Problems chambering with new .458 SOCOM build

[Colin Ward]

So I recently put together a .458 SOCOM using a barrel & bolt pair from Brownells (https://www.brownells.com/rifle-par...sku080001360-113648-208329.aspx?sku=080001360). I'm new to the cartridge and chose it when I was looking to go with a pistol cartridge AR-15 and didn't really like what I saw from the AR-9s & AR-45s. The .458 SOCOM appealed to me primarily because of how few changes had to be made to the basic AR carbine platform. I didn't realize that it wasn't SAAMI standardized yet so clearly I didn't do my homework that well. Regardless, the rifle in it's current state will not go into battery fully without applying considerable force and in doing so it marks up the neck and copper jacket of the round (Factory Underwood ammo). I have read on various forums that there are 2 different reamers out there; the one Tromix uses, and then reverse engineered reamers (PTG) used by everyone else. I have found 2 different cartridge drawing/specs as well. It also appears that Tromix had a small run of incorrect chambers due to an out of spec reamer back around 2016. I don't know who makes the barrel for Brownells as they tend to be tight lipped about that info. I put sharpie on one of the rounds and forced it into battery https://photos.app.goo.gl/K9a25u8BxR87BBej6. I also have a crappy borescope I used to take a look inside the chamber. From the pics of the round you can see the neck is being damaged by the chamber on opposite sides and the jacket of the bullet itself is gouged in the same area as the neck. The scope shows a lot of brass galling in the neck area of the chamber. Considering only about 10 rounds have been chambered in the barrel that seems pretty significant and I think this barrel was chambered incorrectly or to a different spec than the ammo is built to. Sorry for the rambling, just looking for a little advice.

 

[338 dude]

Seems like the chamber neck is very tight do not fire until you know for sure you may have to cast the chamber and measure that

 

[Sandstorm]

Send the barrel back to Brownells...they will make it right. Do not shoot any sounds like 338 Dude said.

 

[deepwater]

Send it back.

 

[BOLTED]

Have you measured the brass (empty unloaded) before and after chambering?

How about measuring the brass before and after loading? Is the brass neck expanding too far after seating a bullet? Check the bullet diameter.
Always check multiple pieces of brass and bullets to get an average for readings.

Does the loaded round seat correctly in a 458 Socom loaded round cartridge gauge? If it fits in the case gauge and not in the barrel chamber, it's a pretty good indicator that it's the barrel.

Know anyone else with a 458? Compare with theirs?
I'm just saying to start measuring and recording everything as the process progresses, ID, OD, of the brass is where I would start first.

Before I sent the barrel back, I would want to be sure everything on my end was checked and double checked.

Best of luck, I love my 458, great choice.

 

[bholcomb]

Tromix and le wilson make a case gauge checker for the ammo ($45-50), it checks the headspace and throat. If all the ammo checks out, send the barrel back.

 

[johnfred1965]

I built a 458 from a Wilson Combat barrel kit. My reloads from a standard set of hornady dies would not go into battery. I discovered the shoulder was not set back far enough. I took .005 off the shell holder to give me a little extra pushback, and now it runs great! A real Thumper!

 

[Coyotefurharvester]

Did you true up the upper before assembly? If not send it back, if you altered the upper you could try a different one first. Looks like contact on the bullet ogive, not good, unshootable.
I have 3 223/556 bcg, 2 interchangeable between a 223,Shilen 17 rem barrel and a 20p BHW barrel about a thousand difference in fired headspace case measurements. The factory 556 Bushmaster rifle(my only factory AR) bcg will not go into battery in the 20p upper. All my assembled uppers are unaltered uppers. I haven't investigated why the Bushmaster bcg will not go into battery in the 20p upper.