Warning about using Magtech CBC shotgun cases in rifles. - Graybeard Outdoors
 
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post #1 of 2 (permalink) Old 05-11-2005, 08:10 PM Thread Starter
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Default Warning about using Magtech CBC shotgun cases in rifles.

Issue:
During fireforming, cases suffered partial head separation and bulged heads.

Equipment:

Rifle: Martini Henry 1878 MkII maker mark faded

Cases: CBC 24 Gauge brass shotgun cases reformed to 577/450 rifle cases.

Observations

The three cases presented experienced partial head separation directly adjacent to rim. Brass extrusion occurred in the area of extractor cutouts and adjacent to rim seat directly in front of rim where separation took place.



One case experienced bugled head.



Loads used in failed cases:

Ruptured cases. 70 gr of GOEX Fg topped with a 50/50 mix of CoW and FFg made using Lee 20 gr dipper, a fiber card wad, a grease cookie, fiber card wad, and CBE .462 500gr bullet.

Bulged case. 70 gr by volume of Pyrodex topped off with 50/50 mix of COW and FFg made using one Lee 20 gr dipper, a fiber card wad, a grease cookie, fiber card wad, and CBE .462 500gr bullet.

Examinations:

The separation on these cases occurred directly in front of the rim with soot from gas flow leading back towards the rim. Examination of the interior seemed to indicate the case were of a balloon head design which was confirmed by sectioning. Sectioning does not show any signs of stretching and web thinning normally associated with head separation. The head separation can be seen at the left side of the CBC case in the section photo.

Discussion :

The separation of case heads is not unusual in rifles with excessive headspace or in rifles in which brass has been swapped from one rifle to another. The separation normally occurs in the web area just ahead of the solid head of the case approximately ¼ inch up from the bottom of the case. The head separation in these cases has occurred directly in front of the head. In the CBC case the head is much thinner than a solid head case. The separation is directly in front of the case head which is adjacent to the junction of the chamber and the rim seat.

Some will argue whether the correct terminology for these cases is balloon head. All the literature I found call these cases balloon head or semi balloon head and in the U.S. they have been called that for over 100 years. This discussion is not about semantics or proper nomenclature. Call them what you want. This discussion is to try and determine why these cases failed.


Bertram Solid head left. MagTec Balloon head Right.


Modern Handloading by George Nonte


Handloading by Wm. C. Davis for the National Rifle Association


The Complete Guide to Handloading by Philip B. Sharpe.

Phil Sharpe in his book The Complete Guide to Handloading written in 1937 describes the problems with what he refers to as semi balloon head cases and his description fits almost identically to what is observed in the cases being discussed here. Sharpe discussed a difference in loading density and that the brass had a tendency to upset and flow into extractor cuts. Sharpe also reported that the protruding primer pockets of these cases tended to break off. Sharpe does say that reason the pockets break, was never clearly defined. He also reports problems with balloon head cases was evident in black powder, smokeless powder and low pressure black powder and smokeless powder loads. Sharpe stated these same problems are rarely seen in modern solid head drawn cases. Sharpe finally noted that although as late 1937 the manufacturers of revolver ammunition still used balloon head cases, all rifle cases since the turn of the century were solid head construction.

The balloon head of the CBC case gives it a far greater volume than the solid head case. This is not bad unto itself. Sharpe touches on this in some experimenting he did with 38 SPL cases he found that when loaded with the same bullet, primer and amount of powder, balloon head cases gave lower pressures values than solid head.

