What caliber AR Upper do you have?

[Hummer]

Tweet
There is some confusion and some have been given soem very bad info. I was the Test Director for the M16A1E1 Rifle at Aberdeen Proving Ground in 1982/3 time frame. This was adopted as the M16A2. Thusly I was there from day 1 when the Marines wanted a souped up M16. We shot up 244,000 rounds on that test from -60F to +140F, mud, dust, salt spray, drop testing etc etc.

The original version A2 heavy barrel was only heavy from the front sight to the flash suppressor. Behind the front sight towards the chamber it was same as previously fabricated.

Troops used to bend M16 barrels by using the rifles and pry bars to break C Rat cartons when they came with steel wire binding. They were also used to break steel bands on palitized material and bent the barrels. Never underestimate what the troops will do with a weapon.

The round handguards were the answer to another problem. The troops broke more left hand guards than they did right handguards so the design was changed so only one handguard needed to be stocked and it was useable as a upper or lower.

The original test weapons and initial delivery had 7 twist not to stabilize the SS109 but from someone copying the specs for the Minimi LMG which called for 7 twist to stabilize the SS110 Tracer which are not issued to infantry but as everyone knows a few kind words applied to the belt gun drivers will get you a hand full.

Ideally the SS109 is stabilized with 8.75" at -60F at sea level. A 10 twist will work just fine for SS109/M855. A M855 bullet will show elongated holes (Yaw) if fired from 12 twist and these are from 30 to 45 degrees.

The SS110 is a much longer projectile requiring it to be spun up faster to stabilize it.

Not to worry if you have a slow twist original AR with 12 twist barrel because a badly yawed round will give outstanding terminal ballistics indoors at point blank range. I used to have the first three in my bedside AR as SS109 followed by 23 rds of M193.

At very close range it is badly yawing. By 100 yards it is just about stabilized but accuracy was very poor. About equal to what I could get with Rem 870 12 ga shooting slugs in unrifled bore. (10 to 12" groups"

Chamber pressure is chamber pressure and length of barrel has nothing to do with how much chamber pressure you have though other things can such as if you have a min dimension bore measurement, tight chamber or short throat that will raise pressures but rarely encountered in a factory production weapon and not at all in a MILSPEC weapon.

A short barrel will however give you increased PORT PRESSURE. For instance the original CARs were produced with the same size gas ports as the 20" barrels resulting is excessive port pressure which gave much more violent extraction forces. Later productions of the CARs, M4s have smaller gas ports thus the pressure bled off the barrel to drive the gas system was similar to original design parameters for the 20" barrel versions.

A short barrel will also give increased pressure at muzzle leading to early deterrioration of the muzzle integrity thus opening up group sizes.

All things being considered you are better off with longer barrels from a accuracy and velocity attainable.

I had a early one and the extraction forces ruined every case fired as it upset the rim pullling the case from the chamber. It was so bad I could not get case in shell holder to reload it ! ! ! ! ! ! I sold it to a guy who wasn't going to reload so it didn't matter to him.

Genuine SS109 ammo made by FN is the finest ball ammo I ever fired insofar as accuracy is concerned. The first runs of M855 were also excellent but then the accuracy specs were relaxed and the late stuff is not any better than M193 55 grain stuff. If you can find SS109 headstamped FN, jump on it.

With SS109 ammo the test rifles held up for 12,000 rounds. With LC loaded M855 initial loading the barrels were at reject at 4800 rounds and completely gone at 6000 and were so bad that the back end of a double decker bus could not be reliably engaged beyond 600 meters.

The new flash suppressor is suprerior to the old one and flash signature is almost non existant. If you want to see excitement shoot a 16" barrel at night with no flash suppressor! ! ! ! ! My 7615 Rem pump will deliver a 15" fireball visible in daylight.

I am seriously considering a 300 AAC Blackout upper assembly w/ 16" barrel but first I am thinking I will get a chamber reamer and build myself a 300 BO on a bolt gun with about a 22" barrel and 12 twist or perhaps 13 twist for the 175 grain and lighter bullets.

[Chefsimms]

Tweet
7.62x51(308 nato)

[drt4lfe]

Tweet
Not sure where 6.8 outperforms 270 ?

[6.5 GRENDEL]

Tweet

I have
.22 LR
5.56x45mm
6.5mm Grendel
7.62x25mm Tokarev
.458 SOCOM

Glad to see a fellow GRENDEL OWNER

[6.5 GRENDEL]

Tweet

Not sure where 6.8 outperforms 270 ?

It doesnt, although its a fine 300 yard rifle with plenty of knockdown power out to that range. But as a combat rifle it definately will out power any .223. But im not trying to start a pissing match about whos gun is better thats just my opinion.
Obviously from my handle im a little partial to the 6.5 Grendel, on the surface it looks like the 6.8 spc and the Grendel would be about the same as the .270 but in fact the Grendel is better ballistically then the 6.8 spc, 270 & .308. As a matter of fact when the .308 goes subsonic at 1000 yards the Grendel is still supersonic.
Its a hell of a deer rifle for those of you that hunt.

[gaLadhon]

Tweet

I know it said AR-15 as the topic but I have an Armalite AR-10, I prefer the .308 round for its knockdown power and ammo is readily available. As a bonus I can also use it for hunting. My next AR will be a AR-15 chambered in a 6.8 SPC which is the equivalent of a .270 which I can also use for hunting and has better knockdown power than a 5.56/.223

Well, I've GOT a 6.8 and its a great boomstick. big hit, little kick! Thing is ammo seems to always be sold out. So bad it got me into reloading. Just ordered a TON of reloading components for ALL my weapons.

When I read the story about the U.N. arms limitation treaty, the first thing I thought of was to get my hands on a collectable war legacy antique. A nonfunctioning 40's era M1 you hang on the wall for show. You replace the barrel and bolt with NIB NM grade parts, artificially age the exterior finish so they look original, and viola youve got an exempt collectors piece!

When I started checking bookmarks for weapons and ammo dealers I was FLOORED at how sales had been skyrocketing since the evening of Nov 6. The moderator of a gun forum I frequent says that we've prolly got a few years before the new legislation becomes a problem. BUT in the meantime, its time to start saving up your pennies folks!

oh, almost forgot to mention, spousal unit put the kibbosh on buying any more weapons, plus I done the math: 6.8 SPC about $1.00 per round, $0.50 reloaded. 7.62 NATO about $0.50 per round (surplus), $0.25 reloaded. 5.56 NATO about $0.50 per round (not surplus), $0.25 reloaded. .22 LR about $0.05 per round, nobody reloads it. So I found a work around. I got one of those CMMG conversion bolt carriers that go in your M4 to let you shoot 22 rimfire ammo without any modifications. Now I can shoot till the cows come home!

[gaLadhon]

Tweet
ok, a quick update on the M4 bolt swap to shoot rimfire - AWESOME for practice and small game! A quick note, however. I DON'T recommend the light load subsonic .22 rimfire ammo, commonly known as "whisper" rounds. They don't generate enough gas to cycle the bolt, so you gotta manually charge EVERY round. Save the whisper rounds for your manual bolt action gun.