rechambering .223 to 5.56

09 January 2014, 03:48

Eland Slayer

I own a Kimber 84M Pro Varmint chambered in .223 Rem, but I would like to be able to shoot 5.56 NATO ammo in it. I have been told by the folks at Kimber NOT to shoot 5.56 ammo in the rifle due to high chamber pressures.

So if that is truly the case....does anyone know a place around Houston where you can have the chamber of a .223 Rem bolt action opened up to safely shoot 5.56mm?

And does anyone have experience with this type of modification?

09 January 2014, 04:06

youngoutdoors

Chamber dimensions are the same unless your Kimber has a tight chamber,neck, or shorter throat. Don't know why they would say not to shoot the 5.56 in it. Someone else may elaborate on this.

God Bless, Louis

09 January 2014, 06:37

plainsman456

Get a throat/lead reamer and adjust.

The throat will give high pressures when shooting 5.56 in a 223 chamber.

Easy to do.

09 January 2014, 07:03

butchloc

whata bunch of bsflag

go shoot

10 January 2014, 08:24

Stonecreek

Thanks for raising the flag, Butch.

The only difference in the two chambers is that the 5.56 has a bit longer leade. While this theoretically reduces chamber pressures the effect is minimal (and less significant than other variables at play). If someone is overloading this cartridge and thinking they can get by with this because someone stamped "5.56" on the barrel, then they are in for a rude awakening.

10 January 2014, 09:34

npd345

From Wikipedia;

While the external case dimensions are very similar, the .223 Remington and 5.56x45mm differ in both maximum pressure and chamber shape. The maximum and mean pressures for some varieties of the 5.56 mm (different cartridge designations have different standards) exceed the SAAMI maximum for the .223 Remington, and the methods for measuring pressures differ between NATO and SAAMI.[2] The 5.56 mm chamber specification has also changed since its adoption, as the current military loading (NATO SS-109 or US M855) uses longer, heavier bullets than the original loading. This has resulted in a lengthening of the throat in the 5.56 mm chamber. Thus, while .223 Remington ammunition can be safely fired in a 5.56 mm chambered gun, firing 5.56 mm ammunition in a .223 Remington chamber may produce pressures in excess of even the 5.56 mm specifications due to the shorter throat.[3]

That being said I have shot thousands of 5.56 rounds thru my 223 Remington, Howa, based rifle with no problems.

10 January 2014, 21:27

PaulS

Lengthening the .223 chamber to a 5.56 length will likely affect your loadings for the .223 as far as accuracy goes. It is the safe thing to do if you want to shoot the 5.56 ammo but think carefully about what the changes will do to your accuracy and if it is an acceptable modification to you.

10 January 2014, 22:03

mete

AS I understood the major difference is the throat because of the very long military bullets used. Your kimber has a 1:9 twist and probably not enough for the long bullets anyway.

10 January 2014, 23:46

Rub Line

I worry about things like mice in the garage, getting to work on time and the price of meat. Shooting .223 in a 5.56, not so much.

10 January 2014, 23:57

Chief Engineer

If you are really concerned, your best bet will be the Wylde Chamber.
It basically splits the difference between .223 and 556 so little if any loss of accuracy when shooting 223 and no pressure worries with 556.
It's what I run in my Ar.

11 January 2014, 05:14

tom holland

the below is suppose to be difference in reamers.

http://www.ar15barrels.com/data/223-556.pdf

11 January 2014, 16:17

RyanB

quote:
Originally posted by mete:
AS I understood the major difference is the throat because of the very long military bullets used. Your kimber has a 1:9 twist and probably not enough for the long bullets anyway.

The 5.56mm chamber comes from the days of 1/14 twists...

Michiguns makes a hand powered reamer for this. It's made for ARs but I expect it works in anything.

11 January 2014, 16:52

Samuel_Hoggson

Cartridge dimension specs are not the same thing as chamber tolerances. Tom's linked chart is a good one. Arfcom has a nice discussion of the difference in something called the "ammo oracle". That said, the throat area is what you would address.

The reason most everyone gets away with shooting 5.56 in .223 dimensioned chambers nowadays - and think the matter deserving of a BS flag - is very few people actually possess M-193 or M-855 NATO spec ammo. Most of what passes for those things at the local Wally/Dick's/gunshows/eieio marts is not loaded to those pressure levels.

