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Posted: 5/5/2015 11:27:07 AM EDT
I'm trying to brush up on my ar knowledge and running into a a lot of bs and "I thinks" online. Before I start I want to make it understood that this is NOT for a build.
.223 : "civilian" standard chambering for the ar15 platform. It can handle shooting 5.56 as well (as far as chamber pressures and design goes)
5.56 : "military" ie nato specced chambering for the ar15. It's not recommended to shoot .223 out of but there are obviously people who still do with no apparent issues.
Is there an advantage/disadvantage that I'm missing with these two? When recommending a rifle build (duty or range use) and the end user doesn't plan on reloading or taking it past 300M is there a reason to choose one chambering over the other?
.223 Wylde is designed to be more accurate than the other two chamberings mentioned at the expense of being a reliable field / duty rife. This is more for the precision target shooters on the ar15 platform.

twist rate :should correlate to the weight grain bullet you shoot; is there a general rule of thumb on choosing the ammunition you're wanting to shoot?  I ask this because a lot of posts out there don't necessarily address this to Shooter's who just buy an ar15 and the cheapest or readily available ammunition nearby regardless of grain.
why do you choose to shoot 55gr, 62gr, 77gr?

barrel choices. I've been following some of the AR crowd mentioned barrels (white oak as one example). Not going into duty vs accuracy use, can some one give me an idea of companies the Ar crowd leans towards who actually make their own barrels instead of rebranding? Shilen is the only one I'm familiar with that's mentioned. I'm sure bartlein, proof, kreiger can do them as well but again not mentioned here as much as others.

Going one more step into barrel choices, the AR crowd would prefer chrome lined (or salt bath intrided) barrels for barrel life. Would the companies you mentioned do that or is that more of an aftermarket?
Link Posted: 5/5/2015 11:55:51 AM EDT
[#1]
You have .223 and 5.56 backwards. It's ok to shoot .223 in a 5.56 barrel, but it is not ok to shoot 5.56 in a .223 barrel (5.56 is a higher pressure than .223). You want a 5.56 barrel.

As far as twist rates go, you generally use a heavier bullet with faster twist rates (lower numbers=faster twist), but that can vary with velocity, barrel length, etc. Your best bet is to try several and find out what your barrel in particular likes. For example, if you have an accurate 1:7 barrel, then you should buy 3-4 manufacturers of 69-77gr loads to see what groups best if you don't reload. If you have a 1:12 twist, then your barrel will prefer the lighter 50-55gr loads.

I don't have much experience with the differences between several brands of barrel manufacturers so I'll let someone else chime in on that, but you generally use a stainless barrel if accuracy is top priority, versus chrome-lined which lasts longer but is less accurate (not by a huge amount, though). Chrome lining is not something that you would have done by an aftermarket company--it is part of the barrel making process and is done before you buy it.
Link Posted: 5/5/2015 12:29:59 PM EDT
[#2]
If this is not for a build, what is the reason for asking?  I guess I just oppose being herded into a "crowd".
Link Posted: 5/5/2015 12:32:17 PM EDT
[#3]
Ok, I'll take a stab at this, or some of it.

You have chamber info backwards.  

The 5.56 barrels are chambered with a longer throat and are proof tested to handle the higher 5.56 pressures.  That means that they can handle both 5.56 and .223 ammo.

Barrels chambered for .223 have a shorter throat and slightly different chamber dimensions.  They can shoot .223 ammo and are not intended to be used with 5.56 ammo both due to the shorter chamber depth and the higher pressures.

While 5.56 and .223 case dimensions are identical, chamber dimensions are not.  Some .223 barrels can handle 5.56 ammo, but some may have issues with excessive pressure in shooting 5.56 ammo because the bullets are closer to the rifling and the higher pressures.

In reality these differences may be more academic than real, but I personally would not shoot any 5.56 ammo in a barrel specifically chambered to SAAMI .223 dimensions.

There are also "tight" chambers and "loose" chambers.   5.56 chambers tend to be on the outside of the tolerance, or a little more "loose' in chamber dimensioins that most .223 chambers.  This is to ensure reliable cycling of ammo that might be dirty or have surface corrosion or other defects.   Tighter chambers tend to be more accurate, but might not cycle with 100% reliability.

There is an intermediate chamber, the "Wylde" chamber that falls between 5.56 and .223 that is popular with precision shooters that also need reliability.  Frankly, I have not studied the precise dimensions of the Wylde chamber.  I'm sure experts will come along.

