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Feet per second question
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22 posts in this topic

So,

I've been reloading 9mm for a while now, just got a .357 wheel gun and picked up the dies and some bullets today. I was looking over my reloading manual and the charges for the two calibers are about the same. I'm loading 158gr LSWC in the 357 and 124gr FMJ's in the 9mm...both of these loads are calling for in the neighborhood of 6.0 - 6.2gr of Unique... With my Lee Auto Disk I'm getting it in the neighborhood of 6.0 - 6.3 grains depending on the throw... Can someone explain to me how the pressures work for these loads. How am I getting pretty close to equal feet per second, with the two calibers? Not to mention when I am using a significantly heavier bullet in the .357 than in the 9mm.

To be clear, I am loading safely and methodically, I just am a newbie, and unfamiliar with ballistics and ammunition sciences. So if someone could give me a crash course on pressures I'd be really appreciative.

-a

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The higher the pressures the higher the FPS. There are seveal ways to increase pressures. Powder weight, bullet weight, seating depth, bullet bearing surface and the bore are some of the contributors to increased pressures.

The 357, with the heavier bullet and higher drag in the bore, is probably giving the extra pressures needed to get to the same velocity as the 124 grain 9mm load. The 9mm bullet probably has less drag than the 357 because of the shorter bearing surface. This is probably why the same velocities are being achieved by a smaller and larger case.

On a side note .3 grains is a big spread. And according to the Alliant load manual 124 grain 9mm has a MAX charge of 5.8 grains. The MAX on your 357 load is 6.0 grains of unique.

Dolomite

Edited by Dolomite_supafly

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Thanks Dolomite,

Figured id hear from you. Thanks. You explained exactly what I needed to know.

And, yeah I load from my manual. The Richard Lee manual gives me 6.2gr not to exceed 6.8gr for my 158gr lswc. Right now my powder measure is throwing 6.3-6.4. I actually have 115gr fmj that I'm loading now. It's the manual says 5.1gr not to exceed 5.5gr for my 9mm.

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I don't know if you're chronographing the load or going by the data in the book. If it's the data in the book, the 357 will usually get it's extra velocity by way of a longer barrel too. I can't remember offhand but I think my Accurate manual lists a 7 inch barrel. You could take the same load in a rifle and possibly see even more velocity than the listed number.

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I don't know if you're chronographing the load or going by the data in the book. If it's the data in the book, the 357 will usually get it's extra velocity by way of a longer barrel too. I can't remember offhand but I think my Accurate manual lists a 7 inch barrel. You could take the same load in a rifle and possibly see even more velocity than the listed number.

Just going by the book, I'll be shooting these out of my 2 1/4" SP101 so I imagine I'll lose some velocity because of the barrel length. :-(

Mostly I was just trying to figure out how the ammo "worked." I process a lot of film (color and b&w) by hand... once I knew the mechanics I was able to control my film to an incredible degree. I find a lot of similarities here.... Except film can't kill ya I guess.

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Just going by the book, I'll be shooting these out of my 2 1/4" SP101 so I imagine I'll lose some velocity because of the barrel length. :-(

Mostly I was just trying to figure out how the ammo "worked." I process a lot of film (color and b&w) by hand... once I knew the mechanics I was able to control my film to an incredible degree. I find a lot of similarities here.... Except film can't kill ya I guess.

I dunno, some of those developing chemicals are rough. They used to use 98% ammonia and that stuff will cripple a rhino.

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I dunno, some of those developing chemicals are rough. They used to use 98% ammonia and that stuff will cripple a rhino.

Yeah, if you huff it though it'll get you crazy high. (kidding)

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ballistics are very, very complicated.

As a starting point... pressure and volume are related:

p1v1 = p2v2 (look up boyle's law for the details)

so as volume decreases (357 case to 9mm) pressure goes up as a multiple of the difference.

so the exact same powder using the exact same bullet (which is possible in these calibers if you wanted to play, use the 9mm bullet in both and it will work out) generates a totally different pressure in the different sized cases. The 9mm has a LOT more due to the much lower volume.

