Barrels

AR/M4 AR General Discussion
1

Talk to me a about barrels. The more I know the more confused I get.

Here is what I “think” I understand.

Twist
1x7 barrels are for heavy bullet 62gr+
1x9 barrels are good for 55gr to 62gr bullets
1x12 is great for varmint bullets and ok with 55gr bullets

Short barrels give less velocity. Longer barrels give more velocity (up to a point).
Military 5.56x45 ammo (M855 and M193) need certain velocities to fragment in the target. (Link www.ammo-oracle.com). Fragmentation in the target is good.

Chrome lined barrels don’t rust (inside the barrel where the chrome is.)
Chrome lined chambers are more reliable in combat situations.
Chrome lined barrels are less accurate than non-chrome lined barrels.

A standard steel barrel will rust fairly rapidly in a nasty environment.

Stainless barrels are usually match quality.
There for stainless barrels are more accurate.

Although there are several different hardnesses of steel that barrels are made from, it really doesn’t make a difference unless I plan on running 10s of thousands of round through the gun.

Light barrels allow you to bring the gun to bare more quickly.
Heavy barrels heat up slower than thin barrels and cool faster than thin barrels

Short barrels are easier to move inside vehicles.
To be legal, I either have to have a 16” barrel (barrel + fixed flash hider) or pay the ATF $200.

Here is where it starts getting fuzzy.
The original M16-A1 had a thin barrel. The A2 has…?

The standard M4 is light under the handguards, then heavy with a cut for the grenade launcher and then heavy again. This makes absolutely no sense to me.

SPRs have an 18” medium heavy barrel.
SPR are Stainless?

My HBAR feels nose heavy to me.

Shouldn’t the SPR be nose heavy?
Shouldn’t a standard HBAR have more velocity because it has a 20” barrel?
Why did they lop off 2 inches?

A match barrel is still as accurate whether it is an HBAR or a thin BAR?

Is a HBAR more accurate on the first round from a cold barrel?

If I don’t plan on rapid fire and wanted a very accurate first round (through 5 rounds) rifle do I “need” an HBAR, or can I get away with a thin match stainless barrel?

2

Generally, yes. 1x7 will do fine with 55 gr. 1x9 will work easily to 69 and sometimes 75 gr. Twist is more about bullet length than weight.

Short barrels give less velocity. Longer barrels give more velocity (up to a point).
Military 5.56x45 ammo (M855 and M193) need certain velocities to fragment in the target. (Link www.ammo-oracle.com). Fragmentation in the target is good.

Ok.

Chrome lined barrels don’t rust (inside the barrel where the chrome is.)
Chrome lined chambers are more reliable in combat situations.
Chrome lined barrels are less accurate than non-chrome lined barrels.

Chrome lined barrels resist rusting and corrosion better than non chrome lined barrels, but in the end, all steel will rust.

A standard steel barrel will rust fairly rapidly in a nasty environment.

More like a poorly maintained and cared for steel barrel will rust fairly rapidly in a nasty (wet or salty) environment.

Stainless barrels are usually match quality.
There for stainless barrels are more accurate.

Stainless barrels may be match quality. It depends on who made the barrel and how well they did with reaming out the chamber and cutting the rifling in the bore.

Although there are several different hardnesses of steel that barrels are made from, it really doesn’t make a difference unless I plan on running 10s of thousands of round through the gun.

You can run 10s of thousands of rounds through a 4140 steel or 416 stainless steel barrel, but if you’re going to do a lot of rapid fire AND perhaps auto fire, then a 4150 CMV barrel may be better for your needs.

Light barrels allow you to bring the gun to bare more quickly.
Heavy barrels heat up slower than thin barrels and cool faster than thin barrels

Heavy barrels heat up slower than thin barrels, and cool more slowly than thin barrels.

Short barrels are easier to move inside vehicles.

Ok.

To be legal, I either have to have a 16” barrel (barrel + fixed flash hider) or pay the ATF $200.

Ok.

Here is where it starts getting fuzzy.
The original M16-A1 had a thin barrel. The A2 has…?

The A1 barrel is light under the handguards, and light forward of the handguards. The A1 has a flash suppressor.
The A2 barrel is just as light as an A1 under the handguards, and heavier forward of the handguards. The A2 has a flash suppressor/compensator.

The standard M4 is light under the handguards, then heavy with a cut for the grenade launcher and then heavy again. This makes absolutely no sense to me.

They wanted a heavier barrel forward of the handguards, but didn’t want to have to get new mounting rings for the M203.

SPRs have an 18” medium heavy barrel.
SPR are Stainless?

Yes.

My HBAR feels nose heavy to me.

Shouldn’t the SPR be nose heavy?

It is.

