The pressure factor

[Pheroze]

When operating within acceptable pressure, does anyone opt for the powder that produces the least pressure for the speed? For example, it would appear that H4831 produces the same velocity but with less pressure than some others. All are within acceptable pressure ranges. So, just curious if that is a factor anyone considers when picking one suitable powder over another. Or, is it irrelevant so long as it's safe?

 

[Wyatt Smith]

I always try to use the highest velocity lowest pressure powder in my rifle. If I can use a minimum load, or a few grains more, to achieve 2500 in my 375 I will.
Without looking at my manual I want to say With h414 there is less than 75fps difference in minimum and max loads. I guess that doesn’t necessarily mean the pressure is low, but it makes me feel better than a max load of another powder just reaching 2450.
I am about to try some H4831 to see if I can avoid compressed loads

 

[Forrest Halley]

I consider it in certain actions. M1 or big bore lever gun has me thinking about it. It seems like powder availabilities govern things more than pressures unless you're a prepared reloader that stocks a bit of resources away. I'm just getting into the .375 and it's interesting to see folks targeting impact velocities as opposed to the fastest bullet and flattest trajectory.

Funny, I have opted to load longer to try and avoid the compression on the 4350, but have not been able to to test the accuracy yet. Single shots are wonderful sometimes and my #1 seems to like its fodder longer than 3.6.

 

[Pheroze]

I was thinking lower pressure would also mean less recoil. Just going from memory, and in rough numbers, H4831 was about 55k for 3000 fps while Varget was closer to 61k for that velocity. So I figured that variance would translate to the shoulder.

Now, I am sure H4831 heats up the barrel faster than others....

 

[Ridgewalker]

As I recall, recoil is calculated using powder weight, rifle weight, bullet weight and velocity. I don’t recall anything in the calculation about pressure.
http://www.jbmballistics.com/cgi-bin/jbmrecoil-5.1.cgi

When I reload, I focus on below max pressure as posted in the manuals but I verify looking for signs in my specific rifle, then accuracy, then velocity to achieve the energy needed.

Just my methodology. Others tend to focus more on energy first.

 

[Alistair]

Can't say I've ever really though about pressure, beyond the usual 'that primer looks a bit flat, might have gone too far here' type of thing on ladder tests.

I usually select powder purely on what's reliably available and single base out of the top 2 or 3 in the book for my round and bullet weight, and only change it up if I want / need more velocity, in which case I might move to something double base. Temp sensitivity is also a factor for some rifles.

Beyond that, I usually load to either achieve a target velocity, or to a load with a low ES, or to pressure signs and then back off a few percent to the maximum safe velocity depending on the intended application of the load. It's my experience that most loadings can be made to shoot pretty well by playing about with seating depth, crimp or neck tension after that and more velocity = better trajectory and more energy.

I'm also not sure tht there is really a reliable method to test pressure available to the average homeloader, so you can only go on what the book states for a given load, and on the rough visible pressure signs on the cases. Quickload is I suppose an indicator as well, but I don't trust it that much. I've seen the same load that works fine in one rifle (S&B cheapy FMJ as an example) give serious pressure indications in others, so it's my view that even slight variations in barrel or chamber dimensions can give fairly substantial swings in the 'real' pressures, despite the book saying that the load should be the same.

I suppose one could say that powders giving higher safe max velocities could give the lower maximum safe velocity of another powder with less pressure, but that generally just means I crank the velocity up a bit more...

 

[JimP]

I like to find a powder and load that will be at the velocity that I want to achieve and if it is a lighter charge than max I like it even better.

For my .340 Weatherby I was shooting a load that was at max loading for the powder bullet combination. I found another powder that achieved the same results but it wasn't at max loading yet for that load. My rifle likes it and I like it. If there is any variation in anything that might increase the pressure a little I am on the safe side.

One funny thing about this load is that while it was a safe load in the manual that I had it is now a couple grains too much in the newer manual. But I'll keep using it.

 

[tarbe]

"So, just curious if that is a factor anyone considers when picking one suitable powder over another".

For sure.

Higher pressure works the brass more...so if you can get the same velocity with lower peak pressure (by flattening out the pressure curve) you should consider that a win.

Good brass is expensive and trimming brass is a pain in the patoochie. So less trimming and more loads from a case is a double-win!

My $0.02 as always.


Tim

 

[Bob Nelson 35Whelen]

When operating within acceptable pressure, does anyone opt for the powder that produces the least pressure for the speed? For example, it would appear that H4831 produces the same velocity but with less pressure than some others. All are within acceptable pressure ranges. So, just curious if that is a factor anyone considers when picking one suitable powder over another. Or, is it irrelevant so long as it's safe?

@Pheroze
I always pick the powder that give the highest velocity with the lowest pressure.
The exception being the 30/06 with 150 grain bullets. My computer program shows that ADI 2206H/H4895 and ADI2209/H4350 give identical velocities at the same pressure.
My chosen loads must also meet my accuracy criteria as well. If it doesn't I try the next slowest powder.
Bob

 

[Bob Nelson 35Whelen]

I always try to use the highest velocity lowest pressure powder in my rifle. If I can use a minimum load, or a few grains more, to achieve 2500 in my 375 I will.
Without looking at my manual I want to say With h414 there is less than 75fps difference in minimum and max loads. I guess that doesn’t necessarily mean the pressure is low, but it makes me feel better than a max load of another powder just reaching 2450.
I am about to try some H4831 to see if I can avoid compressed loads

@ Wyatt Smith
H4831SC is even slower so will need to be compressed even more.
Try H4350 slightly quicker than H414 and should do a good job. Chechnya you manuals for correct charge weight.
Bob

 

[crs]

In general, I use a rifle powder with the lowest peak pressure and since I reload only a few calibers, this works for me. My favorite powder generates a smooth curve (much like a side of an ellipse or a hen egg at rest) and has NO spikes.
Once I saw some pressure traces, it was simple to choose a powder with the least peak pressure and no spikes. The total energy is the area under the curve and the ellipse can have the same energy a a pressure trace with a spike, but the elliptical trace will have less peak pressure.

