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Elasticity of chamber, hot loads and sticky bolt

 
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Old 12-21-2013, 07:01 AM
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Elasticity of chamber, hot loads and sticky bolt

After reviewing some comments regarding stuck bolts and my only really hot load and what rifle it's used in. A useless thing happened, I had a thought.

I have never experienced sticky bolt. I have loaded hot enough to make ejector marks. Not as bad as one posted today but they are there.

Others reported sticky bolt but nothing else.

We know all the metals involved in the firearm and ammo have elasticity characteristics.

so

Is 'sticky bolt' caused when the pressures of the firing process cause some elastic stretch in the chamber such that the brass goes beyond chamber dimensions and when the chamber contracts the brass is captured?
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Old 12-21-2013, 08:18 AM
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Re: Elasticity of chamber, hot loads and sticky bolt

I think besides an overly hot load causing a sticky bolt, my experience has been the there a a few factors that can cause this, even at standard pressure.
-The chamber/headspace of a particular rifle being too long, short, or not concentric.
-Fast burning powders causing the case to take a disproportionate amount of pressure.
-Insufficient resizing of the fired case. Adjust or modify the dye.
It's pretty easy to determine the rifle's headspace and chamber concentricity. I have also reduced sticky bolt effects just by changing brass as they do vary in thickness and composition. When neck sizing only, the cases will eventually have to have the shoulder and/or body resized, and this will be indicated by a sticky bolt . I also have found that while ejector marks or flat/cratered primers are an indicator of high pressure and reason for checking it out, it could very well just be the particular bolt face or stiff ejector button causing this, even at acceptable pressures. IMO
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Old 12-21-2013, 08:55 AM
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Re: Elasticity of chamber, hot loads and sticky bolt

Quote:
Originally Posted by jfseaman View Post
Is 'sticky bolt' caused when the pressures of the firing process cause some elastic stretch in the chamber such that the brass goes beyond chamber dimensions and when the chamber contracts the brass is captured?
Yes, this is true(beyond unfired chamber dimensions), and way overlooked by reloaders, and by those building custom guns lately. Brass changing beyond 1thou yields, and does not springback fully to original dimension, while a chamber certainly does return to original.

There a 3 ways to head it off from the git-go.
-Choose a modern or improved cartridge design.
-Provide sufficient barrel steel around your particular chamber & load.
-Measure brass in-hand before filling out a reamer print, and go no more than 1thou over webline(.200" forward of extraction groove). In fact, you can go 1thou over with every dimension with your reamer w/resp to new in-hand brass. Order the ~$100 reamer, and have your barrel and seating dies finished to match brass that you will produce with fireforming.

If you do these things, you will never need to FL size a piece of brass, because the brass will forever springback this amount. It won't need much in sizing, trimming, annealing, etc.
And, every time you read someone implying a 'requirement' to FL size, recognize that they did not address this issue that suddenly spewed from your brain. They made choices that put them where they are.
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Old 12-21-2013, 09:12 AM
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Re: Elasticity of chamber, hot loads and sticky bolt

When a stiff bolt lift and shiny areas on the case heads are present together on a spent case beware you are treading on dangerous ground, metaphorically speaking. Some rifles/chambers are different when pushed to excessive pressure, for instance another rifle may flatten primers and swell primer pockets so the cases are unusable for another loading but will never exhibit sticky bolt lift. I once had a Winchester rifle chambered in 7STW that when loaded with factory ammo (two different boxes) , after three shots the bolt would hardly open almost to the point of breaking off the bolt handle. This rifle showed no other evidence of excessive pressure what so ever. I sometimes read accounts where handloaders will start load development at the max charge of powder according the their data manual and it makes me cringe because I have had a rifle that if loaded to this level would probably have experienced a KABOOM. I have also read on-line postings by handloaders piously claiming they always adhere to this manual or that one, therefore they never have to worry about their ammo. I have loaded rifles beyond the book and consider data manuals a mostly reliable guideline only.
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