Regarding twist rate, it is not bullet weight, but rather the length of the bullet body that touches the rifling.  Indirectly, weight can be a rough measure, as bullets gets longer as weight increases.  But, the analogy falls apart when we move away from jacketed lead core bullets.   Many modern bullets are monolithic copper (Barnes TSX or Hornady GMX), or are made of bi-metal materials such as the M855 "green tip" or the even newer M855A1 which has no lead at all.  Boat tail bullets have less surface in contact with the rifling than a flat base bullet of the same weight.  VLD (very low drag) bullets have a different shape that also affects optimal twist rate.

Berger Bullets has a handy online calculator to determine best twist based on info you feed into it regarding the details of the bullet construction and weight and the precise velocity of the bullet as it leaves the barrel.  While there are templates for Berger bullets, you can check any bullet, if you know the information from the manufacturer's web site and know the muzzle velocity.

Example: my 1:9 twist barrel can shoot jacketed lead core bullets up to about 75 grains just fine.  But the Barnes TXS 70 grain bullet, because it has no lead, and is all copper, weighs less for the same length.  The 70 grain Barnes TXS is, therefore, much longer than a 70 grain lead core bullet.  I can shoot 70 grain lead core bullets just fine with very good accuracy in 1:9, but the same weight Barnes TXS bullets keyhole badly, even at 5.56 pressure and velocity from that 1:9  16" barrel, striking the target sideways at 100 yards, or not even hitting the target, with extremely poor accuracy.

As to twist rate, there are advocates of 1:9, 1:8 and 1:7.  You will hear praises of each and none are completely wrong in their selection.  If the rifle is to be match grade and the bullets are to be under 70 grains lead core, or 62 grains monolithic, you will probably find that 1:9 twist produces the best gilt edged accuracy if the barrel and rifle are up to the task.

Many 1:7 rifles, perhaps even most, can shoot very accurate groups with light bullets, down to 52 grains, but are likely to shoot even better groups with a slower twist.

1:9 twist will not stabilize heavy bullets above 75 grains lead core.  If you want to shoot the popular 77 grain SMK, you need 1:8 or faster.

I personally see no need for 1:7 other than that guys want to emulate mil-spec which requires 1:7 to stabilize tracer bullets that I never intend to shoot and you probably will not easier.

There are longer bullets that might need 1:7, but such bullets are intended for bolt action guns, as these very long bullets would not fit in and cycle through the relatively short AR15 magazines.

In actuality, it is rpm that stabilized a bullet, not merely twist.  So, it is the combination of twist rate (number of inches of barrel length per rotation), AND velocity of the bullet, which combine to produce rpm.

Thus, the higher the velocity, the slower the twist needs to be to stabilize the bullet.  That is why short barreled rifles or pistols with much lower velocity, need a faster twist to stabilize their bullets,  This may be one legitimate use of 1:7 for shorter bullets.

Some say that too much twist does not hurt.  I think it does.  Overstabilized bullets, if they are not very uniform in their dimensions, like match grade bullets, will "wobble" and accuracy will be degraded.  It may be slight and of no significance if you are not trying to shoot sub MOA groups.   Another phenomenon I have experienced with too much twist is with very light jacketed varmint bullets.   I have a 6mm Remington bolt gun that can push 55 grain bullets at 4,100 fps, far faster than any .223/5.56 with similar weight.  I have found that at that velocity the twist in my bolt gun (1:9), produces such a high rpm that it literally tears the jackets off of some very lightly constructed bullets.  Those bullets literaly explode between the barrel and the target from excessive rpm and often do not even got to the target.  Other slightly thicker jacketed varmint bullets in that weight do just fine.

I have some 35 grain Hornady Superperformance varmint ammo that is very accurate in 1:9.  I have not tried those bullets in a 1:7, but given their very thin jackets and intentionally frangible construction, I would be afraid they would act like those light jacketed bullets in my 6mm and tear the jackets off of the bullets due to rotational forces before getting to the target.  This is speculation, since I've not tried them in a long barreled 1:7, where they might be at risk.

If you are looking for a precision match grade barrel, you are on the right track with Shilen, Bartlein, Kreiger and I would add Lilja to that list.  I think the Lilja 1:8 stainless barrel they make for RECCE rifles for he SEALS may be what I put on my next build.

BTW:  I am an advocate of QPQ SN nitride for precision rifle shooting to extend barrel life.  I doubt you will ever see a chrome lined barrel on the line of any national championship match except where it is required.  Chrome lining is a plating process.  It can be done with a very high degree of uniformity, but it is still a plating and there will be imperfections and irregularities in the thinckness of the plating process that could degrade accuracy.  It also blunts or rounds the edges of cut rifling in barrels that are made that way.  On the other hand, QPQ SN does not alter the dimensions of the bore or its rifling, leaving the contours pristine.  It hardens the surface at the molecular level and is not a coating or plating.  It penetrates the steel and actually hardens the steel, itself.  It can be done to any barrel steel, from "ordinary" 4140, to 4150, to 4150 CMV and to barrels that have been hammer forged.

