The pressure factor

Pheroze

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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

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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

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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

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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

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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.
 

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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

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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.
 

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"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
 
 

 

 

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