Service Rifle AR15

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madharumcheril

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I would like to know what AR15 is best to go with re: barrel lenght? Are 16 inch carbines ok, or is it better with a 24 inch target rifle?

Thanks
K
 
Hmmmmm :cool: Which province are you shooting in?

Just trying to nail down the matches (and their course of fire) be they the older Matches 1-12 or 16 being shot at many Provinces and DCRA's NSCC

or

The Matches 1-4 being shot at CFSAC and the Ontario Rifle Assoc

One thing is for sure... the soldiers with their 20" C7A2's kick butts! :D

I've seen fantastic shooters win with all the mentioned barrel lengths! Where do we start? It's all good!

There... does that help? Clear as mud? :nest:

Cheers,
Barney
 
The heavy 24" barrels are overkill.
What sort of shooting are you going to be doing?
There are a number of good sights. Once again, what shooting will you be doing?
 
For service here in bc either a 16 or a 20 will work the best. 14.5 coming in a distant 3rd. Probably more important is your ammo and scope selection. 69 or 77 grain bullets will do you best. Scope power in bc is limited to 4x unless you want to be in open class. If you are shooting open then a variable that goes from around 2-10x would work very well.
 
It is not "just" the barrel length -- I got suckered into that one. You also need to consider the twist rate.

You will find that heavier bullets (more than 62 grains) won't do as good with the very common 1:9 twist rate as the barrel gets longer (e.g. 16.75" vs 20" barrel). You will also find that the 20" heavy barrel is harder to control as it is front heavy.

Where this really became apparent for me, was the difference between the Hornady 69 grain bullet vs the Sierra 69 grain bullet. I did not get a good group with the Hornady 69 grain bullet when shot through a 1:9 twist. However, I was able to get an acceptable grouping with the Sierra 69 grain bullet, using the very same 1:9 twist barrel.

What was interesting, is how the grouping got larger when the 1:9 twist barrel went from 16.75" to 20" (the grouping seemed to double in size, if I remember correctly).

You cannot make a stabalized bullet more stable! The only reason for extending the barrel beyond 14" is to achieve more velocity in the projectile.

In my opinion, the 16" - 17" barrel with a 1:7 twist is ideal.

The C7 is a 20" barrel (for projectile velocity) with a 1:7 twist.

The newer C8 has a much shorter barrel of 14.5" for many reasons.

I think the "ideal" is in between the two... because the additional bullet velocity is going to be a welcomed advantage over the 14.5" and a competitor does not need to be so concerned with the ability to move around in confined spaces (which is why the Norico CQB Rifles have sorter barrels too).

The C8 has a 368 mm (14.5 in) A1 profile barrel like the Colt Model 653 M16A1 carbine, but with a 1 in 180 mm (7 in) rifling twist appropriate for the 5.56×45mm NATO C77 cartridge.
Click to expand...
http://en.wikipedia.org/wiki/Colt_Canada_C7_rifle
 
IMO unless you found a way to stretch the 16.75 ot 20 inches you had to be using different barrels. I think that is a likely explanation of the difference in group size rather than barrel length.

As far as I know, if the bullet travels faster it requires less twist to get the necessary rotational speed for stability. As such the longer barrel won't make a bullet less stable.

I am prepared to be schooled on this by more knowledgeable members if I am wrong. Flame suit is zipped to the neck. :)
 
cancer said:
Step one, just get a rifle and get into the game. Worrying about specific gear is many iterations down the road.
Click to expand...

True, but getting an educated first stab at a rifle is decent. I would personally grab a 1/7 twist every time if it is available. 1/9 I would consider doable. I would personally not be happy if I grabbed a 1/12 not knowing that better options are available.
 
Bolivar said:
As far as I know, if the bullet travels faster it requires less twist to get the necessary rotational speed for stability. As such the longer barrel won't make a bullet less stable.

I am prepared to be schooled on this by more knowledgeable members if I am wrong. Flame suit is zipped to the neck. :)
Click to expand...

I may not be more knowledgeable, but I did learn the following the "hard way"...

