Chamber Pressures

[Bruce Day]

Not wanting to sound like Mr Knowitall, but here are some figures that some might find interesting when it comes to shooting old shotguns whether composite or fluid steel barrels . I welcome thoughtful discussion. I refer to 12 ga because that is easiest.

1. Most of these old guns were made for a working load max chamber pressure of 10,500 psi and proofed at 13,500. Later the proof was increased to 15,000. These are average pressures .

2. Present working load pressure is 12,000 psi max , proof also increased. Suggest people review SAAMI pdf on line. The interesting point is that these are average pressures, it is allowable to exceed the average by two coefficients of variation, each coefficient being 7.5 percent. That means a SAAMI allowable load could be at 13,800psi , which exceeds what used to be proof loads for vintage guns.

3. The reason we see hot loads today is twofold, first to cycle some autos that are difficult and second to reduce leading the target for shooters who have difficulty with lead( who doesn't). Browning now is selling pheasant loads of 1 1/4 oz at over 1400 fps. These are probably at 12,000 chamber pressure average again . Other manufacturers do the same.

4. So when we speak of "modern" loads and ask if they are permissible to shoot in our vintage guns, fluid or composite steel, what is modern ? There are plenty of modern loads made by manufacturers today that fall under , some well under , the 10,500 psi chamber pressure limitation , and plenty that exceed that and are still SAAMI allowable. Couple a hot load with the allowable two coefficients of standard variation for error, and it can be a hot load indeed.

5. So I personally regularly buy Remington , federal or Winchester loads, but I make sure to stay below the old limitation, with a margin of error for coefficient variation. RST shells are fine too, and Morris seems to understand the need to stay within the older pressure limitations .

6. Some weeks ago we saw a photo of bulged barrels on a 16 ga Damascus Parker. I don't know how this happened, I haven't examined the gun, don't know the chamber wall thickness, but things like this can happen if you start with a load at or near allowable max with higher shot weight and speed and then encounter coefficient of variation increase of up to 15 percent.

Best,
Bruce Day

[Dean Romig]

I find it strange that ammo manufacturers don't print the p.s.i. rating on the box along with the dr. eq., the shot size, ounces of shot, and length of the shell.

Bruce, can you tell us what makes Remington, Federal, and Winchester more acceptable than all of the dozen or more other manufacturers of quality shotgun ammunition?

For those who have difficulty with learning the correct lead to allow in any given shooting situation, I suggest they stick with the exact same load every time they shoot until they have it figured out and are consistently powdering targets. (Notice I didn't suggest practicing on live birds - crippling birds shouldn't be an acceptable part of anyone's learning process.)






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[B. Dudley]

And they will not always tell you what they are if you contact them. Most just tell you to refer to SAAMI specs for the given gauge. Real Help...

[Drew Hause]

The 'ol boys used some boomer loads

DuPont Trophy Oct 24 & 25 1895
http://www.la84foundation.org/Sports.../SL2606012.pdf
Capt. John L. Brewer was using a Greener gun of high grade. His shells were the U.M.C. Trap, 3 1/4 inches long, 4 Drams of DuPont (Bulk) powder by measure; one trap wad, two pink felts, 1/4 inch 11-gauge wad and one ordinary 12-gauge pink edge wad over the powder and 1 1/4 ounces of No. 7 chilled shot; the shell had a very hard square crimp.

From “Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics” by Wallace H Coxe; E.I. du Pont de Nemours & Co., 1927 pressures for 1 1/4 oz. 3 3/4 Dr. Eq.
Ballistite maximum pressure at 1” was 4.9 Long Tons = 15,344 psi by Burrard's conversion
Schultze at 1 3/4” was 4.5 Long Tons = 14,000 psi
DuPont Bulk at 1 2/3” was 4.1 Long Tons = 12,656 psi
All well above SAAMI recommended max. pressure

More information
https://docs.google.com/document/d/1...UOZEFU/preview

[Big D]

Seems to me that velocity is overrated.

Allow me a few simplifying assumptions:
Bird is flying across at 30 mph at 30 yards
Two different loads - 1200 fps and 1400 fps. For simplicity, I will assume the average speed of the shot over the travel to the bird is 900 fps and 1050.

The difference in the movement of the bird between the two loads is about 3".