You can actually QPQ SN a stainless match grade barrel to improve its useful life, too.

Most match grade manufacturers do not do QPQ SN to their barrels nor do they recommend it.   The process requires very careful control of temperatures and if not done properly, can alter the temper of the barrel deep below the surface and weaken the barrel.  Done right by the few companies who know what they are doing, it is a superb way to extend the life of target grade barrels.  QPQ SN stainless target grade barrels are showing up in national competition for this reason.  Those barrels are expensive and have a relatively short life in competition, so even a few hundred extra rounds of match accuracy is important.

The reason the elite barrel makers stay away from QPQ SN in thier own shops is multi-factoral.   I can only speculate.  One reason is that they want to sell more barrels.  The second reason is the concern over potential lack of temperature control in the treatment process which could damage their barrels.   A third reason is that with AR barrels in particular, the process can result in changing the torque value of the attachment of the barrel extension to the barrel.  Those parts really need to be nitrided separately and then assembled.

Now I will pass the baton to others who may agree or disagree, as this is a general subject in which there is not uniform consensus.

Link Posted: 5/5/2015 12:34:20 PM EDT
[#4]
Thanks for the info and correction point man. Used to the 308 vs 7.62 and didn't realize the 5.56/.223 was backwards.

Alex, just wanting to know so I have a better understanding and when it comes in discussions (for my job) I will know the right answer and can actually articulate . I don't like being the guy that says, "good enough for government work". It's also going to be a part of my job so I'm getting a head start with the knowledge base.
Link Posted: 5/5/2015 12:35:18 PM EDT
[#5]

Discussion ForumsJump to Quoted PostQuote History
Quoted:


You have .223 and 5.56 backwards. It's ok to shoot .223 in a 5.56 barrel, but it is not ok to shoot 5.56 in a .223 barrel (5.56 is a higher pressure than .223). You want a 5.56 barrel chamber. Or a .223 Wylde chamber



As far as twist rates go, you generally use a longer (heavier) bullet with faster twist rates (lower numbers=faster twist), but that can vary with velocity, barrel length, etc. Your best bet is to try several and find out what your barrel in particular likes. For example, if you have an accurate 1:7 barrel, then you should buy 3-4 manufacturers of 69-77gr loads to see what groups best if you don't reload. If you have a 1:12 twist, then your barrel will prefer the lighter 50-55gr loads.



I don't have much experience with the differences between several brands of barrel manufacturers so I'll let someone else chime in on that, but you generally use a stainless barrel if accuracy is top priority, versus chrome-lined which lasts longer but is less accurate (not by a huge amount, though). Chrome lining is not something that you would have done by an aftermarket company--it is part of the barrel making process and is done before you buy it.
View Quote




FIFY.


And to clarify, barrel twist rates correlate with the length of the bullet that touches the lands. Longer the bullet = more bullet contact to barrel = faster twist rate (which generally means heavier bullet)


And 55gr projectiles shoot fine in 1:7" barrels



 

Link Posted: 5/5/2015 12:40:42 PM EDT
[#6]
You sure your not trolling to get the OCD crowd upset.!!

For all practical purposes the .223/5.56 chambering issue is a lot of OCD crying.
You will possibly have more chambering/stuck cartridge issues with.223 chamber when dealing with out of spec or reloaded brass.
I have personally gone more toward the 5.56 chamber lately because of this possibility. I do reload.



Now can we get on with the 9MM vs .45 and Beans/no Beans chili squabbles??
Link Posted: 5/5/2015 12:48:44 PM EDT
[#7]
Discussion ForumsJump to Quoted PostQuote History
Quoted:



FIFY.


And to clarify, barrel twist rates correlate with the length of the bullet that touches the lands. Longer the bullet = more bullet contact to barrel = faster twist rate (which generally means heavier bullet)


And 55gr projectiles shoot fine in 1:7" barrels
 


View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Quoted:
Quoted:
You have .223 and 5.56 backwards. It's ok to shoot .223 in a 5.56 barrel, but it is not ok to shoot 5.56 in a .223 barrel (5.56 is a higher pressure than .223). You want a 5.56 barrel chamber. Or a .223 Wylde chamber

As far as twist rates go, you generally use a longer (heavier) bullet with faster twist rates (lower numbers=faster twist), but that can vary with velocity, barrel length, etc. Your best bet is to try several and find out what your barrel in particular likes. For example, if you have an accurate 1:7 barrel, then you should buy 3-4 manufacturers of 69-77gr loads to see what groups best if you don't reload. If you have a 1:12 twist, then your barrel will prefer the lighter 50-55gr loads.

