The relationship between pressure, case capacity, and bullet weight

[Wheelguns 1961]

I have recently come across 2 incidents where a heavier bullet takes up less case capacity in the same cartridge. Example 1: deals with .327 fed mag. I cast several bullets for this cartridge. The mp “mjolnir” comes in at 127gns with my ww alloy. The mp “sledgehammer” comes in at 142gns with the ww. The sledgehammer is a lfn and takes up less case capacity than the mjolnir. So, are my charge weights in the mjolnir safe in the sledgehammer although the sledgehammer weighs 15gns more.

My next example deals with .357 mag. I cast a noe htc bullet that weighs 173gns with my ww alloy. I have some 158gn swc’s that I purchased, that take up considerably more case capacity than the noe htc bullets. Are my charges that I use in the swc’s safe in the heavier noe bullets?

I think the answer is that both affect pressure, and the answer is to start low and work your way up, but without pressure testing equipment or manual data for these particular bullets, how do you know when enough is enough? These loads are primarily dealing with h110, and while I am flattening primers, I have not experienced difficult extraction or primers falling out. Sorry for the long post, but I didn’t want to forget anything. Does anyone have any thoughts on this?

[Hickory]

I don't think I would try to compare one boolit weight against another.
Load each boolit as an individual projectile. Record on paper all data and shy away from maximum loads.
My goal has always been accuracy first then the proper boolit and alloy for the job at hand.
I realize finding loading data for custom boolit can be difficult, but, error on the side of safety.

[Wheelguns 1961]

I always load for accuracy first. When I was developing a load for the noe htc bullet in .357, I worked up to 15.0gns of h110, and this load is the most accurate that I have shot in my gp100. I wish I knew what the pressure was.

[samari46]

Regardless of wether or not you are shooting cast or jacketed bullets I would definitely go by the bullet weight rather than how much space takes up in the case. And if your primers are flattening especially with H110 you may be in uncharted territory. Frank

[gpidaho]

Wheelguns1961: Hodgdon data out of the one book/ one caliber Complete Reloading manual for the 357 Magnum using a 170gr. bullet and H110 powder. A max load for a handgun is 13.5gr. and out of a rifle 14gr. is max With a 174gr. bullet on top of 15gr. I believe you're running pretty hot. A GP 100 is a strong revolver, I have one and it's a favorite but I most surely wouldn't push my luck any higher Gp

[abunaitoo]

Maybe load by case capacity percentage????
Example would be something like.........
Case capacity, with weight of boolet, 40% of that would be 25.0gr of listed powder.
It could list minimum %, and maximun% for that powder and boolet weight.
Just thinking off the top of my head.

[Hickory]

The next thing I'd ask is what are you shooting that you are using over maximum loads? Is there a grizzly bear in you sights every time you pull the trigger?
If you're just plinking, but enjoy shooting heavy kicking guns, let me suggest a S&W 500 magnum.
Even a GP100 will break with consistent abuse!
Flattened primers are a very good reason to back off on your loads! If accuracy is you first objective, switch to Bullseye or Unique and keep the velocity & pressure reasonable.

[Wheelguns 1961]

I was always told, when working with h110, to figure out case capacity minus the bullet. Reduce by 10% and work up to 100%. I am looking for a starting point for the sledgehammer bullet in .327. I load 2 different bullets in this cartridge. They both take up more case capacity than the sledgehammer. They are 119gns and 127gns. My sledgehammers weigh 142gns. I use a Brian Pearce load of 12.0gns of h110 with the others.

[Wheelguns 1961]

Brian Pearce uses 15.5gns with a 173gn lyman 358429 bullet in .357 according to one of his articles. I am interested in flat shooting loads suitable for 100yds and beyond with enough punch for silhouette shooting.

[JBinMN]

ETA: I may not have said things as well as I could for all to understand, but I was making an effort to try to explain my thinking into words & sometimes I have difficulty in doing so. I am NOT trying to dissuade anyone from experimenting on their own, nor am I trying to argue with, or dispute anyone who has posted previously. I am simply making an opinion known about this subject/topic, and some options & possible concerns I think should be considered...

I just wanted to make that clear... Here is the post:
-------------

It is good to remember....
that you are OK to use a heavier projectile load data on a lighter projectile,

but it is Not OK to use a lighter projectile data for a heavier projectile.

(in this case, "load data" meaning, "powder weight in grains of same powder")

You can verify this yourself by looking at & comparing projectiles to the corresponding powder charge weights in any manual. Look at the powder amount for a .327 F.Mag. for a 90 gr. projectile & compare it to one in the same caliber & powder to a 115 gr. projectile, or any caliber & type of powder you choose.