 

[Wyatt Smith]

Bob I think I’ve miss typed, that’s supposed to H4895. I’ve never used H4831.
However I’ve switched to IMR 4350 and like it quite a bit.

 

[fourfive8]

I pretty much approach velocity and pressure like most posts I see here. I set a conservative velocity objective for a bullet, search through all my load manuals then start working with the powder or powders that show lowest ratio of pressure to velocity. I begin a little low, use a chronograph and start the process of 5-10 shots each trial at the range through the chronograph. As I approach my objective velocity, I watch the velocities vs charges to see they are staying correlated. By correlated I mean nothing going squirrely between pressure signs/velocity readings and charge weights where all of a sudden a 1 gr increase in charge shows an unexpected jump in velocity or possibly an early pressure sign like a fattened primer. If that happens well under my objective velocity or if it shows larger SDs than maybe 15-20 fps, I record that in the log as not a good load or as a questionable load and move on to the next powder. Usually, I can find a powder or two I have in my stocks that will work for most any combination of caliber and bullet weight/type I'm working on. All the powders I use for working up hunting loads are within the Hodgdon Extreme group. I have successfully traded off or sold off all my stocks of comparable IMR powders.

In the case of the 375 HH and 300 gr bullets of all flavors, from Bonded Hornady DGX to Barnes TSX to Swift A Frame, the best powders I've found for hunting loads include: Varget, H4895 and H4350. All producing predictable/ stable loads for the 300 gr bullets to between 2450 and 2500 fps with low SDs of velocity, no pressure signs and good accuracy.

In my Win 70 375 HH, I have two loads ready to go for hunting if I decide to use it- 1) 300 gr TSX, H4895 @ 2465 fps. 2) 300 gr A Frame, Varget @ 2485 fps.

 

[Bob Nelson 35Whelen]

In general, I use a rifle powder with the lowest peak pressure and since I reload only a few calibers, this works for me. My favorite powder generates a smooth curve (much like a side of an ellipse or a hen egg at rest) and has NO spikes.
Once I saw some pressure traces, it was simple to choose a powder with the least peak pressure and no spikes. The total energy is the area under the curve and the ellipse can have the same energy a a pressure trace with a spike, but the elliptical trace will have less peak pressure.

@crs
The newer powders like CFE223 and superformance give the longer more sustained pressure curve you describe but the older powders like H4350, H4831sc, H4895 ,IMR 4064 and 3031 all give the parabolic curve. The newer egg shape curve as you call it gives a longer more sustained pressure than the parabolic. Hence the higher velocity achievements than older powders and still within SAFE pressure parameters. This is how it was explained to me by ADI/Thales in Australia.
Bob

 

[PHOENIX PHIL]

Generally I'm only concerned I don't exceed pressure limits, paying attention to brass and bolt lift, regardless of powder. I choose the powder based on what gives me the best accuracy and also gives me a load with velocity in the ballpark expected.

For example if I have the best accuracy load for say a 180gr bullet in my .300WM gives 3000fps, but another powder gives significantly better accuracy at 2950fps, I'll use the latter load. 50fps difference means nothing at reasonable hunting ranges.

Once I have a load I like, I also like to go a bit past it to see if there's some margin to getting high pressure signs.

One example would be my 250gr North Fork load for my .375HH. I can get actually virtually the same velocity and accuracy with H4895 or Varget. But the Varget load only took a little more powder to show pressure signs, whereas the H4895 took a bit more. So the H4895 is the choice for me in that load.

 

[sestoppelman]

@ Wyatt Smith
H4831SC is even slower so will need to be compressed even more.
Try H4350 slightly quicker than H414 and should do a good job. Chechnya you manuals for correct charge weight.
Bob

The short cut version of H4831 is not slower than the long cut version, its just shorter kernels, burn rate is the same, data is completely interchangeable.
The sc version is made only to make it easier to meter in a powder measure.

 

[Bob Nelson 35Whelen]

The short cut version of H4831 is not slower than the long cut version, its just shorter kernels, burn rate is the same, data is completely interchangeable.
The sc version is made only to make it easier to meter in a powder measure.

@sestoppelman
I never said 4831 was slower than 4831sc. I was referring to young mister Smith going from H414 to h4831 or H4831sc which is definitely slower than H414.
Bob

 

[sestoppelman]

Oh, guess I misread your post. A thousand pardons...

 

[crs]

SES - always the gentleman.

Bob Nelson - Indeed. I use Pressure Trace II when I really care to compare and / or control pressures and the traces are VERY revealing.
For this reason and many others, my best low pressure/good velocity powder is VV N133.
This is a good subject for fireside BS , so when I next am in Australia,...
BTW, Peter says he will be stateside soon.

 

[Bob Nelson 35Whelen]

SES - always the gentleman.

Bob Nelson - Indeed. I use Pressure Trace II when I really care to compare and / or control pressures and the traces are VERY revealing.
For this reason and many others, my best low pressure/good velocity powder is VV N133.
This is a good subject for fireside BS , so when I next am in Australia,...
BTW, Peter says he will be stateside soon.

@crs
Any time you are in Australia my door is open and you will be welcomed. VV N133 and 130 are excellent powders in the 222 Remington and a few other rounds. Unfortunately it is as rare as rocking horse poop here.
Bob