Some 458 Socom brass won't size

u could take a shellholder and grind some off the top, this will push the shoulder back some more. o and did u check the case length

Is this the first time loading the 458 SOCOM with these dies? The reason I ask is several yrs ago when I got into the 458 SOCOM dies were all over the place. There was no std so the mfg did what it thought was right. At that time the only mfg not having any problems was Redding, and that is what I bought. I went with the Sherdian case gauge from Tromix, as well as their upper. I would suggest you use a marking solution to determine exactly where your having the trouble at. Inn most all cases on 458 SOCOM it's the shoulder or just below the shoulder. Also confirm the dies were assembled properly, seating stem not swapped with deprimer.

A trick I learned many decades ago is that you can place a shim between the base of the brass and the shell holder. This will raise the brass that much more. Most shell holders have 0.010"+ of extra play. Cut a business card up and slide it in. Most are around 0.005", or if you have shim stock or feeler gauges work good too.

If this works for you you will either have to return the sizer for replacement or have the sizer and/or shell holder shortened.

I had a Lee die that wouldn’t size right and machined a shell holder. It wound up breaking at some point (I’m not sure if it was even sizing Socom stuff at the time) wound up just facing the bottom of the die and we have been happy ever since.

The 458 SOCOM is a very picky round to size due to it's very shallow shoulder. Try the shim trick I suggested above and see it they will size. If a 0.010" does not make it fit you have a bad sizing die. Be very careful if you are crimping on this round. The small shoulder will buckle very easy and then a round will not chamber. I don't crimp any of my rifle rounds. Over on the 458SOCOM Forum most all suggest use the LFCD if you must crimp.

Did you ever smoke or paint the brass to find out where it's having a problem?

What barrel and dies are you using? If you are sizing to full cam over on a single stage press, you shouldnt be seeing this issue.

I would also do what @Blue68f100 suggested. Use a marker on a dummy round that you are having issues with and see where the problem lies.

Only once you have figured out where the issue is, then you can make a decision.

agreed, it's like a huge 300 BLK!

Blue68f100 said:

The 458 SOCOM is a very picky round to size due to it's very shallow shoulder. Try the shim trick I suggested above and see it they will size. If a 0.010" does not make it fit you have a bad sizing die. Be very careful if you are crimping on this round. The small shoulder will buckle very easy and then a round will not chamber. I don't crimp any of my rifle rounds. Over on the 458SOCOM Forum most all suggest use the LFCD if you must crimp.

Did you ever smoke or paint the brass to find out where it's having a problem?

Click to expand...

I'm guessing it's the nickle cases? Those gave me issues as well.
I can't remember if you got your dies from me or not. But if so you need to make sure there's NO light visible
between the shell holder and die bottom on cam over. 90% of the time they are fine but a few of those cases were supper rough to resize properly.

Honestly I'd probably either shave the shell holder, or die, or just toss those cases.

I was looking at information about the 458 socom. The parent case was 50 AE. It might be possible to shave down a shellholder, use an AE sizing die to size the base (which won't push the shoulder back any) and then size as normal. But, two things:

1) This assumes the problem is at the bottom of the brass, which I don't think has been confirmed.
2) If you don't have a 50 AE sizer, are those 50 pieces of brass worth the cost of a sizing die.

I agree with others, mark the cases with something and then try chambering and extracting the cases. See where the marking is scratched away. Once the problem area is narrowed down, it will be a lot easier figuring out how to fix it.

The 458 SOCOM is a low pressure round, 35000 psi. I've shots 100's ( Nickle and brass) through my socom and have never seen any swelling at the base. I don't know who made the barrel but I suspect it may not be in spec if you seeing problems at the base or dies out of spec. Like I said earlier mfg were doing there own twist on what they think the chamber should be ignoring the ones how developed the round. The same can be said for the sizing dies.

Base diameter .541" https://en.m.wikipedia.org/wiki/.458_SOCOM

The 2nd hand brass would seem to have been loaded to hot.

Dies can only size down so far.

I've only got 40 brass, from factory loads originally. I've only loaded them twice so I hadn't really bothered with case length. So, thanks for reminding me, I've ordered a Lee trimmer gauge for it. I don't load real hot, 325gr clocked at 1780fps, we'll see what the long term life of this brass is.

From what I have seen is these 458 do not stretch since they have such a small shoulder. I have some brass that has been fired 4 times, length has not moved. If your going to order a case gauge, get the Sheridan cut away view gauge. Then you can actually see where's it contacting.
https://tromix.com/product/cartridge-slotted-case-gauge/

Edit to add Photos.

458 SOCOM w/ 325gr FTX


Starline Ni 458 SOCOM brass as fired, As you can see the Ni plating is so hard it does not show sizing marks. This one has bee reloaded twice.


Brass in Sheridan Case Gauge. All contact is at the neck.


You can actually wiggle the base, I get NO stretching at the base. Average about 0.003-0.004" stretch.

ya ideally u dont want more then .001 of head expansion.

jeeptim said:

16 nickel.

Click to expand...

In 357 mag, seen well used nickel not spring back after firing, sticky ejection. But it sized normal. Chambered normal.

I would like to know if my Redding dies would size them. So far I have not have any problems with them. I could drop them in my cutaway gauge and see where their binding out.

well 50 cases thats like 40$ in brass so your in the right