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Posted: 3/6/2009 2:06:31 PM EDT
I've got a new Krieger barrel ar15 chambered in .223 match and they said to start with .010 of setback off the rifling for bullet setting depth. I measured the chamber with a stony point guage and came up with 2.375 touching the rifling. backing that off .010 gets me a COL of 2.365 which is way over the 2.260 in the loading manuals and so long it will not fit in my mag's. Anybody have any idea what gives? I'm using Sierra Matchking 77gr bullets and if I seat them to 2.260 it appears they are actually seated to the point of the bullet point actually tapering into the neck space.
Link Posted: 3/6/2009 2:24:29 PM EDT
Link Posted: 3/6/2009 2:33:50 PM EDT
IIRC, that's a Wylde chamber.
'Borg
Link Posted: 3/6/2009 4:51:29 PM EDT
QuickLoad shows a significant pressure increase when seated shorter. Be careful when working close to max loads.
Link Posted: 3/6/2009 5:04:23 PM EDT
The match chamber has the longest freebore of any of the 223 chambers. I guess it's due to being shorter in it's other dimensions. .0680 is the free bore vs. .0250 for .223 rem. or .0566/.0500 for nato.
Even a wylde is only .0619
Link Posted: 3/6/2009 5:05:50 PM EDT
Originally Posted By metoo:
QuickLoad shows a significant pressure increase when seated shorter. Be careful when working close to max loads.

You know,, I shoot a lot of 77 SMK's amd 75 Hor, and seat them to touch the lands and to load in a mag.
My chrono lists the same vel with both, with an over max load.
Mag length or land length,, pressure/vel is the same.
'Borg

Link Posted: 3/6/2009 7:22:48 PM EDT
[Last Edit: 3/6/2009 7:30:21 PM EDT by CCW]
Back check your stoney point with the "smokey point" technique. Use a lighted candle and coat a bullet inserted in a sized casing with soot, no primer no powder. Wipe and re-soot and work the seater stem down in smaller and smaller increments until the soot on the bullet shows it is just not touching the land when you push the cartridge and bullet into the chamber with the bolt or with your finger. Measure the distance between the bullet tip and the cartridge head face. That is your "zero" point. Take your seater stem on down from there to set the bullet to land clearance.

As Aero-E points out, the two requirements "xx to lands" and "work and feed reliably from the AR magazine" can be in conflict.
Link Posted: 3/7/2009 6:49:00 AM EDT
I'm sorry I don't get the idea of the match chamber then. If I can only load to 2.26 or 2.27 and get the rounds in the mag, then what does have the .09 of free bore get me in the match chamber. It appears I would have been better with a std 223 chamber and the bullets would have been closer to the rifling.

I checked my zero and while the bullets does seat on the side it is really deep into the case.

Link Posted: 3/7/2009 7:03:42 AM EDT
[Last Edit: 3/7/2009 7:05:46 AM EDT by AeroE]
Link Posted: 3/7/2009 7:44:10 AM EDT
I'm still confused. If I load to 2.26 I'll have like .095 of free run, which seems huge. If I load to 2.345 which would be ..020 of free run I'll not get the rounds in the mag. The gun was supposely setup for the 77gr MK as an autoloader not a single shot. It appears the match chamber may not have been a good recommendation. Or am I missing something, from the replies it look slike it should have been chambered in std 223 and I would have been much closer to the 2.26 oal that is recommended.

Any help would be greatly appreciated.
Link Posted: 3/7/2009 8:16:52 AM EDT
Just seat them to mag length and shoot them,, you'll like it.
'Borg
Link Posted: 3/7/2009 9:09:28 AM EDT
The .095 is relative. Most AR's shoot M193's and M855 mil-spec rounds with a longer jump to land. My Colt and Bushy run 0.100 to 0.150". No, they are not 1/4 moa tack drivers at this jump, but such is life. You can buy single shot, through the mag well, loader devices to load up the longer rounds or just insert through the ejection port.
Link Posted: 3/7/2009 9:50:07 AM EDT
[Last Edit: 3/7/2009 9:51:18 AM EDT by ma96782]
IMHO........At this point, "Don't worry so much about the theory."

Go shoot.
_____________________________

Consider this...............223 Rem. And 5.56mm chamber specs

http://www.radomski.us/njhp/cart_tech.htm
_____________________________

For those considering a new barrel............

Pick, what YOU figure, will be best FOR YOU. Simple.

Twists, chambers, makers, profile, weights, etc..... They vary.

The mag length "restriction is always there."

Different bullets mfns offer bullets in: various ogive's, weights, construction, measured lengths, etc....

Single loading is always a possibility when using "longer" bullets. And, there are magazine modifications available that might get you loading single cartridges with more confidence.

You could always have it "custom made."

But, in the end.........you've picked what you wanted. Then, you go shooting.

Aloha, Mark




Link Posted: 3/7/2009 2:44:31 PM EDT
Originally Posted By fixit:
The match chamber has the longest freebore of any of the 223 chambers. I guess it's due to being shorter in it's other dimensions. .0680 is the free bore vs. .0250 for .223 rem. or .0566/.0500 for nato.
Even a wylde is only .0619



The .223 Holliger has the longest freebore @ .106
Link Posted: 3/7/2009 2:46:01 PM EDT
Holliger uses the Wylde chamber.
'Borg
Link Posted: 3/7/2009 2:58:36 PM EDT
Just goin by the info here
Link Posted: 3/7/2009 3:24:03 PM EDT
"Match" means different things to different people.

Freebore length is not relevant to accuracy. What is relevant is freebore diameter and freebore concentricity. Not all bullets have to be jammed into the rifling to shoot accurately. Those with tangent ogjives, like Sierra's SMK, jump to the rifling very well. Those with secant ogjives, like Hornady A-Max and most VLD designs, seem to shoot more accurately when loaded close to the rifling.

With that said, a Wylde chamber is nothing more than a NATO chamber with a tight .2242" throat. It allows reliable functioning in semi-auto applications with good accuracy. It accomplishes the accuracy part by aligning the bullet with the bore using a throat only .0005" larger in diameter than the bullet. This way the bullet enters the bore perfectly straight. NATO chambers, on the other hand, allow the bullet to hit the rifling as much as .002" off-center. It is good for 100% reliability in mud and sand, but it is hard to get better than MOA accuracy out of them.

If your rifle has a Wylde chamber, stick to Sierra bullets, load them to magazine length, and forget it. Also, understand that 69gr SMK's outgroup their 77gr brothers, so don't pull your hair out trying to get a half-inch load.
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