1:9 barrel accuracy vs 1:9 barrel accuracy

[Levan9X19]

Ok I would never ever believe in this if someone would told me but I have seen this with my own eyes and I still wonder what can cause such a huge difference in accuracy between two more or less similar weapons using same ammo.

We had two Ar15's, one was built by owner with 16.5 barrel made by High Standard, chrome moly, 1;9 twist rate, , second rifle Mossberg MMR, slightly longer 20" barrel, chrome moly, same twist rate and brand new.

we mostly use green tip ammo, and although it is not very accurate it is very reliable and you can shoot a lot because its cheap here.

With built carbine using green tip ammo we achieved routinely 2 - 1.5 MOA so taking into account Mossberg's longer barrel, free floated handguard and superior optics (4-16x Monarch versus 4x Bushnell AR Optics) we where expecting better accuracy.... but from 100 yards rifle shot groups which barely fit in a A4 paper! Through 16x optic you see crystal clear image of target and the holes from hits, you brake the shot.... and see nothing, than you notice a hole somewhere in very corner of the scope far away from the POA and you are like, damn this was a perfect shot, how it could happen??? We used bipod, than rest, nothing. Group where extraordinary wide. The owner was desperate. AR-s are hard to find here, and are sold for premium price (MMR's price was 1800 USD) so imagine his frustration!

I would never ever suggest that ammo can make such a huge difference on such a short range so I checked the mount, the scope, the barrel, the handguard, everything was looking ok, no wiggle, no dents, no nothing. So I suggested to check the accuracy with match ammo. We than carefully handloaded ammo using Lake City brass and primers and 69 grain Sierra Match King HPBT bullets. Results where very good. Groups where around 1 MOA. Ok, fine. Problem solved, rifle owner smiles again. But we are scratching our heads. How can 3.5 inch difference in length cause such a huge difference? On such a short range? never ever I have witnessed something like this.

Than we shot groups with handloaded ammo from my personal Ar15 with the same High Standard barrel. The groups where between 30mm to 17mm. No surprises. In my carbine Green Tips grouped averagely at 45mm

How come you can get so much difference is beyond me, in ten years of constant shooting for the first time I have witnessed such a dramatic difference in results. Any input from fellow rifle shooters will be appreciated

PS
The ability of my garage built AR15, assembled with parts from dozen of manufacturers, with non free-floated 16.5 inch barrel, with self made trigger job on GI trigger, with modest 4x optics to shoot around 1MOA with quality ammo (after 2500 rounds fired down range) speaks itself for the inherent accuracy of this system. My respect to Eugene Stoner

 

[tuj]

Check the crown of the barrel. Some barrel manufacturers will let really bad barrels go out. Look at the rifling of the barrel and preferably get someone with a good eye to borescope it.

 

[WestKentucky]

And check that mmr out. Something sounds loose or crossthreaded. Barrel, scope, something isn't right.

 

[taliv]

hey, that's why they call it match ammo. it shoots better. 1.5 to 2 moa is pretty typical for ball mil-spec ammo. in precision shooting, details matter and it just doesn't make economical sense to pay attention to those details for billions of rounds of ammo that 1/2 of which will be expended through mag dumps and the other half of which is stockpiled for a decade then sold for scrap.

 

[Tirod]

The difference in ammo may also be amplified by the resonant frequency of the muzzle as the bullet leaves. A different length barrel has a different node - and a different ammo which causes the barrel to vibrate differently than another.

There is no guarantee a longer barrel is inherently more accurate. What the shooters are attempting to do is increase velocity a incremental amount to get a flatter trajectory or shoot further. It's all the other stuff done that combines to make them more accurate in some cases. Same for heavy target profile barrels - no guarantee. They are supposed to accept more heat to prevent warping, but a well made pencil profile with no defects could shoot more accurately than a cheaper HBAR from a low cost blank.

There's no guarantee ANY one feature like twist, profile, length, ammo, crown, or type rifling will make a gun a better shooter. In fact it's often quite random despite the best efforts of the makers, goes to why some are considered One in A Thousand and priced accordingly.

 

[MistWolf]

The difference in accuracy has nothing to do with the difference in length and everything to do with the fact they are two separate barrels. Every barrel is a law unto itself. You can take two separate but identical barrels produced from the same production lot using the same barrel blank and give completely different results in accuracy and ammo preference

 

[Levan9X19]

Th

e difference in accuracy has nothing to do with the difference in length and everything to do with the fact they are two separate barrels. Every barrel is a law unto itself. You can take two separate but identical barrels produced from the same production lot using the same barrel blank and give completely different results in accuracy and ammo preference

yes of course but I would never imagine that the difference could be this much on 100 yards range...

if someone told they shot green tip from more or less similar rifles with similar barrel twist and material, and one shot 40mm and another 350mm and than switching to match ammo will produce similar results in both rifle, I would say bull****, that cannot happen in real life.

