Built a 458 Socom on a Pro2A upper and AERO lower.  It won't chamber the rounds.  I tried filing the front of the magazine down some as I'd read that some mags need that to feed properly but to no avail.  I've used two different mags, three different ammos, and swapped lowers too.   I can drop a round in the chamber and it fires and ejects perfectly but this is what happens every time I try to load normally.  

Any ideas?  Thanks for your time.

Paul

looking at your mag catch, you might try tightening it up a bit and that may raise the magazine so the bolt can have an easier way of stripping the round out of the magazine.

other than that is it an M4 feed ramp barrel extension?

I'll tighten up the mag catch and give it a try.  This is what Pro2A says -

Anderson Mfg 7075 T6 Aluminum Stripped Upper Receiver w/enlarged feed ramps

Tightened up the mag catch and still no joy.

Picture of bbl extension.  

What mags and photo?

Pmag M3 and Lancer L5 AWM.

Pro2A recommends the E-Lander magazines so I just ordered a couple to try out.

Classic person building a .458 SOCOM and not knowing what the hell they are doing when it comes to the bolt.  Look at the ejector.  I bet it looks just like a 5.56 ejector, nice and round with a sharp edge all the way around and there is no hint of a bevel on it.  A .458 SOCOM ejector, done right, will have a bevel on it from about the 4:00 position to the 9:00 position. This is needed to let the rim of the case slide up, depress the ejector and slip under the extractor.  And I also bet the extractor is mucked up, not dehorned correctly and is digging into the brass case as it tries to slip over the rim.

First, go to .458 SOCOM forms and look at what an ejector is supposed to look like.  Bevel it and polish it and see if that helps.  You might also consider buying a properly built extractor from TROMIX.  He also sells properly made ejectors.  The ejector is easy to do yourself but the extractor, should you need it, you are bucks ahead by buying one from TROMIX.

If I see what I think I am seeing in your pictures, I'd be returning that barrel for a refund.  It looks to me like almost all of the center bottom barrel extension lug has been removed.  That is always a tell of someone not knowing what the hell they are doing.  That lug should not be removed and if the maker does have a clue on how to do it right, it will be blended into the feed ramp but still be 90%+ there, offering full support of the bolt locking lug.

Properly made barrel extension which is the old TROMIX style:
Attached File


Current TROMIX barrel extensions have the feed ramp looking like one big feed ramp all the way across but the bottom center lug is still there.
Here is a picture of the current BE:
Attached File

Big-Bore I am always amazed at you expert knowledge of the 458 SOCOM, I know when I was looking at building one, I had looked at multiple manufacturers, but it seemed like TROMIX was the way to to go to save any issues. It seems like their are a bunch of manufacturers out there that have no idea what they are doing.

Thanks for your input, I had bought 5.56 components from these folks in the past and was real happy with it.  I'm a bit confused about the ejector, mine ejects fine after firing a round that I drop into the chamber, it won't pull a round in from the magazine.  I will go check out the Tromix barrel and their design.  I sent these pictures to the vendor as well so hopefully I'll hear back quickly from them.

458 Feeding Issues

A Tromix barrel and bolt are a MUST.

I have had good luck with Wilson Combat modified 458 Lancer mags

Darn that's frustrating OP...

TBH I'd see if the company you purchased from would take it back..

After a year or so of reading alot of first hand accounts I went with a TROMIX upper and besides my 5.56 guns is my most reliable AR.

It has never failed to feed or eject anything from factory ammo to handloads, anything from 300gr HP all the way to 500gr HC boolits. I use unmodified 10, 20 and 30 round lancer mags and haven't had an issue.

Shoots a whole plethora of 325 FTX handloads right around an inch.