Twist is a more practical concern. Extraction, especially with steel cased ammo, can be an issue as well.

Sam

14 January 2014, 21:02

Eland Slayer

quote:
Originally posted by Samuel_Hoggson:
Cartridge dimension specs are not the same thing as chamber tolerances. Tom's linked chart is a good one. Arfcom has a nice discussion of the difference in something called the "ammo oracle". That said, the throat area is what you would address.

The reason most everyone gets away with shooting 5.56 in .223 dimensioned chambers nowadays - and think the matter deserving of a BS flag - is very few people actually possess M-193 or M-855 NATO spec ammo. Most of what passes for those things at the local Wally/Dick's/gunshows/eieio marts is not loaded to those pressure levels.

Twist is a more practical concern. Extraction, especially with steel cased ammo, can be an issue as well.

Sam

All of my 5.56 ammo is Federal "Lake City" brand, using XM855 62 gr. penetrator FMJ's....that's why I asked the question.

I will probably just leave the Kimber alone, since it is an absolute tack driver.

14 January 2014, 21:34

dpcd

Kimber is just covering their ass in case someone tries something stupid; shooting 556 in a 223 chamber is not one of those situations. I do it all the time with NO problems. As for twist, your 9 inch will stabilize 62 grainers; the fast one in 7 twist on the M16A2s is to stabilize long tracers at 20 below zero. Not needed for sporting use. Maybe the 80 grainers; I don't know about that. Anything, I would shoot one and see. Freebore length is the only difference that matters.

15 January 2014, 01:28

JDA-CO

I've been following this thread - This is the first I've heard of it not being safe to shoot 5.56 in a 223. I have been shooting 5.56 in my CZ 527 for several years with no issues. in fact, they shoot to the same POI as the VOR-TX that I use for hunting.

I've also shot 5.56 and the VOR-TX (.223 TSX Hunting loads from Barnes) interchangeably in my AR. No issues whatsoever...

I'm just gonna keep doing what I've been doing and hope I don't blow myself up!

JDA

15 January 2014, 01:30

Jerry Eden

Here's a few other items, that haven't been mentioned yet. While the 5.56 Nato round may use a heavier than 223 Remington bullet, it still has to be seated short/deep enough to fit an Ar magazine. The lead difference between 223 and 5.56 is roughly .080. If the bullets aren't seated out any further than a AR mag will allow, you can't shove the bullet into the lands on a 223 chambered rifle. And, the last time I looked, there isn't an AR in the world that can take the pressures of a modern bolt action rifle. I say BS also!

Jerry

15 January 2014, 03:07

Samuel_Hoggson

Wade, The X designation stuff you can purchase at the boxes is not the same stuff dotgov issues, not loaded to the same average pressure. Federal knows quite well their XM-whatever will find it way into that beater H&R break open that spent last winter in the barn.

The differences in theoretical strength between bolt guns and ARs is not relevant unless they are chambered exactly the same. Max chamber pressure in the long-throated AR firing real M-855 will be less than max chamber pressure firing the same ammo in the short throated, minimal chamber dimensioned .223 target rifle. We need to compare apples to apples. Were we comparing apples to apples the bolt gun would win, yes.

There's the ability to handle a single overpressure load. But how many? Metal fatigue results from X-number of overpressure loads. What is the value of X? How many overpressure loads can your bolt gun manage? The correct answer is: you do not know, nor do you wish to find out. There is a reason we don't recommend shooting a steady diet of proof loads through "built to take it" "three rings of steel" bolt guns.

Sam

15 January 2014, 04:37

Jerry Eden

Still BS IMO!

15 January 2014, 08:45

wasbeeman

The sky is falling, the sky is falling.

15 January 2014, 09:19

Idaho Sharpshooter

If I may be somewhat less than tactful, Kimber is full of shit...

15 January 2014, 14:56

Saeed

Sounds very strange to me!

We have 223 rifles from many different manufacturers, and all of them shoot 5.56 ammo without any problems at all!

15 January 2014, 17:57

Grumulkin

quote:
Originally posted by Rub Line:
I worry about things like mice in the garage, getting to work on time and the price of meat. Shooting .223 in a 5.56, not so much.

Ditto.

15 January 2014, 18:32

HPMaster

If you look, you can find data that states M193/M855 in a 223 rem chamber (.025 freebore) produces upwards of 75k PSI, while M193/M855 in a 556 chamber (.0566 freebore) produces ~55k PSI.

