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#34328 04/05/07 04:28 PM
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Is is safe and ok to use low pressure 2 3/4" 12 gauge shells in a nitro proofed gun with 2 1/2" Chambers? If so, what would be the recommended pressure to stay under? Thanks!

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Steve, absolutley not. Use only 2 1/2" shells and low pressure because that is what that gun was made for when proofed. Others will say it is ok, but the 2 3/4" shell won't open fully causing a lot of extra pressure.
I would stay to around 8,000 psi.

Last edited by JDW; 04/05/07 04:43 PM.

David


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If you need low pressure 2 1/2" cartridges for an older gun, contact Polywad or RST.

http://www.polywad-shotgun-shells.com/

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Just noticed that WLM is now offering 2.5" low-pressure shells for 12 & 16 ga. as well. Website is http://www.williamlarkinmoore.com/product_details.asp?id=1443

Here's what they're offering:

Shotgun & Shooting Accessories, Ammunition, 12 GA & 16GA, 2 1/2, 1180 fps velocity& 7000 psi max pressure, extra hard shot, 1 pc plastic wad, Specially developed and loaded exclusively for us by Thunderbird Cartridge Co. Designed for older guns with 2 1 /2" chambers. For use only in sound, quality guns originally built with 2 1/2" or longer chambers and using smokeless ammuntion. Case price $80.00 per flat of 10 boxes. $9

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JMC: I shoot the WLM 7/8 oz 2 1/2" 16s regularly. The 16s are only available in 8s. Thunderbird is a local outfit and they use Fiocchi cases. Quality loads similar to RST or Polywad.

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Originally Posted By: JDW
Steve, absolutley not. Use only 2 1/2" shells and low pressure because that is what that gun was made for when proofed. Others will say it is ok, but the 2 3/4" shell won't open fully causing a lot of extra pressure.
I would stay to around 8,000 psi.


It is not that simple and Sherman Bells articles in DGJ have shown that it MAY be ok. The ' a lot extra pressure' has not been documented in Bells articles in which a pressure gun was used.

Also the fact that many historic makers often 'short chambered' their guns.

You will also find that many 2 1/2" shells are actually 67.5mm long and standard 2 1/2" chamber is actually 65mm long.

I am not trying to be contrary but the answer is not as simple as JDW has made it seem.


Last edited by Utah Shotgunner; 04/05/07 10:35 PM.

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I have a 2 9/16" singleshot Iver Johnson that replicates the chambers in two damascus sxs guns. I also have a Pressure Trace piezio transducer pressure measurment instrument and a chronograph. The Iver is instrumented and serves as my test gun for pressure testing.

After reading Sherman Bell's article where a true 2 1/2", short forcing cone, chamber was used to test 2 3/4" shells, I went forward with the knowledge that he got a maximum of about 15% increase in pressure after testing a variety of loads, and some had no increased pressure. The average increase in pressure seemed to be about 10%.

I shoot full 2 3/4" paper Fed shells loaded to generate about 6500 psi in the short chambers. The loading manual I have suggests this load should generate around 7000 psi. That loading manual refers to a 2 3/4" chamber pressure gun.

I've shot hundreds of these loads thru my damascus guns. When in doubt, get real data. Everything else is heresay. If someone has direct knowledge that this is an unsafe practice to shoot 2 3/4" shells in a 2 1/2 -2 9/16" chamber, please share.

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The American and British "system" of shotshell lengths is confussing. There are 2,0, 2 1/4, (2 3/8?), 2 1/2, 2 9/16, 2 5/8, 2 3/4, 2 7/8. It is so much simpler with just 65, 67, 70 mm.

Then add actual chamber lenghts -- it is widely reported that USA makers once found that 1/8 inch shorter chambers than fired hulls gave tighter patters. Then add the modern tendency to increace forcing cone lengths in old guns from those essential with card and fiber wads.

Most of my old doubles have 65 or 67 mm chambers and short forcing cones. I shoot 65 and 67 mm ammo in them rather interchangably, as "allowed" by CIP regs. I DO NOT shoot American-made ammo with actual 70 mm hulls and near SAAMI chamber pressures in any of them.

I don't even shoot low pressure handloads in true 70 mm hulls in any of the 65 mm chambers. Reason? More recoil, which can only be higher velocity, which can only be result of increased chamber pressure, which can only be because of additional 5,0 mm of hull in short forcing cone. I do not find this with 65 vs 67 mm hulls.

Some shooters get the short (about 1.0 cm) forcing cones lenghtened to 3-4 cm. They claim it lets them safely shoot 70 mm hulled ammo in these guns, without lengthening the chambers.

Take any simple statements about chamber vs fired hull lenght with ample salt, including Tom Bells qualified statement.

Niklas

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The Winter 2001 Double Gun Journal has the article by Sherman Bell called "Finding Out for Myself" Part V "Long Shells in Short Chambers".

After extensive testing carried out in a very professional manner he concludes:

"With loads that are sensible in a light 2 1/2 inch gun, we see no dangerous pressure levels produced. I see no reason, related to safety, to modify an original 2 1/2 inch chambered gun to shoot 2 3/4 shells, If The 2 3/4 Inch Load You Intend To Use Would Develop Pressure That Is Safe In That Gun, When Fired In A Standard Chamber!

I personally perceive slightly greater recoil with my 2 9/16" chambered 16g LC than with my 2 3/4" chambered 16g LC using the same 2 1/2" shells, and for that reason the brls are with Dan Lammers getting the chambers lengthened right now.

Last edited by revdocdrew; 04/05/07 11:15 PM.
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