Heavier bullet = Less Powder?

[ReeferMac]

Another rookie question on reloading:

Went to Hodgdon's website to research loading data on 115 gr. bullets, reco'd 4.5-4.8 grn's for Speer Gold-Dot HP's (I've got a box of Hornady's XTP).

The 124 gr. FMJ's I've been loading at 3.9 grains of powder... max of 4.1 Speeds show as slightly lower, but pressure's about the same.

 

Why am I using less powder for a heavier bullet? That doesn't seem to make sense to me?

Using Titegroup on 9mm pistol loads.

Thanks for the info.

 

- K
 

[Patton]

It is simply because there is less case capacity with a heavier bullet.

[Grunt81]

Hey bud, to follow up on Patton:

There's less less case capacity because the heavier bullet is longer. Thus, the bullet is seated deeper to meet OAL.

Because the bullet is seated deeper, less powder can fit in the case. However, because there is less space for powder, there is a smaller volume for combustion to occur. Smaller volume for combustion = higher pressure.

Furthermore, even though the heavier bullet starts off slower, because it has a greater mass, it will carry more momentum. Therefore, the 124 grain bullet will have similar penetration and expansion as 115 or 147 grain.

Give me a call if you'd like me to elaborate.

[Sidecarist]

There is also a relationship between bullet weight, powder charged pressure.

The cartridge will only safely handle a specific pressure. Given the same powder charge a heavier bullet will develop higher pressure. Just the higher weight and longer bearing surface will cause pressure to rise.

Like bowling balls... yes are all the same dimension, but heavier ones are harder to throw at the same speed.

[ReeferMac]

4 hours ago, Sidecarist said:

The cartridge will only safely handle a specific pressure. Given the same powder charge a heavier bullet will develop higher pressure. Just the higher weight and longer bearing surface will cause pressure to rise.

Like bowling balls... yes are all the same dimension, but heavier ones are harder to throw at the same speed.

 

Man, do you ever sleep? LOL!
So the inertia of the static bullet in addition to friction from case-contact causes more of the powder to burn inside the case, creating the high(er) pressures w/ less powder? Whereas the smaller bullet gets moving more quickly, and requires more powder to reach the same pressures? Some of the charge possibly burning after the bullet has left the case?

I'm just stuck on the notion that if I put more powder inside the case, it should make a bigger bang? The bigger/heavier bullets require a bigger bang (simplified physics), yet I'm putting LESS powder in the case for the larger bullet. Seem's counter-intuitive? Frankly I'm fearlful to put 4.5 grains of powder in for the little 115 gr. XTP's. Just trying to get my head around the physics of all the stuff that happens in 0.0034 seconds.

Which also makes me wonder about those Berry's bullets w/ the hollowed out tail? Does having that cavity back there create a significant impact on the combustion or does it only affect flight performance? Technically it creates more 'case-space' than exists in a flat-tailed bullet, so that would mean possibly more powder needed? Again, that just seems whacky to me? The opposite of what you'd expect? I 'get' that the combustion happening in a more confined space will raise the pressure... just less powder for more weight seems the opposite of what you'd expect?

 

I de-primed and re-sized a whole bag of cleaned brass last night ( Thanks again! ), so was going to cook up a couple different charges and bullet combinations to test out. I finally got a key to the indoor range at ORSA so can test them out anytime.

 

- K

 

- K

[Jamie Jackson]

Congrats on getting that key my friend! That's one less weekend I have to babysit! LOL

To the best of my knowledge the extremely small additional space created by the hollowing base of a FMJ -type bullet is not significant enough to cause an appreciable pressure increase.

What folks are addressing is that there is an initial fixed amount of available space once a bullet is friction set into a case. This initial space is where the pressure is generated and eventually overcomes the friction fit of the bullet, and following the path of least resistance drives the bullet down the barrel lowering the pressure...this all probably wasn't necessary to say, I'm just trying to make sure I'm clear in what I'm saying/thinking.

That said, some of my loads have compressed powders...ie 5.7 grs of Unique under a 115 gr 9mm bullet. There is generally a few unburned grains of Unique that escape the barrel..this is normal for powders in that burn rate and shape (flaked).

Small ball powders like AA#2, W231/HP-38 and Titegroup require much less volume to generate the required appropriate pressure to send the bullet along it's path.

As has been stated the OAL is critical, not just for proper placement of the bullet relative to the throat of the barrel, but in order to allow the appropriate amount of space within the brass in order for the the correct amount of pressure to be generated.Seating too long of a bullet (ie perhaps a heavier weight bullet) too deep...reducing the available space.. allows too much pressure to occur...

late signs in overpressure include but are not limited to flattening of primers, blown primers (path of least resistance thing), split brass etc.

Too little powder, from my understanding, can cause a detonation within the chamber. I have not seen this myself.

But I have blown up a nice Glock 21 in 45 acp with a double charge of W231...this was nearly 2 decades ago and I haven't had a double charge since...yet..