I believe the helpful poster meant the barrel extension lugs and not the extractor.  The lugs on the barrel extension should be beveled but not removed.  The extractor also needs to be modified, but it's better to have one designed for the cartridge (different radius of the cartridge would cause the extractor claw not to have perfect contact if using traditional 5.56 claw).  The case head is a match for 308 brass, but has a rebated rim (slightly different geometry)

The ejector will work just fine at ejecting, but it should have that bevel to allow the case rim to slip into the bolt face and depress the ejector while chambering a round from the magazine.  This bevel is not needed on the smaller 5.56 case but on the .458, it is quite essential.  While the bolt pushes the 5.56 round out in front of the bolt and it goes pretty much straight back into the bolt face, snapping under the extractor and depressing the ejector, on the wider rimmed .458 case the rim is angling up as it slips into the bolt face.  So the rim has to hit the beveled edge of the ejector before it slides up over it as it is being pushed toward the chamber, then the extractor snaps over the rim.  The extractor needs the horns modified and there needs to be a thicker bottom to the extractor to space the hook out slightly more.  While you can make a 5.56 extractor work, you loose a lot of meat and the extractor is more likely to bend or slip off the rim if the case hangs up for what ever reason.  A properly made extractor, like the TROMIX, still has the full width of the extractor from horn to horn and is spaced out properly so it does not dig into the case with too much tension.  That is another tell of an improperly made bolt.  You should not EVER need an o-ring around the extractor spring.  Some companies modify the extractor to within an inch of its life causing the gripping surface of the extractor to be greatly diminished and prone so slipping off, so rather than make the extractor properly, which is expensive, their solution is to throw an o-ring around the extractor spring to increase tension so it won't slip off.

 I found the ejector bevel to be absolutely essential when I needed a BC and guts for a build and JoeBobs had a ToolCraft .458 SOCOM BCG on sale.  I bought it even though I only needed the BC and guts and had a TROMIX bolt on hand to swap out, but this way I got the BC and guts and could give their .458 S bolt a try.  Right off the bat I could see the supplied bolt did not have a properly modified extractor (looking like an unmodified 6.8 or 6.5G extractor), the ejector was straight out 5.56 with not a hint of a bevel, and it would not feed worth beans, doing exactly what the OPs showed in his post.  I replaced the extractor with the TROMIX, no go, it was hanging up on the ejector.  I then beveled the ejector, close but no cigar.  The bolt face was too small for the case head to completely seat.  I replaced the bolt that came with the TC BCG with the TROMIX bolt and it fed like greased butter.  I later had Paladin open up the bolt face to spec and along with the TROMIX extractor and modified ejector and it now works.  But it shows you that a lot of these Johnny come latelies don't put in the R&D or even research what needs to be done to make a functioning bolt and barrel extension.

Well, spoke with the Pro2A guys this morning and they were convinced it was a magazine issue, and they were right.

I bent the lip up some on one of my Lancer mags and if I only load one round it chambers perfectly, ejects perfectly.  More than one in the mag and the same old deal.  As stated earlier they recommend the E-Lander mags which I have on order or metal mags of which I'm going to go pick up some today.

I'm familiar with this malfunction. Usually caused by the upper not being built by Tromix, Wilson Combat, or RRA.

What ammo/bullets are you shooting? My tromix barrel won’t feed the Buffalo Bore 405gr due to the large meplat. It feeds other bullets just fine, though.

You see, that’s the problem though.  With a properly built .458 SOCOM you should never need to tweak decent magazines.  I’ve never had to tweak a .458 SOCOM mag even a little bit in over 20 years of shooting the round.  This round was designed from day one to work perfectly with unmodified 5.56 mags when shooting JHP, JFN, and spitzer bullets.  If you have to tweak the feed lips to make it work, those mags now might not work properly with 5.56 ammo, feeding the rounds too high to chamber, and that negates the intended design of the .458 SOCOM, which was the ability to simply swap uppers and load the .458 S round in the standard issue magazine.

It looks like you have your problem solved for your situation, and I’m glad, but you should not have to use specific magazines or tweak mags in order to make the .458 SOCOM feed properly.  The only exception is when using bullets with very wide meplats, like LBT LFN and WFN GC cast bullets which need the half moon cut in the front of the mag, or spitzer bullets with P-Mags.  The front rib of P-Mags, which did not exist  when the .458 S was developed, plays hell with feeding spitzer bullets seated to full magazine length.

