BPCR Guide: Powder Charge

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Written by: Dick Trenk

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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.

To avoid this risk, you should do one of the following:

  1. Use only BP loaded to apply “some” compression on the powder charge.
  2. Use only a smokeless powder charge printed by the powder manufacturer which is correct for the bullet you are going to use and, which produces a full pressure upon ignition (not a so called reduced load).
  3. Change to a smaller caliber rifle to obtain reduced recoil affect.

Original (old) BP guns do not have the improved steel alloy as is used in modern replica BP firearms. An original BP firearm should be properly inspected by a gunsmith who is qualified to pronounce it to be in safe firing condition and not every gunsmith would have that qualification.

Various tests such as X-ray, Zyglow and Magnaflux testing can be performed to verify the internal condition of the firearm.

Such original BP firearms should only be fired using the correct grade of BP and NEVER with a smokeless powder charge (even when thought to be moderate in pressure) is not recommended.

Modern made replica guns in good condition may use smokeless (rifle powder) loads providing the pressures generated do not exceed those produced by the original black powder charge it is the owners responsibility to contact the manufacturer of the rifle and obtain their pressure limits.

Note and be advised, that just because a smokeless loading may be rated at the same pressure as a BP loading, the actual pressure spike and time involved is quite different from what happens when BP is ignited. The smokeless can produce a dangerous pressure in both the chamber and barrel! Therefore, consult the gun maker for smokeless pressure limits and if you cannot obtain this data (maker out of business or won’t supply the data) then we strongly advise not to use smokeless powder in any manner.

DO NOT use any smokeless powder unless you have seen the powder manufacturers loading recommendations and pressure data. If you cannot obtain this vital data then DO NOT use that smokeless powder under any circumstances. Contact the powder manufacturer and obtain the official data.

At this time, the only powder company which has published proper test data and load recommendations for just about every old black powder cartridge case is the Accurate Arms Co. , maker of Accurate brand smokeless powders. They have available a superb reloading book which covers all BP calibers as well as all the bullets weights likely to be used properly, and gives the pressure data you will need when using their brand of smokeless powders. This book is titled “Accurate Loading Guide Number Two.”

However, as mentioned earlier, it is risky and uncertain, to use a smokeless powder reduced loading, no matter what the printed book may indicate.

Other powder makers do offer reloading suggestions for their smokeless powders but so far none cover the full range of large BP cartridges and bullet choices as does the Accurate Arms book.

With smokeless powders the safe pressure limits of replica guns can easily be exceeded therefore you must obtain and read the powder makers data sheets first.

The Davide Pedersoli Co. officially authorizes black powder and smokeless powder reloads which do not exceed 29000 psi (or CUP) for all their centerfire cartridge BP rifles. Other replica manufacturers have not openly published their allowable pressure data so you are advised to contact those other firms and request this vital information before reloading near maximum pressures.

WARNING: Recently there has been at least one commercial ammo company (Buffalo Bore Ammo co. ) offering 45-70 ammo which they claim produces around 42,000 psi pressure. Such pressures would definitely be damaging to most old original rifles as well as modern replica rifles if it were used regularly. You are warned against the use of such ammunition.


In an effort to obtain faster muzzle velocity and a less fouled barrel condition, some shooters insert both smokeless and black powder into the ctg. case. This is called a “Duplex Load”.

Be advised that there is obvious danger involved in a duplex loading and there are NO gun manufacturers who officially approve of this type of loading.

In Canada and some other parts of the world, the use of duplex loading is still approved for some long range match conditions but at the time of this being written, the American NRA is considering changing the rules concerning the use of duplex loads and possibly making pure BP mandatory. You are advised to contact the sanctioning organization running any shooting match to verify the current loading rules.

Basically, a duplex load involves putting a small amount of smokeless powder into the case first, then the black powder is placed on top of the smokeless powder.

No wad or material is used to separate the two powders.

The BP is compressed in your usual manner and the over powder wad (if used) installed, then the bullet is seated on the wad in a normal manner.

The smokeless powder selected must be of a fairly slow burning rate, thus a fast burning pistol powder would produce dangerous pressures with possible damage or injury.

While the Canadian rules allow up to 25% of the black powder charge “weight” to be replaced with an equal weight of smokeless powder, this is in the opinion of most US shooters to be both excessive and highly dangerous in even modern made guns.

Experience has shown that Alliant Reloader 7 or IMR 3031 or IMR 4759 powder used in place of 5% to 10 % of the original BP charge weight delivers a large speed increase as well as a very clean barrel condition.

This author has used up to 5% of IMR 4759 with good results and pressures remained in a safe range. I would not use more than 5% because a stronger pressure is simply not needed.

The ASSRA shooters seem to prefer the IMR 4759 powder.

Other powders which have a similar or slower burning rate may also be tried in small percentages and such loads are to always be developed with strict attention paid to pressure indications during firing tests.

The above mentioned Accurate Arms book will provide that firm’s smokeless powder recommendations and other powder firms can be contacted for their suggestions for use of their brands of smokeless powders.

Remember…remove the same percent of weight from the original BP charge and replace it with the same weight of the smokeless powder.

Example of a 10% duplex charge: Original BP charge weighed 70.0 grains. Ten percent would be 7.0 grains.

Therefore the final loading would be 7.0 grains of a proper smokeless powder plus 70.0 minus 7.0 equals 63.0 grains of black powder. The total of both powders comes back up to the original 70.0 grains.

From the very beginning of smokeless powder, the shooters started to add smokeless to their BP loads. They obtained faster muzzle velocities and cleaner barrels just as we get today.

Because accurate pressure testing cannot be done by ordinary shooters, you simply have no way to know the amount of internal chamber pressure and the time lapse in which it occurs.

Such costly and highly technical measurement equipment is found at gun and powder manufacturers, not at home loading benches.

To my knowledge, no powder manufacturer actually publishes any duplex loading suggestions because of the obvious dangers involved. I advise you to consult other shooters who have developed a safe duplex load for your caliber and bullet weight.

This sharing of duplex information is common on the several internet “chat boards” and dedicated BPCR “message boards.”

The Pedersoli company does not officially recommend or authorize the use of any duplex loading due to the impossibility of knowing just what pressure any duplex load would develop. If you decide to shoot duplex you do so at your own risk.