doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 2 3/4" in a 2 1/2" Chamber

I know this sound.
When I try to epxplain the same 2-piper said here on Russian board, some people tell me: Ts-s-s-s! Stupid-heads could hear this and begin to use hot 70 mm ammo in 65 mm guns.
For me it's good idea all stupid-heads would use the hotest loads in their weak guns, but I can bet there are only few of such around the world!

I suppose using a very low pressure 2 3/4 inch shell would be better than using a 2 1/2" round that produces very high pressures!

Another great When is an elephant not an elephant? argument!Been "loads" of fun listening to this and I'd have to say Niklas has got you all ("traindrivers" and otherwise) beat for "in the trenches" empiricism and apparently his research didn't require much more than a cheap slide caliper. When everything's "nominal" there are a heck of a lot of special cases each with its own specific risk factor which our many "take it on authority" gurus seem unable to pin down.

jack

It really is hard to "get one by" ALL of the folks on this board.

Niklas

Smallbore, did you discuss reloaded 2 3/4" cases with the proofmaster, or did you refer only to factory 2 3/4" shells? Many of us here have clearly drawn that distinction--as did both Burrard and Thomas, with their very clear warnings NOT to use American factory 2 3/4" shells in guns with 2 1/2" chambers. All of us agree 100% with those warnings.

We also have the issue of the nominal "67MM" Gamebore shell--which, you will note, I measured with a digital caliper to have a fired length of 2.63". That's almost exactly 2 5/8", or 1/8" longer than the chamber length of a 2 1/2" gun. Yet right on the box, Gamebore will tell you that that shell is suitable for use in guns with 2 1/2" chambers. If case length is the problem, how can that be so? Answer: case length is NOT the problem, per Burrard, Thomas, and Bell. IF the case is loaded to pressure parameters appropriate for the gun in question--and most of us on this side of the pond are reloading VERY low pressure 7/8 oz reloads for our short-chambered 12's, around 6,000 psi--it doesn't make any difference whether the case is 1/8" or 2/10" longer than the chamber. Tests by Burrard, Thomas, and Bell--using instruments to measure pressure--have shown either no increase in pressure from the longer case, or only a very slight increase in pressure.

When the length of the fired hull exceeds the length of the chamber by no more than 1/4", the danger comes not from the extra length, but from what's inside the hull to start with.

Steve-

I think you have masterfully stated in one sentence what has taken 10 pages of discussion! I suspect that a lot of the "do's and don'ts" were very valid for the guns and ammunition for the time of the rule.

This discussion is likely so full of passion because so many of the forum members have been using low pressure reloaded 2 3/4" shells in their shorter chambers for years without any problems and it appears that there is no credible evidence (all things being equal) that the longer shell length significantly increases pressures.

Nonetheless, who among us would not purchase 2 1/2" low pressure loads for our older guns if they were available at $3.59 a box?

I can understand why the larger manufacturers do not cater to this need. It is for the same reason new made private aircraft are no longer widely manufactured...product liability concerns.

Midway markets a very sweet 7/8 oz 2 3/4" 5000psi load which one would think ideal for an older damascus barreled gun...and no doubt Midway and Federal are very much aware that the consumer would use the load for these more delicate applications, so they expressly state that the load is not intended for damascus barrels.

Doug

Builder mentions getting unexpected pressure yield from shortened hull and Hartin crimp which if I remember right is a fold crimp of the remainder of previous factory crimp on top of overshot card. Makes me wonder about the relative "containment" strength of the various crimping methods and if this has any effect on chamber pressure. Does anyone know if either the Hartin or the outmoded roll crimp would generally be associated with a higher pressure yield than would the industry standard fold crimp, given same payload and charge?

jack

I think any of us that have read Sherman Bells articles in DGJ
as well as some of the English articles feel very comfortable with "2 3/4" ammo in 2 1/2 chambers. I use STS cases and 22.5
gr. 7625 with 1 oz of shot and they are low pressure and fine. As stated many times there is only about 100 psi increase and of course the STS and WW are about 2 5/8 in length.

Jack,

I have a bit of information bearing on this. I have long used the hartin crimp on 65 mm hulls (made by cutting down 70 mm hulls) and also under the star crimps of 70 mm hulls to give better (non dished in) crimps. The latter usage is generally with lightened loads that do not fill the case enough for non-dished star crimps. With these lightened loads in 70 mm hulls, I use 12 gauge overshot card wads in 12 gauge and 16 gauge overshot card wads in 16 gauge. "Normal" hartin crimp practice seems to be to use overcard wads one or two gauge size smaller (16 or 20 in 12 gauge, etc.).

With the addition of same gauge overshot card wad under normal star crimps I seem to consistantly get more complete burning of the powder and seem to get this same more complete burning if the hulls have been shortened. This seems as it should be because any strengthing of this "compound" crimp would logically occur along the hull walls. With sub gauge sized overshot card wads this same strengthening would not be expected.

I do have one chamber pressure datum and it does indicate that use of same-gauge sized overshot card wads does increase chamber pressure at least a few hundred psi, maybe even a thousand psi. However, there is not the degree of control on this result that I would like.

Niklas

In my Harten crimp on the cut down 2 1/2" Remington STS hull I was unable to get the 12 gauge overshot card into the hull due to the irregular shape of the open crimp and had to switch to 20 gauge overshot cards. These are the ones I had tested. I attributed it to an error in the published book. Intuitively, I would think that the Harten crimp using the 20 gauge overshot card would lower the pressure since it looks like it would be easier opening than a standard crimp. Intuition does not always work and Jack may have a point.