When bullet weight is pushing the limits of the rifling twist ratio (e.g. 69 grain bullet with a 1:9 twist barrel), the longer the barrel, the less stable the bullet becomes due to the longer influence of the rifling twist and the bullet pushing through it.

Otherwise... what difference is there between a 62 grain bullet and a 75 grain bullet... that would cause the 75 grain bullet to require a 1:7 twist for stability

1:7 is a faster twist than 1:9 ... so there must also be a relationship with how long the bullet is in the barrel when very close to maximum tolerances.
 
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It is expensive to make a "first stabe" at something without getting all of the facts correct first. I have replacing equipment because I was unaware of a limitation, etc.

I am just try to help this chap out.

Although they are obviously not the same barrel -- it was made by the same manufacture and probably just "cut" to different lengths given that they are so made of the same material, etc.

I don't wish to banter over this -- if only somebody had told me before I bought my uppers.

I reiterate and maintain: In my opinion, the 16" - 17" barrel with a 1:7 twist is ideal.
 
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Bolivar said:
IMO unless you found a way to stretch the 16.75 ot 20 inches you had to be using different barrels. I think that is a likely explanation of the difference in group size rather than barrel length.

As far as I know, if the bullet travels faster it requires less twist to get the necessary rotational speed for stability. As such the longer barrel won't make a bullet less stable.

I am prepared to be schooled on this by more knowledgeable members if I am wrong. Flame suit is zipped to the neck. :)
Click to expand...

"If the bullet travels faster it requires less twist to get the necessary rotational speed for stability" is an interesting statement -- the longer the barrel, the faster the bullet travels... so why does a 75 grain bullet not work in a 1:9 twist barrel that is long enough to get the bullet moving fast enough?

The muzzle velocity of the Hornady 5.56 NATO 75 gr BTHP Superformance® Match™ ammo out of a 20" barrel is said to be 2910 ft / sec. See also http://www.hornady.com/store/5.56-NATO-75-gr-BTHP-Superformance-Match/

The muzzle velocity of the NATO 63 grain GP 90 round out of a 20" barrel is said to be 2970 ft / sec. See also http://en.wikipedia.org/wiki/5.56%C3%9745mm_NATO

Does 50 ft/sec really make all that much of a difference???

I'm sorry... I have looked at this the wrong way... LOL

Let us suppose that you are right -- the fact is the longer barrel was not more accurate. Who cares why?

The recommendation remains unchanged:

In my opinion, the 16" - 17" barrel with a 1:7 twist is ideal.

All of my uppers are from Sabre Defence, they are all 1:9 twist, they are all chrome lined, they are all made from the same material, and they all come from the same factory.

The 69 grain Hornady bullet sucked and the Sierra 69 grain was fine in the 14" and 16.75", but started to spread out with the 20"

Those are the facts.

NOTE: Not wanting to change more than is absolutely necessary -- I will be using a 62 grain bullet with my 1:9, 20" upper, it just would have been nice to be able to use a 75 grain bullet, especially when shooting 300 yards+

Sorry, I have no more time for this topic. If I needed to prove myself, I certainly would have used a scope today (two of my uppers have scopes on them and are ready to go). I choose iron sights, because I just wanted the experience and never even thought of actually competing today.

Hope you have a great weekend... I got to go.
 
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Beaver said:
The 69 grain Hornady bullet sucked and the Sierra 69 grain was fine in the 14" and 16.75", but started to spread out with the 20"

Those are the facts.
Click to expand...

Those two bullets are almost completely different. The Hornady 68 grain HPBT has quite a longer bearing surface length than the 69 grain SMK which would explain why one barrel didn't like them over the 69's.
The ogive is also considerably rounder on the SMKs which may play a part in how they group - especially factoring in loading techniques. The SMKs in my experience have slightly more tolerance for runout than similarly loaded 'vld' type bullets.
Barrel length in your instance had nothing to do with what those rounds were doing from an accuracy standpoint.

Back to on topic:
As indicated, picking something with a quality 20" long 7 or 8 twist from a reputable company like Stag Arms, Danial Defence, Rock River Arms or the like will give you the most bang for your buck. The 7 or 8 twist will open up a lot of the heavier bullets to you as options, especially if you are looking to hand load.
 
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