Headspace Discussion For Barrel Swaps

[JW Precision]

Just out of curiosity I will ask this question and I do expect some flaming back. Everyone is bringing up the headspace issue with barrel swaps. I know that headspacing is very important and is a safety issue. People are saying that to headspace even the Savage barrel swaps at home you need the proper headspace gages to do so and not a brand new brass in that caliber.
Could someone explain to me the theory about being so unsafe by lets say being out a couple of thousands? The hair on my head is .004 -.005 thou. thick. My headspace gages I have here are at .001 from a go to a no go. I can't see a safety issue with being out .005. The brass will stretch that much and more without any failure. People fireform brass everyday that have to form and stretch it a hundred times more than that.
I just thought a friendly discussion on this issue would be nice. I know about safety and also about not letting a firearm go out to a customer that isn't safe to the thousandth. I wouldn't let that go either but in essence when I swap a barrel on my Savage with new brass, even if I was out .010, this would all be fireformed on the first shot anyway and I wouldn't even be close to the brass failure limit of stretching. Then from that point on all the brass that was shot would be headspaced.
I'm not saying to do this, what I'm asking is that where is the limit of brass failure you guys have experienced?

 

[Mystic Precision]

John, if shooters really knew how LARGE their chambers were vs their brass and die dimensions, they would be shocked.

Yes, brass has a wonderful ability to expand, within some pretty generous limits, to fill the chamber. A couple of thou of stretch is no big deal. In fact, a positive as it allows for a bit of foreign matter to enter without jamming up a rifle.

Or to allow use of ammo within SAAMI/factory specs - which are very generous.

When we look at neck clearances on tight BR chambers, there is always at least 1 thou, preferably 2 thou of gap. At this level, the contraction of the brass after firing returns the neck to almost the same dimension you would have sized at. In fact, for some tight neck chambers, you don't need to size the necks.

Same goes for chambers. If they are a couple of thou larger, the brass will expand and contract back to prefiring size. This assumes that pressures are within normal limits and the action does not suffer from a spongy bolt.

I don't believe that brass expands and stays that way until it has stretched at least 5 thou which is pretty typical of any SAAMI chamber or if pressures reach some pretty high limits. When brass stretches to the point where there is a ring showing head separation, it has gone much more then that. I am sure someone will know the elastic limits of brass stretching.

I have shot a whole whack of WWI and WWII rifles that had chambered that oversized and still functioned - not my idea of fun mind you.

Ironically, the headspace style on a Savage can actually make things better. With a typical custom rifle, the barrel is installed and headspaced THEN the dies are made to fit. This is a very expensive process.

With the Savage, the chambers are cut so that the case is fully supported with only the extractor groove sticking out. Now brass can be sized in YOUR dies then used to headspace the barrel. The fit you get will be a 'custom' fit to your dies ensuring that you can't oversize the brass or need to spend alot for custom made ones.

This headspace may not fit ALL types of factory ammo (depending on how different your dies are to SAAMI max) but it will function with your handloads which is the whole point.

As always, the end user has to be careful about these things and must take care not to get into a dangerous position. But I have had a barrel nut go loose and the barrel start to unscrew. The only thing that happened was the cases got longer - these got tossed.

Jerry

 

[surfclod]

Now brass can be sized in YOUR dies then used to headspace the barrel. The fit you get will be a 'custom' fit to your dies ensuring that you can't oversize the brass or need to spend alot for custom made ones.

This headspace may not fit ALL types of factory ammo (depending on how different your dies are to SAAMI max) but it will function with your handloads which is the whole point.

Jerry

This is what I did with my recent rebarrel. The Go-gauge left me with a chamber that was a slight bit longer than my dies required so I head spaced it "tight" to lengthen brass life and theoretically gain an edge in accuracy. I also want to make sure I have the option to chamber factory ammo but as it worked out my "tighter" headspacing still allowed this, at least with the types of factory ammo I had on hand.

There was an article in the Alberta Outdoorsmen magazine a few issues ago that talked about a fella's .338 WM that has some brass stretching issues. The rifles chamber was at the large end of SAAMI spec tolerances and the resizing die was at the low end so when combined it caused brass separation near the base after only a few firings. It was a while ago so I may not have all the facts correct but it was a good example if how components can be within SAAMI spec but with the right (or wrong) set of components you can still have problems.

Fortunately with the Savage barrel nut system you can adjust this to get optimum performance from factory components.

 

[tiriaq]

Are you sure that from your Go gauge to your No Go gauge is only .001"? That would be most unusual.
A friend was an engineer at Savage for many years. He conducted an experiment with a .30-06 rifle, which was remotely fired under controlled conditions. The barrel was progressively unscrewed, and fired. As long as the extractor was able to hold the case against the boltface, it would fire. Finally the headspace was so great the rifle would no longer fire.
No cases failed. Every case fireformed.
Nothing happened.
Now, this was with fresh, factory ammuntion. The cases were NOT reloaded.
I suspect that these cases could not be safely reloaded, and that sectionning would show incipient separations. Reloading is the one activity that is most affected by cases being fired in a loose rifle, if the cases are full length sized.
If headspace is held to minimum specs, accuracy can be improved. The rifle could be adjusted for the ammuntion, or the ammuntion taylored to the rifle.
Belted magnums can have loose tolerances. Belt dimension and chamber counterbore for the belt can be sloppy. Chambers can be loose, because base to shoulder size is irrelevant for headspacing. Best results might be obtained if the cases were treated as rimless, not belted.
Many rifles in regular use are beyond SAAMI or CIP specs, and the owners don't ever realize it. Modern brass is very forgiving.
If I am chambering a rifle for my own use in target shooting, I will adjust the chamber so that I can just feel the bolt close on a Go gauge. If I am doing a hunting rifle for someone, I will usually make sure that the bolt closes easily on the Go, and won't on the No Go.