I don't have much experience with the differences between several brands of barrel manufacturers so I'll let someone else chime in on that, but you generally use a stainless barrel if accuracy is top priority, versus chrome-lined which lasts longer but is less accurate (not by a huge amount, though). Chrome lining is not something that you would have done by an aftermarket company--it is part of the barrel making process and is done before you buy it.



FIFY.


And to clarify, barrel twist rates correlate with the length of the bullet that touches the lands. Longer the bullet = more bullet contact to barrel = faster twist rate (which generally means heavier bullet)


And 55gr projectiles shoot fine in 1:7" barrels
 




That depends on how you define "fine".  Some 1:7 barrels are closer to 1:8 when you actually measure twist.  And not all 55 grain bullets are of the same quality.  Match grade 55 and even 52 SMKs can have MOA or even sub-MOA in 1:7, but chances are that lesser quality 55 grain bullets will shoot better with 1:9.  And I doubt that 100 yard benchrest rifles shooting flat base 52 or 55 grain bullets are using 1:7 to shoot consistent 1/3 MOA or better groups.  They will be even slower, probably 1:12.

NRA recently released an article in its "American Rifleman" magazine in which it tested the new military M855A1 ammo in various rifles.  This is a lead free 62 grain bullet that is longer for weight than lead core bullets.  You would expect that it would benefit from the faster 1:7.  But, their testing showed that 1:9 twist rifles produced groups 50% smaller than the same rifles with 1:7 twist.   The article also pointed out that when the military brass demonstrated M855A1 to show that it met its accuracy claims, it somewhat "secretly" used 1:8 barrels.

If you really need to shoot long, heavier bullets and need them to cycle though an AR15 magazine, 1:8 would be the optimal choice.
Link Posted: 5/5/2015 12:49:16 PM EDT
[#8]
What it says in the book will get you so far. Experience speaks volumes. I "read it on some internet forum" is not much better than "Good enough for Gubment work".  You will still have to separate the "Wheat from the Chaff" with experience. I commend you on your quest of knowledge.  Please tell me you are not going to work for the BATFE.
Link Posted: 5/5/2015 12:55:51 PM EDT
[#9]
Ms556 great post thanks! I had to keep my OP under 2k words so left out some backstory.
I'm coming from a precision rifle background so that's why I'm seeking this knowledge base. I hear too many times guys just buy whatever off the shelfs to shoot. While that's acceptable for some , I like to have a knowledge base and reason for my rifles and what they shoot.

Question for you: know any good sources to get The salt bathing done right?

still up in the air, is there a reason a shooter would want to shoot either a lighter grain or heavier grain?
Link Posted: 5/5/2015 1:34:01 PM EDT
[#10]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
There is an intermediate chamber, the "Wylde" chamber that falls between 5.56 and .223 that is popular with precision shooters that also need reliability.  Frankly, I have not studied the precise dimensions of the Wylde chamber.  I'm sure experts will come along.
View Quote

Not exactly and "expert" but...

Wylde actually has a larger chamber than 5.56mm (.3553 and .255 for .223 Rem and 5.56, .3752 and .2568 for Wylde), but the freebore diameter is closer to the bullet diameter.  This means the chamber can digest dirty ammo as well as the M16 but should have slightly better accuracy.  (Whether you are a good enough shot to notice the difference, is another question.  I know I probably couldn't)

Link Posted: 5/5/2015 1:47:15 PM EDT
[#11]
Quoted:
Berger Bullets has a handy online calculator to determine best twist based on info you feed into it regarding the details of the bullet construction and weight and the precise velocity of the bullet as it leaves the barrel.  While there are templates for Berger bullets, you can check any bullet, if you know the information from the manufacturer's web site and know the muzzle velocity....

1:9 twist will not stabilize heavy bullets above 75 grains lead core.  If you want to shoot the popular 77 grain SMK, you need 1:8 or faster....
View Quote

According to that stability calculator (http://www.bergerbullets.com/twist-rate-calculator/) Sierra 77 gr MatchKings are just as stable in a 1:9 twist as 55 gr M193 in a 1:12 twist both come in around 1.3 (1.35 for the 77gr in a 1-9 @ 2650 fps and 1.27 for 55 gr in 1-12 @ 3250 fps).
Link Posted: 5/5/2015 1:49:59 PM EDT
[#12]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
. . . is there a reason a shooter would want to shoot either a lighter grain or heavier grain?
View Quote

Velocity vs Windage
Link Posted: 5/5/2015 1:56:10 PM EDT
[#13]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
That depends on how you define "fine".  Some 1:7 barrels are closer to 1:8 when you actually measure twist.  And not all 55 grain bullets are of the same quality.  Match grade 55 and even 52 SMKs can have MOA or even sub-MOA in 1:7, but chances are that lesser quality 55 grain bullets will shoot better with 1:9.  And I doubt that 100 yard benchrest rifles shooting flat base 52 or 55 grain bullets are using 1:7 to shoot consistent 1/3 MOA or better groups.  They will be even slower, probably 1:12.