You can see that from Hodgdons data for those to boolit weights on their website load data:
http://www.hodgdonreloading.com/data/pistol

Hodgdon for 90gr. LRNFP
Universal(powder) .312" 1.460" 4.3gr.s 1,090 16,600 PSI 5.2gr.s 1,274 27,800 PSI

Hodgdon for 115gr.
Universal(powder) .312" 1.460" 4.2gr.s 1,059 25,200 PSI 5.0gr.s 1,184 40,200 PSI

(Note the pressure differences between the two as well. ;))

As you can see, the heavier boolit gets LESS powder, but also creates MORE pressure in the same firearm/Univ. Receiver bbl. at slightly less velocity. Using "more" powder charge for the "heavier boolits, will most likely create "more" pressure & possibly too much, and that is something to be concerned about.

----

While I can see that you are using B. Pearces load data since you have stated so, and I also understand you are using bullets/boolits that are heavier than what the powder manufacturer used & listed for that 327 F. Mag caliber in their online load data, I am going to suggest you contact Hodgdon about using such projectile weights with H110 & see if they tested such boolits at one time themselves & found some issues with pressures so they did not print them for use. There must be a reason they did not test H110 with their load data in 327 F.Mag..
{They only list the following powders for their 327 F. Mag. data:
231
244
296
572
700-X
800-X
AutoComp
CFE Pistol
Clays
H110
HP-38
HS-6
IMR Target


When looking at a burn rate chart, I do see though that many of those powders are faster burning powders into the more medium rate burn powders in the "Hodgdon/IMR/WInchester powder burn rate list link below(Slowest on the list above is #51 Win572, if I am not mistaken.)
https://www.hodgdon.com/wp-content/uploads/2017/09/burn-rate-color.pdf

There is likely a reason for that.

Another thing you could do is call the mnfr of the mold you are using, or the ones who make those projectiles & ask them about the use of H110 powder with those projectiles to see what they have to say.

------

I understand you are trying to experiment to reach the goal of over 100 yds & silhouette shooting. That is just fine with me, of course, as it is experimenting At Your Own Risk to do so & not me.
;)

That being said, I am trying to help you think about some things & options that you may have already considered & not said anything about( or I missed it here), as well as try to help you keep from causing your firearm , yourself or anyone else any harm, IF you "make a BIG mistake" anywhere in the process of experimenting with such loads...

Please understand that I am not arguing with you or anyone, but pointing out something that goes against what I mentioned about loads in the beginning of this post.

You say B. Pearce, as well as You, have used ( in the 327 F. Mag. for all) a load of 12.0gr. of H110 for the boolit weights of 119gr. & 127gr.(see quote below).


They are 119gns and 127gns. My sledgehammers weigh 142gns. I use a Brian Pearce load of 12.0gns of h110 with the others.

You also say that Brian Pearce uses a load of 15.5gr. of H100 for a boolit of 173gr. in a 357 mag.(see quote below).


Brian Pearce uses 15.5gns with a 173gn lyman 358429 bullet in .357 according to one of his articles.

First off, if both B. Pearce & You, have used 12.0 gr. in 327 F. Mag. to shoot those 119 & 127 gr. boolits, then using the "rule of thumb" I mentioned earlier in this post, you are likely going to want to use LESS powder in the same case for HEAVIER boolits.
(YOUR choice to do otherwise, but I think you are going to be making a mistake, considering you already have flattened primers indicating you are in the "overpressure" zone)

Also...The comparing of the 327 F. MAg. & the 357 Mag. is not a good idea to do & to me is the same as trying to compare a .40 cal with a 357 Mag, or a .38 Spec. to a 327 mag, or any other types of comparison. They just are not the same & should not be used to compare for IMPORTANT things like load data & components & thus PRESSURES when experimenting on a load.

(Oranges & apples are both fruit, and are round, but are still NOT the same color, taste, texture, etc.. Same type of thing as the 327 F. Mag. & the 357 Mag., so I would not compare the two and their load data, when pressure events are involved. To try to use the load data for one to the other is not wise, IMO. Comparing them as gpidaho did earlier for the "results" of the two being used is a bit different as it is demonstrating that they ARE not comparable for load data use. ;) )

Of course, perhaps some would consider me ignorant to say such things, that I am wasting my time, or that I am talking over some peoples experience levels... but I seem to have done right fine by using comparable caliber to caliber, & component to component without having much or any issue(s) using such "rules of thumb" as mentioned before, so I am just passing on some things I see here & might be Well Worth consideration.
;)

I think I have said enough. Do as ya like, but please think things over Very Well before you go about shooting some of these rounds. I do not want to read/hear about some simple mistake causing a whole lot of grief for anyone. Particularly someone who reads what is being written here & decides to go do the same thing that is being discussed, makes mistakes themselves & causes issues that they will regret.

