior ballistics) or outside the barrel (exterior ballistics)?

If you answer correctly then we will be in agreement that what happens inside the barrel is part of the equation ergo all else is not equal as I explained to Petrol & Powder. The OP was using Unique under the 160 gr cast bullet. He needs to use a slower burning powder to sufficiently increase the velocity to flatten the trajectory for his desired same 50 and 100 yard point of impact. Using more Unique powder will not get him there.

Larry Gibson

[abunaitoo]

If I'm getting this correct, a slower powder, pushing the boolet faster, would increase the speed, so it would shoot flatter.
Up to the point that the boolet is being pushed to fast, for it's shape and hardness.
Correct????

[Whitespider]

If I'm getting this correct, a slower powder, pushing the boolet faster, would increase the speed, so it would shoot flatter.
Up to the point that the boolet is being pushed to fast, for it's shape and hardness.
Correct????

Pushing the boolit faster would decrease time of flight to the target, which would result in a flatter trajectory.
Whether-or-not you need to use a slower propellent depends on your current load pressure/velocity verses how much more velocity is required to accomplish your goal. Whether-or-not your goal is obtainable depends on a lot more than just simple velocity... with boolit profile and alloy hardness being only two of those things.

You haven't given much detail about your load... we know it's a 160 boolit (we don't know the boolit profile or the alloy used)... we know you're using Unique (but we don't know at what pressure/velocity level)... and we know the boolit trajectory is not flat enough for your requirements (but we don't know exactly how much POI drops between 50 and 100 yards, and we don't know exactly what would satisfy your requirements).

So... going on the limited, generalized information you've given... I can give a generalized answer that increasing boolit muzzle velocity will flatten trajectory. However, there ain't enough information to conclude that a propellent change is required to accomplish what you want... or even if what you want is obtainable.

When working up a load I find it best to first set specific, realistic goals (such as velocity, ballistic uniformity, and accuracy), and work specifically towards those goals... if you don't know where you're going, how do you know when you get there??
Once those initial goals have been achieved I can set new, more narrowly defined goals to "fine tune" the load... but again, if you don't know where you're going.......??
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[abunaitoo]

Here's what I'm going to try....
Unique 12.0 to 13.0. 1700 to 1800 FPS (my best guess)
IMR4198 22.5 to 24.0. 1900 to 2200 FPS.
I'm hoping the slower powder will push the boolet out softer, rather than kicking it out hard.
Just playing with it.
My reason for cast boolets is to cut down on the cost of shooting.
With the amount of IMR4198 powder used, it may not soot my wants and needs.
This is interesting and fun.

[buckshotshoey]

Here's what I'm going to try....
Unique 12.0 to 13.0. 1700 to 1800 FPS (my best guess)
IMR4198 22.5 to 24.0. 1900 to 2200 FPS.
I'm hoping the slower powder will push the boolet out softer, rather than kicking it out hard.
Just playing with it.
My reason for cast boolets is to cut down on the cost of shooting.
With the amount of IMR4198 powder used, it may not soot my wants and needs.
This is interesting and fun.

Need to know a few things. What is your primary usage. Hunting? Paper punching? Steel plate?

What is the maximum range you intend to shoot?

If you are sacrificing a little trajectory for good accuracy, I would stick with it and just adjust the sights for various ranges. Are you shooting a gas check design? If not, increasing velocity could make accuracy worse.

If the load is really accurate, raising the sight is very repeatable. You might find it was the best option all along.

As for the load shooting dead on at 50, and 3 inches left at 100....is it still a small group?

[abunaitoo]

Used only for paper punching. Club matches.
Maximum is 100yds.
I may just end up moving the sight. Just want to see if it can be done with cast.
At 50yds, center aim 2" groups. sometimes less.
At 100yds, if I move the sight, 4" group. If I don't move the sight it shoots 9" low. both 3" to the left.
All with open sights, off the bench.
I know it will shoot better than I can see.

[Cap'n Morgan]

If you just want the rifle to be dead-on at 50 and 100 it can be done by altering the height of the sight line over the bore line. Fairly easy with a scope, but a little more complicated with metallic sights. If muzzle velocity is known, most ballistic programs can interpolate the needed sight height.

[Tom Myers]

If you just want the rifle to be dead-on at 50 and 100 it can be done by altering the height of the sight line over the bore line. Fairly easy with a scope, but a little more complicated with metallic sights. If muzzle velocity is known, most ballistic programs can interpolate the needed sight height.

Cap'n Morgan.

Yep, you nailed it. I have bee waiting for the "posting problems" to get fixed to display load and trajectory images that will answer abunaitoo's original question.

There are three basic changes to a load that can affect the distance between sight zero ranges.

In a decending order of effectiveness, they are:

1. Firearm sight height (most effective)

2. Bullet velocity (effective)

3. Bullet ballistic coefficient (minimally effective)

All three of these may be manipulated to achieve the O.P.'s original requirements and still remain within the parameters of cast bullet limitations although a muzzle velocity sufficient to maintain cast bullet integrity may be difficult achieve

I load for my SOL's 308 Remington 742 with a scope mounted on see thru mounts with a scope height of 2.2 inches

The barrel sights may also be used with a front sight height of 0.941

The enclosed images are of calculations that visualize the needed parameters and are not the results of actual load and target testing.

The first image displays a barrel sight setting chart using the Lyman 311466 Bullet with a BC of 0.241 and a MV of 1700 fps with a front sight height of 0.80 inches.
Load is 14.5 grains of IMR 4227 with a MV of 1700 fps and the barrel sights zeroed at 100 yards.
The bullet strikes 1.4" high at 50 yards.

The point blank range calculations are residuals and apply only to the calculations of the 2125 fps trajectory.


The second image shows the sight settings using the scope on the see thru mounts. and the same load as with the barrel sight settings.
The bullet now strikes 0.70" high at 50 yards.




The third image shows the bullet velocity increased to a velocity of 2125 fps using a charge of 27.7 grains of IMR 3031
The bullet should now be zeroed at both 50 and 100 yards.



Using a bullet with a higher BC only marginally decreases the muzzle velocity necessary to achieve the 50/100 yard zero.

Hope this helps.

[DougGuy]

Why all the pistol powders in a rifle cartridge? My 308 comes to life with 4895.

[abunaitoo]

Why all the pistol powders in a rifle cartridge? My 308 comes to life with 4895.

Cheap to reload. Way less powder.
Only punching paper at 100yds.
Don't need all the power.

[abunaitoo]

Well the IMR4198 worked OK.
Still not POA at 50 and 100yds.
But getting closer.
I had a BOOBOO and seated a 115gr Carbine Boolet in one round.
Fired it off at 50yds and it did good.
I'm going to go back to Unique and try the 115ge Boolets in place of the 160gr.
Less weight might help it shoot flatter.

[abunaitoo]

Light 115gr boolets didn't work as well as I hoped.
Good at 50yds, but not consistent at 100yds.
Also didn't hit much higher at 100yds.
I'll keep at it.