BP Load Compression


March 11, 2012, 02:37 PM
Has anyone done any experimentation on how accuracy, velocity are effected, or if they are effected at all by the compressing of say 3Fg powder.

My theory, and it’s only a theory mind you, is that the harder a powder is compressed, the slower the burn rate. Two granules of powder, sitting next to one another when the fire travels it will find a path between the two granules and they will burn quickly. However if those two granules are pressed hard together, the fire cannot find a pathway between them and thus travels around them actually slowing the burn rate.

Does this make sense or am I all wet?


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March 11, 2012, 02:40 PM
If you are all wet, your powder won't burn at all! :what::neener:

March 11, 2012, 02:52 PM
If you can explain the physics of:
if those two granules are pressed hard together, the fire cannot find a pathway between them
then perhaps I'd say no, you're not all wet. But it seems to me that heat (which is what causes the individual granules to burn) will easily be more easily transferred between two granules that are pressed hard together.

The heat of the gas from the percussion cap is what initially ignites some of the powder granules; heat, and hot gas, from those burning granules ignites the adjacent granules, etc.

March 11, 2012, 04:08 PM
BP benchrest shooters are most particular about the seating pressure they use. They don't all agree that more pressure results in more or less velocity, but they recognize a variable when they see one.

It has crossed my mind more than once to modify a socket wrench to slip over the rammer on my Old Army, to be used in conjunction with a torque wrench, with the aim of seating all six balls to the same standard. To take best advantage of it, however, I'd have to individually weigh each charge, weigh each ball, find a way to meter the same amount of grease onto the mouth of each chamber..... and suddenly rolling beers cans around on a dirt bank just turned into WORK.

March 11, 2012, 06:00 PM
You are right about that. In fact it can even cause incomplete burning of all the powder.

Black powder as it comes from the can is not compressible. It already has a density of about the same as water. It was pressed when made at about 70 tons.

If you push the ball or bullet into it any more then that bullet just sitting on settled powder, you are crushing or breaking the granules. Some turning back to dust and some to smaller pieces. This happens as each granule is trying to fit into the spaces between the others. This dust and fines can make good differences in velocity from shot to shot.

In bench rest we go through the step of removing all dust and finer broken grains from our powder before it goes in the gun. Then the patched bullet, which slides down the bore with just the weight of the ramrod, is lightly set with that weight on the powder. The patched bullet is only a slip fit in the bore. not in the rifling so it slides very easily. When the charge goes off the bullet swells to fit tight in the rifling.

March 11, 2012, 10:10 PM
The burn rate of [compressed] powders is also affected by the strength of the primer. That may be one of the reasons why 209 primers are being used for modern muzzle loading. They help to increase the burn rate of the highly compressed pellets as well as the densely compacted loose powders.
There's probably rules about the burn rates of every individual powder and exceptions to those rules depending on a host of factors including the precise amount of compaction, the brand of powder or pellet, the strength of the primer and other variables.
For the practical purposes of loading muzzle loaders by hand, it seems that the compaction of loose powders usually produces more velocity, and sometimes consistency too (like with American Pioneer powder).
At some point loading too much powder could become counterproductive for the strength of the primer or the size of the bore to continue delivering an increase in velocity. But generally if staying within the manufacturer's recommended loads, then compacting loose powders usually increases velocity unless there's some exception for the type of powder being loaded (like with 777) or with the type of primer being used.

March 12, 2012, 06:54 AM
For shooting black powder cartridges, a bit of compression is not a bad thing. It promotes cleaner burning with some powders and better accuracy with others.

March 12, 2012, 02:56 PM
Logic tends to suggest that tightly compressed powder would burn more slowly. After all we're all aware as BP shooters that it is bad to have any air gap in the load where the powder can float around loosely. I've always assumed that this is because loose powder will allow the flash to jumble the powder and it will all burn at the same time. Thus producing a harsh pressure spike. On the other hand compessed powder will burn from the source of the ignition forward in a traveling front that takes some small but important amount of time to complete the burn.

So we know it's important to compact it to some degree to ensure there's no abilty of the powder to slop around loosely. But from there it's a different issue. The seating depth at that point also controls the volume of the chamber. And the volume has some effect on the peak pressure that is reached. So in addtion to any burn time variation of the powder we've also got the chamber volume issue. And with a smaller volume and thus a faster pressure build how the powder burns versus the pressure will come into play.

All in all it makes my brain hurt.... :D

It is certainly fair to say that consistency of the pressure AND the seating depth will both be factors related to ultimate accuracy. For those that are keen on such a thing with a revolver they will want to work on better options for controlling the weight/volume of the powder to accurately match the load charges. And since for a given batch of powder the charges will all be the same volume the seating depth isn't so important as it is to achieve the same compaction pressure for each chamber. Doing so will ensure that the chambers are the same volume automatically. But depending on the difference between the chamber shapes the balls may sit a little lower or higher in some cases.

