Exploding M-16's ????

[DaveE]

I also have an old Colt SP-1 in the 57K serial number range. I have owned this rifle for quite a few years and never fired it. On the side it says .223 and the barrel is only marked C MP Chrome bore. I was always told the at the SP-1s were really .556 no matter what it said on the side of the rifle. I now have the urge to fire it but not sure what caliber ammo to buy. My local gun shop has 400 round cases of .556 for less than $200 which seems ok in today's market. I just want to make sure i am getting the correct fodder for the rifle. Thoughts?

Dave

[Col. Colt]

Dave,
Colt produced the SP1 right alongside the M16 - the parts (except for the full auto fire control group) were the same. Colt once did an ad joking as to how their inspectors had to look closely to tell the differance in the factory!

Your barrel is marked the same - and is the same, as an M16 from the same era - and has a 5.56MM chamber. Go to AR15.com and read in their Retro forum about SP1s. Cheers. CC

[DaveE]

Dave,
Colt produced the SP1 right alongside the M16 - the parts (except for the full auto fire control group) were the same. Colt once did an ad joking as to how their inspectors had to look closely to tell the differance in the factory!

Your barrel is marked the same - and is the same, as an M16 from the same era - and has a 5.56MM chamber. Go to AR15.com and read in their Retro forum about SP1s. Cheers. CC

Thanks much, I appreciate the info.

Dave

[bblake]

most Colt 7 twist barrels had overly long chambers. You can purchase a gage to measure throat length that aids in seating your bullets to a given length short of or into the lands and grooves of the barrel. It isn't uncommon to have a throat so long on a colt barrel that an 80 grain sierra bullet seated out to a few thousandths off the lands barely has enough neck tension to hold the bullet. Most of the 7 twist colt barrels shoot well, and more than one person has made master or high master with them, that being said, the throat was a weak point.

Brig Blake

[edlmann]

The Colt HBAR in question is marked .223 and was purchased new in 1990.

Colt has been somewhat inconsistent about this. Is the .223 marking on the lower receiver or on the underside of the barrel? THe barrel marking is more important.

FWIW; AFAIK; IMHO; YMMV; yadda, yadda, yadda.

Regards, Ed Mann

Bobby Bowden is doing a fine job - just leave him alone.

Albert says, "Click here for free Gator wallpaper."

[Jim K]

I have heard that using GI ammo in a "civilian" rifle will blow up the gun. I have also heard that using civilian .223 ammo in a GI spec rifle will cause the rifle to explode like an A-bomb, complete with mushroom cloud. I have even heard that using GI 5.56 ammo in a .223 Remington 700 will destroy it - one of the strongest rifles ever made!

Now one would think that rifles blowing up right and left from using the "wrong" ammo might have come to the notice of the various gun and ammo manufacturers, and suitable warnings issued. Since I have seen neither blown up guns nor any warnings about nuclear bomb ammo, I tend to think the whole thing is nonsense, fed by ignorance and misunderstanding. (Note, I didn't say that all 5.56/.223 ammo will be accurate or even function perfectly in all guns of the caliber; I am addressing the "guns blowing up" issue, not accuracy.)

Jim

[limazulu]

I have heard that using GI ammo in a "civilian" rifle will blow up the gun. I have also heard that using civilian .223 ammo in a GI spec rifle will cause the rifle to explode like an A-bomb, complete with mushroom cloud. I have even heard that using GI 5.56 ammo in a .223 Remington 700 will destroy it - one of the strongest rifles ever made!

Now one would think that rifles blowing up right and left from using the "wrong" ammo might have come to the notice of the various gun and ammo manufacturers, and suitable warnings issued. Since I have seen neither blown up guns nor any warnings about nuclear bomb ammo, I tend to think the whole thing is nonsense, fed by ignorance and misunderstanding.
Jim

I'm beginning to wonder about this myself. Even tight chambers have to accept ammo that fits the magazine so if your ammo is no longer than magazine length there shouldn't be any problem from that. The bullets are the same diameter so the only problem would be in case headspace and possible slamfires.

[ClaudeH]

I'm no expert at all, but I am at least a thoughtful sort. I believe the differences between the chamber specs and loading specs for .223 and 5.56 are way overblown. Real, but overblown. Yes, the pressure spec for 5.56 is nominally higher and the chamber is nominally larger, but I really believe the differences are moot in modern firearms. The breeching of an AR-type rifle or a Model 700 is more than adequate for anything marked 5.56.

I think you should be a little more cautious if you have a firearm of more marginal design strength such as a break-action Savage M24 or a some old one-lug bolt action rifle, so you can't dismiss the differences entirely. But it sure seems to be an overblown issue in regard to AR-type rifles and modern bolt actions.

[Col. Colt]

Guys, I think that there can be a problem, but that it does not usually involve blown up rifles. Claude, you right about the action strength of most designs. But - if you use a "Match" tight .223 chamber with "long throated and hot" 5.56MM GI round you can "pop a primer", letting gas flow back at you and possibly cause some erosion at the firing pin hole. I believe the book, "The Competitive AR-15" by Zeddiker Publishing covers this pretty well.

In the original questions, the worry was about whether a Colt AR marked .223 had a .223 chamber or a 5.56MM chamber. To my knowledge, all standard Colt ARs have the more generous 5.56MM NATO chambers/throat length, regardless of markings. (They did make a few in .222 for export to "No Military Cartridges allowed" countries.) Other makers, I believe, offered a choice of chambers, for those that wanted "tight" Match chambers for the last little bit of accuracy.

So I agree that strength is not a problem - but high pressure can still cause troubles and/or blow hot gas in your face - not a safe or pleasant experience! And so I would want to know which chamber I had, and load accordingly. But "Exploding ARs?" - Not Likely. CC

[Jim K]

I well remember the hoopla and hype when the .223 and the AR-15 were first marketed. Colt bought the rights from Armalite, and launched a high intensity campaign to sell the general public on the gun, so they would pressure the mililtary to buy it. Among the claims for the little round were that a hit anywhere on the body meant instant death; that the bullet would penetrate helmets at 1000 yards, and 1" armor plate at 500; that the shock of a bullet passing close to an enemy soldier would incapacitate him, and on and on. All nonsense, of course.

At one of the NRA conventions, a Colt rep gave me the sales pitch. I told him I would indeed like to try out the cartridge but didn't have a .223 caliber rifle. I said that if I could get hold of some FMJ bullets, I would load my .22-250 down to .223 velocity and experiment. The guy went berserk! "Load DOWN!?" he screamed. "This is the most powerful cartridge in the world, the most powerful round ever developed!" I replied that it looked to me like a medium power varmint cartridge (which it is) and that a .30-'06 made it look pretty sick all around. He almost ran away, presumably to report my heresy to his bosses. I didn't encounter him again.

In fact, the only reason for the existence of the 5.56mm and the M16 is that the combination is reasonably controllable in full auto fire, which is not true of most full power rifles; the M14 is about uncontrollable, the FAL better, and most other guns hopeless. (The AK-47 is not really full power.)

Jim