Thread: headspace in a break open rifle

Originally Posted by Micky Duck

So.... GPM asking questions re 6.5x55mm got my brain chewing things over..that and 60 cases waiting for powder n projectiles to be put into them.
my mind was wondering how/where a fella will see fatigue on a case that is repeatedly fired in a break open rifle.
in a normal bolt/lever/pump rifle we see thinning at the web area..its not supported in any of these actions,so the case has a tiny area where it can expand outwards..but in a break open the case walls are completely enclosed so it can only increase in length... making sence so far???
some time back @akaroa1 was testing a lovely 30/30 in same action and fired same case 10 of so times...it was still good...so MAYBE this is the reason???? the case isnt getting the same fatigue????
yes in theory a rimmed case like 30/30 or 303 doesnt have headspace as such..its rim thickness..but we have learnt over the years that resizing these as little as possible so the body/shoulder such as there is ,dont grow much on sizing.
now Im talking 222remington but its same deal really....
also what will pressure signs be??? flattened primer for sure....no swipe mark,no ejector hole to flow into...
thoughts???

also according to manuals it looks like win748 is hands down the best powder for my 16" barrel....even dropping 50fps per inch it looks to be as good as any ADI powder in longer barrel

Greetings @Micky Duck and all,
The normal sequence of events when a cartridge is fired in any rifle is for the case to be driven as far forward in the chamber as it will go by the firing pin strike and primer ignition backing out the primer. As pressure builds the case body expands and grips the chamber walls. If the pressure is high enough the case head is forced back to touch the bolt or breech face stretching the case just in front of the solid head. In a break open action the case head being forced back can spring the action slightly perhaps making it a little hard to open and the case hard to rechamber. This can happen with bolt actions to but at higher pressure. Most modern bolt actions support the case body right up to the head so essentially there is no difference in case support.
For my little .308 Bergara rifle I full length size using the Redding Competition shell holders so that the cases chamber freely but no more. I also keep the loads down currently loading 41 grains of AR2206H behind the Norma 150 grain projectile for around 2,500 fps in a 20" barrel.
As far as working up a load all of the usual pressure signs are pretty much worthless at the pressure levels you would want to stick to in a break open action. The .30-30 and the .222 load data is reasonably low pressure and for the .308 keeping well away from max loads is wise. Using one of the Hornady headspace comparator sets to keep track of case stretching could be useful and checking the inside of the case just in front of the head with a bent paper clip for a developing groove should be mandatory.
At the end of the day a break open rifle is unlikely to be used firing a 60 shot target match or bomb ups on deer or goats at long range so extended case life is not an issue. Culling the stretched cases before they let go in the rifle is.
More later.
Regards Grandpamac.