I don't buy the "you should never have to tweak magazines" to get the 458 SOCOM to feed bullshit.

I built one, and chose metal GI mags as my first choice because (as others have documented) plastic mags can deform slightly when left loaded for a long time, especially with this cartridge.
That deformation can affect insertion and function too.

It was easy to see that the lip of the cartridge case mouth was hanging up on the front edge of the magazine during feeding, and that took all of 5 minutes to fix with a Dremel rotary file burr.

The cartridge case is radically different from the 5.56, and while a new follower isn't mandatory, there are a dozen maker files for 3D printing one specific for the 458, and these make loading magazines much smoother and easier. These followers even
allow you to know instantly which are your 458 mags (mine are marked 458 in black durabake on the sides).

I don't have a Tromix brand barrel or bolt, and my rifle runs great.

Mine is set up for hog hunting here in Florida (we are even allowed to hunt hogs at night), and it is about as perfect a caliber for that as I've yet seen. (As an aside, I enjoy seeing the European driven hog hunts on the hunting channels, and I've wondered how this
cartridge would do in such a scenario-probably fan-fcking-tastic).

I can see how this might fit in a WTSHTF arsenal, especially with careful, deliberate accuracy, but in that scenario re-supply is the problem (I don't have thousands of rounds of this like 5.56).

Amazing cartridge for such a small autoloading rifle. Definitely needs it's own magazines though.

Except for very wide meplat bullets, they cannot hit the front edge of the magazine during feeding because the bullet tip is above the ledge, and then the bullet tip hits the feed ramp on the BE and lifts the case mouth over the front edge of the magazine.  Live fire feeding is totally a different game than pushing the rounds out of the magazine when the mag is out of the rifle.  
That's why I half-moon the front of the mag, so when unloading unfired rounds the mouth of the case does not snag on the front of the mag.  The bullets I shoot, spitzer and RN and small meplat FN and HP, the case mouth never hits the front of the magazine and I have fired thousands and thousands of rounds over the last 20 years using mags that did not have the half-moon cut and I have never had a problem.  If you shoot wide meplat bullets, like the LBT LFN and WLN cast, then yes, you need to cut the half moon cut, but not for JHP, RN, and spitzer jacketed bullets, not if the rifle is built correctly.

People have created lots of fixes for rifles that were not built correctly and proclaim their problems solved, and they are right, their problem is solved until the band-aid comes off and they have to use a mag that has not been tweaked, then the problem re-arises.  For a rifle that was designed for hard target interdiction using a standard M4 or M16 lower with a fast upper swap, with no modifications to the lower or magazine, having to use tweaked mags was and is a deal breaker.  That was the beauty of the .458 SOCOM.  You could go from a 5.56 to a .458 with only an upper swap in seconds in the field and you did not have to keep your magazines segregated.  Pop on the upper, pop in the magazine with the right ammo, and get on with business, no fumbling around with special magazines.  You should not have to tweak anything to make a brand new rifle operate correctly with standard ammunition.  Why are people happy with paying good money for something then having to dick with the thing to make it function correctly?  I don't get it and I guess I never will.

And you know what happens if you get in a hurry and throw in a mag full of 5.56 or .300 BO in a .458 upper?  Nothing, that's what.  The cartridge strips from the mag and slides down the barrel.  Tip the barrel down and it will fall out the end of the muzzle.  Try putting a .458 round in a 5.56 or .300 BO upper and again, nothing will happen because it will jam up good and tight but cannot fire.  Try mixing up a .300 BO and a 5.56 and see what happens.  One way the result is interesting but not USUALLY dangerous, the other way, is a catastrophic failure of the upper and possible injuries to the shooter and bystanders.

After trying half a dozen mags and still having issues with feeding my LGS is installing a Tromix barrel extension on my rifle.

Should be about a week or so to get it done.  

