Accuracy Testing The Vintage 1/12 Milspec Barrel


Accuracy in modern carbines is always a popular topic on the various gun boards and news stand  slick gun rags. People want the newest barrel some company is making that promises more accuracy.  New chamber types, coatings, contours , linings and materials are all shown to us to try to win your money.

If you have read this website for a while you know I like to take a chance to convince people that their barrels on stock rack grade AR15s is already a lot better than they think and honestly more accurate that most of their users, The modern M4 carbine milspec barrel’s accuracy potential should not be ignored or tossed aside for something that costs a lot more and may not really offer any real gains.    I think I have preached this until I am blue in the face. Even stock milspec barrels are fine now a days.

But what about those from 40plus years ago?  Everyone knows those M16A1s and CAR15s weren’t all that accurate right?  We have had plenty of ‘Nam vets  tell us   Don’t forget those   cold war national guard  vets (with those old worn out A1s left over from Nam waiting to be replaced with A2s ) around to tell us how bad they were. Why , they couldn’t even qualify with them  at 25 yards with reduced range targets!!    You won’t find many people ready to argue with that.   Why would you even bother?   Those older 1/12 twist barrels won’t handle modern match rounds in the 77 or 69gr range.     But what if?..

What if that’s all you have?  Maybe you like A1 profile barrels and retro guns?  Maybe you just can’t give up your nostalgia or you just want to be different.   Or you are curious like me,  So I gave it a try.

I borrowed my friends Colt SP-1 AR15 carbine to find out.  The gun  has everything an early AR15 could be given to it by Colt.  The A1 sights, the A1 profile barrel and the 1/12 twist chrome lined Mil-spec bore.      I set the gun up on rest with bags front and read and got it as locked down as I could get it and started shooting with match quality hand loads,

Groups where shot at 50, 75 and 100 yards.  The A1 sights being a limit for me.  The older A1 front sight post shape has always been harder for me to  get the best out of it.   I used bullet weights close to the M193 load used the most during its heyday.  I selected and loaded bullets I have experience with that have always squeezed all the accuracy I could get  for shorter ranges.   Not being able to use 9 or 77 grain bullets int he 1/12 barrel I did not try for longer range accuracy testing.

The 50 and 55gr Blitzking sierra bullets are excellent, really excellent.   Those  two have always been go to bullets when loading for shots   400  yards and under when I want higher velocities, flatter trajectories and more explosive effect on targets when using rounds like the .218Bee  or .223 from a bolt action varmint rifle .   All groups are 5 round groups, You can see above how well those two weights perform.

The 55 gr Vmax from hornady is also a dependable bullet if you want an accurate bullet for varmint or target use. I used the  50 and 40gr Vmax .22cal bullets almost exclusively when I wanted a ballistic tip before sierra introduced the Blitzking.    Not to say that I think the BlitzKing is the end all be all for ballistic tip bullets,  They just shoot a bit better in some of my varmint guns.   The 40gr Vmax is still the bullet I would recommed for varmint use on small targets  in rounds that are not in the class of 22-250 or 220 swift.

Since I am on the topic, I will save my handloading component choices for a different post.

The real dependable money maker for  300 or less accuracy for milspec AR15s  is the 53 grain flat base HP matchking.  The bullet performs well in a 556 NATO chamber for a few reasons and its fairly well known.  I will go into this in a later post, but for now I will just show you the results,    The bullet is an old fav for seeing what  a milspec barrel and NATO chamber can do.   Give it a try if you handload and no one has ever told you about it.

I’m guessing that some of you may be let down that I didn’t shoot further.   I just couldn’t be sure I could use those sights well enough to shoot to the guns potential to 100 yards and beyond.  So I used the most accurate loads and fired groups at 50 and 75. I think this was a decent balance for distance and what I could see.   I did shoot some at 100 yards and the strain it put on my eyes gave me a raging headache.   When it gets like that, you can’t tell if bad groups are you, the gun or the ammo or the weather.     I rested and did the final record group of  a10 shot string.  I feel this shows what the gun could do at 100 yards or at least gives and idea of the potential it has if optics had been mounted and a better trigger added.  Neither of which I would bother to do on this classic rifle anyway.

Above is group I fired for record at 100  yards.  It is a 10 round group fired from the bench and bags at 100 yards using the 55gr blitzking.  I chose the Bltizking 55gr because it seemed to me to slightly edge out the others and I had run our of the 53gr flat base HP.  Otherwise I would have shot 100 with  the 53 grain matchking  without hesitation.

