Case Expansion, problem when necksizing?

Status
Not open for further replies.
N

Noah Chisholm

Member
Joined
Jan 9, 2019
Messages
14
Hi guys, this is my second 303 brit post, but I'm very new to reloading, and im not sure if this is a stupid question or not.

My SMLE NO1 MKIII* Shot amazing on it's first trip out, 174gr Round nose .312 projectiles backed by 35gn IMR 3031 (Was seeing some low pressure signs) but I digress, when I got home I compared a fired shell to some unused ones I had, and there was a drastic difference. The fired shell's shoulder was bumped up, and the cases walls are at much less of an angle, more akin to a strait walled case. I read on some other forum That the shoulder bump and decrease in wall angle can cause an increase in pressure, and you should reduce loads after first firing.

I thought the pressure would be the same, as the case undergoes the expansion on first firing, before the bullet flys. I just would rather be safe than sorry.

Does the case expansion change pressures, and should I drop my loads before firing again?

(Pics included, unfired on the left, fired on the right)
20181201_153717_HDR.jpg
 

Attachments

  • 20181201_153602_HDR.jpg
    20181201_153602_HDR.jpg
    54.8 KB · Views: 3
Noah Chisholm said:
The fired shell's shoulder was bumped up,
Click to expand...

Some .303s are notorious for excess headspace and many people size cases to fit the chamber to control brass stretching near the case head instead of just running the sizing die down until it touches the shellholder.

You don't need to worry about pressure with the cases, they will blow out to fill the chamber regardless. Check how far the shoulder moved from new to fired, it may be too much. If it is, you can control that by not over sizing.
 
Walkalong said:
Some .303s are notorious for excess headspace and many people size cases to fit the chamber to control brass stretching near the case head instead of just running the sizing die down until it touches the shellholder.

You don't need to worry about pressure with the cases, they will blow out to fill the chamber regardless. Check how far the shoulder moved from new to fired, it may be too much. If it is, you can control that by not over sizing.
Click to expand...
I'm using a Lee Loader, as far as I know that doesnt touch the shoulder, so im in the clear?
 
No, you still need to measure where the shoulder is after firing and not move it back more than say .003 when sizing. I suspect you have a good bit more than a .003 difference between the new or sized cases you have vs fired.
 
Other 303 before and after photo.

303.jpg
Noah Chisholm said:
Lee Loader,
Click to expand...

If using the "Classic" loader, with a hammer. It only neck sizes. Do watch for case separations.

Neck tension can be controled by how far you hammer the case into the neck sizing die. p-658.jpg

The pressure and load should be fine if using Lee load data. If load data still comes with it? Have not used a hammer loader in over 40 years.
 
Last edited:
243winxb said:
Other 303 before and after photo.

View attachment 823744

If using the "Classic" loader, with a hammer. It only neck sizes. Do watch for case separations.

Neck tension can be controled by how far you hammer the case into the neck sizing die. View attachment 823727

The pressure and load should be fine if using Lee load data. If load data still comes with it? Have not used a hammer loader in over 40 years.
Click to expand...
I'm not using Lee Load data, as IMR 3031 hasnt been listed on there lee loaders for (20 years?) Though I have found old load charts, and many people using older loaders using 36gr, I'm using 35.1, Hornady Book #2 Suggests a Max charge if 37gr for the .312 Round Nose Flat Base, 174gr. I was just wondering if the change in case dimensions affects pressure, thank you for your reply
 
Walkalong said:
Some .303s are notorious for excess headspace and many people size cases to fit the chamber to control brass stretching near the case head instead of just running the sizing die down until it touches the shellholder.

You don't need to worry about pressure with the cases, they will blow out to fill the chamber regardless. Check how far the shoulder moved from new to fired, it may be too much. If it is, you can control that by not over sizing.
Click to expand...
Walk along, im kind of confused with your replys. (This could very well be due to me not putting much detail into my reply/post) You say not to over size but I am ONLY sizing the neck, not the shoulder. The shoulder is not even touched by the loading tool. Do I need to worry about the shoulder bump forward after first firing? I was told this is called "fireforming" and is common with 303 shooters, due to stresses on the case with full length sizing and shoulder bumping. Thank you for the reply!
 
