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Double Rifles, Single Shots & Combinations >> Building Double Rifles & Gunsmithing
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2Barrels
.224 member


Reged: 23/06/12
Posts: 17
Loc: Moving USA
Case Rim Thickness Issue
      #235173 - 05/09/13 03:25 PM

Just received a 450/400 NE 3" that I had built on a J.P. Sauer SxS 12ga shotgun, and ran across an issue that I'm not sure how to go about having corrected.

I have 10rnds of live Hornady ammo left over from a previous 450/500 NE 3" and 80 or so brand new Hornady 450/400 NE 3" brass. Went to shoot the gun tonight just to see how it handled. Of the 10rnds, I was only able to completely close the gun on 4 rnds. By completely close, I mean, top lever back to center or just right of center, and the Greener cross-bolt flush with the receiver.
Took some initial measurements of the brass rim thickness. Cases with a rim thickness of .058" or less allow complete closure and lock-up of the action. Thicker rimmed cases do not allow full closure and lock-up. Measured pretty much every case - loaded and unprimed new brass that I have. Rim thickness falls between .057" and .062". From what I can tell the case rim thickness should be .065" from the case drawing I was able to locate. I could understand having an issue if the rim thickness of the brass I have exceeded .065" but it doesn't. This issue does not bode well with me and not sure how to go about correcting it. The gun closes and locks up tight when the chambers are empty - every time.

http://www.loaddata.com/members/search_detail.cfm?MetallicID=5750

What's the next step?

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500Nitro
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Reged: 06/01/03
Posts: 7244
Loc: Victoria, Australia
Re: Case Rim Thickness Issue [Re: 2Barrels]
      #235174 - 05/09/13 03:29 PM


It's a pain when you get a gun like that.
Have occasionally found it myself.

Solution
Get the rim of the chambers reamed out.


In the old days when ammo was scarce,
people who had the 3 1/4" guns had the
chamber rims reamed to take the 3" rim
thickness ammo.

So it does work.

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xausa
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Reged: 07/03/07
Posts: 2037
Loc: Tennessee, USA
Re: Case Rim Thickness Issue [Re: 2Barrels]
      #235193 - 06/09/13 12:35 AM

Quote:

What's the next step?



In your place I would ask the maker of the gun how he headspaced it. It could be that he made it with insufficient headspace to compensate for any initial loosening of the action. In any case, you should have the final say as to how it is headspaced. Since it will only accept forty percent of factory rounds, I would say that that is grounds for concern.

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transvaal
.300 member


Reged: 19/01/13
Posts: 131
Loc: South Carolina
Re: Case Rim Thickness Issue [Re: xausa]
      #235199 - 06/09/13 03:47 AM

Gunmakers that are experienced cut the rim for the cambering of large nitrox express cartridges to the very minimum, as excessive space will cause excessive felt recoil. .002" depth of rim of your barrels in excess of the maximum rim thickness is all that I would cut if I were making the gun.

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aromakr
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Reged: 20/04/11
Posts: 849
Loc: Hamilton, Montana
Re: Case Rim Thickness Issue [Re: transvaal]
      #235211 - 06/09/13 09:41 AM

First off I would check the chambers and rim recess to make sure there is no crud build up, .007 is not very thick, that's about 1/4 of the thickness of a piece of computer paper. With the case spec's calling for a .065 and your rifle not closing completely until .058 there is something holding that case up. A chamber cast would be my next step. Do you know who built the rifle? If so I would contact him for advise.

Something else you could try. take something like a popsicle stick, cut the end square and scrape the rim recess, if there is a burr it will show up by stopping the movement of the stick, if its a burr the only recourse I can see is re-chambering,
Bob

Edited by aromakr (06/09/13 09:48 AM)

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twobobbwana
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Reged: 25/11/11
Posts: 299
Loc: Queensland, Australia
Re: Case Rim Thickness Issue [Re: aromakr]
      #235213 - 06/09/13 10:45 AM

2 Barrells,

If the correct dimensions are .065" and your rifle won't close on anything thicker than .058" then the rim section of the chamber is too shallow and you should get your gunsmith to correct this. I'd probably get it cut to .062", being the greatest thickness of rim you'll encounter (??).......but that doesn't allow for crud in the rim section of the chamber.

