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Cas City Forum Hall & CAS-L  |  CAS TOPICS  |  Gunsmithing  |  Topic: .45LC SAA headspace ? 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: .45LC SAA headspace ?  (Read 1816 times)
Marshal Deadwood
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« on: March 27, 2007, 06:39:56 pm »


How much headspace is 'acceptable' in a SAA .45LC ?
Thank you

Marshal Deadwood

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Sagebrush Burns
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« Reply #1 on: March 27, 2007, 11:35:40 pm »

45 Colt and all rimmed cartridges (such as 44-40, 45-70, 357 mag.) headspace on the rim.  It not like a bottleneck rifle case (30-06, 243, etc.) that headspace on the shoulder.  As (I think) I understand your question, there is no such thing.
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Marshal Deadwood
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« Reply #2 on: March 28, 2007, 01:18:08 am »

Sagebrush, your thinking 'shoulder space' and not headspace. Headspace is rearward, the distance between the rim and frame of the revolver.

Marshal Deadwood
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Driftwood Johnson
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« Reply #3 on: March 28, 2007, 09:40:22 am »

Howdy

Actually the term 'headspace' has a couple of meanings. It can refer to the method by which a cartridge comes to rest in the chamber, as in '45ACP headspaces on the case mouth, or 45 Colt head spaces on the rim'.

It can also refer to the amount of free space behind the bolt when the breech has been closed. This dual use of the same term oftem leads to exactly the kind of confusion we have just seen.


'Headspace' with the SAA is not a hard number. It varies slightly by cartridge. In the case of the SAA, headspace is defined as the distance between the rear of the cylinder and the front of the recoil shield, not the clearance between the rear of the rim, and the recoil shield, as rim thickness can vary.

Here is what Kuhnahausen has to say on the subject:

Cartridge        Case Rim Thickness              Case Head Clearance      Headspace Gauge Rim WIdth
45 Colt           .049 min/.060 max                .006                             .062 (go)  .067 (no go)
44-40             .055 min/.065 max                .006                             .067 (go)  .072 (no go)
44 Special       .049 min/.060 max                .006                             .062 (go)  .067 (no go)   
38-40             .055 min/.065 max                .006                             .067 (go)  .072 (no go) 
38 Special       .048 min/.059 max                .006                             .060 (go)  .066 (no go)
357 Magnum   .049 min/.060 max                .006                             .060 (go)  .067 (no go)
32-20             .055 min/.065max                 .006                             .067 (go)  .072 (no go)

Notice that in this chart, the headspace is a range, not a single dimension. This would be the numbers under the Headspace Gauge Rim Width column. The 'Case Head Clearance' number is just an average, it will depend on the actual rim thickness. So with a wost case 45 Colt rim thickness of .060, the smallest allowable head space of .062 will still allow .002 of clearance between the rim and the recoil shield. Whereas the thinnest rim, or .049 and the widest allowable headspace of .067 will allow .018 of clearance. As with all mechanical tolerances, there are usually other considerations too. Firing pin protrusion for the SAA is specified as .045 min and .056 max. If there is too much clearance between the rim of a cartridge and the recoil shield, it is conceivable that a firing pin may not protrude enough to reliably fire a cartridge.

It also needs to be stated that these numbers assume zero endshake. "Although headspace can be estimated with the cylinder pushed to the rear, accurate measurement requires that cylinder endplay be reduced to as close to zero as possible." Kuhnhausen
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Thats bad business! How long do you think Id stay in operation if it cost me money every time I pulled a job? If hed pay me that much to stop robbing him, Id stop robbing him.

Ya probably inherited every penny ya got!
Sagebrush Burns
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« Reply #4 on: March 28, 2007, 11:35:13 am »

Thanks for the information - you learn something new every day if you will...
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