The British had a nasty trick -- they would bore chambers deeper than they should. The idea was that cruddy, corroded ammo would push the crud ahead of them into the shoulder area and allow you to chamber ammo you really shouldn't fire. Cases ejected from rifles that have had that treatment are waaaaay out of standard, sometime too much to be reloaded. You have three choices:

1. Neck size only, and accept that you will only get a few reloads per case.
2. Have a custom resizing die made to fit cases fired in your rifle -- $$$$$
3. Give up on handloading and use factory ammo only.
 
The 303 runs at 49,000 PSI at maximum loading. Neck sizing may only work so long, till the brass will no longer chamber easly. It may need full length sizing , soon or later? I know my 30-06 did, but it runs at a lot higher pressures.

1970 Lyman data in photo. 20190130_190401.jpg

There is cast bullet data, if you need it.

I would keep using this.
My SMLE NO1 MKIII* Shot amazing on it's first trip out, 174gr Round nose .312 projectiles backed by 35gn IMR 3031
Click to expand...
The fire formed brass should produce less pressure.
 
Last edited:
The problem is, when neck sizing no longer works, how do you size the case? As you can see from the pictures, it probably will not go into a full-length .303 sizing die without a lot of force -- perhaps enough to collapse cases.

I have a Model 1905 Ross that has the chamber "hogged out" British fashion, and fired cases will NOT go into a full length die.
 
I'm guessing we're overwhelming the OP with details. I load a lot of military rifles, the most applicable being a Finnish M39 and Soviet 91-30 with an oversized chamber. Still within headspace specs but barely. This is a rimmed round that shares a lot of similarity with the .303 Brit.

Pressure question. GENERALLY the higher the case capacity, the lower the pressure. I.E. your neck sized brass SHOULD develop a lower pressure than virgin or SAAMI spec FL resized all else being equal. Pressure can be a funny animal, so follow all usual reloading precautions.

Extra credit question...brass life/headspace/accuracy potential in a rimmed service round. Neck sizing is a wonderful thing in this style cartridge. You are moving the point of headspace from the rim to the case shoulder. This almost universally improves accuracy and case life in these cartridges, as it does in my 7.62x54Rs. Eventually, you will notice significantly increased camming pressure needed to close the bolt. A small amount is normal, looking for a rubber mallet is not. At this point you will need to acquire a basic reloading press and a .303 die set or else chuck your brass and start over. The inexpensive Lee "stapler" press should work well enough. Now you want to back the die off until it doesn't touch the shoulder at all. Then gradually tighten it down, checking the fired case for function. When you get to this point, of slight camming action to close into battery, you're resized appropriately for your rifle. For hunting ammo or ammo to be used in rapid fire I'd recommend sizing closer to SAAMI specs.
 
Last edited:
Noah Chisholm said:
Walk along, im kind of confused with your replys. (This could very well be due to me not putting much detail into my reply/post) You say not to over size but I am ONLY sizing the neck, not the shoulder.
Click to expand...
My bad, never mind, but I would full length size them to fit the chamber, assuming you have the means. Didn't see anything about the Lee Loader in the first post.
 
All good advise. Another trick I didn't see mentioned is to put a small O ring over the case down to the rim to hold the case back against the bolt face. When it's fires the case will blow out to fill the chamber without stretching the web where case head separations occur. Then partial or neck size the cases. Good luck
 
The Lee Enfield .303 chambers do not match the shape of factory ammo and they vary alot from one to another. That is not desirable but there is little you can do about it. US made loading dies are made to standard dimension that match factory ammo so they do not match .303 chambers either.
The best you can do is neck size the brass.
If you can always use PPU brass since it is the largest ahead of the rim. It will last longer before separating.
Your Lee Loader is a good tool to use with Lee Enfields.
Don't be too concerned about the change of case shape.
The enlarged volume of the case actually results in a little lower pressure.
 
Status
Not open for further replies.
Back
Top