Bolt head sizes? |
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Goosic
Senior Member Joined: September 12 2017 Location: Phoenix Arizona Status: Offline Points: 8792 |
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Typically between .0042" - .0050" is acceptable...
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scottz63
Senior Member Joined: November 08 2021 Location: Mid Mo Status: Offline Points: 829 |
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Got it. Thanks!
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14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer
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britrifles
Senior Member Joined: February 03 2018 Location: Atlanta, GA Status: Online Points: 6539 |
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0.04 to 0.05 inches for striker protrusion from bolt head face.
One of my No. 4 rifles has only 0.03 inches of striker protrusion, not had any issues with primers not igniting. I suspect that is in part due to a fairly tight headspace, in that the cartridge can’t move very far away from the bolt head face before the rim hits the back of the chamber face. This was a rifle that headspace exceeded 0.070 (don’t know by how much) and I replaced the #1 bolt head with a #3 bolt head which brought headspace to between 0.064 and 0.070, which I suspect reduced the headspace by .005 to 0.010. |
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Shamu
Admin Group Logo Designer / Donating Member Joined: April 25 2007 Location: MD, USA. Status: Offline Points: 17603 |
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People go on about "headspace" but I see little to nothing about "Free Headspace"! Whats the difference? Rim thickness! If your rifle has a loose, but within limits headspace & the rim is thin then, the rim doesn't fill the space available. The gap is the Free Headspace. There's always a little, there has to be, but when it gets excessive it can cause issues like primers backing out & cases stretching excessively.
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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Goosic
Senior Member Joined: September 12 2017 Location: Phoenix Arizona Status: Offline Points: 8792 |
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The, "Free Space" can be made near non-existent if you consistently use cartridge cases with the same rim thickness in combination with the longest bolthead available that will almost fail a .070" NoGo gauge.
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britrifles
Senior Member Joined: February 03 2018 Location: Atlanta, GA Status: Online Points: 6539 |
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I agree Shamu.
I could see a condition where striker protrusion is on the low side, headspace on the high side and rim thickness on the low side combining to result in erratic primer ignition (as one problem that can occur with these combined issues). The cartridge will first get pushed forward by the striker until the rim contacts the back of the chamber. A cartridge case that has been fire formed and then neck sized will then “headspace” on the shoulder and take up the “free headspace” that you described. |
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britrifles
Senior Member Joined: February 03 2018 Location: Atlanta, GA Status: Online Points: 6539 |
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It’s mostly an issue with commercial cases made to SAAMI specs, which specifies a rim thickness of 0.054 to 0.064 inches. I’ve measured some cases with rims very close to this minimum (0.054 inches).
Combine that with headspace at or near Field (0.074) then we get a awful lot of “free headspace”. Potentially as much as 0.020 inches. One of the things I like about PPU brass is that it has rim thicknesses in the 0.060 to 0.062 inches. The Canadian military brass I have has rims in the 0.062 to 0.064 range. |
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Shamu
Admin Group Logo Designer / Donating Member Joined: April 25 2007 Location: MD, USA. Status: Offline Points: 17603 |
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We're all experienced L-E owners so we're familiar with these things. But we do have several members on here concerned with head-spacing & new to the rimmed .303 rounds peculiarities. I just figured I'd run it up the flagpole & see if anyone saluted. |
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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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scottz63
Senior Member Joined: November 08 2021 Location: Mid Mo Status: Offline Points: 829 |
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Thanks everyone for all the info. .303 is a new cartridge for me. I have 30 plus years of Military surplus experience, but .303 has eluded me until now, somehow. Lol
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14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer
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scottz63
Senior Member Joined: November 08 2021 Location: Mid Mo Status: Offline Points: 829 |
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Just checked a couple of S&B .303 rounds for rim thickness. .061
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14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer
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Goosic
Senior Member Joined: September 12 2017 Location: Phoenix Arizona Status: Offline Points: 8792 |
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All of my Herters brass has a rim thickness of 0.060"
Using a Forster .070" gauge, the bolt almost closes. I made a set of custom brass feeler gauges that I can slip between the cartridge case rim and the bolt, face with the bolt closed. My "free space" is only 0.008"
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britrifles
Senior Member Joined: February 03 2018 Location: Atlanta, GA Status: Online Points: 6539 |
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Just for grins, I check several R-P cases I have. Rim thickness measured 0.056 to 0.058. A bit on the thin side.
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scottz63
Senior Member Joined: November 08 2021 Location: Mid Mo Status: Offline Points: 829 |
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I have a couple of WW2 303 rounds. Going to go check what they are.
Edit: "U" marked .054 "CAC" marked .057 |
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14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer
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scottz63
Senior Member Joined: November 08 2021 Location: Mid Mo Status: Offline Points: 829 |
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What Arkansas stone should I get? There is hard, medium, and soft. Also different hardness scale ones. Thanks, Scott
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14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer
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Shamu
Admin Group Logo Designer / Donating Member Joined: April 25 2007 Location: MD, USA. Status: Offline Points: 17603 |
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Hard
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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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scottz63
Senior Member Joined: November 08 2021 Location: Mid Mo Status: Offline Points: 829 |
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Got it. Thanks!
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14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer
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