Opinions on 115 vs 124 gr 9mm

[Noodle]

http://www.chuckhawks.com/ammo_by_anonymous.htm

Some interesting comments about 9mm ammo in the above article. Totally down on 147 grain...

[Hunter Rose]

http://www.chuckhawks.com/ammo_by_anonymous.htm

Some interesting comments about 9mm ammo in the above article. Totally down on 147 grain...

That article's been around for years. Not really accurate and based on old data/conclusions before Winchester Ranger T, Federal HST, Speer Gold Dots, etc. were around.

[okie john]

http://www.chuckhawks.com/ammo_by_anonymous.htm

Chuck Hawks can safely be ignored.


Okie John

[Raven Armament]

115 ammo... Most of it is also not manufactured to rigerous standards. The fact that it has less powder, lead, and QC is probably why it is cheaper.

Sorry, but no.

115gr ammunition is manufactured to the same quality standard of other weight bullets. Bullet weight has no effect on the assembling quality of a cartridge.

115gr ammunition will also have more powder than heavier bullet ammunition. A 115gr round has up to 7gr of powder whereas the 147gr round has up to 5gr of powder. So, no it doesn't have to do with [b]less[/] powder and nothing to do with quality control.

Material cost is, however, a noted factor in the bullet cost. Difference between 115gr and 124gr is 9gr, so very little, but it's 23gr difference between the 124gr and 147gr that makes it enough to alter the price.

So does anyone out there know some physics? Shouldn't a lighter (115 gr) bullet generate less energy to "push" against the bolt than a heavier (124 gr) bullet given equal powder charges and other conditions? If the answer is yes wouldn't that suggest a more consistant "cycling" potential of the SMG's bolt?

A lighter bullet has less resistance to overcome case mouth tension than a heavier bullet.

What you heard about the 124gr bullet being designed to function 9mm pistols is tip-toeing around the issue. Quite simply, the 9mm was developed using an 8 gram bullet weight right from the start. Eight grams is just under 124 grains, 123.458867 grains to be exact. The .45 ACP was designed with a 200gr bullet, the 10mm Auto with a 200gr bullet, and the .40 S&W was designed with a 180gr bullet.

[omega21]

A lighter he bullet has less resistance to overcome case mouth tension than a heavier bullet.

Why? surface area in contact with the brass is the same, no?

What you heard about the 124gr bullet being designed to function 9mm pistols is tip-toeing around the issue. Quite simply, the 9mm was developed using an 8 gram bullet weight right from the start. Eight grams is just under 124 grains, 123.458867 grains to be exact.

ok, so what's the implication of what you are saying? What's the issue being tip toed around?

[Raven Armament]

Why? surface area in contact with the brass is the same, no?

No. The 124gr bullet is longer than the 115gr bullet, so the bearing surface of the bullet is increased with the 124gr bullet over the 115gr bullet. Not only is there more surface bearing which increases friction, it takes more force to move more weight. With more bullet in contact with the case, there is more tension to overcome with heavier bullets because there is more friction when the bullet starts to move from the case. The pressure has to overcome the tension from the case mouth on the bullet as well as the friction of the bullet moving forward out of the case and down the barrel. More tension, more friction, more weight (mass) means more force required to do the same work, ie get the bullet out of the barrel.

L to R: 115gr, 124gr, 147gr bullet with 9mm case for comparison. Note as bullet weight increases, so does the length of the bullet and thus the bearing surface of the bullet, which is the shank or flat sides of the bullet.

ok, so what's the implication of what you are saying? What's the issue being tip toed around?

Already said it:

Quite simply, the 9mm was developed using an 8 gram bullet weight right from the start.

^ That was the issue being tip-toed around.

[omega21]

Raven Armament - this is such a good education for me! Thanks for taking the time to lay out that explanation - now I totally get it. Picture says a 1000 words too! Thank you! So by the logic you have laid out, the heavier the bullet the higher the chamber pressure (recognizing the differences may be very very small) and thus one could infer that there would be more force applied to the bolt as well to cycle it more "reliably" (or we could say more forcefully). Right?

[TiroFijo]

No... recoil impulse (bullet mass*bullet velocity + powder mass*gas exit velocity) is what governs the cycle.

It doesn't matter the chamber pressure or bullet type/weight, there is a certain window of recoil impulse that balances best in a certain design.

[Raven Armament]

So by the logic you have laid out, the heavier the bullet the higher the chamber pressure (recognizing the differences may be very very small) and thus one could infer that there would be more force applied to the bolt as well to cycle it more "reliably" (or we could say more forcefully). Right?

When you get into internal ballistics (the moment the firing pin strikes the primer to when the bullet leaves the barrel), things get hinky and there are so many variables involved.

The pressure increase like you say would happen if you use the same powder charge of the same powder and seat two different weight bullets to the same overall length (OAL) of the cartridge. What you have here is the same potential energy (same powder and charge) but two different powder space capacities. When the bullet is seated to an OAL, there is air space and space for the powder. If you seat a long bullet to the same OAL of the short bullet, there will be less powder space, since the longer bullet reaches deeper into the case. Same amount of powder in a smaller space will increase pressure, sometimes dramatically. Couple that with a bullet with more mass and more bearing surface, it could spell disaster. Bullet weight is a variable in creating chamber pressure, but just because a load has a heavier bullet doesn't necessarily mean the pressure is higher. I've got a 9mm 147gr subsonic load that only generates 28,000psi when my 115gr load generates 33,500psi.

What TiroFijo said, "recoil impulse governs the cycle" is correct. To further complicate matters, ammunition loaders (and handloaders as well) can experiment with bullet weight, seating depth (OAL), powder burn rate, and powder charge to operate a weapon using a load with safe pressure, enough pressure to operate the weapon reliably, yet have a smooth recoil impulse that is less than lighter bullet loads.

This is exactly what "gamers" do. For the 9mm they will take a 147gr bullet just fast enough to make the required ballistics threshold called a Power Factor, which is bullet weight x velocity divided by 1,000. "Minor power factor" is 125. Most factory 9mm is about 135-140. Let's say you wanted to load a 125 PF load. You can load 5.3gr of powder A with a 115gr bullet to make 1087fps or you can load 3.6gr of powder B with a 147gr bullet to make 851fps. If you use a faster powder with a heavier bullet you can manipulate the recoil impulse to operate the gun reliably but have less felt recoil than the other load, even though theoretically the 115gr load should recoil less. Both loads have the same Power Factor (just a competition term to loosely quantify momentum easier).

[Straight Shooter]

MY M9 shoots 115 grainers like a freakin laser beam. I mean unreal accurate. It shoots 124 grainers well, and it is beside me now loaded
with 124+P Hydra-Shok ammo.
It shoots 147 gr. ammo WAY LOW, I was shocked at that. So, I stick with 115 or 124 +P's.
I still get a kick outta the 9mm vs. .45 debate....I swear its kept alive by people who have NO firearms experiance. BOTH are reliable manstoppers WHEN USING HIGH QUALITY JHP's.
Of course I DO prefer the .45 ACP......