Service Rifle AR15

A given rifle will "like" one bullet and "puke" another. Each barrel is different. To see a difference and then ascribe it to something like twist or length is usually a mistake.

It usually takes 10 'identical" barrels in a controlled test to create a suspicion about such a issue.

When i was pressuring Savage to go to a fast twist for their 223 rifle, they sent me 20 prototype rifles to test. These had 1:9 barrels. I tested and found they would all shoot the Sierra 80MK (a very long bullet). The only change I made the the barrels was a throating reamer to the Wylde dimensions.

If these 1:9 would shoot 80 gr, it is silly to suggest a 1:9 won't handle the 68 or 69.
 
Ganderite said:
If these 1:9 would shoot 80 gr, it is silly to suggest a 1:9 won't handle the 68 or 69.
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I said the group got bigger, not that it did not work at all.

Last year, my best match scores were with the 16.75" barrel and my worse scores with the 20" barrel. However, there were a lot of names below mine, even with my worest scored matches.

My testing was done via bench rest.

Much of my subsequent research was based on my desire to use the 75 grain Hornady superformance.


I am not going to argue about anything and will let the reader decide if Sabre Defence firearms are well made, or not.


There has been a lot of misinformation. When the AR-15 was first introduced, it was not issued with a cleaning kit, because it was thought to be "self-cleaning".


The accuracy issue that I observed could have been due to a lot of things related to twist and barrel length...

One of the reasons the barrel is chrome lined, is because of the change in powder. When the AR-15 was first developed, it used grain power charges which did not produce as much fowling. When the AR-15 went into production, they used ball powder, which created far more fowling.

They later found that a chromed lined barrel will not have as much fowling (reducing the use of ball powder ammo issue), and it would also last longer being a stronger metal. They also started issuing cleaning kits ;)

The longer barrel means that there is more opportunity for the fowling to build up unevenly (perhaps near the end of the barrel).

Another factor is heat. The more you shoot, the hotter the barrel gets. There have been claims (true or not, I don't know), that the barrel will change slightly as it gets hot and the longer the barrel is, the more that change is going to impact the projectiles trojectory (or at least be a "less consistent" shot).


Some claim that "resonance" is a factor in getting "the perfect load". "Resonance occurs when a system is able to store and easily transfer energy between two or more different storage modes." (http://en.wikipedia.org/wiki/Resonance). Resonance involves waves of energy. The length of a barrel would be a very significant factor, if resonance plays a role in a firearm, because waves have lengths (they are called "wavelengths"). Certain length barrels may provide better resonance than others... but all of that stuff is beyond me.


In the end... there is nothing I can find to justify the extension of a M4/M16/AR15 beyond 17". The three extra inches to 20" can only add velocity to the projectile, but also means that the rifle is going to be that much more front end heavy and more difficult to move around in close quarters.


My loading was a little on the light side...

20" 1:9 CMV with 69 grain Sierra & 24 grain H355 = 2,805 ft/sec
16.75" 1:9 CMV with 69 grain Sierra & 24 grain H355 = 2,688 ft/sec
14.5" 1:9 CMV with 69 grain Sierra & 24 grain H355 = 2,644 ft/sec

Shorter than 14.5" will have a huge drop off on velocity, which is probably why they decided on 14.5" for the C8.


In conclusion, if I had simply purchased a well made 16" - 17" barrel with a 1:7 twist... I would not be considering the purchase of a new upper with that configuration now for the 75 grain Hornady Superformance (approx. $1,000 savings).
 
Bolivar said:
Curious, why not just change out the barrel rather than the whole upper? Not saying you are considering a wrong route here, just wondering. :)
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I think it is better to have a complete set(s) for back-up, etc., rather than pay for tools and/or labour. For example... having a spare charging handle when in a pinch ;)

Having multiple uppers and lowers ready-to-go (and properly registered with the Gov't), provide for a lot of flexibility and contingency.


Shifting the focus back to the original topic.

I don't think my groupings changed with the 55 grain ammo across different lengthed uppers... it was only applicable to the 69 grain. Those are the two bullets that I have focused on over the last two years.

I will do comparison grouping tests again this year, as making mistakes is okay (it is part of a learning process).

Being attached to a flawed idea is terrible... so I am always willing to listen and evaluate the information presented by others.