Modern standardization of measurements and tolerances provided a means of duplicating rifle chambers from one gun to the next. Standardization made mass production possible and allowed ammunition makers to make ammo that fit every rifle. I have not been able to find any recorded information listing the correct or standard headspace measurements for the Martini Henry rifle chamber at time of manufacturer. Chamber dimensions can be found, but tolerances are not defined. The 577/450 cartridge is a rimmed cartridge and headspace in a rimmed chamber is defined by modern standards as the distance from the datum line to the breech face. The datum line is the surface in the rimmed chamber where the front of the case rim contacts the chamber. Multiple drawings with a myriad of dimensions exist for the various versions of the 577/450 cartridge. The majority of drawings I have observed show a rim dimension of .050 for the Martini cartridge. Applying modern standards there can be up to +0.006 difference in the headspace length and still be serviceable (NO-GO gauge). For battle field dimensions the difference could up to +0.010 (FIELD gauge). See Ackley’s Handbook for Shooters and Reloaders for a good discussion on headspace.

Measurements:

Measurements were taken from several Martini rifles to try and establish a pattern or norm for headspace dimensions. The proper way to take these measurements would have been with a series of precision rim gauges to measure the headspace. Not having such gauges, I utilized several new unfired cases and three original rounds for measuring.


Feeler gauge measurements

The measurements consisted of chambering a round in the gun and closing the breech with a feeler gauge between case head and breech block. This method of measuring does not give a measurement of the headspace of the chamber, it simply gives the gap between cartridge head and breech face or the headspace of the given cartridge. The cartridge rim becomes the GO gauge. Any measurement in excess of 0.006 would exceed the NO-GO dimensions for that particular cartridge case. In excess of 0.010 would exceed FIELD dimensions for the given cartridge case.


Chart

Examination of the CBC cases disclosed the rim seat or forward edge of the rim is not flat. The rim seat surface is angular making it difficult to get a consistent repeatable reference point on the rim. This angular surface affects the cartridge headspace by allowing the cartridge to go deeper in the chamber than it would if it had a flat rim seat and increases head to breech gap.


CBC left, Kynoch right.

In an attempt to chamber the various test rounds in the various chambers it became very evident that there existed a wide variation in chamber dimensions from one Martini rifle to another. Difference in body taper and shoulder shape from one chamber to another in 577/450 Martini’s were noted. The Kynoch and Bertram cases fit in every chamber tried. In some cases the CBC round could not even be forced into the chamber. This is most likely a product of the form die used and has nothing to do with the case itself. After chambering the foil case cartridge in all the chambers, measurements were retaken with different results. It appeared that the foil case due to its thin walls reformed itself to the chamber with the smallest dimensions.

Case Volume:
An empty new unfired Kynoch case, empty new unfired Bertram case and an empty new unfired MagTech case were weighed. Cases were primed with a dead primer before weighing. Each case was then filled with water and reweighed. The cases were dried and filled to the top of the case with GOEX Fg and that charge was weighed. The cases were emptied and refilled by visual observation to the bottom of the neck.



It is obvious that the CBC balloon head case has a far greater volume than the solid head cases.

As a side note Temple and Skennerton reported that the proof load used to test the Martini Henry was 137 grs. of FG and a 715 gr. Bullet.

Firing Tests:

Test #1

Three Bertram new unfired solid head, three Kynoch new unfired solid head and six CBC new unfired balloon head cases were primed with Winchester Large rifle primers and loaded with the traditional LoC load of 85 grs. of Fg, card wad, wax wad, card wad and 500gr. bullet. Air space was filled with 0.6 grs of kapok. After loading of the cartridges the head of each round was checked with a straight edge for flatness. After firing the head flatness was checked again. When loaded in the rifle each round was checked for head to breech face gap. After firing gap measurements where checked.

Test results:
No head separation of any type was experienced. All cases had varying degrees of primer protrusion. One Bertram case and two CBC cases experienced pierced primers. As expected it was not possible to measure a gap between any case head and breech face after firing. All CBC case showed varying degrees of head bulging. No solid head case showed any sign of head bulging. Sectioning of case heads showed no thinning of webs in any of the three cases.


L to R, Bertram, CBC, and Kynoch

TEST #2

Five Bertram new unfired solid head and five CBC new unfired balloon head cases were load with various combinations of the original load that had resulted in head separations.