Shouldn’t a standard HBAR have more velocity because it has a 20” barrel?
Why did they lop off 2 inches?

HBAR has nothing to do with velocity. Generally, length, along with twist, and the cartridge itself have to do with velocity.

A match barrel is still as accurate whether it is an HBAR or a thin BAR?

Yes. As long as the barrel maker did a good job on cutting the chamber and rifling, a barrel will have a better chance of being accurate. Heavier barrels take longer to heat up as well as don’t vibrate as much as a light barrel, therefore groups can be more consistant, longer, than with a thin barrel.

Is a HBAR more accurate on the first round from a cold barrel?

No.

If I don’t plan on rapid fire and wanted a very accurate first round (through 5 rounds) rifle do I “need” an HBAR, or can I get away with a thin match stainless barrel?

Thin. I’ve got two 1x12 A1 barrels that with regular 55gr will shoot very well until they get hot, which is more than 5 rounds. With 52gr Match, they’ll shoot even better.

3

Wrong. Stainless barrels are easier to make more accurate. Stainless is easier to work with and easier to polish. Stainless is more expensive.

The reason more barrel makers use stainless is that it requires less in tooling and labor costs. The downside is that stainless is more expensive.

Stainless barrels will also suffer throat erosion faster than non-stainless barrels, especially under rapid fire and automatic fire.

Heavy barrels heat up slower than thin barrels and cool faster than thin barrels

Nope. Heavy barrels do heat up more slowly, but they also take longer to cool. It’s simple physics. A heavy barrel has less barrel whip and less harmonic resonance than a light barrel, so will deviate less when it starts to heat.

4

In my experience:

1x7 barrels are good with 50-80gr (80gr requires a different throat)
1x9 barrels are good for 45gr to 69gr bullets generally (some 1x9 bbls will stabilize 73, 75 & 77gr usually longer ones 20-24" bbls)
1x12 barrels are good for 45gr to 60gr bullets

Shorter barrels do give less velocity. With short light bullets, velocity is key for good fast fragmentation. If using short barreled AR for defensive use you should use fast twist (1x7) and long bullets (73, 75, 77gr) for best terminal ballistics.

Chrome-lining is good as it makes the barrels easier to clean, same for the chamber. Chrome-lined barrels are generally less accurate than non chrome-lined ones. On a fighting rifle/carbine the difference in accuracy is very little unless you’re running magnified optics you probably won’t ever see the difference.

Stainless barrels aren’t necessarily MATCH quality barrels. I’ve fired some non chrome-lined, chrome moly barrels that were more accurate than many stainless barrels. The best AR barrels made today are probably the HK416 hammer forged barrels which are very accurate and very durable. But these aren’t available from HK other than acquiring a HK416. MATCH grade in barrels means different things, usually tighter chambers, target crowns and air gauged barrels etc.

To me, for semi auto ARs lighter barrels are much more desirable. On a semi auto, go as light as .625" profile or even better an ABS carbon fiber barrel made on a 5R barrel. For a full auto, I think you should have a least a medium weight or heavy barrel. Other than full auto I think heavier barrels are at home on varmint rifles and competition service rifles (Camp Perry stuff).

Generally the shorter the barrel on a direct impingement (DI) AR the harder it is to get it to run correctly, 14.5" usually runs very well. 11.5" is a good compromise. 10.5" and shorter is probably the worse to get to run good. DI short barreled ARs are very hard on bolts, bbls and gas ports. Piston guns with short barrels typically run very well (example: 10" HK416). If you want a 10.5" gun and can’t get a HK416 I’d suggest a LMT factory 10.5" upper.

The M16A1 had a 20" version of this barrel:

M16A2/A3/A4 has this profile (aka Gov’t profile):

I don’t know why they made the 203 notch either instead of just leaving it light at the front. Possibly to make the M203 stable (can’t slide back and forth?) They made the cut thinner than the rest of the barrel to avoid having to modify the existing 203s in inventory which fit the M16A1 & A2.

The SPR uses a 18" barrel probably because it would be suppressed most if not all of the time and had a longer gas system than a M4 (longer is better, even better when suppressed). It works very well with 77gr out to 600yds+.

HBARs vs. Gov’t profile. It can be hit or miss. Some HBARs will be more accurate than Gov’t profile, in a chrome lined service grade issue rifle the difference is so little that most shooters can’t shoot well enough to see the difference.

The stiffer a barrel the more likely it’ll be accurate and consistant. Barrel length doesn’t equal accuracy as many believe it does. More length just gets you more velocity and flatter trajectories. If using iron sights shorter barrels can be harder to shoot as accurately due to the sights being closer together. The further you can get the iron sights apart the more likely you’ll shoot it accurately.

This is why for 3gun in Limited division you’ll sometimes see rifles set up like below (in Limited you can’t have optics).