However you could restrict use of cartridges to .058" or less rim thickness.

Or get a buddy with a lathe to turn the inside of the rims to suit the chamber and enjoy "perfect" headspace.

Whichever way you go do not force the gun close. This is very hard on hinged guns.

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500Nitro
.450 member


Reged: 06/01/03
Posts: 7244
Loc: Victoria, Australia
Re: Case Rim Thickness Issue [Re: twobobbwana]
      #235214 - 06/09/13 10:52 AM

"However you could restrict use of cartridges to .058" or less rim thickness."

No, don't do this.

It is a Big Time PITA.

I have a gun, original that is like this, only likes
thinner thin rim brass and it is a pain.

Cut to max as he said above, allows for oil, crud etc.
Once the cases stretch the first time and you only
neck size, it doesn't really matter.

Edited by 500Nitro (06/09/13 02:04 PM)

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transvaal
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Reged: 19/01/13
Posts: 131
Loc: South Carolina
Re: Case Rim Thickness Issue [Re: 500Nitro]
      #235218 - 06/09/13 12:41 PM

Page 30 of the 1954 issue of the British "rules of proof" delineates that the "Maximum Dimension of the rim thickness of .450/.400 Nitro Express 3 inch Cartridges to be: .065 Inch.

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aromakr
.375 member


Reged: 20/04/11
Posts: 849
Loc: Hamilton, Montana
Re: Case Rim Thickness Issue [Re: transvaal]
      #235234 - 07/09/13 12:43 AM

One other thing I thought of last night. Giving the gunsmith that built it the benefit of the doubt, it probably left his shop working correctly, that makes me think something mechanical has happened to keep the case from seating properly in the chamber. Another place to look will be under the extractor. There should be a small screw on the underside and between the barrels, remove that screw this will allow the extractor to be removed. If powder residue has built up in that area it prevent the extractor from seating all the way down, thus holding the case up slightly, again .007 isn't very much, it would not take much build up to cause this to happen.
Bob

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2Barrels
.224 member


Reged: 23/06/12
Posts: 17
Loc: Moving USA
Re: Case Rim Thickness Issue [Re: aromakr]
      #235372 - 10/09/13 12:03 AM

Bob/aromkr,

You make a good point about removing the extractor and checking for and removing any build-up. I did so in the process of trying to locate the 'issue'. Pretty much eliminated the extractor, or build-up under it when I tried chambering a round w/o the extractor installed. That scenario also proved to be a 'no-go' situation.

I have the reamer and gauges on the way. They're on the brown truck scheduled for delivery later today. I'll go from there.

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DarylS
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Reged: 10/08/05
Posts: 26992
Loc: Beautiful British Columbia, Ca...
Re: Case Rim Thickness Issue [Re: 2Barrels]
      #235373 - 10/09/13 12:39 AM

2-barrels - if the extractor's rim recess sits proud of the barrel's extractor cuttout, it will have to be 'reamed' along with the chamber/s.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

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2Barrels
.224 member


Reged: 23/06/12
Posts: 17
Loc: Moving USA
Re: Case Rim Thickness Issue [Re: DarylS]
      #235609 - 14/09/13 06:26 AM

Quote:

2-barrels - if the extractor's rim recess sits proud of the barrel's extractor cuttout, it will have to be 'reamed' along with the chamber/s.



Correct. I took that into account when reaming the chambers.

Chambers have been reamed and the rim cut measures .065 all the way around in both barrels. Head-space gage is dead-flush and I verified that the action can, and does, close properly all of the brass and loaded ammo I have.

I'll have the gun out for an extended test drive this weekend.

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