NRA recently released an article in its "American Rifleman" magazine in which it tested the new military M855A1 ammo in various rifles.  This is a lead free 62 grain bullet that is longer for weight than lead core bullets.  You would expect that it would benefit from the faster 1:7.  But, their testing showed that 1:9 twist rifles produced groups 50% smaller than the same rifles with 1:7 twist.   The article also pointed out that when the military brass demonstrated M855A1 to show that it met its accuracy claims, it somewhat "secretly" used 1:8 barrels.

If you really need to shoot long, heavier bullets and need them to cycle though an AR15 magazine, 1:8 would be the optimal choice.
View Quote

http://www.m4carbine.net/showthread.php?168388-An-Accuracy-Comparison-of-M855-When-Fired-From-1-9”-Twist-and-1-7”-Twist-Barrels/page3
Post #15 or thereabouts....

The upshot is good bullets shot well in good barrels, it doesn't matter much about twist...bad bullets, well they never shoot all that well in anything.
Link Posted: 5/5/2015 2:24:22 PM EDT
[#14]
Discussion ForumsJump to Quoted PostQuote History
Quoted:

In actuality, it is rpm that stabilized a bullet, not merely twist.  So, it is the combination of twist rate (number of inches of barrel length per rotation), AND velocity of the bullet, which combine to produce rpm.

Thus, the higher the velocity, the slower the twist needs to be to stabilize the bullet.  That is why short barreled rifles or pistols with much lower velocity, need a faster twist to stabilize their bullets,  This may be one legitimate use of 1:7 for shorter bullets.

View Quote

While technically correct, it takes a large drop in muzzle velocity (Vm) to get an appreciable loss in stability.

Let's take our 77gr SMK (BC = .362, Caliber = .224, weight 77gr length = 1.00") and drop in into Berger's twist rate calculator.  We'll start with a Vm of 2750fps out of a 1-8 twist barrel on a 59 degree day at sea level.

The stability factor is 1.71

If we drop the Vm to 1850 fps, the stability factor is still good at 1.50 right at the limit for comfortable stability. Dropping the Vm to 1400 fps puts the stability right where it is for M193 55 grain bullets.  To get the bullet unstable we have to drop the VM to below 600 fpm.

You normally loose around 50 fps per inch of barrel, so going from a 20 inch barrel with a Vm of 2750 fps with 77 SMKs to a 10.5 inch barrel will still allow for reasonable stability.
Link Posted: 5/5/2015 2:38:18 PM EDT
[#15]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
Ok, I'll take a stab at this, or some of it.

You have chamber info backwards.  

The 5.56 barrels are chambered with a longer throat and are proof tested to handle the higher 5.56 pressures.  That means that they can handle both 5.56 and .223 ammo.

Barrels chambered for .223 have a shorter throat and slightly different chamber dimensions.  They can shoot .223 ammo and are not intended to be used with 5.56 ammo both due to the shorter chamber depth and the higher pressures.

While 5.56 and .223 case dimensions are identical, chamber dimensions are not.  Some .223 barrels can handle 5.56 ammo, but some may have issues with excessive pressure in shooting 5.56 ammo because the bullets are closer to the rifling and the higher pressures.

In reality these differences may be more academic than real, but I personally would not shoot any 5.56 ammo in a barrel specifically chambered to SAAMI .223 dimensions.

There are also "tight" chambers and "loose" chambers.   5.56 chambers tend to be on the outside of the tolerance, or a little more "loose' in chamber dimensioins that most .223 chambers.  This is to ensure reliable cycling of ammo that might be dirty or have surface corrosion or other defects.   Tighter chambers tend to be more accurate, but might not cycle with 100% reliability.

There is an intermediate chamber, the "Wylde" chamber that falls between 5.56 and .223 that is popular with precision shooters that also need reliability.  Frankly, I have not studied the precise dimensions of the Wylde chamber.  I'm sure experts will come along.

Regarding twist rate, it is not bullet weight, but rather the length of the bullet body that touches the rifling.  Indirectly, weight can be a rough measure, as bullets gets longer as weight increases.  But, the analogy falls apart when we move away from jacketed lead core bullets.   Many modern bullets are monolithic copper (Barnes TSX or Hornady GMX), or are made of bi-metal materials such as the M855 "green tip" or the even newer M855A1 which has no lead at all.  Boat tail bullets have less surface in contact with the rifling than a flat base bullet of the same weight.  VLD (very low drag) bullets have a different shape that also affects optimal twist rate.

