Velocity vs Bullet Wt vs Powder Load

MJL

MJL

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We started loading .40 S&W and we are working up a load to shoot IPSC Major. In the process of putting all the chrono data into a spreadsheet, I notice that for a constant muzzle velocity, the amount of powder goes DOWN as the weight of the bullet goes UP :confused: Checked the Lyman book and shows the same effect.

This is counter-intuitive - at first glance you would expect larger mass requires larger PUNCH to get it up to speed .....

Any ideas?

MJL
 
A larger bulet wants to remain stationary and will allow a smaller charge to build up more pressure before the bullet moves.

Um, hate to be a nanny, but, if you are already at the "loading for major" stage, shouldn't you have read the first part of that manual you are using?

Really, there is a wealth of useful knowledge in almost every reloading manual that you should read before you start throwing powder. IMHO.
 
True, there is TONS of info in the books ( I have Lymans Pistol and Revolver handbook, as well as a .40S&W specific handbook) both of which are chock full of appropriate cautions, tips, and tables. Nothing I have read (yet) talks about the combustion physics behind what we are doing.

Dunno - maybe it is the scientist in me, but I prefer to understand from first principles, as opposed to memorising rules without understanding why ! ;)
 
I would have said that muzzle velocity is not a constant. As soon as bullet weight goes up, velocity drops.
I'll take another look at my manuals, but that's what happens with rifle cartridges.
 
Code: 
Caliber: .30-06 Springfield					
Brass: Winchester					
Primer: Winchester WLR					
Powder: H-4350					
Firearm: Ruger 77R					

Bullet	Powder	Vel.	Press.	Energy	
Weight	Weight	FPS	PSI	Lbs.Ft.	
240	50.8	2401	58K	3072	
220	50.8	2402	50K	2820	
200	50.6	2403	43K	2565	
190	50.4	2402	40K	2435	
180	50.4	2401	38K	2304	
175	50.4	2402	36K	2242	
168	50.5	2403	34K	2154	
165	50.6	2401	34K	2113	
155	50.6	2401	31K	1985	
150	50.6	2403	30K	1924	
					
All bullets were Sierra HPBT

With bullet weights from 150 grains to 240 grains, and maintaining essentially the same powder load, velocity does not change. However, the pressure generated drops.

If I wanted to maintain the 58K PSI pressure with the 150 grain bullet it would have required 62.8 grains of powder (really compressed), and would have resulted in a velocity of 3025 FPS and an energy of 3047 Lbs.Ft.
 
I believe the problems lies with the concept of how all of this happens. Remember we are dealing with pressure and not an an explosive.

The process of building pressure is not a constant of powder.

Heavier bullet will allow for the a smaller load of powder to build more pressure. Its the resistance if you wish of the volume. As the powder is ignited it will build pressure, the primer will move back out of the case, the case will expand to tightly squeeze the wall and the bullet will start its journey. With a heavier bullet the bullet will not move forward with the same velocity and it will not start at the same time as the its lighter counterpart. The pressure will increase thus giving you a a higher velocity at the end of the barrel.

ITS IS VERY IMPORTANT THAT YOU DO NOT SUBSTITUE BULLETS .

The same powder load with a heavier bullet can give you very disastrous results.

This is my verbose explaination, but both Hornaday and Lee handloader manual explain it very well.

READ

TG
 
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