Pete D.
March 13, 2012, 07:36 AM
After all we're all aware as BP shooters that it is bad to have any air gap in the load…
I have read, fairly recently (please don't ask me where as I don't recall), that the "no air space" idea regarding BP cartridge loading, is a myth; it is a holdover from muzzleloading where it is important.
Anyone else come upon this and have a reference?

March 13, 2012, 09:52 AM
Pete D. Quote:
After all we're all aware as BP shooters that it is bad to have any air gap in the load…

I have read, fairly recently (please don't ask me where as I don't recall), that the "no air space" idea regarding BP cartridge loading, is a myth; it is a holdover from muzzleloading where it is important.
Anyone else come upon this and have a reference?

No direct reference I an cite but the old string shooters who used a single cartridge and breech seated the bullet left air space between the bullet and powdered casing. It did not seem to bother them. However, it was inportant enough of an issue that when the gov't used a reduced load in the 45-70, they had a variety of methods to insure there was no space between bullet and powder. I don't breech seat the bullets so I lean to the no space side of the camp but allow for the good shooting done by the ODGs.

Foto Joe
March 15, 2012, 10:47 AM
I haven't chronographed "compressed vs un-compressed" cartridge loads but....

Before I started using a compression die I was compressing/seating the powder in 45Colt and 44 Special using a dowel with a "T Handle" mounted on it. It wasn't the best method for consistancy so being slightly anal (my wife accused me of this, I still haven't admitted it) I purchased a Montana Precision compression die.

Before I started using the compression die I had noticed via the chronograph that my cartridge loads were pretty spread out velocity wise. After the compression die I noticed that the velocities tightened up, a LOT. The velocities didn't increase appreciably if at all, but the consistancy was much better.

So as far as your original question, I'm afraid the answer is open to interperatation. I happen to dis-agree with TheRodDoc on his theory but that doesn't mean he's incorrect, it just means that there are at least two opinions out there on compression. Personally, it works for me although I lack the brain cells that engineers have so I can't give you the reason why.

Find what works for "you". No matter how much we want to, none of us has all the answers to the true meaning of life, let alone Black Powder shooting. We just think we do ;)

Skinny 1950
March 18, 2012, 03:24 AM
I think that air is the variable, the chemical composition of the powder should be the same regardless of the granulation. If you want more air then a coarse granulation is what you want. Coarse granulations are used in long guns because the burn slower,very fine granulations are used in the pans of flint locks to make for shorter ignition times (also to fill the touch hole).
Air has oxygen and an almost inert "filler" ie:Nitrogen ... both of these gasses are non-condensible at normal temperatures. They do expand when heated at close to the same rate but the oxygen will tend to combine with the other chemicals in the reaction.

March 18, 2012, 05:02 AM
When loading .45-70 cartridges, I compress useing a drop tube, and I never, ever, leave any air space. In my 1884 rifle [cut to carbine length] I use a 405 gr. bullet, and 60 grains of 2F Goex, with a grease cookie and a fiber wad on top of the powder. You can use whatever load you feel is best, but air gaps in a black powder rifle, cartridge type or muzzle loader are to be avoided.YMMV.

March 18, 2012, 07:40 AM
I think that air is the variable
Uh, black powder creates it's own oxygen as part of the reaction, so 'air' isn't a variable.

Pete D.
March 18, 2012, 07:54 AM
but air gaps in a black powder rifle, cartridge type or muzzle loader are to be avoided.
Just askin', not arguin'. Asking because I have never yet read an answer to the "why?"

Jim Watson
March 18, 2012, 08:13 AM
As I posted on TFL...

The concern with airspace over a black powder load is the risk that the burning powder mass will hit the base of the bullet like an obstruction and ring-bulge the barrel.
I have always wondered why the Scheutzen shooters don't ring barrels with their breech seated bullets and wadded powder only cartridges behind them. The answer seems to be that they do, just that the ring is where it does not affect accuracy of the breech seated bullet or extraction of the brass. Not every time, but in some cases.

I also wonder about the Swiss Federal .41 and its Wild System ramrod with shoulder to stop the bullet about .10" over the standard powder charge. I don't guess a ring would be noticed there, either.

One reason for compressing the powder charge in a cartridge is to get more in at a usable OAL. I load only 56 gr Swiss 1.5 in my .40-65 with light compression; velocity is adequate and consistent and accuracy is good. Why change? But another guy here gets in 63 grains of powder with heavy compression to get best results out of HIS rifle.

The 70 grains in a .45-70-405 is well compressed. It is heavily compressed in the later .45-70-500. Articles describe the "long burn" primers designed to break up the cake of powder and get it going. A lot of early modern BPCR shooters used magnum primers for that reason. Nowadays the trend is to standard primers and even pistol primers for mild ignition and better accuracy. But target shooters blowtube or wipe every shot. If I were loading hunting ammo, I would try magnum primers in hopes of a cleaner burn and repeat shots without cleaning.