Do you have a chronograph yet my friend? They really help in safe load development.

More powder doesn't mean a more accurate load, but loading within the published guidelines allows safe load development.

While I have used powders outside of their "normal" published loads during the past few years of powder shortages, I approached the load development with caution and trepidation, and received help both here at TGO and from the powder companies themselves.

 

Well I hope I've adequately muddied the waters and that others will straighten my mess out!

 

Keep up the good work K!

 

 

[gregintenn]

In addition to the longer bullet reducing case capacity, it also has a larger bearing surface, which, in addition to the heavier weight, makes it more difficult to push down the bore. This will also cause higher pressure, which would require less powder to reach the same pressure level you're getting with the lighter bullet.

 

Another anomaly I've found with shooting and reloading is that a heavier bullet from a handgun generally hits the target higher than a lighter bullet, while the heavier bullet in a rifle prints lower on the target than it's lighter counterpart. I believe the lighter bullet prints lower from a handgun because it leaves the barrel faster, before muzzle flip can raise the point of impact as much as with the heavier, slower projectile. This isn't as much of an issue with a rifle.

[Jamie Jackson]

Great points on POA vs POI as it relates to bullet weight.

 

As it was explained to me by my handloading mentors long ago...now this is in relation to handguns...various calibers of fixed sights are factory regulated to a specific bullet weight. 9mm was at that time (1985) 115 gr, .38/.357 was 158 gr, .44 mag was 240 gr and 45 acp was 230 gr. That account for a specific amount of muzzle rise before the projectile left the barrel...heavier bullets hit higher because of greater rise and lighter bullets hit lower because of less rise. I don't know if this is necessarily still true...but I bought into it LOL.

[No_0ne]

The Lee loading manual has a good explanation of powder selection versus various other parameters (OAL, case volume, seating depth, bullet weight, etc.) in the early chapters before the actual load data is presented, you might want to pick up a copy of it just for "light reading".

Edited May 22, 2016 by No_0ne

[Sidecarist]

How's your high school physics memory...

Let me try this another way. Max allowable pressure is always constant right?

Given that, then this is really just newton's law. It takes more energy to move a heavier object. Because your available energy is limited by the allowable pressure you have to lower the powder charge on heavier bullets to prevent going over the pressure limit.

I'm ignoring some things like case volume and increased friction due to longer bearing surface. These have some effect on pressure, but the bullet weight change is the biggest reason for less powder.

The hollow base on the berry's really just moves the center of gravity forward, kind of like a dart or shuttle cock. It won't have much if any effect on pressure.

(No not much sleep lately I'm on a long commute from one homestead to the other)

[ReeferMac]

6 hours ago, Sidecarist said:

(No not much sleep lately I'm on a long commute from one homestead to the other)

ooooooohhh... grab me a can of Timmy's!!!!

LOL!

- K
 

[tmauto769]

From what I have found about Concave base or "hollow base" bullets is that to get the weight with the cavity the bullets need to be made longer, therefore you should be reducing the charge a little from the typical charge weights for flat based bullets. There really isn't a whole lot of load info out there on concave base bullets. I bought 4k of FMJ RN concave base 115gr bullets a couple of months ago and have been liking them. I worked up to 6gr of power pistol with them which seems to be a bit hot. So I backed it back down to 5.7gr of PP and they have been great other than the massive fireball that comes with using PP.

[Sidecarist]

The Hodgdon data lists the hollow base 124gr bullet so the data is about as accurate as it can be in this case. yes most hollow base bullets have somewhat longer bearing surface and there is some risk if increased pressures if not using data specifically for them.

 

[ReeferMac]

48 minutes ago, Sidecarist said:

The Hodgdon data lists the hollow base 124gr bullet

 

Where? I couldn't find that (admittedly, site doesn't work too well w/ my browser)

(Or, if you remember the load off-hand...)

Put together about 300 rds. over the weekend, mostly @ 3.9 grains (as I've used it and it works), put up some @ 4.1 grains, and made 2 sets of test-groups w/the Hornady XTP 115 grain bullets at different charges (min and max listed) to see how they perform.

 

- K

[Sidecarist]

The load is 3.6 to 4.1gr titegroup with the berry 124gr HBRN

PM inbound

Edited May 23, 2016 by Sidecarist
typo on load data!

[ReeferMac]

I ran a batch of 3.6 grains, and it was a real creampuff compared to the 3.9s. I was surprised such a small diff. in powder made as big a diff. in my hand?

 

- K

[Sidecarist]

3.6 is a big difference even though it doesn't seem like it. when you look at the range of 3.6 min to 4.1 MAX that's only 0.5gr total between min and MAX.

Titegroup is a pretty high energy powder and while not the easiest to start with because of that you also don't need to run near MAX all the time. I'm using 3.8 or 3.9 for my match loads and they run just fine.

If the 3.6gr loads functioned OK then that's you r most economical load as its the least powder. It works out to about 150 more rounds per pound! if cash is tight that makes a difference for sure