Berger Bullets has a handy online calculator to determine best twist based on info you feed into it regarding the details of the bullet construction and weight and the precise velocity of the bullet as it leaves the barrel.  While there are templates for Berger bullets, you can check any bullet, if you know the information from the manufacturer's web site and know the muzzle velocity.

Example: my 1:9 twist barrel can shoot jacketed lead core bullets up to about 75 grains just fine.  But the Barnes TXS 70 grain bullet, because it has no lead, and is all copper, weighs less for the same length.  The 70 grain Barnes TXS is, therefore, much longer than a 70 grain lead core bullet.  I can shoot 70 grain lead core bullets just fine with very good accuracy in 1:9, but the same weight Barnes TXS bullets keyhole badly, even at 5.56 pressure and velocity from that 1:9  16" barrel, striking the target sideways at 100 yards, or not even hitting the target, with extremely poor accuracy.

As to twist rate, there are advocates of 1:9, 1:8 and 1:7.  You will hear praises of each and none are completely wrong in their selection.  If the rifle is to be match grade and the bullets are to be under 70 grains lead core, or 62 grains monolithic, you will probably find that 1:9 twist produces the best gilt edged accuracy if the barrel and rifle are up to the task.

Many 1:7 rifles, perhaps even most, can shoot very accurate groups with light bullets, down to 52 grains, but are likely to shoot even better groups with a slower twist.

1:9 twist will not stabilize heavy bullets above 75 grains lead core.  If you want to shoot the popular 77 grain SMK, you need 1:8 or faster.

I personally see no need for 1:7 other than that guys want to emulate mil-spec which requires 1:7 to stabilize tracer bullets that I never intend to shoot and you probably will not easier.

There are longer bullets that might need 1:7, but such bullets are intended for bolt action guns, as these very long bullets would not fit in and cycle through the relatively short AR15 magazines.

In actuality, it is rpm that stabilized a bullet, not merely twist.  So, it is the combination of twist rate (number of inches of barrel length per rotation), AND velocity of the bullet, which combine to produce rpm.

Thus, the higher the velocity, the slower the twist needs to be to stabilize the bullet.  That is why short barreled rifles or pistols with much lower velocity, need a faster twist to stabilize their bullets,  This may be one legitimate use of 1:7 for shorter bullets.

Some say that too much twist does not hurt.  I think it does.  Overstabilized bullets, if they are not very uniform in their dimensions, like match grade bullets, will "wobble" and accuracy will be degraded.  It may be slight and of no significance if you are not trying to shoot sub MOA groups.   Another phenomenon I have experienced with too much twist is with very light jacketed varmint bullets.   I have a 6mm Remington bolt gun that can push 55 grain bullets at 4,100 fps, far faster than any .223/5.56 with similar weight.  I have found that at that velocity the twist in my bolt gun (1:9), produces such a high rpm that it literally tears the jackets off of some very lightly constructed bullets.  Those bullets literaly explode between the barrel and the target from excessive rpm and often do not even got to the target.  Other slightly thicker jacketed varmint bullets in that weight do just fine.

I have some 35 grain Hornady Superperformance varmint ammo that is very accurate in 1:9.  I have not tried those bullets in a 1:7, but given their very thin jackets and intentionally frangible construction, I would be afraid they would act like those light jacketed bullets in my 6mm and tear the jackets off of the bullets due to rotational forces before getting to the target.  This is speculation, since I've not tried them in a long barreled 1:7, where they might be at risk.

If you are looking for a precision match grade barrel, you are on the right track with Shilen, Bartlein, Kreiger and I would add Lilja to that list.  I think the Lilja 1:8 stainless barrel they make for RECCE rifles for he SEALS may be what I put on my next build.

BTW:  I am an advocate of QPQ SN nitride for precision rifle shooting to extend barrel life.  I doubt you will ever see a chrome lined barrel on the line of any national championship match except where it is required.  Chrome lining is a plating process.  It can be done with a very high degree of uniformity, but it is still a plating and there will be imperfections and irregularities in the thinckness of the plating process that could degrade accuracy.  It also blunts or rounds the edges of cut rifling in barrels that are made that way.  On the other hand, QPQ SN does not alter the dimensions of the bore or its rifling, leaving the contours pristine.  It hardens the surface at the molecular level and is not a coating or plating.  It penetrates the steel and actually hardens the steel, itself.  It can be done to any barrel steel, from "ordinary" 4140, to 4150, to 4150 CMV and to barrels that have been hammer forged.

You can actually QPQ SN a stainless match grade barrel to improve its useful life, too.

