Enlarged Primer Pockets

[p246]

The PPU .303 brass has held up really well through 10 or more reloads without head separation or overly enlarged primer pockets. It has a slightly smaller powder charge than the .30-06 which probably helps. By only neck-sizing the cases, I noticed the walls of the cases have expanded to fit the generous No. 4 Mk 1* chamber to the point where they've become difficult to chamber and eject. Have you noticed this? I've not seen this happen with the .30-06 cartridges.

If you neck size the body will expand to the point it needs full length resized every so often. I full length everything in 303 and 30-06 because I want to be able to shoot it out of all my L.Es and American Mil Surps, so no direct advise. On others I have singles (example 1918 Carl Gustav 6.5 X 55) I full length resize every fourth firing. Others might be able to tell you what they are doing in 303 and 30-06. A chamber gauge could be used but in military 303 bores I've been told it's hit or miss due to bore size differences. Good luck.

[Merc]

If you neck size the body will expand to the point it needs full length resized every so often. I full length everything in 303 and 30-06 because I want to be able to shoot it out of all my L.Es and American Mil Surps, so no direct advise. On others I have singles (example 1918 Carl Gustav 6.5 X 55) I full length resize every fourth firing. Others might be able to tell you what they are doing in 303 and 30-06. A chamber gauge could be used but in military 303 bores I've been told it's hit or miss due to bore size differences. Good luck.

I've been thinking that I'd eventually have to full length size the 303 cases. Forcing the expanded cartridges into the chamber is probably a great way to wear out the locking lugs. Do you occasionally experience case head separation in either caliber?

[bigedp51]

The cause is an enlarged flash hole which allows to much gas pressure on the primer which in turn stretches the pocket,

The same amount of pressure will go through the small hole as a large hole, meaning the size of the hole doesn't change the amount of chamber pressure. All the hole size changes is "flow or volume" just like the nozzle on your garden hose.

Over sized primer pockets/base expansion is caused when the chamber pressure exceeds the strength of the case. Meaning brass hardness and case design and a thicker flash hole web adds radial strength to the base of the case. And if you notice below the flash hole web is "below" the supported part of the case and the case starts to expand "above" the flash hole web.



The link below does not tell you chamber pressure, it tells you the strength of your brass and loading limits. Meaning how much pressure the brass can take before it reaches its elastic limits and can not spring back to its original shape.

Simple Trick for Monitoring Pressure of Your Rifle Reloads
http://www.hodgdonreloading.com/relo...-rifle-reloads

[Merc]

Big Ed,

Thanks for the info. The stiff extraction I'm experiencing from the expanded 303 cases which, according to the link, is one of the signs of high pressure. As previously mentioned, I'm using starting loads BUT neck size only. These expanded 303 cases have been fired and reloaded multiple times which has probably caused or allowed progressive body expansion to reach its current size. Would you agree that a better test might be to evaluate a new or full length sized case for symptoms of stress, i.e. expansion, extraction stiffness, etc. after it's been fired only once?

[PhillipM]

Are you using the appropriate head space gauge to set your sizing dies?
Sam

How do you use a headspace gauge for that?

I have an RCBS case mic which while checking fired brass, my chambers are all on the minimum end of the scale.

p.s.

I hope your health is improving.

[p246]

I've been thinking that I'd eventually have to full length size the 303 cases. Forcing the expanded cartridges into the chamber is probably a great way to wear out the locking lugs. Do you occasionally experience case head separation in either caliber?

No so far I've been lucky. I was fortunate to have someone much older spend time with a young dumb kid. He didn't mind stupid questions and like to teach others. He had saved different cases that had failed or were close to failing, bad primer pockets, cracked necks etc. He gave me the tools to inspect brass pretty good when I was in my twenties. Without his help I'd probably have blown myself up by now.

[bigedp51]

Big Ed,

Thanks for the info. The stiff extraction I'm experiencing from the expanded 303 cases which, according to the link, is one of the signs of high pressure. As previously mentioned, I'm using starting loads BUT neck size only. These expanded 303 cases have been fired and reloaded multiple times which has probably caused or allowed progressive body expansion to reach its current size. Would you agree that a better test might be to evaluate a new or full length sized case for symptoms of stress, i.e. expansion, extraction stiffness, etc. after it's been fired only once?

Normally a full length resized case should be .003 to .005 smaller in diameter than its fired case diameter. This allows the case to "spring back" from the chamber walls after firing, and attempt to go back to its resized diameter. And a neck sized case looses its spring back ability each time the case is fired and hammered to chamber dimensions.

I think its time to "partially full length resize" your cases to reduce the body diameter, and you will need to "play" with how much smaller in diameter required for proper spring back from the chamber walls. I use a Redding .303 British case forming and trim die to bump the case shoulders back. This die does not touch the body or neck of the case and only contacts the case shoulder. If you place a fired case all the way in the form and trim die the case will fall out of the die when inverted. (Redding 83154 Form & Trim - Series B .303 British)

If you use a full length resizing die to bump the case shoulder you will over resize the case and shorten case life. In 1914 the Enfield rifles chamberers were reamed larger in diameter and longer and the chambers are no where close to American SAAMI dimensions. Meaning the dies are very undersized compared to the military chamber.

[p246]

I use Redding dies on my bench rest stuff. They are a very good product but expect to pay for them. I have slowly replaced a few milsurps rifle dies with Redding stuff, but I always hit the budget wall too fast. 303 is on my short list to upgrade. Now if we could get a flat based .311 Mark VII bullet.