The older  SP1 Colts are still great shooters unless you  haveone some one ( or you) mistreated.  The original A1 barrels on original A1 or SP1 uppers have the same potential. They are the same Colt ( or made to colt spec by  another company for the gov at the time) made Milspec barrels.   Just because it is a 1/12 doesn’t hurt accuracy,  just accuracywith heavier bullets.  Many varmint bolt actions rifles came with 1/12 twist for 223 remington for years.  It’s about knowing  the limits of the barrels twist rate , not the quality of the barrel.    I think it is odd that a lot of AR15 users make a lot of noise about  faster twist rates in their modern guns when they never shoot anything heavier that 55gr M193 type ammo.   I suppose it’s just the thought.

If you have one of these or you have made yourself a “retro clone” with original parts, maybe you will look at it in a little different light now, or maybe some of those stories told  at the gun store round table BS sessions will seem less like wisdom and more like what they are.

Lastly. the gun ran perfectly.  It is a vintage Colt AR15  SP-1 carbine. AS you can see it has the original CAR15 metal stock which is much sought after these days and is in near mint condition.   Below is the  test carbine with Sp1 rifle.  A classic pair to be sure.




  1. I have a 1/7 Colt HBAR 20 inch on the way.

    Do you think it is stiff enough and accurate enough to run in a high power match without a free float rail?

    No need to come in first place, but im curious if it could keep up while I save for a quality tube.

  2. I believe some of the originals came in a 1/14 twist,could find one of those dinosaurs would like a review,probably collector item barrels at this point!

    • Yep the winchester barrels. Like you said though rare as a puppy with two peckers. Believe me, I would loooooooooove to get my hands on one to test out., I have never even touched one with my own hands but some of the boys in the arfcom retro forum have them

      • From what I have read from old reprints of early ar articles in mags that was changed pretty quick,was a move based on old .22 barrels and was not that impressive,still,would be a coup for a article if you can find someone with one(that is also willing to have some ammo sent through it0.

        • I don’t want to test it from an accuracy standpoint, I want to shoot it just to demonstrate the presence of or lack of the supposed extreme tumbling of the rounds after hitting a target. i would make sure to get gel for that one. I’d also test it in as cold as weather as I could fine to see how much accuracy is lost.

  3. I accidentally ended up with a heavy profile barrel on an upper I ordered. Apparently selecting crome lining defaults to an inch thick brick of a barrel. But man is it stiff. Could do without the weight but have been very happy with the accuracy out of my generic barrel. Went 1/8 because I had no illusions of shooting nice ammo out of it.

    Have a beat up SP1 and it does just fine (not as well as the one above) but the only thing holding it back is me.

    Had some gun store schmuck convincing my father in law that his $2k faxon barreled AR he had just got was useless beyond 300 yards! Oh that BS always gets me going. As you can see by my rambling rant. Haha.

    Anyways, another great article.

    • yea I hear that as well. I always try to send them to my “AR15 at 1000 yards” article , but they always mumble some crap about they cant even see that far or some other BS. If you handload and want to see what that SP1 or any milspec barrel with NATO 556 can do, try those 53 grain sierra flat base hollow point matchkings. Those things will milk all a barrel has got. the shortness of the bullet isnt as effected by the bigger chamber

  4. In 2008, I bought two Colt AR-15 SP1’s… they are easily 1-1/4″ group guns at 100 yards and 20 rounds of Federal 55 gr. GMM (using a scope). When I found that Green Mountain Barrel makes a pencil profile noodle with a 1:14 twist… I had to give it a try. I built-up a CMMG mil-spec fire control into an AeroPrecision receiver set with the Green Mountain barrel and Colt free-float aluminum tube fore end, and topped it off with a Nikon M223 Model 8487 scope. It shoots 1-1/4″ groups at 100 yards with Federal XM193 mil-spec. And with the air-ripping velocity that the rifle was intended to produce… 3200+ fps! I can’t wait to to see what it will do with match grade ammo! Perhaps those 53 gr. loads are in her future. I’ve already bought all the parts for another one, except a Keymod forearm instead of that very heavy Colt free-float tube which my girlfriend says is too heavy.


Please enter your comment!
Please enter your name here