So, if you use the exact same bullet, powder chage, and barrel length, and ignore the small diameter issue (9mm in a 357 may let a little gas past unless the charge can seal the bullet to the barrel) the 9mm willl be going at a higher FPS. For them to be equal in FPS, you have to have a multivariable equation where the combination of other factors changes things.

Edited by Jonnin

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Very cool, thanks.

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Barrel length is measured differently in a revolver vs an automatic. The revolver barrel is measured from the cylinder gap forward. An automatic barrel includes the chamber. So, for a revolver and automatic both having 4" barrels, the revolver has an extra 1.5" of effective barrel length.

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Also, you can't go by the load data for velocity.

I have chronographed a lot of loads (factory and handloads) and NONE have matched. I have never had a factory load match the numbers on the side of the box. Some where close, as in within 50 fps but I have never had the numbers be within 25 fps. There are so many variables that affect velocity that you need a chronograph to determine actual velocity. Even with the same barrel length the numbers can vary greatly.

Dolomite

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Yeah, at this point in my shooting career, I'm just looking for the ability to send rounds down range at a little more affordable rate than going to Wally World every time and spending 60$ on ammo. I also like the ability to manufacture ammo when/if commercial ammo supplies get harder to come by/expensive.

-a

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If you are wanting the ultimate in savings then cast your own. The equipment to cast can be had for under $100 and you will have an endless supply of bullets.

It costs me under a nickel a shot for both 9mm and 45 acp now. It has a very low learning curve and you can get materials from most automotive repair shops. For 9mm you can cast over 50 bullets per pound of lead and over 30 45 acp.

Dolomite

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well, anytime commercial ammo is hard to get, primers are also. So you want to stockpile some.

If all you want is ammo that goes bang, you can ignore the velocity and pressure and all that. Just used published load data and it will do all you asked for.

By all means, study ballistics if interested, but you don't need it to load ammo. Its fun, but extremely complicated... you almost need a physics degree or aerospace degree to really get into it deeply, or the background to understand that stuff anyway.

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If you are wanting the ultimate in savings then cast your own. The equipment to cast can be had for under $100 and you will have an endless supply of bullets.

It costs me under a nickel a shot for both 9mm and 45 acp now. It has a very low learning curve and you can get materials from most automotive repair shops. For 9mm you can cast over 50 bullets per pound of lead and over 30 45 acp.

Dolomite

What all is required?? I'm currently unemployed (looking for a job) but once I have a source of income again I may be interested in trying that for everything but my Glocks.

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well, anytime commercial ammo is hard to get, primers are also. So you want to stockpile some.

If all you want is ammo that goes bang, you can ignore the velocity and pressure and all that. Just used published load data and it will do all you asked for.

By all means, study ballistics if interested, but you don't need it to load ammo. Its fun, but extremely complicated... you almost need a physics degree or aerospace degree to really get into it deeply, or the background to understand that stuff anyway.

Yeah, just interested to a degree. I wanna know if my ammo does one thing, what I can do to increase, or decrease that effect.... I'm gettin there.

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And you're right about Primers... soon as I've got some more $ I'll pick up a few thousand.

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An "intuitive" discussion of one factor (not that I know anything about it)-- Different powders have different burn rates. Have noticed for instance on 9mm and .357 that recipes typically use more powder for light bullets and less powder for heavy bullets, and this ratio seems higher with fast powders and lower with slow powders.

I think it is because light bullets have less inertia and get moving quicker. After ignition, the light bullet scoots out of the way to "open up" extra space for the powder to burn in, reducing the initial pressure spike.

On the other hand in that tiny 9mm case, a fast powder with a heavy bullet-- Because of inertia, the heavy bullet doesn't get out of the way quick enough. The powder is still burning quick and producing lots of gas, but with a heavy bullet the initial burned gas gets stuffed into a smaller space because the heavy bullet ain't moving out of the way quick enough.

Heavier bullets encourage a high pressure spike immediately after ignition, even though perhaps average pressure (until the bullet exits the barrel) might be tolerable. Bad things can happen if the initial pressure spike is too high. The paradox where a heavier bullet uses less powder, especially with fast-burning powder. Otherwise that early initial pressure spike might rupture the case.