One Bertram and one CBC case were loaded with 90 grs. GOEX Fg with 0.6 grs. Kapok filler.

Two Bertram and two CBC cases were load with 70 grs. of GOEX Fg, and a 50/50 CoW mix of 19.8 grs. of GOEX Fg and an equivalent volume of CoW*.

One Bertram and one CBC case were loaded with 90 grs. GOEX FFg with 0.6 grs. Kapok filler.

One Bertram and one CBC case were load with 70 grs. of GOEX FFg, and a 50/50 CoW mix of 19.8 grs. of GOEX FFg and an equivalent volume of CoW*.

All cartridges were topped off with a card wad, wax wad, card wad and 500gr. bullet. Remington large rifle primers were used in this test After loading of the cartridges the head of each round was checked with a straight edge for flatness. After firing the head flatness was checked again.

*A Lee 1.3 cc powder dipper was used to make the original 50/50 CoW. FFg was weighed from this dipper and found to deliver 19.8 grs. A volume powder measure was adjusted to hold this weighed 19.8 grs. of powder and that was used to measure the CoW.

All powder charges in all the tests in this report were weighed.

Test results:
No head separation of any type was experienced. All cases had varying degrees of minor primer protrusion. No cases experienced pierced primers. All CBC case showed varying degrees of head bulging. CBC cases using FFg had the most extreme case head bulge.


CBC case head flatness check, before firing.


CBC case head flatness check, after firing.


Same CBC case head sectioned.


Bertram case head flatness check, after firing.


Conclusions

In the U.S. the type case construction used in the CBC cases is called balloon head. (or call it what ever you want) This type of case construction has a long documented history of not be being as strong as the solid head design. The use of this type of case construction was discontinued by makers of rifle ammunition prior to 1900 because of its inherent design weakness.

If excessive cartridge headspace exists, these cases can fail.

Fg and FFg grade black power caused distortion of these balloon head cases. FFG caused extreme distortion.

This rifle has excessive cartridge headspace when used with CBC cases.


Recommendations:

Before shooting any cartridge in a Martini, check the head space of the cartridge to be used. Insert an empty new unfired case in the chamber and make sure it is fully seated. Place a 0.006 inch feeler gauge at the back of the cartridge head and close the breech block. If the gauge is not held by the breech block the rifle should be considered to have failed the NO-GO headspace and it is not recommended to be fired with that case. Repeat the test with a 0.010 inch feeler gauge. If the feeler gauge is not held when the breech block is closed the gun is considered to have failed the FIELD test and should not be fired with that case.

Use solid head cases only.

If you must use balloon head cases use FG powder only. If a brand other than GOEX Fg is used, do test firing and check for head bulging. Head bulging can be checked by placing a straight edge like a steel ruler on the head of the case, and holding the case and ruler up to the light. Tilt the ruler at 45 degrees toward you and look for the light between the head and ruler.


Do not volume load black powder particularly in CBC cases! Weigh all charges and filler on a scale. Do not fill these case to the bottom of the neck with black powder and load.
.
Bibliography:

[Philip B. Sharpe, The Complete Guide to Handloading, Funk and Wagnall Company, Third Edition, Second revision copyright 1937, 1941, 1949, 1952 and 1953.

Parker O. Ackley, Handbook for Shooters and Reloaders, Volume 1, Plaza Publishing, copyright 1962.

B.A. Temple & I.D. Skennerton, A Treatise on the British Military Martini, The Martini-Henry, 1869-C1900 B.A. Temple Publisher, copyright 1983
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post #2 of 2 (permalink) Old 10-22-2018, 11:33 AM
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My Martini Endfield was re-barrelled and cambered for Bell brass. When I switched to Magtec brass I found the rim to thin for a good head space. I epoxied a thin steal ring (trimmed key ring) on top of the rim to get a .050 rim thickness. For light loads so far so good.
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