March 18, 2012, 02:09 PM
Jim got it in one! A ringed barrel is no fun, I found out about air gap in a muzzle loader Kentucky I was particularly fond of, many moons ago.

March 18, 2012, 03:02 PM
To compensate for low powder levels in the chambers, I have found it best to use a filler such as Cream Of Wheat in order to get compression and compaction of the charge.

Pete D.
March 18, 2012, 05:55 PM
The concern with airspace over a black powder load is the risk that the burning powder mass will hit the base of the bullet like an obstruction and ring-bulge the barrel.
I don't see that. It doesn't happen with less than 100% density smokeless charges. As far as ringing the chamber of a MLer,...that is a different animal altogether.
About the Schutzen chambers....are we to believe that they ring their chambers every shot in the same place? And the gun survives?

March 18, 2012, 06:24 PM
Smokeless and black powder are two different animals. Black powder burns MUCH faster. Smokeless burns progressively so the bullet has already started to move before all the powder is burned and thus the bullet is not a bore obstruction. Does that make any sense to you?

March 18, 2012, 06:37 PM
I have found that different black powders react differently to compression. Goex usually shoots more consistently with moderate compression, but the Swiss I used to shoot in the early '00s didn't like compression at all.

March 18, 2012, 09:23 PM
''I don't see that. It doesn't happen with less than 100% density smokeless charges...''
Black powder is an explosive, smokeless is a propellant. As junkman pointed out these are completely different animals.

Pete D.
March 19, 2012, 08:26 AM
Black powder burns MUCH faster.
Does it? Does it really? BP confined in a firearm produces a pressure curve (it doesn't just explode) and propagates a flame front that is subsonic - that is why it is a "low explosive". Smokeless propellants (btw...if they are both pushing bullets, ie: propelling them, they are both propellants) do burn progressively and the speed of combustion is much affected by confinement in a case. Typically, smokeless powders produce much higher pressures faster.

Understand that I load a lot of BP and that I do not leave airspace in any shell or Mler that I use.....but I am always interested in discovering whether there is hard researched evidence - as opposed to anecdotal evidence - to back up some of the things that we believe.

Progressive burning is related to increasing pressure within the case after the primer has lit the charge. As the pressure increases in that nanosecond, the burn rate speeds up. Primers in cases -whether BP or Smkls - light up more than the end of the charge the spark propagates through the charge (though, certainly, the end nearest the primer bears the brunt of the flame.) and both produce a pressure curve, indicating a progressive burn in both. Though.....on the other hand....we are told that BP is relatively insensitive to pressure so that it burns at the same rate whether confined or not....so which is true?
I can readily find graphs of pressure curves for Smkls propellants - Bell curves all. I have been unable to find such a graph for BP - I have read that it is a "spike/taper", indictating a more explosive burn. I continue to wonder why leaving an airspace would be a problem even in that case. The bullet is against the charge when it goes off - pressure spikes and tapers. The bullet is 1/8" away from the charge, the pressure spikes and tapers. So?


March 19, 2012, 09:38 AM
I found the excerpts below on the following BPCR reference page which attempts to address both powder compression and no air space allowed.

The BP Cartridge Rifle Reloading Guide (rev. 9/18/03)

by Dick Trenk (Competition Events Coordinator, Davide Pedersoli & Co. )


The author prefaces by stating:

This is a different kind of reloading instruction text. You will not just be advised how to do things but you will also be given the reason why it is done that way. Many frank warnings and opinions will also be seen throughout this text.

Such remarks and opinions are those of the author and do not necessarily agree with those of manufacturers or other experienced shooters and reloaders. The shooting of black powder cartridge rifles is a great challenge and one which has very few finite rules.

The powder charge dumped quickly into the case or, the charge poured slowly down a drop tube, or powder dispensed from a hopper type powder measure, is considered to be "uncompressed". What you have after use of a long drop tube or the use of a vibration device, is a "settled" powder charge not a compressed charge.

All black powders respond for better or worse, when additional compression is applied. By far, the usual result of applying additional compression results in improvement to both accuracy and velocity. Sometimes you will also find lower barrel fouling as well.

Experimentation is required to determine what your powder likes best.

Match grade ammunition should always be compressed using a special "powder compression die". Using the bullet seating operation to compress the powder strongly may deform the soft bullet ogive in a manner so slight as to be unseen by your eyes, resulting in inaccuracy and possible jamming in the chamber.

