Excessive headspace on semi auto pistols?


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Fire8523
February 10, 2014, 07:40 PM
Hello all

Working on a project of a 460 rowland conversion.

I have all the specs for the case lengths and such of the 45 acp and the 460
I'm measuring with my depth from rim for my headspace of .952 the gun chambers the go gauge and hangs up on the no go but then closes. It's catching the extractor and then breaks free and chambers. I did a fire test on it and had a good solid primer strike and good ejection. No case markings other than some scratches from reaming.

My question is is there a such thing as excessive headspace on semi auto pistols? Some say that it's silly to think so

I have chambered many rifles on the lathe but a pistol was my first

If there is such a thing as excessive headspace is there a way to correct it on a 1911 non ramped barrel

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rcmodel
February 10, 2014, 08:25 PM
1. Yes, there is such a thing.

See this Sticky in Gunsmithing about that.
http://www.thehighroad.org/showthread.php?t=176251

I don't consider it a deal breaker in .45 auto, except in very accurate match guns.

However, it can result in breach-face battering in higher pressure calibers from the cases blowing back and hammering the slide.

2. No, if the chamber headspace step is reamed too deep, there is no fixing it, short of a new barrel.

rc

BBBBill
February 10, 2014, 10:28 PM
Take the extractor out. It should not be installed when checking headspace. Also, be aware that dynamic headspace is different from static headspace. Just because the chamber is reamed to minimum does not mean that the dynamic headspace is safe. You have to consider the amount of slack in the fore aft mating of the locking lugs which is directly related to the amount of gap between the hood and the breachface. Also, many 1911 barrels are over throated leaving too much unsupported case. You can live with it on a 19,000 PSI 45ACP, but a 460 Rowland will probably blow out and tear up your gun, not to mention your hand. All of that to encourage you to know exactly what you are doing. If in doubt, find a real pro to check your work.

Fire8523
February 10, 2014, 11:01 PM
I will take the extractor out and check it the lugs lock and the breach closes and the case is well supported. Thanks guys for the tips.

log man
February 13, 2014, 12:16 PM
To get a more accurate result of actual head space. First slip in feeler gauges between the hood end and breech face by pulling the slide back a little and allow to return to battery. Once you have established how much it takes to stop it from going to battery and just will close to battery, you will have the number to add to the hood end to chamber shoulder. That is the only head space number that matters. As the instant the primer is ignited that is the dimension between the shoulder and breech. The hood does not control head space.

LOG

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