SigSauer M400 jam

[cypress]

With new rifle and twenty rds in new Sig 30rd polymer mag, about halfway through a the spent was ejected and a fresh round chambered but the bolt jammed about half open over a another round partially pushed out of the mag. The point of the jammed round was just short of the chambered round while the back was still below the mag lips. There was enough clearance to hook the rim of the chambered round and slide it back and out of rifle. 2102 Lake City 55gr fmj. Input from seasoned AR owners on malfunction welcomed.

[Technosavant]

Double feed?

Most of the time that's going to be a magazine issue- it's letting more than one round out of the thing at a time. Is it happening with every mag you have or just one of them?

I'd try it with some other mags and see if it continues (maybe get a mix of GI style from companies like Brownells, some Pmag, maybe some Troy or TangoDown ARC too) and see which ones perform the best. Then buy a bunch of those.

[Ridge_Runner_5]

I agree, sounds like a mag issue.

Skip the other aluminum mags and just get a Pmag or two. Most reliable rifle magazine you will ever own.

[Destructo6]

The SIG polymer mag is junk.

Buy good metal mags or Pmags.

[halfcocked]

Ditto the Sig mags are crap. I almost cried when I took my 556 out for the first time. After switching to GI mags, never a hiccup since.

[compdocjoe]

Yup, SIG mag bad, PMAG good!

[Micropterus]

Does Sig make their own magazine? My M400 came with an aluminum GI mag. The enhanced version M400, AFAIK, comes with PMAGs or a PMAG.

[ratsandwich]

Bought one of these M400 Enhanced.
It came with a Pmag and jams constantly with;

1. Pmag(s) of six Pmags
2. Metal Mags, 3 different kinds
3. Winchester 5.56, 223 Remiongton, 223 Wolf Steel Case, 223 PMC
4. Included Lube, Hoppe's (2 kinds) Oil, Tri-Flow, Moly Lube (dry lube)
5. HEAVY, MEDUIM, LIGHT, and Practically NO Lube.

How you like this? I'm SUPER impressed wig SIG. What a great gun, how badly can an AR platform FAIL, here is THE benchmark. Double loads, Fail to load, Fail to catch bolt on empty clip...

Sometimes, seemingly random, SEVERELY dented brass. 223, 5.56, all mags/lube combo's.

The only thing I can even guess is some kind of timing failure, a possible gas malfunction, or my hunch: a buffer spring failure of some kind.

This gun is at Sig now and I am expecting them to find nothing, fix nothing, clean it again, send it back and have the same problems after shooting 30 rds.

Do Not Buy One Of These Guns. There are sooooo many options out there, you don't even need to EVER even look at Sig AR's.

Lets's hear from the pro's now.

[MikeGunz]

If its brand new did you clean it before firing it? They ship with packing grease that is more for preservation than function.

[knowledge_is_power]

I just picked up an M400 enhanced my self. Before I shot it, I throughly cleaned it and applied copious amounts of lube to it. I put about 200 rounds through it with out a single malfunction. I'm no expert and this is the first AR I bought. But four years in the Marine Corps I've learned that despite what they say about running a dry bolt, it is in fact best to run it wet. Never had a malfunction in any of the M4/M16's I ran in Corps as long as it was well lubed. I do believe that there are lemons out there though. But no reason to flat out condemn them all.

[MikeGunz]

I agree knowledge is power, I was in the corps too and found running a m16 dry would almost guarantee a malfunction. Nice light coat of miltec and daily cleaning kept my rifle, 240, and m9 running perfectly.

[ratsandwich]

I have indeed cleaned the entire upper and lower.

I sent it back to SIG and the note upon return says:
"We replaced the gas return o rings and ran 2 clips (60 rnds) through it and had no malfunctions. " - Sig

I have read that the enhanced has a shorter travel in the bolt and cycles faster sometimes causing feeding problems. You can see this on Youtube http://youtu.be/mSbLragkC54

I quote:
"The rate at which the bolt carrier assembly recoils rearward can have an effect on reliable extraction and ejection, even if extractor and ejector dimensions and springs are absolutely correct. The period of time during which the bolt is behind the stack of rounds in the magazine, neither traveling rearward or forward, has an effect on reliability in that the magazine may not have enough time to push the next round into place before the bolt comes forward again, resulting in a "bolt over base" malfunction that is most commonly seen on suppressed rifles, as they have much greater rates of fire. Also, high forward bolt carrier velocity can result in extreme bolt bounce, as noted previously, while low forward bolt carrier velocity could mean that there isn't enough force to overcome strong magazine springs, dirt or debris in the action, etc."

This is causing the feeding issues as well as the possibility that the o rings fail in the gas piston.

I am not impressed. I think the enhanced version is a loser and the solution is replacing the upper with another Make, at a SIGnificant cost to me.

We shall see what happens when I pick that gun up at my friends shop and shoot another 120 rounds through it. If it jams even once I'm going to be ripSh1t.

[Ridge_Runner_5]

Did the SIG guys really say clips?

[Destructo6]

I sent it back to SIG and the note upon return says:
"We replaced the gas return o rings and ran 2 clips (60 rnds) through it and had no malfunctions. " - Sig

Sig apparently came to the same conclusion that others did in your other thread hijack: undergassed/short stroking.
Then you quote this:

I quote:
"The rate at which the bolt carrier assembly recoils rearward can have an effect on reliable extraction and ejection, even if extractor and ejector dimensions and springs are absolutely correct. The period of time during which the bolt is behind the stack of rounds in the magazine, neither traveling rearward or forward, has an effect on reliability in that the magazine may not have enough time to push the next round into place before the bolt comes forward again,

Which describes overgassing.

It's one or the other.

[ratsandwich]

Thanks Destructo. Fountain of knowledge. Appreciated. Don't give the slightest **** about your other opinions but I really appreciate your constructive input.

Yes that was a real quote "Clips" from sig tech guy. Really

Good news guys. I think I have the answers I need.

[sailskidrive]

Interesting. Does any know if the M400 is the equivalent of the 516? I have a 716 and have not had a single issue with it. However, having dorked around with other piston ARs I have come to the conclusion that the best design for the platform is probably the original DI design. If you want a piston 556, buy a SCAR.

[454 Super Redhawk]

i think the 516 is piston driven