Brass deformation - rimmed (303) vs shoulder (308)

Guys,

Can anyone pls shed some light on the differences between how brass deforms and "grows" during firing when comparing a case like 308 that headspaces on the shoulder vs a rimmed case like 303 British.

My normal reloading routine for "shoulder" brass is to bump the shoulder 2 thou back, and then use a collet neck die, as I want to work the neck the least amount possible.

Looking at reloading 303, but not sure if the same logic would apply, or if there are specific considerations for tapered, rimmed cases like the 303.

Ta, ebf

I would think the same logic applies. Bump it back a bit to make sure it chambers properly.

I think I am going to have to reload for my 303 and I think from my research they like just a neck size too, not full length.

I think a lot comes down to individual actions and chambers.
I reload for a Savage 99 in 243 and have to full length resize every time else I can't get the brass to re-chamber, hence I have to neck trim every time from the second use. (Tight chamber)
I have just started re-loading for a Savage 99 in 358 Win and only have to neck size hence after 2-3 firings I still have not had to neck trim.
Both loaded to 1 grain under new book maxs.
My custom bolt action loaded to close to book max just take's neck sizing and after >5 reloads I still have not had to trim any brass.
(buy good quality brass)
Zq

The shallow shoulder design on the .303 causes it to “flow” more, and probably require trimming more, especially for warmer loads.

ZQLewis, the 99 has a rear locking action, and typically does require full length resizing, again this becomes more necessary with higher pressure loads. When I had one in .308 I could get away with two reloads just neck sizing, after that needed a full length. That was at book max.

I remember shooting my dads .303 Jungle Carbine and noticing with factory ammo the shoulder move forward several mm. I'd be careful you were only bumping back a small amount. A normal F/L die might work the brass too much.

it will still seperate in same area(just forward of web) if you use a semi full length eg set die up as per normal but turn die back out 1/2 turn rather than 1/2 turn in try case in rifle and tootoo with amount you set die to you will in effect set up die for your chamber...if its a bit longer the brass will only need to stretch once. Ive heard of guys with possible headspace issues putting a tiny rubber band like ones for teeth braces in front of rim to help hold it back against bolt face for first fireing..

With 303 brass i keep cases from each rifle separate and only neck size. There are quite a wide range of chamber dimensions and fl or half sizing will rapidly overwork the brass.

I would think it is still the same. It will not be stretching on the rim as the pressure from inside the case will be pushing the rim back to the bolt and the shoulder forward and the sides out just the same to fill the chamber. With a rear locking bolt there is probably more room for movement along the bolt than with front locking.

X2 on what the last 4 posters said.

Most 303s have generous headspace, neck size only after first firing and just bump the shoulder the minimum necessary to effect closing the bolt without undue force and only when required.

The cartridge has a reputation for both growing brass(requiring trimming) and case head separation both of which are mostly a result of full length sizing and sizing to excessive headspace.

Even old rifles with excessive head space can have very good brass life if sized correctly and not excessively loaded.

I doubt you would be over loading them.

After first firing treat them like they are headspaced on the shoulder and you will be good to go.

Hello ebf. My preference is to use a 308 FL die, set to necksize 303 brass. Swap out the 308 expander plug for a 311 plug.
The 308 die is large enough to not touch anything but the neck when adjusted correctly.
When you see your first cracked neck, its time for the blowtorch.
You already know that brass is individual to a rifle.
If you want to fine tune stuff, take a walk over to Karori and talk to Duncan.

Tx John. Taking a break from fullbore, but I do see Duncan at service rifle shoots.

Also been trying to get hold of Mike, but he is a hard guy to get on the other side of a phone :thumbsup: