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View Full Version : Starting AR build, barrel twist vs. longevity and AMMO?


the86d
09-19-2011, 4:52 AM
1:7 twist on my USMC service issued M16A2 barrel back in the day. Getting 3 lowers to build off of, and I KNOW since I want to go featureless on at least one, there are parts I will not like. Backup to a backup is better too!

I never had any issues with the M16A2, but I KNOW we put some rounds & BLANKS through ALL of those while the armorers never had to have even one gas-tube, nor barrel replaced.

"1:7 1:8 1:9" without the quiotes seems to give "0" results here, probably due to vBulletin issue?

Q1) Is the life of a 1:7 barrel shorter than a 1:8, or 1:9 due to the twist being higher?

Q2) Is the Federal green tipped ammo (NATO 5.56) the same as (or close to) what I used to shoot in the USMC?

Q3) Is the Federal green tipped ammo (NATO 5.56) any good, because it states "not for duty use"?

Q4) Will accuracy be a major player if I am firing .223, or will the barrel wear differently?

Q5) Anyone ONLY shoot .223 in a 5.56 NATO chamber, and for how long?

The War Wagon
09-19-2011, 5:25 AM
Q1) Is the life of a 1:7 barrel shorter than a 1:8, or 1:9 due to the twist being higher?

Q2) Is the Federal green tipped ammo (NATO 5.56) the same as (or close to) what I used to shoot in the USMC?

Q3) Is the Federal green tipped ammo (NATO 5.56) any good, because it states "not for duty use"?

Q4) Will accuracy be a major player if I am firing .223, or will the barrel wear differently?

Q5) Anyone ONLY shoot .223 in a 5.56 NATO chamber, and for how long?

1) the lower the second number, the higher the twist rate. 1: 7 is a HIGHER twist than a 1: 9 - it has no collelation to barrel length. You could get a 26" bbl with a 1: 7 rate, although I'm not sure WHY you would... :confused:. HIGHER twist allows you to shoot HEAVIER bullets accurately; lower twist allows for shooting LIGHTER bullets accurately.

2) Yes.

3) Probably factory seconds. Watch out for the 'unleaded' M855A1 - it's NOTHING like REAL M855.

4) All things being equal, accurate ammo is just that - the QC is higher, for better performance, and better perfomance from round to round. Unless you're building a stainless barrel for match competition, you have MANY thousands of rounds to blow downrange before a chrome-lined barrel needs replacing.

5) In my case, no. I'm mostly a milsurp shooter, although I just got my first SPR. Now I gotta go put Black Hills Ammunition's books in the black for the year! http://www.calguns.net/calgunforum/images/icons/icon11.gif

dieselpower
09-19-2011, 6:59 AM
1:7 twist on my USMC service issued M16A2 barrel back in the day. Getting 3 lowers to build off of, and I KNOW since I want to go featureless on at least one, there are parts I will not like. Backup to a backup is better too!

I never had any issues with the M16A2, but I KNOW we put some rounds & BLANKS through ALL of those while the armorers never had to have even one gas-tube, nor barrel replaced.

"1:7 1:8 1:9" without the quiotes seems to give "0" results here, probably due to vBulletin issue?

Q1) Is the life of a 1:7 barrel shorter than a 1:8, or 1:9 due to the twist being higher? It can be, depends on what ammo. 40gr FMJ & 77gr JHP will produce different wear trends. Overall as a General purpose rifle it will not matter as much as people say it will. From what I know the 1:9 shooting 55gr will outlast most others, but you are dealing with 20,000 rounds vs 25,000...

Q2) Is the Federal green tipped ammo (NATO 5.56) the same as (or close to) what I used to shoot in the USMC? I was told it was made to the same spec, but the powder is a different formula as per some FBI/ATF policy on civilian ammo... could be tin foil hat time... I don't know.

Q3) Is the Federal green tipped ammo (NATO 5.56) any good, because it states "not for duty use"? Its cheap range ammo. Its safer than Wolf or Tula. It preforms well for training. Its not as good as higher end ammo.

Q4) Will accuracy be a major player if I am firing .223, or will the barrel wear differently? A 5.56 chamber is loose as compared to a .223. Both chrome lining and a 5.56 chamber contribute to less accuracy with .223. Chrome helps the barrel sustain high heat from rapid firing and aids in cleaning. It degrades accuracy due to imperfections in the chroming process and the fact the rifling had to be over-sized to accommodate the added layer of chrome. When a smaller .223 jumps the 5.56 throat leade it will do so at varying angles causing inconsistent lock up with the rifling. This leads to uneven wear on the leade, inconsistent Point of impact on the target and fouling of the chamber. In the grand scheme of things its not a big deal. It is only a big deal if you measure success in hundreds of an inch. To the average guy its nothing to worry about. For the accuracy shooter it doesn't matter, the barrel is set up for accuracy and longevity isn't a factor. It can last 3,000 rds and gets changed out. The most accurate AR15 barrel will be a 1:8, .223, non-chrome lined 20"

Q5) Anyone ONLY shoot .223 in a 5.56 NATO chamber, and for how long? I shoot 55gr.223 90% of the time. I will kick off a box or two of 77gr 5.56every few months or so. This year I haven't done much MK262 due to ammo prices. My barrel is a 4140 HBAR, 5.56 chamber, non-chrome lined from ArmaLite. It has about 8,000 - 10,000 rounds down it [I lost my range book :facepalm: ] and is still accurate enough for me. I am only looking for 3-4 inch groups @ 100 yards. I just want to hit center mass. I can still kill a pig, yot or rabbit easy. I have taken a rabbit's head off at 40ish. I can also consistently hit a hanging tennis ball at 50 yards.... and I do not shoot from a bench or prone. I stand or kneel with a sling.

Hope this helps. YMMV. Its a rifle and just like a car no two are 100% identical nor with you get the same results as the next guy.

the86d
09-19-2011, 7:20 AM
Thanks for the replies!

I will go with a 1:7-1:9 depending on what other options are available, like I was used to about 10+ (er-hmmm) years ago...

I should get a .223 dedicated upper and barrel and just keep the cheaper .223 (not by much) stockpiled in case of... issues. The stripper clips on that Federal Green Tips like I used to use would make the commie rule of 10 rounders a bit more "do-able".

Again, thanks for the assist!

dieselpower
09-19-2011, 7:36 AM
Just remember a 5.56 shooting .223 will only matter for grouping, not for accuracy. You will still hit a man sized target at 400 yards shooting .223 out of a 5.56, it just will have a larger POI grouping than a 5.56.

So the "in case of issue" really wouldn't matter. I would go with 5.56 on all barrels for a General Purpose gun. Stick with the major manufacturers and you should have no trouble. Even a DPMS, non-chrome lined 5.56, 4140 CM, 20" will shoot 55gr .223 out to 400 yards with 3MOA accuracy. (man's chest sized groups) And still get 20,000 rounds out of it if you clean it religiously.