Now, while both ARs and modern bolt guns can handle 75k PSI, some brass will not.

Since most of not all M193/855 spec ammo will be in NATO marked/spec'd brass, it probably will be no problem, however, I tend not to like such pressures next to my face....

The X/XM variety of mil ball ammo is rejected from the Military due to some performance isses, and not manufactured specifically for the commercial market.... As Federal or Win.

15 January 2014, 20:26

Jerry Eden

Here's some more info. I guess you have to make up your own mind on this, as I can't see where all the red flags are comming from.

According to Cartridges of The World 12th Edition, the M855 Mil Spec round fires a 62 grain bullet @ 3100fps. The same book lists a factory loaded 223, 60 grain bullet @3100fps, they also list a load in 223,for an 80 grain bullet @2869 fps. You can only get so much powder in a cartridge case period. The length of the bullet, as you all know will limit that case capacity, as will the construction of the brass. Also,cartridges of the world lists a differnt oal for the 2 rounds, with the 5.56 @2.26 and the 223 @ 2.16. Tight chambers do produce problems in AR'S much more than they ever do in bolt guns. I bought a barrel from DPMS, went to use my normal across the course loads with 69 and 77 grain bullets, and it tore the rims off, leaving the empty case in the chamber, which had to be removed with a cleaning rod. The solution? I had to reduce the loads, until I got 1.5 grains below MINIMUM listed loads before velocities and performance became acceptable.

Jerry

15 January 2014, 20:44

Macs B

Show me a manufacturer who will state in writing that ANYTHING other than the "specified" "proofed""caliber on the barrel" ammunition is safe to shoot in their weapon. Not going to happen for all of the silly legal reasons.

15 January 2014, 23:09

Samuel_Hoggson

Tight chambers in ARs do produce more problems with primary extraction vs bolt guns. This has nothing whatsoever to do with the ultimate strength of either action. You can not get to the bolt knob of your 700 fast enough to manually unlock ahead of case relaxation. An AR will tear rims off completely normal pressure loads as a function of chamber dirt/stickiness/smallish dimension/whatever. Or.....it will fail to hold onto the rim through ejection. This stuff is more likely to be an issue with carbine gas systems and short bbls (ie., short dwell). You can read about "dropped extraction". Mack Gwynn told me a failure of primary extraction "almost" (but not quite) happens even with rifle length systems and good ammo. This is why a couple of my shortys need D-rings or X-power extractor rings to help overcome button ejector spring force. There is something to be said for fixed blade ejectors and slotted bolts, after all, at least in gas mechanisms.

Sam

15 January 2014, 23:27

Jerry Eden

Sam: In my case none of these factors you present were an issue with my AR. Still as to strength, I'll go with a bolt gun in the same calibre everytime.

Jerry

15 January 2014, 23:28

Jerry Eden

quote:
Originally posted by Jerry Eden:
Sam: In my case none of these factors you present were an issue with my AR. Still as to strength, I'll go with a bolt gun in the same calibre everytime.

Jerry

16 January 2014, 01:22

TomP

quote:
Originally posted by youngoutdoors:
Chamber dimensions are the same unless your Kimber has a tight chamber,neck, or shorter throat. Don't know why they would say not to shoot the 5.56 in it. Someone else may elaborate on this.

God Bless, Louis

I had a Savage 24V in .223/20 gauge which would not shoot 5.56 at all, firing pin left a mark but no ignition.

Mini-14 is not nearly so fussy, both work well enough (but shoot miserable groups).

16 January 2014, 05:10

BigNate

No dog in the fight really as I don't shoot mil crap outta my bolt gun, and my Mini's and AR's seem to be fine with anything that'll fit.
But......

18 January 2014, 03:31

Samuel_Hoggson

quote:
Originally posted by HPMaster:
The X/XM variety of mil ball ammo is rejected from the Military due to some performance isses, and not manufactured specifically for the commercial market.... As Federal or Win.

I've read that on the arfcom site. But here's something I had pasted from the Federal website some time back. I can't find it on their website now. But you can google it to see it referenced elsewhere:

"• XM193 product is first run, first quality product manufactured at Lake City Army Ammunition Plant for Federal Cartridge and is made to Federal specifications typical for commercial ammunition."

