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Old January 13, 2013, 11:35 PM   #1
toolguy2006
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Cycling issues with Sig Sauer AR10

I recently purchased a Sig Sauer AR10, and naturally started to reload for it. I have been using the "bible load" (168gr A-Max over 40.5 gr of IMR 4895, CCI primer, and 2.8" col), which worked well in my M1A.

The issue that I have been running into, is that occasionally the rounds don't want to chamber all the way. The rounds that don't want to chamber properly usually come back out of the rifle with a shiny spot on top of the case, and the shoulder has a dark ring around it.

The rifle runs factory ammo just fine, and I have compared measurements between my sized brass and the factory stuff, and they come out awful close. I measured case diameter in several spots, as well as base to shoulder (with a Hornady head space comparator). The only real difference that I can find between my loads and the factory stuff is that the factory stuff is crimped.

The sizing die that I have been using is a standard RCBS full length sizing die. I'm not sure of a model on the die, if there is one. My uncle bought them in the mid-1960's, and never used them.

Any thoughts??

Last edited by toolguy2006; January 14, 2013 at 12:12 AM.
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Old January 14, 2013, 12:58 AM   #2
dmazur
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It may seem like an obvious question, but are you trimming the cases?

If the cases are too long, the mouth will jam in the rifling. This can lead to failure to chamber. It can also lead to dangerous overpressure if the round does chamber (as the rifling "crimps" the case mouth).

Also, "darn close" is relative. The difference between headspace GO and NOGO for many calibers is only 0.006", and sometimes less.

If your resized cases aren't 0.003" less than the fired cases (using your headspace comparator), you can have chambering problems.
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Old January 14, 2013, 01:08 AM   #3
toolguy2006
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dmazur:

The cases are trimmed. I just pulled five from the box of cases that came back from the range today, and all but one are 2.005 or shorter. Max length on .308 is 2.015.

Also, my sized brass that I checked measured .005" shorter than the fired brass that came out of the rifle, as measured with the head space comparator.
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Old January 14, 2013, 01:27 AM   #4
chris in va
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Try using a new resizing die and Lee factory crimp die.
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Old January 14, 2013, 03:29 AM   #5
dmazur
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Everything is within spec and they still don't chamber?

If factory ammo always chambers, then there is something different.

When you measured diameters of fired cases, was there any increase in diameter near the head?

While I believe it is rare, sometimes small base dies are necessary.

Also, when you say "shiny spot on top of the case", just where do you mean?
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Old January 14, 2013, 10:19 AM   #6
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Are you crimping the rounds while seating the bullets? That may buldge the cases just enough to casue an issue.
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Old January 14, 2013, 10:38 AM   #7
toolguy2006
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I have not been crimping.

The factory cases measure .002" to .003" smaller in diameter, depending on where they are measured.
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Old January 14, 2013, 02:26 PM   #8
dmazur
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If the rifle has a tight chamber, that 0.002" can be enough.

Even the "old standby" LE Wilson cartridge headspace gauge may not catch this, as those gauges are reamed deliberately oversized in diameter to make sure there isn't any interference with measuring base-shoulder. (And the neck hole is also oversized.)

Another thing that can occur is an "out of round" chamber. Unless the case is aligned with the axes of the ellipse, it may appear to be tight just because it isn't round. If there is a "shiny spot" on the side of the case, this could be the out of round chamber fighting the case.

If you have the patience, you could try inserting a fired (not resized) case using different orientations and see if there is a difference. Ideally, there won't be.
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Old January 15, 2013, 01:14 AM   #9
toolguy2006
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A thought on crimping.

Someone at the gun store where I purchased the mentioned AR10 told me that a light crimp will help ensure that the round being chambered will slide smoothly from the magazine, over the feed ramps, and into the chamber. Does this make sense to anybody? I kinda dismissed the idea at the time, but.........

Also, since I own neither a small base die or a die that will crimp .308, I started looking at options. I was looking at either Redding or Forster. Anybody have any thoughts?
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Old January 15, 2013, 11:19 AM   #10
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Not to me. A little crimp wouldn't do much more than a decent deburring of the case mouth, and then too much crimp could make the cases hang up on that end, and shiny spots would show up at the mouth. Were your shiny spots in the bottom 1/3t nearest base? Try cycling factory Wolf, or blue box Federals....if these do the same thing you have a tight chamber. (those cartridges are best used in Nato chambers). Order a Small-based sizer from RCBS, and that will likely end the problem....or use Dillon dies (which are always small-based). I had the same problem with my new .308 Remington R25 (DPMS). Added a small-base sizer to my .308 die set and the problem went away. Mine would not cycle Wolf or Federal blue box factory ammo either.