Fer example looking at some Ramshot 9mm data-- They have the same brand bullets listed for several powders. Comparing Rainier plated soft lead (just for example) in 115 gn and 147 gn (the ratio is near 1.5X comparing 90 gn bullet against 147 gn, but they don't have a 90 gn Rainier FMJ listed so I can't "directly compare")--

Fastest powder, 115 gn bullet uses 1.2X more powder than 147 gn.

Slightly slower fast powder, 115 gn bullet uses 1.23X more powder than 147 gn

Medium pistol powder, 115 gn bullet uses 1.2X more powder than 147 gn

Slightly-slow pistol powder, 115 gn bullet uses 1.14X more powder than 147 gn

The slower powders can get the heavy bullets going better because they continue burning while the bullet is traveling down the barrel, and the initial pressure spike isn't so high because the powder doesn't burn so fast immediately after ignition. There is a good chance that slower powder could have a higher "average pressure" thru the entire burn, with a smaller "initial pressure spike" in comparison to a faster powder.

Just eyeballing the data, it looks like the max published load, the same bullet designs in the same barrels, get faster velocity from Max loads of the slower powders, and the fastest powders give the slowest max-load velocity. That seems even to apply to the light bullets, though surely there could be exceptions. So if you want a powerful load then one of the slower powders (for the type of cartridge) is probably what you are looking for. Perhaps the fast powders are generally better for powderpuff rounds (and the fast powders use less weight and so the cost per round is lower).

People load light practice .357 mag with some pretty fast powders, but the typical "high performance" .357 Mag powders with heavier bullets, tend to be on the slow side. A little slower than MOST people ever use for 9mm. But on the other hand such "slow" pistol powders burn faster than typical rifle powders.

Not that a slow powder is likely to matter to velocity in your snubbie, unless you just like fireballs. I don't really know. MAYBE partial combustion outside your short barrel does provide some acceleration? Have read some threads claiming that sometimes 3" .357 Mag revolvers have HIGHER velocity than 4" .357 Mag revolvers, having something to do with the aerodynamics of the exit gas in the shorter barrel. Or maybe those guys were completely wrong.

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What all is required?? I'm currently unemployed (looking for a job) but once I have a source of income again I may be interested in trying that for everything but my Glocks.

At a minimum: lead, heat source to melt it, something to hold it while it's melting, bullet mold, a way to lubricate the bullets. You may or may not need to size them depending on type of bullet and what diameter they drop from the mold. It can be gotten into very inexpensively.

Oh yeah, a mindset to be safe! Molten lead is HOT and the vapors are nasty.

There are probably some good threads out there and Caster can speak from tons of experience.

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Great thread guys. Thanks for all the info.

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Also, you can't go by the load data for velocity.

I have chronographed a lot of loads (factory and handloads) and NONE have matched. I have never had a factory load match the numbers on the side of the box. Some where close, as in within 50 fps but I have never had the numbers be within 25 fps. There are so many variables that affect velocity that you need a chronograph to determine actual velocity. Even with the same barrel length the numbers can vary greatly.

Dolomite

From reading some of the handbooks I gather that the published loads are higher on their fps. Is that consistent with what you see? I don't have a chrono yet, but down the road I can see myslef getting one.

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From reading some of the handbooks I gather that the published loads are higher on their fps. Is that consistent with what you see? I don't have a chrono yet, but down the road I can see myslef getting one.

Maybe the published loads tend to be higher (I don't know one way or the other). The last two loads I chrono'd, measured faster than the published specs, and I'm pretty sure my parameters and powder weight were very close to the recipe. I was kinda surprised it was a good bit faster than published.

Perhaps temperature could be one reason for variance against published specs? My "surprisingly hot" loads used Ramhot Silhouette powder, which is said to have a negative temp coefficient, where it is hotter in cold weather and vice-versa. Most powders get hotter in hot weather.

So anyway I chrono'd those Silhouette loads when it was dang cold outside for a southern boy. So I plan to chrono the same loads in the middle of this summer and see if they measure noticeably different because of the temp.

Edited by Lester Weevils

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