What's going on with this upper?

[Lone spur]

About a week ago I took my rifle out to the range. I fired about 50rds through the 223 upper, then switched to my RRA 458 upper. The rifle fired 3 rounds, had one FTFire, fired one round, then would not fire anymore.
When I pulled the trigger I could hear the hammer drop but nothing happened. I checked the primers, no indication of any firing pin strike. The upper was clean (only 20rds down the tube since the last intensive cleaning). I checked the bolt and firing pin for any broken parts, nothing.
I did notice difficulty extracting about half of the unfired rounds (this was also a problem when the upper was new but RRA polished it and it has been fine since). The only things that I can isolate as variables from its previous flawless performance is: use of a standard rifle buffer spring, a mildly dirty lower, and single digit temperatures.
When I got home I completely disassembled the rifle and cleaned it to like new condition and reinstalled the green RRA buffer spring. Friday morning I took the rifle back to the range (still single digit temps here in MI). It fired 3 rounds without a problem. I reloaded the mag and after that it would not fire. Same deal as before. Again about half of the unfired rounds extracted hard, but the chamber seems clean still. Incidentally, I threw the 223 upper on after the 458 gave up. The 223 didn't have a single issue. Could the temp be the cause of the problem? Could this be a bigger issue?
It's gonna be about a week before I can take it out in temperatures over 30.

[drdougrx]

How long was the upper in the cold???  Sometimes the firing pin and its spring get sluuish when the oil solidifies.  I've had that happen.

[Lone spur]

From the time it walked out of the house to the time it quit firing last was probably about an hour and a half. We'll see what happens today. It's supposed to be in the upper 50s so I'm gonna try to sneak out to the range this afternoon. I finally was able to get Rock River on the phone, they said send it in, but they are so swamped they have no idea when they could even get to it.

[Lloyd Smale]

my guess is either its still a chamber problem or you may want to try a new set of dies as it sounds like your ammo isnt chambering corectly. Also you might want to experiment with bullet seating as just seating a tad deaper might cure your problem. Smoke one of your bullets and see if it is hitting the rifling in the throat. Also check to see if your action will close and lock up properly and extract easily with both your loaded ammo and some sized brass. If you are crimping stop. The crimp could be swelling the neck of your brass enough to cause problems. Also reevalutate your load. If your pushing it to the max drop it off a bit as ars dont like real hot loads and squeazing the last 100 fps out of a socom is getting you nothing in performance. One more thing is if your not trimming your brass start.

[Savage]

Could be a quick chamber check of your loaded ammo will reveal the problem. Sounds like the bolt may not be going into full battery. Machinist's blue or smoking the round before chamber checking should tell the tale. Your chamber may require the use of a small base resizing die. Hope you can get it sorted out without having to return your upper!
Savage

[Lloyd Smale]

savage made a good point. Small base dies. I use them ALL OF THE TIME in any battle rifle. I allways figured it was a bit of extra insurance my ammo will run. Accuracy isnt the most important thing with theses guns its reliability. One other problem you could be running into is your brass. If your using surplus military brass thats been fired before some of it gets shot in machine guns and some of them have LARGE chambers which cause the brass to swell at the base. In some instances even full lenght sizing with a small base die would take the bulge out at the very bottom of the case.

[Lone spur]

Wouldn't you know it, yesterday was the nicest day of the year so of course the range was closed for maintance. Guess I'll have to wait a little longer to get some more testing in. The brass is all Starline (the only people who make 458 SOCOM brass) and all the firings have been in my chamber. I wish there was a source of surplus 458 SOCOM brass, that would definately be worth some added effort.
I did get my hands back on my supply of CorBon factory loads and tried cycling some rounds yesterday afternoon. They did seem to extract a little easier but for some reason so did my handloads. A note on my handloads, I trim and full length size every time and I use an absolute minimal crimp. Also, I am happy with the performance at the starting load level and have left them there so they definately aren't hotrods.
I am still a fairly green reloader so could you expand on what you mean by "small base dies"? I'm not opposed to making an investment in a new set of dies if I have to but not many companies are making 458 SOCOM dies right now. This leaves me rather limited.

[Savage]

The small base sizing die do just what the name implies. They are designed to reduce the case to factory specs in the web area. This can be a critical step in auto loaders to insure function. In a business rifle like the AR, all my reloads go thru small base dies. Mine get a substantial crimp as well using the Lee Factory Crimp Die. I consider those two steps essential for ammo that absolutely MUST function in any weapon I might use them in.  I use the Redding small base dies.
Just curious, does anyone make an "off the shelf" chamber gauge for the 458 SOCOM?
Savage

[Lone spur]

The only source I have heard of for a 458 SOCOM chamber gauge is Marty at Teppo Jutsu.

[Lloyd Smale]

what about seating dept? Have you tried seating the bullet a tad deaper.

[Lone spur]

I haven't been able to get to my bench to try that yet but the rounds I smoked didn't show any signs of hitting the lands. The bullets I've been using are 300gr Rem JHPs. Previously, I've shot 405gr Rem SPs which are much longer so I know I've got plenty of clearance. I did measure and compare every dimension I could think of between my 300gr loads and the 300gr CorBon loads (which appear to use 300gr Rem JHPs also) and they seemed identical.
I do have a couple pieces of brass waiting to be loaded. I'll give a shorter OAL a try.

[Lone spur]

Well, I got out to the range Sat afternoon and the rifle ran flawlessly. The temp was up a little, hovering around freezing. It also worked during a yote hunt yesterday.

[drdougrx]

still think it was gummy from the cold.

[Lone spur]

That's the only variable. The gun was lubed with Rem Dri Lube which has teflon in it. I have always liked the dri stuff for gas operated and blow back guns. Admittedly, I've never heard anything offically on what to expect from it in the cold so that could be a factor but it has always done great in my other guns.