Using my calipers I found that the RCBS small-based sizer only squeezes the bases .001 or .002, in addition to that from a regular sizer, at the very most. Most factory is smaller yet.

You could grind your shell holder down a thousandth or two and size the base down enough, but then you are bumping the shoulder that much more. IME the shoulders are usually bumped too much anyway using regular dies adjusted to "cam-over," for an AR10 type chamber. Small-based dies also allow you to adjust the die out a bit and bump less. That actually would work your brass less. My reloads work super using those dies. 168gr Nosler Ballistic Tips over 40.2 gr of IMR 4895, CCI primer.

I'm betting your chamber is commercial .308...should say on the barrel...which is tighter than Nato chambers. (Trying to squeeze more accuracy, perhaps? Pun intended)
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Last edited by GWS; January 16, 2013 at 05:33 PM.
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Old January 16, 2013, 05:27 PM   #11
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Quote:
The issue that I have been running into, is that occasionally the rounds don't want to chamber all the way. The rounds that don't want to chamber properly usually come back out of the rifle with a shiny spot on top of the case, and the shoulder has a dark ring around it.
I reread your first post and realized I had missed that you said the shoulder had a dark ring around it.

If you couldn't chamber the round and fire it then why the dark ring? The only thing that comes to mind is carbon in the chamber and/or your shoulder is not bumped back enough, so the case rubs some of that carbon off, or the carbon has built-up in the chamber's shoulder enough to prevent the case and bolt from going into battery.

After making sure the chamber is clean does it still not go into battery? Also you mentioned a shiny spot on the case. And dmazur asked you where the shiny spot was exactly.....you didn't enlighten us...so where was the shiny spot?
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Old January 16, 2013, 06:24 PM   #12
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My thinking is to screw your sizing die down about another half turn for extra cam over. See if that stops the problem. If not you may need to get a small base sizing die. They are made with the sole intent to make reloads chamber easily in semi auto guns.
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Old January 16, 2013, 09:36 PM   #13
toolguy2006
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The shiny spot....

Sorry for not elaborating.

On the rounds that fail to chamber, there is a shiny spot on top of the case as if it rubbed on the roof of the chamber on the way in. Also, a tidbit I forgot to mention: when I experienced a round that wouldn't chamber, I had to beat the charging handle to get the action open. I couldn't pull the charging handle back with my hands.

Also, the rifle is brand new. It only has 162 rounds through it, including the 50 that were fired last weekend.

I splurged a bit and bought a RCBS small base die set today (its what was available locally, and much cheaper than the redding set). I plan on trying this, with a range trip planned this weekend.

Last edited by toolguy2006; January 16, 2013 at 10:54 PM.
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Old January 17, 2013, 01:46 PM   #14
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Tool guy

Did you buy the AR series RCBS die set? They come in a black box. I have a set of those in .308 and .223/5.56, they are small base dies and i have had zero problems with 2 AR-15's and 1 AR-10. They came strongly recommended from an old timer reloader I ran into at the store who loads religiously for AR's. I'm glad I took his advice, because I feel I saved on money, time and headaches.

Of course I also spent the money on Wilson case Gage's to setup my dies.
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Old January 17, 2013, 01:59 PM   #15
toolguy2006
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Actually I did buy the "AR" series dies because they came with a taper crimp seating die, and I wanted that option.
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Old January 18, 2013, 01:51 AM   #16
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Awesome!
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Old January 20, 2013, 06:52 PM   #17
toolguy2006
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Well, I just got back from the range.

The ammo sized with the new small base die seems to function perfectly!

Thanks everyone for your help.

The best group of the day was 5 shots at 1.539" using 165 grain Speer Boat Tail Soft Points. I borrowed an ancient four power Bushnell scope so that I couldn't blame my crappy eye sight/iron sights

Last edited by toolguy2006; January 21, 2013 at 12:52 AM.
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Old January 20, 2013, 11:42 PM   #18
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You're welcome......glad you found an easy fix!
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