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Topic: BRASS and Sizing for the AR-10 6.5 CM (Read 440 times) previous topic - next topic

Re: BRASS and Sizing for the AR-10 6.5 CM

Reply #30
John –

Here are a few suggestions to get your 6.5 CM semi running for you.

Newly built AR’s, (15 or 10) rifles need to break-in, same as a barrel rifling needs rounds fired to smooth it out.
To help with break-in, pull your bolt carrier group and thoroughly oil until there is oil dripping off.
Lightly wipe off the excess oil, and install the BCG back in your upper.
With NO ammo, and empty mag.. Hand cycle the BCG from lock back to fully locked in battery.
Release the bolt and allow the BCG to slam forward to fully locked.  Do this a minimum of 100 times.  200x is better.
This hard cycling action will smooth up any rough anodizing on the inside of your upper, and will mate your bolt lugs to the barrel extension.
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Next, get a brass chamber brush the same size as a 308 or 6.5CM case diameter, attach to a short cleaning rod (about 12” length).
Wrap a couple of 2x2”, or 3x3" cleaning patches around the brass brush, and lightly coat with either Flitz or Iosso paste.
Run the brush and cleaning rod with an electric drill to clean the chamber in a movement like honing cylinders on a motor build..
You do not want to achieve a mirror finish in the chamber,, just run for 2 to 3 minutes to clean up the chamber wall.
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Now,  CLEAN all the junk splattered in the chamber, bore, barrel extension/lugs and inside of your upper receiver.
You should expect to use lots of 2x2”, or 3x3" patches around the brass chamber brush to get the chamber, barrel extension and lugs sparkling clean.
Brownells, Midway, etc sell 6 inch or so - Q-tips that are useful for cleaning the barrel extension/lugs…
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After cleaning, make certain there is NO oil on the bolt lugs, and no oil in the chamber...
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For your next range trip, suggest you leave the handloads at home.
To get things tuned and running smoothly, need to fire factory ammo to get cycling dialed in.
Hornady ELD’s work great for this.  The factory brass is sized correctly and pressure will help get your adjustable gas block set.
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Load one single round in the magazine, chamber and fire…
Did the bolt lock back on the empty mag ?
If not, open the AGB setting one click and try again. 
Once the bolt face locks back on the mag, open the gas block one additional click for reliability.
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Ask for help to see where your brass ejects.  1 – 2 oclock is overgassed.  3 – 4 oclock is perfect.  5 – 6 is undergassed.
Again, adjust the gas block setting for 3 – 4 oclock ejection.
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Measure your fired factory brass for length from base to shoulder datum.
Suggest using Hornady Lock-N-Load Headspace gauge comparator and calipers.  The correct comparator is Hornady B-375 to measure the 6.5CM cases.
40 bucks at Midway for the set.  https://www.midwayusa.com/product/1012743827?pid=479704
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Using your full length size die, bump the shoulder datum measurement .004” shorter than the fired length…
Neck size dies should not be used for any semi-auto,,  bolt guns only.
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Now load and test your new reloads, and welcome to the forum!

Dennis
NRA Endowment Life Member
Hog count: 205.... Sus Hog: 17... Canis 18... Lynx rufus 1 … Thermal cal. - 30 Herrett AR -  AR15Performance.

Re: BRASS and Sizing for the AR-10 6.5 CM

Reply #31
Your chamber is tighter than your gauge.

RCBS makes a SB die for 6.5CM
https://www.midwayusa.com/product/1011284542?pid=120240
(Throw away the crimp die.)
Modify Everything

Re: BRASS and Sizing for the AR-10 6.5 CM

Reply #32
@Homebrewer , man that HAS TO BE the single best response I've gotten. Holy shit bro. Thank you. That was systematic, methodical, and very well stated. I will do everything u suggested, although I will say that my brass is ejecting way forward of my poz. Deff @the 1-2 o clock. So would that eliminate under gassed ?  I'll lube that hateful bitch up good this afternoon and keep working her hard until she decides to cooperate, ( had to do the same to my ex wife).  And I got 3 boxes of Hornady match for the range tomorrow. Thanks again, man this forum rocks!!!

Re: BRASS and Sizing for the AR-10 6.5 CM

Reply #33
For setting the gas block I usually close it off, rotate 2 clicks (if it has a detent mechanism), load one round and fire. Usually the bolt will not hold open. Open one more click, try again until the bolt holds open. I'll go one more click to account for changing conditions and call it good. That spot on the gas block is just over the minimum needed to reliably cycle. I keep track of the clicks from closed needed for normal versus suppressed fire so I don't have to think too much, at my age thinking too much hurts :(
Chris

Re: BRASS and Sizing for the AR-10 6.5 CM

Reply #34
@Homebrewer  Hey Dennis whats up ? wanted to reach out and share some findings. I went out and got some Hornady Match ammo. came home ,,, Lubed the living crap outta the BCG. and hard cycled it for maybe 50 times,, then decided to see if one of the rounds  that slides right into the gauge would cycle in it by hand,So I loaded  it in the mag, mag in the rifle, and sent the bolt home. She locked in but Deff. sounded softer than the hard cycle. , but upon attempting to eject it ? pfffff man i had a BITCH of a time getting the bolt to unlock and travel backward, but ended up poppin it out.. THEN I took one of the Factory Hornady rounds loaded it in the mag , mag in the rifle  sent her home nice loud Audible Ka Chink,, and then when I ejected it? she slid right out  I measured the base of all three cases of Hornady and the One I reloaded ,,, the Hornady cases were ALL 2 thou smaller. I posted two pics ,,, the three Hornady rounds ,,, there are marks on the leads and whats more interesting is the small Dings on the primers,, I'm assuming thats from the free floating firing pin bumping in when the bolt slams closed. Oh and one more thing,,,, do you have an email address?  I'd Love to chat with you on this and really hear your take on it , you sound like my Unicorn here buddy. lol what say you ?

