throat of a gun barrel.i

Discussion in 'Technical Questions & Information' started by gnbrown97, Apr 27, 2011.

  1. gnbrown97

    gnbrown97 New Member

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    i am confused about the throat in a barrel. is this the distance a shell fits into the barrel? i have heard about throat erosion? an example is a 23/4 shell as compared to a 3" that fits into the barrel. can you shoot a 3" shell in 23/4 barrel?:):cool:
  2. Jim K

    Jim K New Member

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    Last question first. NO, you can't fire a 3" shotgun shell in a gun chambered for 2 3/4; it won't go all the way in. You can fire a 2 3/4 in a 3" chamber, though it might not operate a semi auto.

    Now as to throat. That term is normally applied to rifles and means the area of the barrel immediately ahead of the cartridge case where the bullet sits before firing. It is also sometimes called the "leade". The equivalent term in a shotgun is normally "forcing cone" since it forces the shot charge into a more compact mass before it enters the barrel.

    Throat (forcing cone) erosion is not a significant problem in shotguns since pressures are low and the shotgun wads prevent the gas escape that causes erosion in rifles. Let me explain a bit.

    When a rifle is fired, one of the first things the gas pressure from the burning powder does is to expand the thin brass at the case neck and mouth. This leaves the bullet free of the case and for an instant it sort of sits there, held in place by its own inertia.

    The high pressure gas, meantime, moves around the bullet and acts, in that confined space, much like a cutting torch. It is that effect that eventually erodes the steel of the barrel at the throat, causing what is called throat erosion. If it gets bad enough, the bullet leaving the case does not enter a tight barrel throat but rather exits into an open space in which it can skid or skew, being scraped, twisted or bent, none of which is good for accuracy when the bullet finally exits the barrel.

    Jim
  3. Hawg

    Hawg Active Member

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    Ummm Jim, yes it will chamber. Shotgun shell length is measured once the shell is fired not before. The problem arises when the 3 inch shell is fired the crimp opens up over the forcing cone raising pressure drastically. I have accidentally fired 3 inchers out of 2 3/4 chambers with no problems but I don't recommend it.
  4. gnbrown97

    gnbrown97 New Member

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    thank u guys. i understand. this forum seems to work compared to some others. by the way iam an older gent getting ready to go to machine school for gunsmithing, actually a fully disabled veteran & proud!
  5. Hawg

    Hawg Active Member

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    Thank you for your service.
  6. Warith

    Warith Member

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    Welcome to the site gnbrown97 and thanks for your service.
  7. Jim K

    Jim K New Member

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    Gnbrown, ditto on the thanks for your service.

    Hawg, good point, but fit of the longer shell seems to depend on the chambering, and maybe on the maker, and I probably should have said "sometimes." I have tried to put 3" shells into 2 3/4" chambers and had to force them in if they went in at all, because the body of the longer shell will ride into the leade of the forcing cone. Sometimes they will go in OK and fire, as you say, with the only concern being pressure. Regardless, firing 3" shells in a 2 3/4" barrel is not advisable and they won't feed or eject in most pump and semi-auto guns.

    Jim
  8. Hawg

    Hawg Active Member

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    I dunno Jim. I even accidentally fired one out of my 1887 Winchester. Thankfully with no damage to the gun. Didn't do the shell much good tho.:D

    [​IMG]
  9. Jim Hauff

    Jim Hauff New Member

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    I got a 1930's vintage Win. Mod. 12 at a great price and gave it to my oldest nephew as a b'day present. My Nephew, BIL and I went out to the range and were firing stuff, when the kid pulled out the M12 and began blasting away. I checked a couple of his fired hulls and they looked like the one Hawg posted above. The nephew had bought a box of 3"ers and the gun was chambered for 2 3/4"ers. They fed and extracted, but firing them sure screwed up the hulls. Got to give a little lesson on shotguns and ammo - BIL needed some edgecation also.
  10. Jim K

    Jim K New Member

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    Wow! Is that the plastic base actually backing out of the shell?

    Jim
  11. Hawg

    Hawg Active Member

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    Yeah, the case head split and the upper half went into the action. The gun was an original 1887 winchester with a 2 9/16 inch chamber. I'm just glad no damage was done to the gun. I grew up hunting with it with 2 3/4 smokeless loads because I didn't know any better. Now I cut down shells and reload with black powder and a roll crimp. I was just careless one day and got a 3 inch shell mixed in with my reloads and didn't notice it when I loaded it. I don't even own a gun chambered for 3 inch shells but I got a bunch of loose ones when my dad died. He didn't have a 3 inch gun either so I dunno why he had them. I've since gone back and cut down all the 3 inch ones so it wont happen again.
  12. Jim K

    Jim K New Member

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    I am surprised a 3" would even feed in an '87, the way they work. The result there looks almost like a headspace problem since it would seem to me something had to give to allow the base wad to come back like that.

    Jim
  13. Hawg

    Hawg Active Member

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    No headspace problem. It still works fine. It didn't feed. That one got loaded directly into the chamber.
    Last edited: Apr 28, 2011
  14. gunplumber

    gunplumber New Member

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    I've had a few shotguns where folks were shooting 3in and the bbl was chambered for 2.75. The complaint was feeding and ejection. A couple times I fired the thangs without checking the ammo used and while they did fire, it made you want to say very bad things (esp after picking up a 3in hull fired from a shorter cham). It gets very hard on the shoulder, not to mention the underwear.
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