A friend put togather an AR 15. It functions fine but he brought me some fired cases that have a slight bulge on one side just above the web. Factory Federal and imported "military" ammo with the same results. The upper had the barrel installed when he got it. What do you guys think, headspace or a chamber problem?
Thanks

It sounds to me like the chamber is mis-shaped. If the rifle extracts without issues I don't think it will be a problem. I have seen deformities in chambers that have been filled with JBweld and then polished smooth that then functioned without a hiccup. The chamber must be totally clean and oil free before the JBweld is applied.

Piss on JB Weld. Duct tape or chewing gum is cheaper and works just as well. But you do have to let the chewing gum dry at least 12 hours in direct sunlight.

However, I do insist on genuine hose clamps to hold my buttstocks on. Baling wire leave those sharp ends where you twist it together with pliers to contend with.

My buddy has an '06 that does the same thing to his brass. He checked into it and found that this sometimes happens on the extractor side of the chamber for some reason.

My gunsmith says it's nothing to worry about.

Does your occur on the extractor side of the chamber?

It does appear to be on the extractor side.
Thanks for the help.

Can't say I would suggest using JBWeld or any other compound to work in a chamber. Unless the "bulge" is extreme, most likely will not cause any problems. Reamer must have "wobbled" a bit when the chamber was cut, poor workmanship, but I have seen the same thing on various factory rifles over the years.

quote:

Originally posted by Nimrod308:
...It functions fine but he brought me some fired cases that have a slight bulge on one side just above the web. ...What do you guys think, headspace or a chamber problem?
...

I'd say there is probably nothing wrong at all. What I'll "guess" you have noticed is normal Pressure Ring Expansion(PRE).

If you have access to a 0.0001" capable Micrometer, measure 3-5 of them and post what that Diameter is on the Fired cases.

Does it look like this and covers about half of the case?

http://38super.net/Smart%20Fig.../G-ManBartFigure.gif


If so it is probably just case head expansion as HC said. Most likely it is caused by a generous chamber. Case heads rarely expand uniformly in over-sized chambers. One side is usually weaker and it gives there resulting in a lopsided effect. Take a caliper and measure around the circumference of the expansion ring at several spots. Note if it is consistent. Also measure the diameter of an unfired case at the web. If the measurement is consistent the chamber is round and will rule that out. If there is a .006 or more difference in unfired to fired case measurements that's probably the issue.

Could it possibly be the timing of the bolt? What buffer and buffer spring are you using? That could be one area to look. Could be the gas system is causing the bolt to unlock before it is supposed to.

Hello Nimrod:

I get this question probably 3-5 times a week. USUALLY it's a tolerance stack-up between cartridge and chamber dimensions.

If you review a SAAMI spec sheet you'll note dimensions are given for max. cartridge and minimum chamber. Cartridge diameters are allowed to vary by as much as MINUS .008", while chamber diameters can be as much as .002" LARGER than minimum. With .0010"-.0015" clearance between min chamber and max. cartridge, a min-spec case can be as much as .011" smaller than a max-spec chamber--this difference is guaranteed to produce a bulge in the thin side of a case with 55K chamber pressure.

Fired cases have to shrink slightly from chamber diameter for extraction to occur, so a fired case will never measure the same as the chamber. Nonetheless, if we know the diameter of the bulge, we can usually say whether it was caused by small brass, an oversized chamber, or both. If the bulge measures .3789" or greater, it's likely the chamber is large. If you measure the case between the bulge and the extractor groove--and get a good, consistent reading--you can often state whether the case is undersize. At this point, the case should measure no smaller than .367"

My experience tells me it's likely everything is within tolerance, but you have cases on the small side. Measure them and let us know.

Dave Manson

Many years ago I had an '06 that did that... I took some of the cases to my then gunsmith and asked him what was going on. What I was told was this:

The extractor claw is holding the case tight against the left side of the chamber. When the round is fired, since there is "room" on the extractor side of the chamber, the case head swells there.

It seemed a simple enough explanation to me, and I shot the rifle a fair amount without any problems before turning it into a custom 7 X 57 for my then nine year old son...