Factory primers backing out?

[Swamp Fox]

A while back I sighted in a new scope with a box of factory federal ammo. Everything went fine and I got my rifle sighted in without a problem. The other day I was looking for some brass and opened the box I had saved from sighting in. Looking at it I can see that the primers have backed out until they are just barely sticking out above the brass. I examined another box I had shot (Remington), and everything looked normal. Same with some reloads I had already made and shot.

What’s going on here? If it was excessive headspace I would expect it with every load or brand. Some of my reloads were pretty light and they looked fine too.

[Bird]

Different manufacturers, different batches, will all vary slightly in headspace.

[BK7saum]

What caliber? Typically we dont see high primers because the case will stretch above the case head and reseat the primer. (it will be flat). What you appear to have is slight headspace, but the load was weaker or the brass was stronger and the case held the pressure and did not stretch. However, the primers stayed backed out to show the excess headspace. It seems that unfired brass will have around 0.005" +/- excess headspace, but we hardly ever see an indication unless we measure with a comparator before and after.

[jsizemore]

I have measured factory ammo with .020" headspace difference before and after firing.

[M-Tecs]

All primers back out when fired unless the flashhole's are enlarged. On some loads the pressure is low enough that the primer does not get resetted.

[Swamp Fox]

This was a 150 grain 300 savage load by federal. I have read they may use softer brass than other manufacturers. I didn’t chronograph the hem but they seemed comparable to other manufacturers loads I have shot. Just wanted to make sure it’s not a rifle issue, but if it was I would suspect it would show up in any load. Maybe federal leaves more headspace in their brass than others, for this caliber at least? I’m

[M-Tecs]

The softer Federal cases may be gripping the chamber walls more and not allowing the case head to reset the primer. Federal brass does tend to run on the softer side.

If the primers are out more than .010" that would indicate over sizing or headspace. Most likely it's a rough chamber and that's not an issue unless you are getting sticky extraction.

[jsizemore]

How old is the gun and was it custom smithed? Some of the older guns had chamber reamers that were all over the place in dimensions because of no SAAMI standards.

[Swamp Fox]

Factory gun built in 1954.

[Hickory]

Get a set of go-no go gauges and do some investigating! You may find the problem.

[M-Tecs]

While this article is geared around the bolt thrust on Ackley Improved cartridges it does demonstrate primers backing out due to the case gripping the chamber wall. https://gundigest.com/gear-ammo/ammunition/experimenting-with-bolt-thrust

I highly recommend the Hornady Lock-N-Load® Headspace Comparator. https://www.hornady.com/headspace-bushings#!/

It's doesn't give you a direct headspace reading but you can compare to factory and how much the case grows and more importantly how much you are setting the shoulder back when sizing. If used with an actual headspace gauge it because a direct reading measurement.

To me this type of tool is a must have for anyone that reloads any volume of bottle neck cases.

Checking the shoulder starts at about 8:30
https://www.youtube.com/watch?v=cX1M3Nk_CkM

[GooseGestapo]

Low pressure indicator.
I see it frequently with fact .30-30 ammo (ofb) I pick up at ranges.

As others stated, not enough pressure to reset case head back against the bolt face to reseat the primer. Also a modest amount of headspace.

[M-Tecs]

http://castboolits.gunloads.com/showthread.php?402890-Primer-bullet-push-amp-primer-setback