Sig 5.56 chamber end of the barrel question...

[winxp_man]

My Sig 5.56 has issues feeding ammo like the partizan match ammo. The tip of the bullet hits the end of the barrel at the chamber end before it lifts to go inside the chamber. I looked at my Bushmaster chamber end of the barrel and it has two cuts at before the chamber so if the cartridge rolls passed the feedramps and it does not have enough height to chamber the round then rolls past and does not come to a dead end stop right before the round goes into the chamber. Here is a little drawing maybe someone can compare it with there Sig if there are people with the rifle out there. Thanks

 

[gstaylorg]

Re: Sig 5.56 chamber end of the barrel question...

1st question is what kind of mags are you using? If they're Sig factory mags, place them gently in an appropriate cylindrical receptacle, then get yourself some P-Mags and see if the feeding issues don't disappear. I have several Sig 556s, none of which has had any feeding problems [that could be attributed to the ammo] using many different types of factory ammo. However, I have seen many FTFs due to the Sig factory mags. This was particularly noticeable using longer rounds, such as 75 gr and 77 gr match BTHPs, which I believe is caused by the bullet meplat dragging against the inside wall of the Sig mags (they are quite short internally [lengthwise] as compared to P-Mags). The flat meplat of the longer BTHP match rounds seems to get hung up on the inside wall of the mag. This type of problem did not occur using Sig mags with non-HP or plastic-tipped HP loads of similar length, I'm guessing because the shape of the tip was less of a problem for proper feeding even though these rounds also actually would touch the inside wall of the mag. These issues disappeared after I switched to P-Mags.

Alternatively, you didn't state exactly which Prvi match ammo you were using (69 gr?, 75 gr?), but have you tried a similar load from a different manufacturer to see whether they behave similarly? You may be right about the shape of the chamber area, although it doesn't seem as though that is the most likely thing to check first. Also, have you talked to Sig about this issue? In any case, good luck with it!

 

[winxp_man]

Re: Sig 5.56 chamber end of the barrel question...

Well I have the sig mag, c-products, p-mag, and Remington mag that I used and still the same issue. It's not the mags that the ammo is catching on it's On the barrel right before going inside the chamber. On my bushmaster it hits the same place right before going inside the chamber, but because The Busaster has that extra bevel cut before the chamber starts is there the partizan 69gr ammo rolls right into the chamber with out hanging up in the barrel. My bushmaster feeds all the ammo just fine the sig feeds everything but the HPBT 69gr partizan ammo and the FGMM 69gr.

 

[gstaylorg]

Re: Sig 5.56 chamber end of the barrel question...

I'm sorry to hear that, it sounds like that may be a tough fix. I currently have 2-556 pistols, a DMR, 2-556 SWATs, and a 556 SCM. I have not experienced the problem you're descibing with any of them, and I often shoot FGMM 69 gr (as well as BH 69s, and 77s from several manufacturers).

Do you think this is some kind of QC issue from the factory? If the chamber dimensions for the 556 are standard, you'd think that many people would have had the same issue. I'm a regular at both SigForum and SigArms556 forum and I have yet to hear someone describe this specific issue until now. The only other thing that comes to mind is do you think it's possible you could have a feed ramp issue that might be exacerbating the effect of the chamber edge/shape during feeding?

In any case, you might try posting at either of the Sig-specific forums and/or calling Sig to see what they say. Unfortunately, I strongly suspect it will be to send it back to Sig. Best of luck with it and let us know how things turn out.

 

[winxp_man]

Re: Sig 5.56 chamber end of the barrel question...

Well called sig today and they sent me a overnight shipping label. There going to have there gun smith take a look at it and make sure that before it's sent back its going to work with all ammo like it's supposed to. Oh and forgot to mention the actual model is the sig 516 sorry about that. I will post some pics tonight of the Sig chamber and the bushmaster chamber.

 

[Slippery_Pete]

Re: Sig 5.56 chamber end of the barrel question...

I've shipped some stuff back to Sig and they usually handle it pretty well. Give you the label, and hook you up with little things, like a case or something when returned.