AR Sponsor
Posted: 6/20/2014 4:50:24 PM EDT
| Im building an AR15 and a friend of mine told me I will shorten the barrel life on my barrel shooting 62 grain rounds through my barrel. I think it's a 1:7 twist but it could be a 1:9 twist. I don't actually know because it's it's still in the mail and it was taken down off of the website. |
|
Quoted:
Im building an AR15 and a friend of mine told me I will shorten the barrel life on my barrel shooting 62 grain rounds through my barrel. I think it's a 1:7 twist but it could be a 1:9 twist. I don't actually know because it's it's still in the mail and it was taken down off of the website. First post, so watch out.. 
From all my readings bullet weight has nothing to do with barrel life. Only thing that will give you problems is twist and weight. I'll leave that to the experts. Only thing I have ever read is bimetallic rounds affecting barrel life. If I remember correctly, a 1:9 will stabilize anything up too a 70ish grain. Some have stated they can even go higher than that. Hope that helps. |
|
Bi-metal jacket bullets (lead bullets with a jacket of copper plated mild steel) can increase wear... a couple tests available online show chrome lined barrels at about half the barrel life of standard FMJ when using Bi-metal. Cheap steel cased ammo tends to be bi-metal... which is why I do not use them in precision builds or non-chrome lined rifles.
Bullet weight doesn't matter to barrel life... faster twist rates can shorten barrel life, but not by very much. |
|
Quoted:
First post, so watch out..
From all my readings bullet weight has nothing to do with barrel life. Only thing that will give you problems is twist and weight. I'll leave that to the experts. Only thing I have ever read is bimetallic rounds affecting barrel life. If I remember correctly, a 1:9 will stabilize anything up too a 70ish grain. Some have stated they can even go higher than that. Hope that helps. Quoted:
Quoted:
Im building an AR15 and a friend of mine told me I will shorten the barrel life on my barrel shooting 62 grain rounds through my barrel. I think it's a 1:7 twist but it could be a 1:9 twist. I don't actually know because it's it's still in the mail and it was taken down off of the website. First post, so watch out..
From all my readings bullet weight has nothing to do with barrel life. Only thing that will give you problems is twist and weight. I'll leave that to the experts. Only thing I have ever read is bimetallic rounds affecting barrel life. If I remember correctly, a 1:9 will stabilize anything up too a 70ish grain. Some have stated they can even go higher than that. Hope that helps. That's incorrect. A 1/9 may begin to have problems starting at 62gn. Almost all major mfg's are using 1/7 or 1/8 for 55 to 77gn. |
|
Quoted:That's incorrect. A 1/9 may begin to have problems starting at 62gn. The Army Research Institute's report ARI Research Note 86-19 — Analysis of M16A2 Rifle Characteristics and Recommended Improvements dated February 1986 says otherwise. Barrel Twist. The SAW has a 1:7 twist, because it was reported that this amount of twist was required to stabilize the tracer round at extended
ranges. No alternative to a 1:7 twist has been tested for the rifle. The general rule seems to be that, for bullets of the same diameter, more twist is required to stabilize a round in flight as the length of the round increases. Our measurements indicate the following lengths: o Current ball (M193) - 19 m o Current tracer (M196) - 22-1/2 mm o New ball (XM855) - 23 mm o New tracer (XM856) - 29-1/4 mm While any alternative must be tested, previous firing tests have confirmed that a 1:9 twist will provide for stability of a bullet similar to the new ball round. Reducing barrel twist to 1:9 will result in less stress on the bullet, barrel life will be improved, and barrel fouling will be reduced. While this twist may not fully stabilize the tracer round to maximum range, the rifle tracer is normally used as a marking round at extended ranges and precise accuracy is not required. The M16A1 has one twist (rifling) for each 12 inches of barrel length and it has very effective terminal ballistics against personnel targets. It is generally accepted that less bullet stability will enhance terminal ballistics. Therefore, the increased twist of the M16A2, one twist in seven inches, should be tested against a one in nine twist barrel, which would probably produce better terminal ballistics against personnel targets. A very important consideration is that reducing twist to 1:9 will probably improve accuracy at all ranges, particularly at 25 meters and in the primary range band out to 300 meters. A general rule is that minimum twist should be used to stablilize the round. Any additional twist will increase variability, causing the bullet to move in a corkscrew-type pattern at closer ranges. With the Army dependence on 25-meter ranges, this factor is much more important to the Army than the Marine Corps. An example of appropriate twist may be seen in the Army Marksmanship Unit rifles which have a 1:10 twist for firing at ranges up to 1000 yards. When the same type rifle and ammunition is used for 300-meter competition, the twist is reduced from 1:10 to 1:14 to obtain greater accuracy. From reviewing available firing data and giving consideration to terminal ballistics, employment ranges, barrel fouling, accuracy, and compatibility with M193 ammunition, a 1:9 twist appears optimum for the Army rifle. |
|
Quoted:
I'll just leave this here so you can all stop throwing random stuff out there. lol http://s19.postimg.org/4sbr48obn/Twist_VS_Grain.jpg I believe this graph depicts pretty much what I said...that a 1/9 may begin to have issues at 62gn. |
|
It has more to do with bullet length the reason milspec barrels use 1/7 is because the longer tracer rounds the military use now stabilize better, the 62gr actually stabilize better out of a 1/9. OP the point at point at which you might see your groups open up is using heavier than 70 gr bullets with a 1/9 barrel. As far as barrel life the bullet gr has nothing to do with it, but multiple mag dumps until your barrel is red hot is not good for it.
