25 Souper Neck OD Issue

Randy Tidwell

Randy Tidwell

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Hello fellow shooters.

Recently I finished a project I have been planning for years. 25 Souper built on a Model 70 SA with a 9 twist Shilen barrel. I excited to start tuning this rifle for Whitetail this year.

I necked down New Lapua 308 cases to 25 cal. After fire forming the first 50 cases and breaking in the barrel, I discovered the OD of a loaded round was a bit to tight for my liking.
I caught this because a fired case is will not allow a bullet to slip in? So I started doing some detailed measuring.

Turns out the chamber ID is .291, loaded round is .290, way to tight in my book. For a BR chamber, I have always shot for .0015-.002" clearance. For a hunting rifle between .004-.005 clearance.

In further measurements, found the brass does not have a uniform wall thickness. After measuring the neck thickness, found it was between .0155-.0175. Actually found one case that was .018, not good for Lapua brass.

I have 4 different neck turning tools, of course I don't have a 25 cal mandrel, lol. I ordered a 25 cal Mandrel from Brownell, plan to turn these cases to .015-.0155. In theory that will give me a .0286-.287 neck diameter.

I think I may order some Peterson 260 Rem Brass to see how it turns out after necking down.

I know I am being way to anal about this, but details are what make a rifle shoot and gives me confidence, IMHO.

Ignore the messy work bench and the color, it will be dipped in a camo pastern, lol
 

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Very Nice
308 down to 257.
Look at the 243 case, just a thought.

What bullet are you thinking of?
 
Randy Tidwell said:
Hello fellow shooters.

Recently I finished a project I have been planning for years. 25 Souper built on a Model 70 SA with a 9 twist Shilen barrel. I excited to start tuning this rifle for Whitetail this year.

I necked down New Lapua 308 cases to 25 cal. After fire forming the first 50 cases and breaking in the barrel, I discovered the OD of a loaded round was a bit to tight for my liking.
I caught this because a fired case is will not allow a bullet to slip in? So I started doing some detailed measuring.

Turns out the chamber ID is .291, loaded round is .290, way to tight in my book. For a BR chamber, I have always shot for .0015-.002" clearance. For a hunting rifle between .004-.005 clearance.

In further measurements, found the brass does not have a uniform wall thickness. After measuring the neck thickness, found it was between .0155-.0175. Actually found one case that was .018, not good for Lapua brass.

I have 4 different neck turning tools, of course I don't have a 25 cal mandrel, lol. I ordered a 25 cal Mandrel from Brownell, plan to turn these cases to .015-.0155. In theory that will give me a .0286-.287 neck diameter.

I think I may order some Peterson 260 Rem Brass to see how it turns out after necking down.

I know I am being way to anal about this, but details are what make a rifle shoot and gives me confidence, IMHO.

Ignore the messy work bench and the color, it will be dipped in a camo pastern, lol
Click to expand...
@Bghunter338
 
Randy, Web dia may also give you fits with the Lapua brass, I hope not, CIP spec brass vs SAAMI chamber. I have run into this problem with Lapua 223, 22/250, 243, and 30/06 brass. Using a micrometer that measures to the .0001 reveals volumes.

Also, if you neck turn at 30 caliber, then neck down, this helps ****** doughnut growth. If run out after neck down is more than .0002, then a nit pickers like a clean up cut at 25 caliber, but more often than not, it is not needed. Once you try this method, you will see exactly what I mean.
 
Last edited:
K.E.C. Darkside said:
Very Nice
308 down to 257.
Look at the 243 case, just a thought.

What bullet are you thinking of?
Click to expand...
My goal is to shoot 90-115 grain bullets.

I have assortment of 25 cal stuff now, 87 Spear, 100 Sierra SPBT, 115 Partitians and Ballistic Tips. Also have a supply of 100gr TTSX on hand.

I just ordered some Berger 115 VLD Hunters to try. Also want to try some AccuBonds.

I built a Souper for my hunting partner in CA years ago, because of the lead ban there, he is limited to Monos. The 100 TTSX work great in his rifle.

I tried expanding some Lapua 243 to 25, neck ends up being too short.
 
VinceMule said:
Randy, Web dia may also give you fits with the Lapua brass, I hope not, CIP spec brass vs SAAMI chamber. I have run into this problem with Lapua 223, 22/250, 243, and 30/06 brass. Using a micrometer that measures to the .0001 reveals volumes.
Click to expand...
I have ran into the same trouble with Lapua 223 with web issues in both AR and Bolt platforms. Never had an issue with other cases, interesting.

All measurements were taken with a quality micrometer. Calipers are only good for quick checks.
 
It's a good reason to measure every case before choosing to use them. Right?
On neck clearances, there is no basis for excess neck clearances. 1thou clearance might as well be 1mile to bullet release.
 
Mikecr said:
It's a good reason to measure every case before choosing to use them. Right?
On neck clearances, there is no basis for excess neck clearances. 1thou clearance might as well be 1mile to bullet release.
Click to expand...
In a clean chamber, correct.
Some guns spend a lot of time in the field, run dirty powders etc.
Why be bound to such a tight tolerance? I mean unless you have tight neck comp gun I guess.
 
No need to make a big production - just turn necks down so bullets slip fit into fired brass.

Like .257 (bullet diameter) + (unknown neck wall thickness * 2) = less than .291

present situation : .291 = .257 + (.017 * 2) = .291 or more, no slip fit, thick & variable neck walls from .308 brass, necked down to .25 caliber
possible solution : .291 = .257 + (.015 * 2) = .287, .291-.287 = .004 clearance, should be nice fit, turn neck walls to .015 or neck OD ((.257 + .030) = .287
Allow for some brass spring back after mandrel is pulled out of brass neck. Try to avoid work hardening necks by excessive neck sizing.

Back then I had a .25 Souper and used once fired 7mm - 08 brass from OnceFiredBrass.com. I usually bought 200 pieces. Necks were turned to very slightly below shoulder, mitigate donut. My rifle allowed bullets to be seated out far enought so bullets did not touch donut.

The .25 Souper killed deers real good.

Lee will make you a nice .25 Souper collet die for $100 with custom diameter mandrel. I use lots of Lee stuff because it is cheap but innovative & works real good. I F/L size every time but no expander in die. After F/L size I sized neck with collet die, avoid neck run out.

Lots of real nice .257 bullets, long & pointy enough for faster twists like 9 or less.

I never had a bright flame orange gun stock. Is this for safety, like a orange vest or to find a weapon left in weed or such?
 
Lower neck clearance seals necks quicker, setting consistent neck IDs through firing, lowering ES. It mitigates carbon ring formation, and all the sooting you likely have on your cases, and in your chambers. Less than excess clearance allows less than excess sizing (both ways). Lotta good things in it.

Bullets dropping freely into fired necks is an extreme standard.
There NEVER HAS been a need for that.
Forget magazine articles and mob notions. Think things through to reality.
As far as cases being too thick, if you really think so, they should not be loaded and fired that way.
Basic Reloading 101
 
K.E.C. Darkside said:
Very Nice
308 down to 257.
Look at the 243 case, just a thought.

What bullet are you thinking of?
Click to expand...
My 25 Souper has a .291 neck and this is what I do.

My reamer lets me use the full length 2.045" brass, but even if yours is 2.015" I'd think it'd be easier to trim a little than turn the necks on everything.
 

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