Most match grade manufacturers do not do QPQ SN to their barrels nor do they recommend it.   The process requires very careful control of temperatures and if not done properly, can alter the temper of the barrel deep below the surface and weaken the barrel.  Done right by the few companies who know what they are doing, it is a superb way to extend the life of target grade barrels.  QPQ SN stainless target grade barrels are showing up in national competition for this reason.  Those barrels are expensive and have a relatively short life in competition, so even a few hundred extra rounds of match accuracy is important.

The reason the elite barrel makers stay away from QPQ SN in thier own shops is multi-factoral.   I can only speculate.  One reason is that they want to sell more barrels.  The second reason is the concern over potential lack of temperature control in the treatment process which could damage their barrels.   A third reason is that with AR barrels in particular, the process can result in changing the torque value of the attachment of the barrel extension to the barrel.  Those parts really need to be nitrided separately and then assembled.

Now I will pass the baton to others who may agree or disagree, as this is a general subject in which there is not uniform consensus.

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A copy of this should accompany every AR sold
Link Posted: 5/5/2015 4:43:20 PM EDT
[#16]
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According to that stability calculator (http://www.bergerbullets.com/twist-rate-calculator/) Sierra 77 gr MatchKings are just as stable in a 1:9 twist as 55 gr M193 in a 1:12 twist both come in around 1.3 (1.35 for the 77gr in a 1-9 @ 2650 fps and 1.27 for 55 gr in 1-12 @ 3250 fps).
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Berger Bullets has a handy online calculator to determine best twist based on info you feed into it regarding the details of the bullet construction and weight and the precise velocity of the bullet as it leaves the barrel.  While there are templates for Berger bullets, you can check any bullet, if you know the information from the manufacturer's web site and know the muzzle velocity....

1:9 twist will not stabilize heavy bullets above 75 grains lead core.  If you want to shoot the popular 77 grain SMK, you need 1:8 or faster....

According to that stability calculator (http://www.bergerbullets.com/twist-rate-calculator/) Sierra 77 gr MatchKings are just as stable in a 1:9 twist as 55 gr M193 in a 1:12 twist both come in around 1.3 (1.35 for the 77gr in a 1-9 @ 2650 fps and 1.27 for 55 gr in 1-12 @ 3250 fps).


Ideal stability is 1.5 to 2.0. Some 1/9 twist barrels shoot 77 grain bullets very well, the problem is some are horrible. 1/9 is borderline for bullets weighing 75/77 grains. You have to try them in your rifle to see if they will work.

Never buy a 1/9 if you intend to feed it a steady diet of 75/77 grain bullets (NRA/CMP high power) or you'll take a chance at being disappointed. I own a 1/9 twist Winchester 26" barreled .223 rifle that hammers with Hornady 75's. It's a crap shoot whether any given barrel will shoot them until you get the twist to 1/8 or 1/7. Those twists always work.
Link Posted: 5/5/2015 5:49:39 PM EDT
[#17]
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Ideal stability is 1.5 to 2.0. Some 1/9 twist barrels shoot 77 grain bullets very well, the problem is some are horrible. 1/9 is borderline for bullets weighing 75/77 grains. You have to try them in your rifle to see if they will work.

Never buy a 1/9 if you intend to feed it a steady diet of 75/77 grain bullets (NRA/CMP high power) or you'll take a chance at being disappointed. I own a 1/9 twist Winchester 26" barreled .223 rifle that hammers with Hornady 75's. It's a crap shoot whether any given barrel will shoot them until you get the twist to 1/8 or 1/7. Those twists always work.
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Berger Bullets has a handy online calculator to determine best twist based on info you feed into it regarding the details of the bullet construction and weight and the precise velocity of the bullet as it leaves the barrel.  While there are templates for Berger bullets, you can check any bullet, if you know the information from the manufacturer's web site and know the muzzle velocity....

1:9 twist will not stabilize heavy bullets above 75 grains lead core.  If you want to shoot the popular 77 grain SMK, you need 1:8 or faster....

According to that stability calculator (http://www.bergerbullets.com/twist-rate-calculator/) Sierra 77 gr MatchKings are just as stable in a 1:9 twist as 55 gr M193 in a 1:12 twist both come in around 1.3 (1.35 for the 77gr in a 1-9 @ 2650 fps and 1.27 for 55 gr in 1-12 @ 3250 fps).


Ideal stability is 1.5 to 2.0. Some 1/9 twist barrels shoot 77 grain bullets very well, the problem is some are horrible. 1/9 is borderline for bullets weighing 75/77 grains. You have to try them in your rifle to see if they will work.