 

[<*(((><]

Sounds to me like it something of the following in order of likelihood:

1. Loose scope mount, rings, etc.
2. Loose barrel
3. Something contacting the barrel
4. Barrel extremely leaded, copper fouled, or shot out.

It's pretty hard to find a newer rifle nowadays that shoots that inaccurately. My bet is something is being missed on the rifle that is causing it.

I was having the same issues with my Mossberg MVP (shots all over the paper), scope was nice and tight in the rings and the rings were tight on the bases but and it ended up being the small picatinnay base mounts worked themselves loose. The movement was really isolated and it wasn't until i started pushing and pulling on different areas of the scope did I figure out what was loose. I took everything off and threadlocked the mounts back on and haven't had a problem since and it is a great shooter now.

 

[MistWolf]

My bet is something is being missed on the rifle that is causing it

Green tip ammo accuracy is known to be inconsistent from rifle to rifle.

In this case, if it were the rifle, it would be inaccurate with ALL types of ammo, not just the green tip

 

[<*(((><]

Green tip ammo accuracy is known to be inconsistent from rifle to rifle.

In this case, if it were the rifle, it would be inaccurate with ALL types of ammo, not just the green tip

Sorry I missed a paragraph of the OP first post, didn't see where he tried the match ammo and checked all the optic mounting points. Disregard my previous post. I wouldn't have thought there could be that much difference.

 

[Sunray]

The green tip ammo is AP. Milsurp ammo isn't made for accuracy. Match ammo is.
A scope will not make a rifle that doesn't shoot well with irons, do so. A scope only allows you to see the target better.
"...How can 3.5 inch difference in length..." Velocity. 16.5" rifles aren't made for accuracy either and they lose velocity.
"...Results where very good..." You got lucky. Match ammo needs to be worked up for the rifle just like any ammo.

 

[JamieC]

I'm missing something, many are saying to check for loose mounts, bad crown, etc., that wouldn't explain the good accuracy shooting the match ammo. Could the MMR be THAT bad with the green tip and accurate with the match ammo?

 

[GooseGestapo]

It could be that the green-tips are coming apart from the added velocity of the longer barrel. Could be that the longer barrel has a rougher bore doing something to the bullets.

Many, many possibilities. Not necessarily a fault with the rifle.

My Mossberg needed about 300rds through it before it settled down and started shooting decent. With 53gr v-max loads with BLC2, or BenchMark to start with it was shooting 3-4" groups.
After shooting it in, it's now shooting them to less than 3/4".
It shoots 70gr Berger VLD's to 1/2" over RL15.

 

[Tirod]

if someone told they shot green tip from more or less similar rifles with similar barrel twist and material, and one shot 40mm and another 350mm and than switching to match ammo will produce similar results in both rifle, I would say bull****, that cannot happen in real life.

And yet, someone is. And posting about it, because it certainly can happen.

Military green tip ammo is loaded on automatic machinery running thousands of rounds an hour to fulfill a contract for millions of rounds. It's tested to meet a military standard of 2MOA with a ten shot group, that is all. The pressure is more controlled than the accuracy as there has to be enough gas to operate ALL the various barrel lengths of Stoner actions in the military inventory, including 10.5", 14.5" and 20".

How it shoots in a civilian made rifle with whatever barrel it may have is something else. One factor, just sticking to milspec, is that the chrome lined bores aren't specified for accuracy, but for corrosion resistance. Chrome does not plate evenly and one barrel may have bore deviancies of a much larger order than another -enough to actually be dangerous. A nitride bore is much more consistent, and a hammer forged bore, too. Button rifled chromed is cheap and meets spec but isn't the best option. And because of the variance one barrel may shoot circles around another that sequentially followed it in production.

Again, barrel length, rifling, twist, profile, crown, whatever, none are the one and only thing that can affect accuracy. Some good barrels may actually be suffering from a defect in one feature, but it shoots good enough and the owner doesn't know or care. If that seems to be improbable, then someone hasn't been shooting enough to encounter it.

 

[Welding Rod]

It's tested to meet a military standard of 2MOA with a ten shot group, that is all.

Is that a fact Tirod? If so, that is good to hear, I didn't think the standard was that tight.

 

[Skylerbone]

I was thinking 4MOA, but I'm often wrong. Nothing to see here really, post #4 explains pretty clearly. It's why the only factory rounds through my AR to date were run through it for the sake of having matched headstamp brass and a bit of fun.

Mine hasn't been overly squirrly about any of the loads I've tried but it certainly has favorites and they stand out on paper.