Live and learn.  It's not a super expensive fix but if anyone asks me I will echo the voices from this forum.   Start with TROMIX!

How are they timing the BE to the gas port?

If you have a good smith who is willing to invest the time and not rape you, they can do it.  I've had it done by Paladin and I know Tony of TROMIX has done it in the past.  The only problem is that it can be time consuming and sometimes you have to try multiple BEs before finding one that will time correctly.  If you only have one BE to work with then you have more of a problem but to a guy who knows how to cut metal, it's not insurmountable.  They might have to set the barrel back some, recut the chamber and move the shoulder back for the gas block, but the hole in the gas block is quite a bit bigger than the port in the barrel, so there is a bit of wiggle room there.

 The only reason more don't do it, and why I think Tony does not do it anymore, is because of the time it takes, and time is money.  If a guy were to run into trouble finding one that will time or you have to set the barrel back, recut the chamber, and recut the shoulder on the gas block seat, you could end up paying a heck of a lot of money if he charges you buy the hour.  Most good smiths just charge for the job on something like this and hope  the difficult ones balance out with the easy ones and they break even in the end, but more importantly, they keep their customers really happy and a happy customer comes back and spends more money later on.

If someone would sell unthreaded bbl extensions, more bbls could be saved.  I suspect it would be pretty hard to cut the threads in a bbl extension that had already been heat treated, though.

@Akaviator Looking at the picture in your first post leads me back to the subject Big Bore asked about and you sort of skipped over the point of his question. The case rim is sitting right about where the bottom of the ejector would be located, makes me believe the ejector has not been rounded on the bottom edge as he mentioned. Can you take an up close picture of your bolt face? The feed ramp while not perfect may not be the root cause of the issue, if this is the case it could save some headache having a smith fit the new BE.

What makes you so certain the extension is the problem?  I'd wager the bolt is the culprit, and a much easier fix than installing an extension.

This is a cartridge that doesn't like to enter the chamber at too steep an angle.

Anything you can do to have the bullet/cartridge enter parallel to the bore makes it work so much smoother.

The first thing I would do is remove material from the front lip of the magazine in a gentle semi-circle from one side to the other.

The second thing I would do is 3D print a new follower. You can buy these as well (eBay), but some 3D prints are not very smooth, so you'd need
to sand the edges of the follower with 600 grit sandpaper to make them slick. (My trick is to cover them in salt, bake in an oven at 375 degrees for 4 hours, and then paint them with durabake; I'm set up
to durabake all kinds of things, so for me it's not a big deal)

A new follower will make a huge difference. As far as I know, none of the big manufacturers are making these. An alternative (where you don't have to do any work)
is using a magazine made for .410 shot shells. I have a few of those as I built one for the wifey. She likes it. Maybe too much. Maybe in an unhealthy way.
Google "410 magzine AR" and you'll see what I'm talking about. (Awesome for shooting skeet in the living room)

Your entire goal is getting the cartridge into the chamber in as straight a line as possible. Lot's of ways to skin this cat.
You don't need to spend a lot of money to do it (but you do need to spend some time figuring out your rifle).

There reason no big manufacturer is making these sled type followers on a huge scale is because they are not needed unless you live in a state that requires your magazine to be limited to 10 rounds and cannot hold any other cartridge.  If the BE and bolt are made correctly, there are no mods needed to the follower.  I have dozens and dozens of magazines that I routinely use in 5.56 and .458 S and none of the followers are anything but stock.  That's the beauty of the .458 S and its design from the get go: no special mags needed.  If you use the sled type follower, it will still function with 5.56 rounds until you get to the last two or three, then it dumps them all at once, so by some states requirements, that limits the 30 round magazine to 11 rounds, no matter if it is 5.56 or .458.

 Some of the states, so I have been told, are fussy and if it holds 30 rounds of 5.56 (or 20 rounds of 5.56) and functions properly, even though you are using the mag in the .458, you are technically in violation because the law says you cannot use a magazine that holds more than 10 rounds, hence you need the sled follower.  In my state of IN, on certain cartridges you cannot have more than 10 rounds in your possession, not mag, but in YOUR POSSESSION while hunting, but you can have a 90 round drum in there if you want, so no special follower or limiter is needed.

