I had a large bag full of 308 cases. When I purchased a 7mm08 I thought I'd try necking the 308 cases down to 7mm08. Worked perfectly. just bought a 243 so thought I'd try necking the 308 cases to 243. Didn't work well. I took some 7mm08 cases that I'd necked down and tried to neck them to 243. I found if you took your time and pushed the cases up very slowly, a little at a time they came out perfect. they chambered flawlessly.
resizing cases
- Thread starter xgunner
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vagrantviking
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Those are conversions that can work but be careful about the brass thickness in the neck.
Sized cases might chamber fine but then the outside diameter can be too larger when a bullet is seated. If the cartridge is then crammed into the chamber the neck tension can be many times higher than it should be. There's no room for the neck to open as the pressure builds and inconsistent pressure spikes might be dangerous.
Compare the outside diameter of the neck with a bullet seated to factory ammo or cartridges loaded in brass with the correct headstamp.
Sized cases might chamber fine but then the outside diameter can be too larger when a bullet is seated. If the cartridge is then crammed into the chamber the neck tension can be many times higher than it should be. There's no room for the neck to open as the pressure builds and inconsistent pressure spikes might be dangerous.
Compare the outside diameter of the neck with a bullet seated to factory ammo or cartridges loaded in brass with the correct headstamp.
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This^^^^^ Good advice.
Do you have a tube (ball) micrometer to measure your neck thicknesses for those .243 neck downs? You might want to do this for those cases, and if they are getting too thick, use a neck turning tool to turn the neck thicknesses down. How thick? Well I don't shoot .243 Win (nor 7mm-08), so I don't know what typical .243 brass neck thickness is, so don't listen to me.
But I looked ups the SAAMI chamber spec for .243 Win and it shows a neck mouth of 0.277. 0.277 - 0.243 = 0.034. Divide by 2 for each side = 0.017". But you need about 2 thou clearance for chambering and expansion on each side, so 0.017 - 0.004 = 0.013" neck wall thickness.
I suggest doing the same measurments and SAAMI spec check for your 7mm-08 neck downs.
Be safe.
(P.S. I do shoot .260 Rem which is of the .308 Win case family. I bought new Lapua .260 Rem brass and its necks averaged 0.014" with some high spots, so I turned them down to an even 0.014". Never had a hard bolt lift or pressure issues in my Tikka .260 with this Lapua brass).
Factory chambers usually have necks that are oversize IMHO, so worrying about neck wall thickness isn't a problem. It may even help with accuracy.
It may not be a problem but it is something that should be considered and measured. I have converted 221 Fireball brass into 17 Fireball and a small percentage of the rounds will not even chamber because the neck is too thick.
- Location
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Perhaps 25 years ago, I took some IVI 7.62 NATO brass and ran into an RCBS Full Length 243 Win sizing die. Was a good grunt - on a single leverage RCBS press - I think I used a pipe extension over the press handle, and managed to slightly bend that handle - but did not break or crack anything. I did own a HOT case neck peeling tool, but do not think that was needed - loaded up 85 grain Speer SPBT and we fired that multiple times in a Rem 788 243 Win. Seemed to work just fine - might even still be some of those initial 50 cases still left. Measuring case necks a good idea to know - but I think drawings of families of cartridges - like Winchester 458 Win Mag, 338 Win Mag, 264 Win Mag often showed that the smaller case necks get thicker than the largest ones - as if done deliberately when those cases designed?
I am sure if I was going to do that again today, would be a lot easier to use an intermediate size - like 7mm-08 or 260 Rem or similar - to do in more than one step - but, as mentioned - I did that in one go - once - about 50 cases in that session. My current compound leverage press would likely make that to be less effort, as well.
I am sure if I was going to do that again today, would be a lot easier to use an intermediate size - like 7mm-08 or 260 Rem or similar - to do in more than one step - but, as mentioned - I did that in one go - once - about 50 cases in that session. My current compound leverage press would likely make that to be less effort, as well.
You're comparing apples to oranges to make a spurious point.
I agree that measurments should be taken, if there is a problem. If neck dimensions are so tight that such conversions are an issue, which they could be with VARMINT cartridges, there will usually be feeding issues as the cartridge won't fit into the chamber far enough to allow the bolt to close.
.002 in is enough expansion.
When I reform cases I always find out what the neck wall thickness should be. A reduction in neck is always going to increase neck thickness. When I made 6.5x53R from 303 British I measured other 6.5 necks, Carcano, Swedish and M/S and found 12 thousand thickness was the common reading so I thinned necks to 12 thousand.
Some rifles have large throats so I always check with a dummy round before neck thinning. Pre thinning the 6.5x53R was hard chambering, neck was needed.
Some rifles have large throats so I always check with a dummy round before neck thinning. Pre thinning the 6.5x53R was hard chambering, neck was needed.
vagrantviking
CGN Ultra frequent flyer
- Location
- High River, Alberta
It might not be an issue in every necking down conversion but it can. I think I was making 6mm Remington where it came into play. Most common situation it would crop up would be if a case is being shortened as well as necked down.
If a hard chambering round is thought to be an oversize base or slightly long headspace it's probably not going to increase pressure much at all but if it's a case of a pinched bullet due to excessive case length or neck thickness it's going to be very difficult to guess how peak pressure might be affected.
Whether or not it's always going to happen it's good to be aware of the possibility just in case.
A too thick neck is a big problem. I recently ran into it when i tried some 310 bullets in a 308. Blew the case head off.
A quick way to see if you are close is to take a loaded round and try to chamber it. If there is any scuff on the neck, you lack clearance.
A quick way to see if you are close is to take a loaded round and try to chamber it. If there is any scuff on the neck, you lack clearance.
It is definitely not always a problem. I have sized 308 down to 243 with no issues
