doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com "Long Shells in Short Chambers"

Many thanks to Bill Johnson for scanning and sending �Long Shells in Short Chambers�, Sherman Bell with technical assistance from Tom Armbrust in �Finding Out for Myself� Part V, Double Gun Journal, Winter 2001

The test barrel was a �heavy� Krieger barrel with piezo-electric transducer at 1� from the breech and an Oehler velocity gauge 2 5/16� from the breech.
Tests were performed:
1. 2 1/2� chamber with a 7/16� forcing cone � �British chamber� (BC)
2. 2 1/2� chamber with a 1 1/4� forcing cone � �Modified British chamber� (MBC)
3. 2 3/4� chamber with a 1� forcing cone � �American Chamber� (AC)
Each load was tested in each chamber at least 5 times.
No significant change in velocity was noted between the 3 test chambers
It was not unusual to have 300-600 psi spread between shots

LOADS
1. 7/8 oz. in Federal plastic hull at 1185 fps in the 2 3/4� chamber
2. 7/8 oz. in Estate plastic hull at 1206 fps
3. 1 oz. in Federal paper hull at 1137 fps
4. 1 1/8 oz. in Federal paper hull at 1120 fps
5. 1 oz. in Remington plastic hull at 1205 fps
6. 1 1/8 oz. in Winchester plastic hull at 1186 fps
7. 1 1/4 oz. in Federal plastic hull at 1091 fps
8. 1 1/4 oz. in Winchester plastic hull at 1136 fps
9. 1 1/8 oz. with GOEX FFFg in Federal paper at 1184 fps
10. 1 1/8 oz. Bismuth in Federal plastic at 1091 fps
I only include the standard target or game loads that were tested

��..BC��...MBC�....AC�..Difference BCvsAC
1�..5725��.5905�..4834��891 psi
2�..6225��.6065�..5009��1216 psi
3�..5865��.5325�..5263��602 psi�..�long cones do reduce pressure�
4�..5845��.5665�..5058��787 psi
5�..7805��.7845�..7577��228 psi
6�.11,125�.11,045�10,787�338 psi
7�..6892��.6805�..5953��939 psi
8�..8765��.8545�..7870��895 psi
9�..5405��.5265�..4603��802 psi
10�6765��.6365�..6380��385 psi

Interpretation and caution:
1. Results in light British 12b or American small bore barrels may be different.
2. Results in YOUR barrel would require drilling the chamber for the transducer thereby destroying your gun.
3. Paper hulls with star crimps showed little difference compared to plastic hulls. NO roll crimp paper hulls were tested.
4. The increase in pressure comparing 1 oz., 1 1/8 oz., and 1 1/4 oz. loads was similar.
5. Longer cones MAY reduce pressure. This was NOT a comparison of standard 1� with 2 1/2� cones however.
6. �Shooting 2 3/4� shells in 2 1/2� chambers does make them produce more pressure-but in most cases it is less than a 1000 psi increase. I see no reason, related to safety, to modify an original 2 1/2� chambered gun to shoot 2 3/4� shells, if the 2 3/4� load you intend to use would develop pressure that is safe in that gun, when fired in a standard chamber!�
7. �We found that lengthening the forcing cone in a 2 1/2� chamber usually helps mitigate the pressure increase that comes from shooting 2 3/4� or 3� shells in the short chamber.�
8. �Shooting heavy 2 3/4� loads in a light gun is a dumb thing to do. Shooting 3� magnum duck loads is even dumber.�
9. This is not a study of the effect on RECOIL of shooting long shells in short chambers. Vintage 20g doubles may have chambers shorter than 2 1/2�, and it has been my experience that recoil is markedly increased if 2 3/4� shells are used.



Corrections, thoughts, opinions?

As for me, I use short 3/4 oz. RST shells in my 1906 2 9/16" chambered damascus 0E 16g Smith.
I lengthened the FCs in my 2 5/8" chambered 1913 12g Fox and use 2 3/4" B&P 7/8 oz. Competition One.
I lengthened the FCs in my 2 3/4" 1908 Smith pheasant gun which I use (rarely) with B&P MB Classic 1 1/8 oz. at 1330 fps BUT have had the stock glasbedded.
And I could have just wasted money.

Oh my. Now that is a summary!
Excellent.
When I read the article, I did a speed read and hurried to the summary. Thanks for making it EZ to interpret Drew.

I just left a message for Mr. Armbrust about testing a 20ga load.
This is the load I am considering shooting in my 2-1/2" damascus Flues. My thought was to see if he is setup with a 2-1/2" chambered 20ga test barrel and see if he would be willing to test my 2-3/4" load in that barrel. That would take some of the guesswork out of the total pressure number. Still may be a bit of variation due to forcing cone shape/length.
Fun stuff!

AA hull
3/4 oz shot
Win 209 primer
14.5 20/28 Powder
CB 1075-20 Wad
7,200PSI

1 grain of powder up yields 1250FPS and 7900psi
Hopefully 1 grain down will yield 1150FPS and 6500psi
Then add 1000psi for short chambers and 7500psi


This caught my eye as well
It was not unusual to have 300-600 psi spread between shots

Bill

Thanks Drew!!!! Darn good of you to post this!

Best,

Greg

Drew,
I am not surprised by the results posted. What appears to be overlooked in tests of this type is the importance of recording the expanded length of the shell and the wall thickness of the shell casing.
A modern day 2 3/4 plastic shell case when fired/ expanded measures 2 5/8,inches approximately thus entering a 2 1/2 chambered guns forcing cone by approximately 1/8 of an inch. A typical plastic shell case wall is .025 thick. If we consider that the Diameter of the chamber at the mouth of the forcing cone on a 12G is .800 approximately a 1/8 protrusion into the forcing cone dose not create a reduction in diameter that is likely influence breech pressure. As seen from the test results the recorded breech pressure varies from the combination of powder plus cap, plus charge of shot and weight of wad in the test charge.
It was a much different scenario in the 1870-1900's when a 2 3/4 shell measured exactly that and shell cases used a card tube which was thicker than todays plastic. The net result was bore restriction if chambered in a 2 1/2 chambered gun.[ie always assuming you had the strength to close the action!]
The key safety issue in so far as, "In proof" English guns is concerned is to is to make sure the shells used do not exceed the approved breech pressure. I think it was Burrard writing on this subject who said," no shell case ever burst a gun."

Doc Drew, very nice summary! Thanks for posting.

Bill, I've used that same 3/4 oz 20ga load you're sending out for testing. I dropped down a bushing, using 13.8gr 20/28. Very reliable, even in cold weather. I haven't had any tested for pressure, but from the "book" numbers, it certainly looks as if you'd be under 7,000 psi with that load. And that's pretty darned low in 20ga. I use the load in a Damascus-barreled British 20ga, still 2 1/2" but reproofed at 3 tons. Those 3/4 oz 20's are GREAT to shoot in lightweight guns!

Larry,
Good morning.
Excellent news! Thanks for posting. Saved me $50.00+/-.

Are you loading it to 2-3/4" or "rolling your own" at 2-1/2"?

Best,
Bill

I've shot those loads in several 20's, Bill--most with 2 3/4" chambers. I use also use them in 2 3/4" hulls in my 2 1/2" gun. Even though that's pretty low pressure, I might worry about it more were it not for the gun's modern 3 ton reproof.

With that said, I'll have them tested at 13.8 with a 2-1/2" rolled crimp. When I get the results, I'll let you know how they look.

Thanks!

To all upthread - I gotta thank you for posting this load. I've been looking for a light/low-pressure load I can run through my 20 ga and I think you just posted it.

Even better - at trap the other day someone tossed 3 boxes of once-fired 20 ga AA hulls. They came home with me.

Please let us know how the 2 1/2 rolled crimp tests out.

Thanks again!

Dave,
Please confirm the load on the Alliant site.
I'd hate to think I made a mistake.

Look toward the bottom of the AA hull data for the 7200psi load.
I believe you will find that @ 7200psi the load is 14.5gr.


Best,
Bill