Brazilian single shot SB1 head space. - Graybeard Outdoors
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post #1 of 13 (permalink) Old 07-22-2019, 04:21 PM Thread Starter
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Default Brazilian single shot SB1 head space.

I aquired a beater single barrel 12ga that I had what I thought was the barrel for it the barrel locks up tight but for some reason I have a hunch its not the barrel it had originally, the problem is it wont fire any of the cartridges Ive tried in it, not even a hint of a dent.
Yet the hammer and fireing pin seem to work well.
Even the firing pin protrusion seems like it should fire it but it wont.
How can I check the cartrige headspace?
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post #2 of 13 (permalink) Old 07-22-2019, 04:31 PM
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A GO-NO GO gauge is the proper way but I've heard of putting layers of Scotch tape on an empty new shell till it won't close or lock up. Seems like Scotch tape was .002 thick, your mileage may vary.

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post #3 of 13 (permalink) Old 07-23-2019, 06:44 AM
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Sounds to me like the rim recess is too deep. If you have a dial indicator gauge, you could measure the depth of the rim recess with a shell in the chamber. If not, northwood's tape method will get you close enough.

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post #4 of 13 (permalink) Old 07-23-2019, 07:07 AM
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Hold your gun so it's pointed straight up in the air and fire it. The cartridge should be setting flush against the bolt face in this position. If it doesn't fire you should still get a dent of some sort on the primer to indicated that it is indeed a head space issue.

Since it is a shotgun it does headspace off of the rim. So PDKfishing is spot on!
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post #5 of 13 (permalink) Old 07-23-2019, 01:56 PM
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Excuse me for playing Captain Obvious, but is the firing pin broken? Be much easier to eliminate that possibility by taking the hammer to full kock, and slowly letting it down with the trigger depressed while watching to see if it sticks out the hole.

My father bought an LC Smith side by side 12 ga that had BOTH firing pins broken. It happens.

(But I'm sure that was the first thing you checked.)
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post #6 of 13 (permalink) Old 07-26-2019, 04:25 PM Thread Starter
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Yes the the firing pin protrudes when the trigger is pulled and the hammer is thumbed forward and pushed fully forward as it would in firing, the nose of the firing pin sticks out.
(I already thought of a broken FP)
I also replaced the hammer strut spring thinking it might have taken a set, thinking a weak hammer spring was not throwing the hammer far eonough or with sufficent force.
The paper head space trick is usefull, Id used that trick before on a barreled Mosin that had no bolt.
I found I could close the bolt on a cartridge with one layer of Post-It paper (not the sticky end) it closed on one layer but not two.
In Highschool shop class it was normal to clean the measuring surfaces of your micrometer using a sheet of tablet paper, I noticed over time that paper can have amazingly consistant thickness (noted when cleaning)
Paper is somewhat compressable but it gives you something to work with.
In another forum one poster was askibg about using cellophane tape to check head space in a arm chambered in 7.9233mm kurz.

Last edited by Rex in OTZ; 07-26-2019 at 04:33 PM.
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post #7 of 13 (permalink) Old 07-27-2019, 10:07 PM
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An easy check for headspace of a single shot's barrel is to place a cartridge in the chamber and place a straight edge across the end of the barrel. The headspace of the cartridge being used can then be measured using feeler gauges. If that checks out okay, then you can check the fit of the barrel to the frame using sight, feeler gauges, or paper strips. Close the barrel and look at the side with a light on the opposite side. If light shines between the frame and barrel, then the gap can be measured with paper or feeler gauges. Up to .002 gap between frame and barrel is of very little concern. Cartridge head to end of barrel should be .005 or less, ideally but up to.008 should still be safe. If the cartridge has been reloaded with properly adjusted dies, your headspace measurement should be .001-.002. If you use a variety of ammunition sources, you may find variation in headspace measurements from one to the next. Using a commercial go gage and feeler gages will allow you to know if headspace is within SAAMI specs.

2120-September 1, 1945
To: D A MacArthur /C H Nimitz
From: H S Truman
Political Correctness is a doctrine, recently fostered by a delusional , illogical minority and promoted by a sick mainstream media, which holds forth the proposition that it is entirely possible to pick up a piece of cr*p by the clean end!

Now, with special thanks to the Truman Museum and Harry himself, you and I finally have a full understanding of what "POLITICAL CORRECTNESS" really means.....
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post #8 of 13 (permalink) Old 07-28-2019, 10:03 PM Thread Starter
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Well today I dug it out and measured the firing pin protrusion.
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post #9 of 13 (permalink) Old 07-28-2019, 10:29 PM
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The FP tip is way too flat! Is that a reading of .10 inches? Should be .050-.060 inches.

2120-September 1, 1945
To: D A MacArthur /C H Nimitz
From: H S Truman
Political Correctness is a doctrine, recently fostered by a delusional , illogical minority and promoted by a sick mainstream media, which holds forth the proposition that it is entirely possible to pick up a piece of cr*p by the clean end!

Now, with special thanks to the Truman Museum and Harry himself, you and I finally have a full understanding of what "POLITICAL CORRECTNESS" really means.....
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post #10 of 13 (permalink) Old 07-29-2019, 12:35 AM Thread Starter
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I had some Post-It paper, I measured the paper.
I was able to fit 4 over the cartridge base, 3 sheets worked fine but tight, the 4th sheet, I had to push the barrel lock closed, otherwise I wouldnt lock closed on its own.
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