 

[bfoosh006]

The difference in accuracy has nothing to do with the difference in length and everything to do with the fact they are two separate barrels. Every barrel is a law unto itself. You can take two separate but identical barrels produced from the same production lot using the same barrel blank and give completely different results in accuracy and ammo preference

A lot of truth there. Barrels can be surprisingly fussy.

Here is another example...

http://www.leverguns.com/articles/ballisticians.htm

 

[Andrew Leigh]

Ammo would be produced with a certain barrel length in mind. Green tip according to Wikipedia was tailored around the M16 which had a 20" barrel so I would have expected the Mosssberg to have performed the best. Every calibre has a rough sweet spot which allows commercial ammunition to be produced that generally works well in most firearms it is produced for.

Now roughly modelling in Quickload, a 63gr. DM11 load fired down a 16.5" barrel at 3 070fps you would be damn close to being on Accuracy node 8 according to the OBT theory. The same load fired down a 20" barrel would have you in the middle of two accuracy nodes i.e. not shooting well.

Barrel length has little to do with accuracy, only if each load was prepared for the said barrel length. You will have rather variable results trying to shoot ammo loaded for a 24" barrel from a 16.5" barrel. It could be that coincidently the 24" load happens to coincide with an accuracy node on the 16.5" barrel but that would be pure luck. Thin barrels can be a problem and are more prone to accuracy issues.

I supply steel into the barrel making industry and do not observe massive differences from barrel to barrel. Poor heat treatment of a barrel can cause major problems in that this leads to a walking barrel where shots print all over the place. This is very rare and most production barrel steel is batch annealed, in my case of 12 000lbs lots.

My exposure to AR barrels is limited and we have just provided steel for 14 prototypes. The results are remarkably consistent but this could be due to the additional care and attention in the prototyping stage as well as the fact that the rifling is cut and not buttoned.

 

[Johnny_B_Goode]

You mentioned the Mossberg was brand new. A new barrel needs to be broken in. During the manufacturing process no matter how good a barrel maybe there are microscopic burs and scratches in the barrel. Depending on the caliber and hardness of the barrel it can take 200 rounds for a barrel to begin shooting it's best.

Another issue you run into is sighting in the gun, especially with light bullets, it takes a couple tries to shoot dead on due to the wind. But I wouldn't make any sort accuracy comparison with ammo that is known to be not so accurate. All you really discovered is one gun shoots crappy ammo better than the other.

 

[Andrew Leigh]

You mentioned the Mossberg was brand new. A new barrel needs to be broken in. During the manufacturing process no matter how good a barrel maybe there are microscopic burs and scratches in the barrel. Depending on the caliber and hardness of the barrel it can take 200 rounds for a barrel to begin shooting it's best.

Not everyone would agree with this. The process used to "cut" the rifling has a large bearing on the need to shoot in a barrel. Barrel that are hammer forged with the chamber integral have no need. Button swaged barrels and cut barrels could / would require some shooting. Generally a barrel with cut rifling will be lapped so these barrel is already in fine condition.

Contrary to popular belief you do not shoot in the barrel but the lands. You see this is where the problem arises, the sharp edges left by the reamer are literally eroded away through firing. This allows for a smoother surface allowing the bullet to enter the lands more efficiently.

I have two CZ's and a Sako, neither of which required a barrel shoot in process by the manufacturer as all three are hammer forged barrels. ALL are 0.5MOA but these are hunting rifles and not AR's. I have also not observed a barrel shoot in process that exceeds 25 rounds.

 

[hq]

Check the crown of the barrel. Some barrel manufacturers will let really bad barrels go out. Look at the rifling of the barrel and preferably get someone with a good eye to borescope it.

I second that. Crown is essential for accuracy, but sometimes there are quite a few imperfections in rifling, which can be smoothed out by either fire lapping or hand lapping. Re-crowning, proper hand lapping and MoS2-treatment can make a huge difference, my personal record is from 3.5MOA with handloads to sub-MOA with virtually any ammo, far less tendency to copper fouling and an average of +40fps at the muzzle. Similar specs don't mean that two barrels are the same in practise, it all boils down to how well they're finished, either by factory or by hand.

 

[Andrew Leigh]

I read this some time ago with mixed feelings.

http://www.accuratereloading.com/crownr.html

 

[Johnny_B_Goode]

I read this some time ago with mixed feelings.

http://www.accuratereloading.com/crownr.html

I have my doubts about the hacksaw job myself. I could see fragments of metal hanging in the bore. They might have done alright for 5 shots but it is just a matter of time until enough copper builds up affect the accuracy of the rifle. They could have just got lucky with that one rifle.

Doing something once does not prove anything.