Re: BRASS and Sizing for the AR-10 6.5 CM

Reply #35
I know enough to be dangerous but the firing pin marks on the primers would make me nervous.
Chris

Re: BRASS and Sizing for the AR-10 6.5 CM

Reply #36
well for what it's worth ,,,,, I've not had a slam fire yet . lol and I'm guessing it's just the pin loosely bumpin it. lol

Re: BRASS and Sizing for the AR-10 6.5 CM

Reply #37
MRMAGAUSA

Scratches on the bullets are likely from the bullets scraping the sharp edges of the feed ramp/locking lugs as they are fed. Smoothing them out might help. Or could be from the sharp edges of the bolt scraping the next round in the mag. Does this only occur on chambered rounds, or does the next round in the mag show this without chambering? That would determine where/when the scrape is happening. But this is not likely related to the sticking cases issue.



The factory Hornady rounds (usually factory ammo is sized VERY small, to fit even the tightest spec chambers) chamber, fire and eject properly, AND you measure them .002" smaller diameter than your reloads. Yet another indication of the tight dimensions of your chamber?

The primer issue is apparently fairly common, and not an issue unless live rounds are repeatedly chambered without firing.
Modify Everything

Re: BRASS and Sizing for the AR-10 6.5 CM

Reply #38
MRMAGAUSA

Scratches on the bullets are likely from the bullets scraping the sharp edges of the feed ramp/locking lugs as they are fed. Smoothing them out might help. Or could be from the sharp edges of the bolt scraping the next round in the mag. Does this only occur on chambered rounds, or does the next round in the mag show this without chambering? That would determine where/when the scrape is happening. But this is not likely related to the sticking cases issue.



The factory Hornady rounds (usually factory ammo is sized VERY small, to fit even the tightest spec chambers) chamber, fire and eject properly, AND you measure them .002" smaller diameter than your reloads. Yet another indication of the tight dimensions of your chamber?

The primer issue is apparently fairly common, and not an issue unless live rounds are repeatedly chambered without firing.

KRC nailed it.
Scratches on your rounds are from the sharp edges of the lugs of the barrel extension.
To solve or reduce this, when building my rifles I use a Cratex bullet point on a Dremel tool to just break the forward sharp edges of the lugs...and to polish the feed ramps.  Makes for much easier/reliable feeding a semi, and reduce/eliminate scratches on your brass.
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https://www.brownells.com/gunsmith-tools-supplies/power-tools-accessories/rubber-abrasive-tools/rubber-abrasive-bullet-points/point-coarse-8-bullet-1-16-arbor-sku190025081-41792-11943.aspx
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Check the inside edge of the feed lips on your mag.  Possibly they are sharp and would benefit from a light polish to break that edge..

Sent you a PM.

Dennis
NRA Endowment Life Member
Hog count: 205.... Sus Hog: 17... Canis 18... Lynx rufus 1 … Thermal cal. - 30 Herrett AR -  AR15Performance.

Re: BRASS and Sizing for the AR-10 6.5 CM

Reply #39
Have not read how things worked out after you ordered the small base die.  Full length sizing and bumping the shoulder does the trick for me. 

In reading your post(s) it sounds like you did use premium components for your build.  But, did not mention what magazines or bolt you used.   If your SM Die did not settle your problem, I'd give Darkker a +1 for his comment:

<<"1) could be a mag issue, could be a bolt issue. Especially once coated, sometimes things don't side properly. Is the BCG moving freely? Is the bolt itself turning freely, or are the rings "tight"?">> 

In semi auto, including if not especially  pistols, the magazine can be the cause of failures to feed.   While I bought my AR-10 platform as a rifle, the favorite bolt I read about when building is JP's high pressure. 

By now you probably have this sorted.  If so, I'd be curious to know of your outcome.  lg

PS:  yes, this is a much better place for help and info than 'the Hide'.   Much better.  

 

Re: BRASS and Sizing for the AR-10 6.5 CM

Reply #40
Hey thanks for the response.. Well I can tell you this much . It's ALL in the shoulder. I actually went ahead and purchased some BRAND NEW never fired brass Hornady brand so i KNOW IT'S NOT  junk . anyway I used my 6.5 to test several shells they ALL dropped in perfectly ( as expected ). THEN ,,,,,, as I loaded one i NOTICED  IT WAS NORTH OF THE 2,800 c.o.l  by 3 thou. i.e. 2,803 so I slid the case back in and ran it up again  giving it a little EXTRA nudge , and I'll be damned if that Little extra didnt cause the case to  NO fit Perfectly back into the gauge . I was very tight and stuck up about a couple thogh ,, so i decided to sacrifice that round and put in back in the press and really bump it GOOD and show nuff ,,, after that it wouldn't even fit half way in the gauge .So the moral to this story ??????  

It's the added extra pressure of the press AFTER the bullet has been seated that is causing the case to expand and be "over sized" if thats the right application for the term . So from now On if the bullet is seated long by a thou or three , instead of trying to force/ bump it in from the bottom UP i need to just adjust the seating insert form the top down  and run it up again ,,,, GENTLY . So yeah ,,,,, After a BUTT LOAD of trial and error I've dialed in on the problem ,,,,,,, Now i have to figure out why she double tapps with one trigger pull ..... SMH it's always something . Tanks ALL for the helpful  suggestions and the patients

John