That suggests there may be more to the X than lot rejection based on variation, or whatever. Or the designation may mean different things from different manufacturers (Fed/ATK vs IMI vs ???). Like you I'd prefer to take the cautious route.

Sam

18 January 2014, 05:38

youngoutdoors

My error guys. What I should have stated is CASE dimensions are the same. Thats what happens when you are in a hurry and I apoligize. Military brass may tend to be a little thicker which may increase pressure also. Glad you guys cleared up my mistake.

God Bless, Louis

18 January 2014, 08:32

RyanB

XM193 isn't rejected ammo it's overruns.

19 January 2014, 11:29

Rule 303

I would suspect that Mil dimentions of chamber and throat to be slightly larger than Civil as the Mil weapons have to function in far worse conditions.

223 V 5.56, 308 v 7.62 X 51. If a bolt gun won't handle any pressure difference then it is a lousy unsafe bolt gun.

19 January 2014, 19:34

B L O'Connor

Does anyone actually know of an instance where firing a 5.56 round in a bolt action .223 rifle in good condition has resulted in a problem?

In the broader world outside this forum, firing 5.56 in .223 rifles must happen fairly often. Or so I'd imagine.

Is there any empirical data on this?

19 January 2014, 23:17

PaulS

quote:
Originally posted by B L O'Connor:
Does anyone actually know of an instance where firing a 5.56 round in a bolt action .223 rifle in good condition has resulted in a problem?

In the broader world outside this forum, firing 5.56 in .223 rifles must happen fairly often. Or so I'd imagine.

Is there any empirical data on this?

No, I have never heard of a bolt gun not handling both the 223 and 556.
You can't even compare printed pressures from the military and SAAMI because the military check pressure in front of the chamber and SAAMI checks the pressure within the chamber. The NATO pressure specs are even harder to understand; WTH is CIP and how do they arrive at it?

SAAMI lists the same maximum and deviant pressures for both cartridges as the same. To me that means that the only difference is in the military chamber and not the loading.
I could be wrong - it has happened in the past but it won't make any difference in a bolt gun.

20 January 2014, 03:56

B L O'Connor

Thanks Paul.

Do you know, or does anyone, what the pressure gain might be of using the same propellant charges (by weight) in commercial .223 brass versus 5.56 military brass (like LC which, I gather, has thicker brass and therefore less case capacity).

What I mean is this: If, for example, a maximum load for a 55 grain bullet in commercial .223 brass is 21 grains of H-4195, and that yields 47,600 CUP, how much pressure gain would there be using the same charge in LC brass with the same bullet and barrel?

Is there evidence that the pressure gain in the mil 5.56 brass would be statistically greater than in the commercial .223 brass?

Is there any empirical evidence that loading mil brass as if it were commercial brass produces objective signs of excessive pressure?

20 January 2014, 06:35

metalbeater

Shoot both 223 and 5.56 in both my Remington R 15 and Bushmaster carbon fiber upper/Plum crazy lower. Only issue I've had is 1 in 50 5.56 misfire in the R15 due to the hard mil spec primer. As it weighs twice as much as the synthetic gun, it's a ambush hunting rifle whereas the carbon gun @5 pounds is my "handi rifle".

20 January 2014, 22:10

PaulS

quote:
Originally posted by B L O'Connor:
Thanks Paul.

Do you know, or does anyone, what the pressure gain might be of using the same propellant charges (by weight) in commercial .223 brass versus 5.56 military brass (like LC which, I gather, has thicker brass and therefore less case capacity).

What I mean is this: If, for example, a maximum load for a 55 grain bullet in commercial .223 brass is 21 grains of H-4195, and that yields 47,600 CUP, how much pressure gain would there be using the same charge in LC brass with the same bullet and barrel?

Is there evidence that the pressure gain in the mil 5.56 brass would be statistically greater than in the commercial .223 brass?

Is there any empirical evidence that loading mil brass as if it were commercial brass produces objective signs of excessive pressure?

I have used both military and commercial cases and found very little difference in the case capacity between them. I believe - untested - that the difference between military and commercial brass varied about the same as that between the commercial producers. If you work your loads up for a particular brass and then change brass you should reduce the charge and work it back up to your accurate load. This is true whether you are changing between Remington and Winchester brass or between the Remington and military brass. This game of reloading can be unforgiving of bad practices and ignorance so always reduce your loads when changing any component and work back up while watching for signs of excessive pressure.