July is my rifle match in Bulgaria... so I want to have all of my ____ together before then.


To all: Thank you very much for your comments and feedback!
 
Bolivar said:
Not everybody here gets to travel all the way to Bulgaria, that is for sure.

I would think a quality barrel of any length is a good thing. You will likely be very happy with your final choice. Confidence in your equipment does wonders for the mental side of shooting.
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There are no other Canadian competitors going to Bulgaria.

I had to make a sacrafice to get into the match -- I will basically live on the range for almost the entire two weeks of the match, because when I am not shooting it, I will be working (probably doing Stats).

Oh... I was able to get a reference that supports my claim that a short barrel can be more accurate. Please remember, it is not some idea that I came up with, but rather based on observations and information that I have found.

Shorter barrels are actually often more accurate than their longer counterparts. A rifle barrel is a cantilevered beam and as such they sag. More sag results in more whip and vibration as the bullet travels down the bore. Barrel sag induces longitudinal stress that can cause stringing of shots. Using a shorter, heavier barrel minimizes reduces stress and accuracy-robbing barrel vibration. A shorter barrel is stiffer and vibrates at a less.

Barrel length and contour determines the relative "stiffness" of a barrel, i.e., how much a barrel will tend to vibrate. Shorter barrels generally have oscillations of smaller amplitude. than longer barrels. Thicker barrels generally have fewer vibration nodes than slimmer barrels. The ringing frequency of a thicker barrel is higher and the oscillations are of a smaller amplitude and of a shorter duration. This equates to less barrel motion at the muzzle. The use of a shorter barrel also allows the use of a heavier contour without making the rifle unwieldy.

The use of a heavier contour tends to provide less variation between a cold shot and any subsequent follow-up shots. Barrels expand as they heat up. As the barrel expands any stress on or in the barrel will cause stringing of the shots. Bore expansion results in an increase in group size. Heavier barrels tend to be more consistent because they take longer to heat up.

See also:
BARREL LENGTH AND THE PRECISION RIFLE
Why shorter barrels may often be better
by
Eugene Nielsen
http://www.tacticaloperations.com/SWATbarrel/
 
Not sure why people cant get it through their heads that yes shorter stiffer barrels are more accurate.At least at 100m they are. Once you start stretching its legs VELOCITY is going to do a whole bunch more for your accuracy than a short stiff barrel. Its the reason target and Fclass guys who are looking to get the MOST accuracy out of their rifles don't all use 12inch barrels. The longer the better!

I'm not following what the arguement is here anyways?One bullet worked and another didn't.So what? Make a load with the one that did and call it a day. Different bullets work differently in different guns on different days. Find the one that shoots best in said gun and bobs your uncle.
 
Fact: One bullet grouped better than the other.

Conclusion: Use the bullet that worked.

The variation in so called "identical" barrels accounts for this outcome all the time. I have seen similar results in high quality benchrest barrels made by the same maker, consecutively, from the same blanks and chambered by the same reamer.

If you try to assign a reason for this grouping difference, you would probably be wrong. The difference you see is too small and is lost in the noise of all the other variables.

For sure twist has nothing to do with it. The 1:9 will easily stabilize the 75gr HP.

For sure, at 100 yrds, barrel length has nothing to do with it, but it would also be fair to say that a short barrel at 100 yards is at no disadvantage. At 300, it would not be so good, due to velocity loss (wind).

For offhand shooting, shorter is better due to less barrel time.
 
The 1-7 twist was introduced for the specific purpose of stabilizing the very long tracer bullet. It was entirely unnecessary for any conventional bullet then in use.
There have been long, heavy, very low drag bullets developed since, that can be effectively used in .223 rifles with 1-7 twist barrels. 90gr VLDs for example.
As previously mentionned, there is more variation from barrel to barrel than from length to length, from diameter to diameter.
In a service type rifle, functionning as a repeater, internal magazine length is a deciding factor in selecting bullet weight and style. It also affects powder capacity. There are a series of compromises which must be made.

Then again, perhaps an 8" barrel, 1 1/2" or 2" in diameter, with a 1-7 twist (and a tubular extension to keep from blowing one's support arm off) would be ideal for competition to 300m.
 
Ganderite

Curious, you mentioned testing barrels with 1/9 twist and getting good results with 80 Gn bullets. What was the barrel length?