|
|
Quoted:
Wasn't the 62gr made for the 1:7? Nope, 1:7 was made to stabilize the longer M856 tracer round in use by the military. Bullet weight in and of itself doesn't really matter for round stabilization, it's the length of the bullet that matters and dictates what twist you need. It just so happens heavier rounds tend to be longer. ETA: OP, bullet weight has nothing to do with barrel wear. It has already been stated, but bi-metal jacket bullets will wear your barrel more quickly, particularly in the gas port and throat areas. These types of bullets are almost always found in Russian manufactured ammunition. I still shoot the bi-metal jacket stuff because even if it does wear my barrel out more quickly, I still have saved enough money from cheaper ammo over brass cased ammo to purchase a new barrel a couple times over. |
|
Quoted:
I believe this graph depicts pretty much what I said...that a 1/9 may begin to have issues at 62gn. Quoted:
Quoted:
I'll just leave this here so you can all stop throwing random stuff out there. lol http://s19.postimg.org/4sbr48obn/Twist_VS_Grain.jpg I believe this graph depicts pretty much what I said...that a 1/9 may begin to have issues at 62gn. It depicts nothing more than a random internet guy who went into MS paint and drew that up based on his own opinion. |
|
Quoted:
I believe this graph depicts pretty much what I said...that a 1/9 may begin to have issues at 62gn. Quoted:
Quoted:
I'll just leave this here so you can all stop throwing random stuff out there. lol http://s19.postimg.org/4sbr48obn/Twist_VS_Grain.jpg I believe this graph depicts pretty much what I said...that a 1/9 may begin to have issues at 62gn. And it may not. PLENTY of members shoot 77gr out of 9 twist barrels |
|
Back to barrel wear -
A rifle barrel gets "worn out" from the volume and temperature of the gas torching the throat out of the gun. A .223 Rem chamber grows about 0.001 inches for every 100 rounds fired. Wear at the crown and damage in the bore can be avoided by cleaning with good tools, a bore guide, and care and handling of the barrel crown. Also, 9 twist barrels pretty well poop out at bullets of around 70 grains weight, but that all depends on the length of the bullet, a short stubby bullet with a fat ogive will stabilize just fine, but it won't fly worth a damn in the wind. Still, if a squirrel needs to be shot with a short stubby bullet ... |
It is doubtful that you will ever shoot out a barrel unless this is all you do in your spare time or you are in the shooting business. If you are like most, you get to the range once or twice a month and put 2-3 hundred rounds thru your rifle. At that rate it will take you 8-10 years to shoot out a barrel...and that is if it is your only AR. We all know you will soon be building/buying another.  Barrels are relatively cheap in the grand scheme of things and easily replaced. Shoot it with all sorts of different rounds and see what your rifle likes best. BRD is infectious.
|
|
Quoted: A .223 Rem chamber grows about 0.001 inches for every 100 rounds fired. When you say grows, are you referring to headspace? If you are referring to headspace, a 5.56 chamner would be shot out by 900 rounds having the minimum amount of headspace of 1.4646". Since, a headspace measurement of 1.4736" is when a chamber becomes out of spec. |
|
Quoted:
When you say grows, are you referring to headspace? If you are referring to headspace, a 5.56 chamner would be shot out by 900 rounds having the minimum amount of headspace of 1.4646". Since, a headspace measurement of 1.4736" is when a chamber becomes out of spec. Quoted:
Quoted: A .223 Rem chamber grows about 0.001 inches for every 100 rounds fired. When you say grows, are you referring to headspace? If you are referring to headspace, a 5.56 chamner would be shot out by 900 rounds having the minimum amount of headspace of 1.4646". Since, a headspace measurement of 1.4736" is when a chamber becomes out of spec. No, read what I wrote; the throat and chamber end of the bore get shot out due to torching from the hot gas. That has no effect on headspace. A rifle will continue to shoot with the rifling completely missing from many inches of the bore, it just might not shoot with much accuracy. |
AR Sponsor