G'Luck!
:)

[RED BEAR]

H110 is a great powder that i use a lot but as stared above if primers are flatting then be careful you can get into trouble with it. Loads give a max charge by weight also most give the seating depth for load. Both can be important i am not sure seating a bullet out a little will change pressure that much but can guarantee that seating it to deep can get you in trouble.

[reddog81]

One of the problems with buying “unique” molds is that you are left to your own devices when coming up with load data. The best you can do is try and find a similar bullet. My first point of reference is trying to find a bullet that gets seated into the case at the same depth as this is the primary thing that will effect pressure. I feel that using this method will get you close to comparable load data, however I would be concerned about the flattened primers.

Whether your load is hotter or weaker with a heavier bullet seated shallower is not something anyone on this forum can tell you.

[Larry Gibson]

I recently ran a psi vs seating depth pressure test in the 357 Magnum. I used the Lee 158 TL bullet over 6 gr Green Dot. The tests were with OAL starting at 1.632" with 10 shot tests in increments with the bullet seated 0.050 further into the case. I stopped at 1.432". The psi went from 24,500 with the 1.632 OAL to 35,700 psi with the 1.432 OAL. That's an increase in psi of 11,200 with just a 0.200" seating depth increase.

I also tested various different 44 caliber bullet of 240 - 260 gr in the 44 magnum with Green Dot. The seating depth of the various bullets proved more critical to psi than the difference in bullet weight. The thread should still be on this forum.

[Wheelguns 1961]

I would like to thank everybody for participating. Larry Gibson this is the exact kind of information I was hoping to get. After doing further research, I found a thread on single actions forum with some very good information. Alot of it dealing specifically with the .32 sledgehammer in the .327 cartridge. If I am to believe this information, I have a margin to work up to. As usual, I will work up in small increments until I get the desired accuracy and velocity, with accuracy being top priority. Again, thanks everybody.

[RED BEAR]

I will caution if you are already flattening out primers not sure i would increase.

[curioushooter]

A thing to realize about 357 magnum and the data is that older data runs hotter, at 40k PSI. The newer data (after ~1995) runs at a max of 35kPSI. So when you are running the newer data there is a healthy "safety margin" built in. Hodgdon puts out old data that runs at 40k. Alliant and Accurate put out 35k data since 95 or so.

I have a friend who runs a GP100 with 16.5 grains of 2400 (a faster powder than 110 either Alliant or Herc) and 158s. This is well over 40K psi and he has run this for years in Rossi 92s (using 38 special brass!!!) as well. That would be quite a surprise if somebody stuffed that into a little old 38 special revolver! That said, he's had no problems. He uses CCI primers because they are the cheapest. They also tend to be harder. I've noticed that Federal primers that are soft may flatten out more easily. If you are using CCI and they are flattening that would alarm me.

If I were you I would just go with the 110 data for 180 grainers at the 40K PSI level and use it as a max load. That happens to be 13.5 grains. I suspect you are well over where you should be. In my experience bullet weight matters a whole lot more than seating depth. The bullet is only going to be at the depth for a very short time anyway when the volume of space occupied by the expanding gases is increasing. The weight of the bullet (so its resistance to expansion due to inertia) is a constant.

I've found that with Win296, which is similar if not identical to 110, that it likes to be run hot. Generally the hotter the more accurate it becomes, too. It also likes to be 100% case fill or even gently compressed. The problem is that it is almost always overpressure in 357 magnum due to the large size of that case with the usual seating depths. It also does goofy stuff with temperature extremes. It can run cold it seems but in the heat (think Silhouette firing-line in July) it seems to have crazy pressure spikes. I only use 296 in Condenders these days for this reason. I used it in 32-20 and 357 and 44 mag. Once it is gone I wont be buying it again.

300 MP is the best max power powder for 357 magnum I think with 158s or 170s. I've only been working with it for a couple months so no hot weather yet. It is slower than 296 but is more well behaved so far and seems to be perfectly adjusted for max case fill with 158s at the usual seating depths. It works well with my RCBS 158 SWCGC and every jacketed bullet I've tried. It is as accurate or more accurate, as clean or cleaner, and meters better as the ultrafine particle size of 296 can sometimes result in it getting between the rotor and the body of the powder measure. 300MP is a bit larger and more granular and doesn't do this. It is like it was designed to be the optimal powder for max powder 357 Magnum loads with heavy bullets. It works well in pistols, revolvers, and rifles, too.

2400 is the best for full power powder loads from 140 on up. It is a bit faster than 110/296 without all the drama. In revolvers with normal barrel lengths (4-6") it seems get the same velocities as 296. In Condenders 110/296 pulls away from 2400. But 300 MP pulls away from 296 in rifles.