[Bruce Day]

Dean, I buy Fed , Rem or Win because my mind can only remember so many load pressures. I don't know Rio, Fiocci , Kent etc and it's only because I haven't looked. A smart fellow would know them all.

Drew, yes those early fellows blew some very stout loads without problem. Bulk smokeless is measure in drams same as black, dense smokeless in drams equivalent black.

You know I forget to factor in the small pressure increase of short chambers, 3 to 5 percent I understand. Not significant in itself but combined with up to 15 variation , it could be.

[Bruce Day]

Originally Posted by John Dallas

Seems to me that velocity is overrated.

Allow me a few simplifying assumptions:
Bird is flying across at 30 mph at 30 yards
Two different loads - 1200 fps and 1400 fps. For simplicity, I will assume the average speed of the shot over the travel to the bird is 900 fps and 1050.

The difference in the movement of the bird between the two loads is about 3".

You are preaching to the choir. And absolutely correct. But it allows a manufacturer to sell a customer on his annual pheasant hunt , at Cabelas in Mitchell South Dakota , a box of 1 1/4 oz 5's at 1400 fps for $15 instead of a box of 1 1/8 oz 6's at 1180 for $8. And if I keep on missing , it must be because I need more powerful shells.

[Drew Hause]

"Bulk smokeless is measure in drams same as black, dense smokeless in drams equivalent black."

Indeed, and the reason for many of the damascus bursts

Sporting Life Sept. 10, 1904
“Burst Gun Barrels”
http://library.la84.org/SportsLibrar.../SL4326021.pdf
The number of burst gun-barrels which, comes to the attention of the shooting public is remarkably small, considering the thousands of guns in use throughout the country. The main reason for the comparatively small number of guns burst is the great use of factory-loaded shells, or the hand-loaded of reliable dealers. The day of loading one’s own shells is pretty well passed, therefore, the over-loaded or double-charged cartridge is very seldom found. Very often a burst barrel is blamed on the gunmaker or the shell-maker, but more often on the manufacturer of the powder. Cases are known where a party blowing out a gun-barrel, using an extra heavy charge of dense powder, blamed it on a bulk powder. A suit for damages was quickly withdrawn after an examination of the gun had been made.

1907 Sears, Roebuck & Co. Catalogue No. 116 courtesy of Gary Rennles

“Nitro powder should only be used by people familiar with it; and dense nitro powder should be weighed by an apothecary’s scale and not measured.”



A 3 Dr. Eq. (Dram Equivalent) load of “E.C.” No. 1 or “Schultze” was 42 grains by weight. 3 Dr. Eq. of Dense Smokeless Ballistite was 24 grains; Infallible 21 grains. The pressure of a 3 Dram (82 grains by volume) load of Black Powder propelling 1 1/8 oz. of shot at 1200 fps is about 5000 psi. The pressure of 1 1/8 oz. 3 Dr. Eq. of BULK Smokeless was 6500 - 7500 psi; 3 Dr. Eq. of DENSE Smokeless was 9000 - 10,000 psi.

Substituting a Dense Smokeless powder for Black or Bulk Smokeless powder would double the charge. It has been estimated that 50 grains of Infallible or Unique could reach 30,000 psi. Combine this error with a 3” shell in a 2 5/8” or 2 1/2” chamber, and a barrel rupture might occur in any barrel, fluid steel or Pattern Welded.

[Drew Hause]

1902 Sears catalog No. 112

"Gun and rifle barrels can only burst by having some obstruction in the barrel or by overloading with Nitro powder."



THE PARKER GUNS: ALL ARE BORED FOR NITRO OR BLACK POWDER

[Mike Poindexter]

Bruce, I once had a 90% 1927 VH on a 1 1/2 frame with very slight barrel bulges about 4 inches out from the breech. So slight I missed them on the 3 day inspection, and was SOL with the seller on Gunbroker. My bad. The point is, after reading Sherman Bell's series of overload articles, and assuming that there was no obstruction causing the bulge (both bulges were identical in form and location) I just wonder what kind of load must have caused those bulges?? Perhaps a 3" magnum in a 2 3/4 or 2 5/8 chamber? Bell ran up some massive pressures without deformation on his junker test barrels. Just wondering. ( I sold the gun to a pawn shop with full disclosure of the bulges for half price--I didnt feel the bulges were unsafe with low pressure loads, only unsightly. Complex situational ethics. Others may have handled it differently.)