 For instance, the TROMIX sled follower has a longer tail on one end that takes a 30R 5.56 mag, which normally holds 11 rounds of .458, and makes it so it will only hold 10 rounds of .458 as well as not allow proper functioning of a mag loaded with 5.56 if loaded into a 5.56 rifle.  I don't know if other sled followers reduce the capacity of a 30 round mag by 1 .458 but I would assume so since the use of a sled follower is all about reducing capacity and functioning only with one cartridge.  They simply are not needed for smooth feeding or functioning in a properly built rifle.  Now on straight walled cases, like the .50 B and the .450 BM, I understand they are quite useful, but the bottle neck case of the .458 makes them much more forgiving when it comes to feed angle since the bullet is considerably smaller than the hole it is starting into (the chamber), which is not the case on straight walled cases.  So for a .458 to need the mags tweaked in order to make them feed properly, something is screwed up, BE, upper or lower spec, or bolt.  Or the magazine is truly one mucked up POS.

Of course, if a sled type follower is used when the ejector is not made properly and beveled correctly, then it may be so that keeping the round feeding more in a straight line so that the rim is not snagging on the bottom of the ejector might solve the feeding problem.  But it is not the sled that is actually 'fixing' things, it is the band-aid that is getting around a improperly made ejector.  If you switch to a standard mag with a standard follower, the problem will return.

Tromix barrel and bolt are a must when building a 458

For what it's worth, I had a bunch of SBR 300grn that would just not chamber. They pulled up and started ok, but failed to go fully in to battery. They where also very difficult to eject. After several attempts to get them to chamber I ended up pulling the bullets and resizing the brass. Then reloaded the same powder and bullet. Every one of them cycled fine after that. Not sure if this is what you've seen, but just tossing it out there.

This was a while ago wasn't it?  I seem to recall at one time either Cor-Bon or SBR (I cannot recall for certain which one it was) was not sizing the Starline brass before loading, and that is a huge NO-NO. It MUST be sized and trimmed before loading.  To skip those two steps is inviting a world of hurt.  A ton of people have had problems chambering new brass that they didn't size first and either SBR or Cor-Bon was making that mistake for a while.  Cor-Bon dropped the standard .458 SOCOM loading because of the trouble they had with it, loading it too hot and other silly mistakes, and I have not heard of any problems with SBR ammo in a very long time so I had assumed that they saw the error of their ways and fixed the problem, so please, let us know if this was with new SBR ammo purchased within the last two or three years.

Was new SBR bought about 11 months ago. Not sure how long the dealer had them before I bought them. LOT# is 20140702. Guessing made around July of 2014. I went through and reworked them back in May. Had a partial older box with 20110305 and they ran fine.

That would be about the time frame that I recall there being problems with the ammo not being sized, if that lot number is the date of manufacture and it sure seems like it would be.  Problem is, I still cannot recall if it was SBR or Cor-Bon, or both!

Tromix to the rescue, my AR is finally a reliable weapon

I got the Tromix 16.25" heavy barrel and extension with matched bolt installed today.  It works absolutely flawlessly, first round and five rounds rapid fired chambered perfectly.   It's been a learning experience for me, and I want to say thanks again to the folks in the know here.

Will have it as a camp gun at gold mining camp this year, ain't no bear wanting a piece of that!

People don't think Tromix be like it is, but it do.

It would be awesome to have stripped forged or billet uppers without M4 feedramps, but beveled to match this and annodized on top vs dremeling.

Absolutely

Today I finally took it out to the range.   What a great shooter!   I mounted an Eotech HWS512 on it and got in dialed in with rounds 8, 9, and 10 putting them all within an inch at 25 yards.  Of course I didn't bring my rest or anything today but the rifle is so easy shooting not a big deal.  I'm confident with my sand bag rest I could get all three touching.