My thought is the ONE of the many factors is velocity of the bullet which combined with twist generates ration rate. A longer barrel will generally generate more velocity and thus faster spin.

AR15 barrels are generally shorter than bolt actions so velocities are generally lower (a lot of generalities here I know). If 1/9 twist is marginal in a bolt action length barrel it may prove to be too slow in an AR15 length barrel....maybe?

Incidentally, my own limited testing shows my 1/9 14.5 inch Norc barrel shoots 68 Gn Horn at about 1.5 to 1.75 MOA at 100 yards IIRC. My 1/8 twist 20.25 inch DPMS barrel shoots the same load about 1/4 MOA better, again IIRC. I consider both satisfactory for my needs.
 
Ganderite said:
Fact: One bullet grouped better than the other.

Conclusion: Use the bullet that worked.

The variation in so called "identical" barrels accounts for this outcome all the time. I have seen similar results in high quality benchrest barrels made by the same maker, consecutively, from the same blanks and chambered by the same reamer.

If you try to assign a reason for this grouping difference, you would probably be wrong. The difference you see is too small and is lost in the noise of all the other variables.

For sure twist has nothing to do with it. The 1:9 will easily stabilize the 75gr HP.

For sure, at 100 yrds, barrel length has nothing to do with it, but it would also be fair to say that a short barrel at 100 yards is at no disadvantage. At 300, it would not be so good, due to velocity loss (wind).

For offhand shooting, shorter is better due to less barrel time.
Click to expand...

Great! I have not had an opportunity to use the 75 grain Superformance... and was really hoping that it will work well with a 1:9. Somebody else had suggested that the twist was not fast enough for the weight.

Hopefully, I will get my hands on a box to see what is what very soon!
 
tiriaq said:
The 1-7 twist was introduced for the specific purpose of stabilizing the very long tracer bullet. It was entirely unnecessary for any conventional bullet then in use.
There have been long, heavy, very low drag bullets developed since, that can be effectively used in .223 rifles with 1-7 twist barrels. 90gr VLDs for example.
As previously mentionned, there is more variation from barrel to barrel than from length to length, from diameter to diameter.
In a service type rifle, functionning as a repeater, internal magazine length is a deciding factor in selecting bullet weight and style. It also affects powder capacity. There are a series of compromises which must be made.

Then again, perhaps an 8" barrel, 1 1/2" or 2" in diameter, with a 1-7 twist (and a tubular extension to keep from blowing one's support arm off) would be ideal for competition to 300m.
Click to expand...

LOL... I am wondering how long the barrel needs to be to stablize the bullet (one revolution?)

Regardless, the loss of velocity with a 8" barrel would be so great that I would rather use a pistol ... ROFL
 
Friend has a short shorty, piston gun. 7 1/2" - 8"? Chronographed it. Velocity was a lot more than we anticipated. We expected .22WRM levels, was over 2400 fps.
 
Bolivar said:
Ganderite

Curious, you mentioned testing barrels with 1/9 twist and getting good results with 80 Gn bullets. What was the barrel length?

My thought is the ONE of the many factors is velocity of the bullet which combined with twist generates ration rate. A longer barrel will generally generate more velocity and thus faster spin.

AR15 barrels are generally shorter than bolt actions so velocities are generally lower (a lot of generalities here I know). If 1/9 twist is marginal in a bolt action length barrel it may prove to be too slow in an AR15 length barrel....maybe?

Incidentally, my own limited testing shows my 1/9 14.5 inch Norc barrel shoots 68 Gn Horn at about 1.5 to 1.75 MOA at 100 yards IIRC. My 1/8 twist 20.25 inch DPMS barrel shoots the same load about 1/4 MOA better, again IIRC. I consider both satisfactory for my needs.
Click to expand...

hehe ... see, that is how I got to were I am now :)

Regarding the 16" Daniel Defense ... Farmboy is great! Would always enjoy purchasing stuff from him. However, I am wondering if the "gas hole" issue has been addressed with these 16" Daniel Defense rifles.

What gas hole issue??? Daniel Defense barrel issue information was extracted out of the Daniel Defense 16" barrel reviews found on this page...
http://www.brownells.com/.aspx/pid=29320/Product/M4-STRIPPED-BARREL
 
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