Is there a formula/equation to determine FPS of reduced loads?

[Rule3]

Is there a formula or equation that can be used to determine the velocity of a reduced load?

If a known charge delivers (x) fps is there a way to interpolate (guesstimate) what a 10% reduction in powder would equal?

Say a 110gr bullet goes 1,745 fps with 12 grains, what would 10.8 grains equal in FPS?

No, no chronographs.

 

[Rule3]

Is there a formula or equation that can be used to determine the velocity of a reduced load?

If a known charge delivers (x) fps is there a way to interpolate (guesstimate) what a 10% reduction in powder would equal?

Say a 110gr bullet goes 1,745 fps with 12 grains, what would 10.8 grains equal in FPS?

No, no chronographs.

 

[max]

IMHO no, way too many variables.

 

[38-44HD45]

Here it is: Midway USA Website + Credit Card = Chronograph

 

[Paul5388]

Since powders usually aren't linear in their velocities, it's hard to have a formula. Lee does have some reduced cast bullet load charts, with velocities, in Lee's 2nd Edition of "Modern Reloading".

 

[Sgt Preston]

Sgt Preston here. My Hornady Handbook of Cartridge Reloading (7th edition) charts some of the speed versus load data. For example, they list a 45ACP with a 200 grain lead SWC loaded with WIN 231 powder. They list a base load of 5.2 grains of WIN 231 at 800 FPS, 5.6 grains = 850 FPS, 6.1 grains = 900. They list a MAXIMUM use with caution load of 6.5 grains at 950 FPS. I'm sure their charts are general in nature & depend on the exact bullet shape, the overall length, amount & type of crimp, etc. Using their numbers, you should be able to create a graph to vectorially extrapolate & predict what the speed might be at loads in between those listed. However, one of the most important estimates is what is the minimum amount of powder required to cycle your gun. Hope this helps. Sgt Preston USMC LLA

 

[Guest]

With each firearm doing some Very different things under even very 'slightly different' conditions the only "Real" answer is the Chronograph that has already been suggested. But, with that in "mind" you'll need to be willing to 'Write Your Own Book' if this information is going to do you any good.

 

[Alk8944]

Believe it or not, you can calculate an aproximate velocity easily provided you know precisely what you have noted, chronographed velocity of a specific load and the reduced load weight. Divide the reduced load weight by the chronographed load weight and multiply the result by the original velocity: 10.8/12.0 = .9x1745 = 1570.5 This assumes the new load will be fired in the same firearm the chronographed load was fired. It will be a good aproximation and works whether reducing or increasing the load.

Anyone who doesn't believe this and has a chronograph try it and report your results. If you have never used a chronograph then don't make unfounded statements about a subject you have no knowledge of.

 

[Paul5388]

Lyman's 49th Edition lists a 125 gr bullet with 17.7 gr of 2400 at 1478 fps. They also list 13.0 gr at 1159 fps. Using your "formula", 13.0/17.7=.73446*1478=1085 fps. That's 6% less than the actual velocity, but I suppose it's approximate.

 

[Hook686]

The reduced load calcuator at

http://www.handloads.com/calc/reduced.asp

might be useful for estimating a reduced load. Then chronograph would need be used to determine what the fps really is for that reduced load.

This calculator indicates about 1600 fps for your noted 10.8 grain load (1745 fps with a 12.0 grain charge).

 

[Rule3]

Originally posted by Hook686:
The reduced load calcuator at

http://www.handloads.com/calc/reduced.asp

might be useful for estimating a reduced load. Then chronograph would need be used to determine what the fps really is for that reduced load.

This calculator indicates about 1600 fps for your noted 10.8 grain load (1745 fps with a 12.0 grain charge).

Thank you. The calculator is only about 30 fps different than the equation listed by ALK8944.
So using either is close enough for me. I realize it is not exact but gets me in the ball park.
It doesn't make sense to me to have to actually fire a unknown load to determine the FPS. I would like to know at least a approximate value before shooting it. Useful for shooting plated bullets were there is no published data for plated or lead.

 

[Paul5388]

Yep, I knew it was on Handloads.com, I was just exhibiting how fully CRS (Can't Remember Stuff) has set in.

The address in my signature line will offer quite a few aids in the quest for knowledge, along with some good articles.

 

[primersp]

hello
i have used a logiciel" load-tech" which the data is nearby the velocity that i read in the chrono
a huge variety of podwers and bullets and a adjust of your reload
i don't know if the company is out
regards

 

[Rule3]

Originally posted by primersp:
hello
i have used a logiciel" load-tech" which the data is nearby the velocity that i read in the chrono
a huge variety of podwers and bullets and a adjust of your reload
i don't know if the company is out
regards

Is that a computer program? Not exactly sure what you are referring to?

Paul.
The mind is the first to go and a terrible thing to waste.

 

[jrplourde]

Originally posted by Alk8944:
Believe it or not, you can calculate an aproximate velocity easily provided you know precisely what you have noted, chronographed velocity of a specific load and the reduced load weight. Divide the reduced load weight by the chronographed load weight and multiply the result by the original velocity: 10.8/12.0 = .9x1745 = 1570.5 This assumes the new load will be fired in the same firearm the chronographed load was fired. It will be a good aproximation and works whether reducing or increasing the load.

Absolutely correct approximation. The ratio of velocity/charge is, with proper data, near constant. Simple algebra will predict an increase or decrease in load wt (same powder of course). In short, determine the ratio of the original velocity divided by the charge and multiply that number by the new charge.

bob