Never buy a 1/9 if you intend to feed it a steady diet of 75/77 grain bullets (NRA/CMP high power) or you'll take a chance at being disappointed. I own a 1/9 twist Winchester 26" barreled .223 rifle that hammers with Hornady 75's. It's a crap shoot whether any given barrel will shoot them until you get the twist to 1/8 or 1/7. Those twists always work.

A bullet either spins fast enough to stabilize or they don't.  1-9 twist is enough to keep a 77 grain bullet going straight.

Seems a lot of people have found this out...http://www.ar15.com/forums/t_3_118/255677_77gr_SMK_and_1_9_twist.html
Link Posted: 5/5/2015 5:58:43 PM EDT
[#18]
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Not exactly and "expert" but...

Wylde actually has a larger chamber than 5.56mm (.3553 and .255 for .223 Rem and 5.56, .3752 and .2568 for Wylde), but the freebore diameter is closer to the bullet diameter.  This means the chamber can digest dirty ammo as well as the M16 but should have slightly better accuracy.  (Whether you are a good enough shot to notice the difference, is another question.  I know I probably couldn't)

http://i129.photobucket.com/albums/p203/CHRIS65-IL/223-vs-NATO-vs-WYLDE-chambers.jpg
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There is an intermediate chamber, the "Wylde" chamber that falls between 5.56 and .223 that is popular with precision shooters that also need reliability.  Frankly, I have not studied the precise dimensions of the Wylde chamber.  I'm sure experts will come along.

Not exactly and "expert" but...

Wylde actually has a larger chamber than 5.56mm (.3553 and .255 for .223 Rem and 5.56, .3752 and .2568 for Wylde), but the freebore diameter is closer to the bullet diameter.  This means the chamber can digest dirty ammo as well as the M16 but should have slightly better accuracy.  (Whether you are a good enough shot to notice the difference, is another question.  I know I probably couldn't)

http://i129.photobucket.com/albums/p203/CHRIS65-IL/223-vs-NATO-vs-WYLDE-chambers.jpg


Thank you for the knowledge on the Wylde chamber.  This was a big gap in my already limited knowledge of the exact chamber dimensions.
Link Posted: 5/5/2015 6:05:28 PM EDT
[#19]
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Ideal stability is 1.5 to 2.0. Some 1/9 twist barrels shoot 77 grain bullets very well, the problem is some are horrible. 1/9 is borderline for bullets weighing 75/77 grains. You have to try them in your rifle to see if they will work.

Never buy a 1/9 if you intend to feed it a steady diet of 75/77 grain bullets (NRA/CMP high power) or you'll take a chance at being disappointed. I own a 1/9 twist Winchester 26" barreled .223 rifle that hammers with Hornady 75's. It's a crap shoot whether any given barrel will shoot them until you get the twist to 1/8 or 1/7. Those twists always work.
View Quote View All Quotes
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Discussion ForumsJump to Quoted PostQuote History
Quoted:
Quoted:
Quoted:
Berger Bullets has a handy online calculator to determine best twist based on info you feed into it regarding the details of the bullet construction and weight and the precise velocity of the bullet as it leaves the barrel.  While there are templates for Berger bullets, you can check any bullet, if you know the information from the manufacturer's web site and know the muzzle velocity....

1:9 twist will not stabilize heavy bullets above 75 grains lead core.  If you want to shoot the popular 77 grain SMK, you need 1:8 or faster....

According to that stability calculator (http://www.bergerbullets.com/twist-rate-calculator/) Sierra 77 gr MatchKings are just as stable in a 1:9 twist as 55 gr M193 in a 1:12 twist both come in around 1.3 (1.35 for the 77gr in a 1-9 @ 2650 fps and 1.27 for 55 gr in 1-12 @ 3250 fps).


Ideal stability is 1.5 to 2.0. Some 1/9 twist barrels shoot 77 grain bullets very well, the problem is some are horrible. 1/9 is borderline for bullets weighing 75/77 grains. You have to try them in your rifle to see if they will work.

Never buy a 1/9 if you intend to feed it a steady diet of 75/77 grain bullets (NRA/CMP high power) or you'll take a chance at being disappointed. I own a 1/9 twist Winchester 26" barreled .223 rifle that hammers with Hornady 75's. It's a crap shoot whether any given barrel will shoot them until you get the twist to 1/8 or 1/7. Those twists always work.


I can't shoot the 77 SMK's in this particular barrel.  Well, they don't keyhole badly like the Barnes 70 grain TSX, but accuracy is not good.  Any lead core bullets lighter do very well, and it especially likes 62-70 grain lead core bullets and does well up to 75 grain lead core, and up to 62 grains monolithic.   Indeed, each rifle barrel can produce variations from the tables when you get into the borderline stability regions.  FWIW:  It shoots handloaded 62 grain TSX bullets right at MOA, and they are hunting bullets, not intended for target work.
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