You may find best speed or accuracy is obtained using an uncompressed charge or that compression as high a .300" produces better results. Due to grain crushing effect with excessive powder compression, it is not recommended to compress black powder more than .300". (Note that when duplicating 45-70 original military type ammunition used in Springfield Trapdoor models, very high amounts of compression is required. This should not be done for non-military type reloading in Trapdoor and other types of BP rifles. )

As mentioned above, bullets and wads must be in actual contact with the settled or compressed powder charge. If a significant amount of air space is present between powder and bullet, a dangerous pressure spike may occur which can "ring the chamber" or cause other forms of damage including personal injury.

Experts are not in agreement about this "chamber ringing" problem but to stay on the safe side I am advising not to allow more than 1/16" of air space between powder and wad or powder and bullet base.

Never intentionally load a small amount of black powder into a case which would create an unfilled air space larger than this distance.

March 19, 2012, 10:20 AM
Under powder charge, the author explains further about the risks associated with reduced loads. There's more written about it than is contained in this excerpt.

With a few exceptions, the original black powder era cartridge cases were designed to be fully filled with the appropriate black powder and partial filling was rarely permitted! If BP is fired in a partially filled case having a large amount of air space there may be a danger of producing a dangerous pressure spike which can "ring" the chamber or bulge the barrel. A small amount of air space not exceeding about 1/16 inch seems to be harmless but there is no good reason to have any air space at all and in fact a slight amount of powder compression is always recommended to hold the powder column in a rigid manner and promote consistent ignition pressures.

Unless you are working with one of those rare calibers mentioned above, do not leave significant air space inside the loaded case.

In an attempt to produce a mild reduced loading using black powder, some reloaders will put various light weight materials over the powder charge. As long as there is no free air space created these "fillers" seemed to cause no problems but accuracy will usually suffer a bit.

However, you will see some warnings and advice listed below.

If you do experiment with fillers, make certain to inspect your barrel after "all" the first few shots to see if there is any material being deposited inside the barrel.

If nothing seems to be accumulating in the barrel it may be safe to continue using that material but you should check frequently for possible buildup of burned material which may not wipe out easily and could cause inaccuracy or barrel damage.

Long ago, shooters found that Cream Of Wheat cereal, Dacron and other light fluffy material seemed to work well as a filler for reduced black powder loadings.

Lately, we have learned of problems and possible dangers with the use of fillers.

A recent product called "Pufflon" is made specifically to take up air space in smokeless powder cases or in BP cases. The maker's literature is full of advice but when I made a personal call and discussed it with the head man I was told they really have almost no experience using Pufflon with black powder and with BP size cases. I cannot make any remarks or opinions about Pufflon but would suggest avoiding reduced loads which require some sort of filler material.

It seems that common medical cotton balls, (opened up to increase their size) may be the safest material to use. With any type of filler, do not pack the filler tightly but leave it semi-loosely fitted over the powder charge.

Many shooters desire to use a smokeless powder charge in these large capacity BP cases. When done properly and with strict monitoring of the powder makers load data, this is not necessarily a dangerous thing to do in a modern-made BPCR.

I would under no circumstances use any sort of smokeless powder in an original old BPCR.

Recently there has be quite a few reports in the USA concerning modern BPCR which have suffered "rings" or "bulges" in their barrel or chamber region.

All these have been cause when smokeless powder loads were being fired.

Such damage can of course be caused by black powder as well but NEVER when a BP charge is made which has zero air space inside and when there is NO obstruction inside the barrel.

The reports I have been seeing concern smokeless powder charges printed in powder company, or reloading equipment catalogs. It appears that some powders can position themselves in such a manner inside the large cartridge case and when ignited, they can produce a shock wave or spike of pressure which may exceed 100,000 psi. Such a pressure can and will bulge, ring or actually burst the barrel or chamber.

Lots of opinions and research has been done on this problem but the answers are not yet settled among the many ballistics experts and master gunsmiths. If you elect to use a smokeless powder which produces a reduced pressure (lower recoil) you may be risking damage to your rifle, yourself and those nearby....


Foto Joe
March 19, 2012, 12:02 PM

Great reading, thanks. It seems that those of us who use fillers i.e. cornmeal in my case, are delving into the unknown according to the author. I agree that care should be taken when choosing a filler but cotton balls, really?

Pete D.
March 19, 2012, 01:18 PM
Arctic: Thanks for that. It was good reading. Personally, I use Pufflon in my loads that require a filler. There is some anecdotal evidence that the cereal fillers solidify if left for a while (how long?) and may do more damage as an obstruction than as a filler. I have not had a problem with Pufflon in either my 45-70 carbine loads nor for the large 577-450 Martini case (a bottle necked case with a long neck and a very wide base). The latter is especially difficult to load with a compressed charge because of its shape.
Based on the text that you provided, the jury is still out finding a definitive answer to my question.
I do know that Cabelas sold - and maybe still sells - 577/450 BP ammo in which there is no filler and plenty of air space. I had some and dismantled them but I am still curious - as you can tell.

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