Different grains in 9mm ammo = big difference in shooting?

[Canuck44]

That is why it is called perceived recoil. For a given PF, the total recoil force applied is identical regardless of bullet weight. That is physics, Newton's Second Law of Motion to be specific.

However because the recoil is distributed over a longer time, your hand/arm/body, can "absorb" and "control" the recoil better. Result is the gun feels and is more controllable.

Well not quite. You are forgetting the effect of powder charge weight and the amount of gases ejected which all factor in to the amount of recoil produced. Newton applies and your statement would be true IF it took the same amount of powder to achieve the same PF with bullets of different weight. It doesn't.

Take Care

Bob

 

[BCRider]

It is the difference in the rate of ACCELERATION of the mass of the bullet that makes the difference in PERCEIVED recoil. Even when the muzzle energy is the same.

Nohing perceived about it. Ther simply is less recoil at the same power factor ie Bullet weight x Velocity. If you load three bullets weighing 115, 125 and 147 grains all at the same power factor of say 130 recoil as evidenced by muzzle flip and felt recoil will be the most with the lightest bullet and the least with the heavier bullet.

Take Care

Bob

Um... you guys just said the same thing but in different ways.

 

[BCRider]

Bob, you're right that it takes different amounts of powder for each of the 3 bullets to reach the same power factor. In my own recent cases 4.0 gns of Bullseye behind 124 TMJ's gave me very nearly the same PF as 3.8 gns behind the 147TMJ. A very match actually allowing for the velocity spread range I'm getting.

But part of that is due to the PF being an imperfect way to compare bullet energy and part is due to the 147 being a longer bullet and when sitting back a little to compensate it reduces the case volume so there's a little more initial pressure or faster pressure rise before the bullet gets moving too far.

 

[SandRoad]

Well not quite. You are forgetting the effect of powder charge weight and the amount of gases ejected which all factor in to the amount of recoil produced. Newton applies and your statement would be true IF it took the same amount of powder to achieve the same PF with bullets of different weight. It doesn't.

Yes, but the difference is only a couple %, nothing that you would notice. I have calculated it below, using fairly wide ranging values for the powder charges.

I ......PF..Wb...Vb..Wc..Vc

0.68 130 115 1130 8 3000
0.66 130 124 1048 6 3000
0.63 130 147 .884 4 3000

I = (Wb*Vb + Wc*Vc)/225400

Where:
I = recoil impulse, lb.-sec.
PF = Power Factor
Wb = bullet weight, grains
Vb = muzzle velocity of bullet, f.p.s.
Wc = weight of powder charge, grains
Vc = velocity of powder gases, f.p.s. (3,000 in these calcs.)
225400 = unit correction factor (7000 gr./lb.*32.2 f.p.s.2)

http://www.loadammo.com/Topics/August01.htm

 

[BCRider]

I'm still trying to zero in on hitting the 130PF consistently but so far the difference between the impulses of 0.66 for the 124 and the 0.63 for the 147's seems to be greater than the simple 7.5% difference would indicate. I'm doing some more chrono and load accuracy testing later this week so I'll be able to confirm this "feel" a little better.

 

[SandRoad]

But part of that is due to the PF being an imperfect way to compare bullet energy and part is due to the 147 being a longer bullet and when sitting back a little to compensate it reduces the case volume so there's a little more initial pressure or faster pressure rise before the bullet gets moving too far.

That is not really correct. The pressure and case volume have nothing to do with bullet ENERGY when it leaves the muzzle.

But the internal ballistics does have everything to do with HOW the bullet gets moving.

Bullet weight, case volume, powder characteristics, etc, etc, and the resulting pressure curve, and velocity, are complicated relationships. If you really want to understand it, then study the Appendix of the QuickLoad manual (quiz next week ). You will not really understand it if you just read it. The manual is included when you download the free QuickLoad demo.

 

[SandRoad]

I'm still trying to zero in on hitting the 130PF consistently but so far the difference between the impulses of 0.66 for the 124 and the 0.63 for the 147's seems to be greater than the simple 7.5% difference would indicate. I'm doing some more chrono and load accuracy testing later this week so I'll be able to confirm this "feel" a little better.

I set that table up in a spreadsheet, and it calculates the velocity backward from the PF, and the values shown in the table above are rounded.

PM me your email and I will send the spreadsheet. Note that the spread in weight of the powder charges I used are exaggerated which accounts for the high difference in impulse recoil values.

When the powder difference between the 124 and 147 is only 0.2 gr the difference in impulse recoil is 0.003 or 0.5%

 

[Canuck44]

Yes, but the difference is only a couple %, nothing that you would notice. I have calculated it below, using fairly wide ranging values for the powder charges.

I ......PF..Wb...Vb..Wc..Vc

0.68 130 115 1130 8 3000
0.66 130 124 1048 6 3000
0.63 130 147 .884 4 3000

I = (Wb*Vb + Wc*Vc)/225400

Where:
I = recoil impulse, lb.-sec.
PF = Power Factor
Wb = bullet weight, grains
Vb = muzzle velocity of bullet, f.p.s.
Wc = weight of powder charge, grains
Vc = velocity of powder gases, f.p.s. (3,000 in these calcs.)
225400 = unit correction factor (7000 gr./lb.*32.2 f.p.s.2)

http://www.loadammo.com/Topics/August01.htm

What you haven't calculated is the energy in ft lbs of recoil. Gen. Hatcher, who I will differ to states the energy of the recoil of a gun is equal to 1/2 the mass of the gun times teh square of the recoil velocity. He uses 32.2 as the acceleration of gravity.

In his book he calculates the recoil energy of a 9MM 125 gr bullet travelling 1040 ft per sec out of a 31/3oz gun to be 3.1 ft lbs. This was achieved using 4 gr of unnamed powder.

It has been 40 years since I played with Physics so I'll leave it to you to calculate what the result would be using 115 and 147 gr bullets. I think once you are done you will notice a wider variance in ft lbs of energy then your calculations suggest.

Take Care

Bob

 

[Zephram]

I just got back from the range where I fired off 100 rounds of the LE Winchester Ranger 147gr FMJ. This ammo is the bomb. I was shooting extremely tight groups with it out of a Beretta M9A1 and I think its my new favorite load, except I stopped by the gun shop on the way to the range to pick up some targets and they were sold out of the Ranger. I hope they get more, that stuff is awesome! I have fired 115gr, 124gr and 147gr and didn't notice any difference in recoil either.