I have a great problem: I can't decide which of my 5.56 piston carbines should be "go to" in an emergency. Each design has positive and negative attributes.

Bushmaster ACR

Positive Attributes

+ Hammer forged free floating barrel with 20k service life;
+ Side folding stock;
+ Durable stock design with maximum adjustment capabilities;
+ Monolithic upper rail (not really a benefit, but some like it);
+ (Ambi) Reciprocating charging handle with "real" forward assist capability;
+ Effective flash suppressor;
+ Ease of bolt group disassembly;
+ Multiple QD sling ports.

Negative Attributes

- Factory BUIS are PLASTIC;
- Two position adjustable gas is only for "regular" and "suppressor" use. An "adverse setting" does not exist;
- Rifle is HEAVY and unbalanced feeling;
- Rifle lacks extensive military testing;
- Safety feels "mushy" and is not positive.

FN Scar-16S

Positive Attributes

+ Extensively tested by US Military;
+ Hammer forged free floating barrel with 20k service life;
+ Side folding stock;
+ Monolithic upper rail (not really a benefit, but some like it);
+ (Ambi) Reciprocating charging handle with "real" forward assist capability;
+ Light weight;
+ Effective muzzle brake;
+ Ease of bolt group disassembly;
+ Multiple sling ports.

Negative Attributes

- Chrome lined bore (I've grown to prefer nitrided bores);
- Rear BUIS does not lock into up position;
- Removing gas piston (after extensive firing) is difficult;
- Plastic stock latch is prone to break;
- Non standard (read: AR15) trigger components (not an issue as I have a spare set + a Geissele Super Scar);
- Non standard sling ports are prone to wear with HK style hooks and therefore require unconventional attachment solutions;
- Buttstock has nice adjustable cheek weld, but polymer feels very flimsy;
- Two position adjustable gas is only for "regular" and "suppressor" use. An "adverse setting" does not exist.

LWRC M6 Individual Carbine - Enhanced

Positive Attributes

+ Hammer forged free floating spiral fluted barrel with 20k service life;
+ Barrel weight is 20% lighter than unfluted of same diameter;
+ All gas components are NiCorr treated.
+ Unlimited pistol grip options (AR15);
+ Unlimited stock options (AR15);
+ Monoforge upper provides enough "receiver" rail for RDS and magnifier;
+ Ambi charging handle is enhanced with superior construction and oversized pivot pins;
+ HIGLY effective tuned flash suppressor;
+ Ease of bolt group disassembly;
+ Fail Zero coated BCG adds lubricity and is easy to clean;
+ 100% ambi lower (bolt release; mag release; safety);
+ 9" free float handguard system that allows user to install rail sections were needed;
+ Factory BUIS are best on market;
+ Multiple QD sling ports;
+ Lightweight for rifle with mid-heavy barrel.

Negative Attributes

- Two position adjustable gas is only for "regular" and "suppressor" use. An "adverse setting" does not exist;
- Factory trigger is awful;
- Rifle did not pass the military's Individual Carbine tests (neither did the HK 416...).

POF P-15 Minuteman

Positive Attributes

+ Hammer forged barrel with 20k service life;
+ All gas components are nitride treated or stainless;
+ Unlimited pistol grip options (AR15);
+ Unlimited stock options (AR15);
+ Charging handle is reinforced and easy to manipulate;
+ Ease of bolt group disassembly;
+ Fail Zero coated BC and chrome add lubricity and are easy to clean;
+ Roller cam pin reduces wear on the receiver, and makes operation very smooth;
+ E2 extraction technology (simple description: modified and IMPROVED HK fluting) works amazingly well for such a simple concept - all 5.56 rifles should use this tech;
+ Amazingly crisp 4.5# factory trigger group;
+ Gas piston system is essential FAL and easiest of all four designs to disassemble.

Negative Attributes

- Three position adjustable gas is only for "regular" and "suppressor" and "off" use. An "adverse setting" does not exist;
- Rifle does not include BUIS (however the front BUIS mounts on the gas block which is a positive attribute);
- Rifle is limited to MagPul "MOE" midlength handguard owing to the gas piston design;
- Rifle lacks extensive military testing.

Here's a summary analysis...

Bushmaster ACR

This rifle had unlimited potential, but Bushmaster's "engineers" (I use this term exceedingly loosely) were unable to capitalize on Magpul's vision. From everything I've read, the Remington Defense version addresses the issues I have with this gun:

1) Its way to front heavy. The QD barrel and stupid M4 profile added to this problem.

2) The rifle is too heavy overall. Remington's revised rails system and "ultra light" allow lower should help.

3) The safety is plastic and not positive. Remington uses an allow lower, and hopefully metal safety components.

All of this is academic, because I have the Bushmaster version and the RD version is not available to civilians.

FN Scar-16S

This is clearly a rifle designed for special operations troops. It has great pedigree (its FN) and is manufactured by a company I trust (again, FN). However, owing to the need for lightweight construction I worry about the durability of the buttstock assembly. Additionally, why not add 0.01 ounce of weight and have a locking rear sight? The front sight has a complex locking mechanism.

LWRC M6 Individual Carbine - Enhanced

This is likely the finest evolution of the AR15 design to date. It addresses virtually every concern I've had with AR15s. The factory trigger group is AWFUL, but this is easily remedied. I have a Geissele SSA-E in mine.

POF P-15 Minuteman

I feel like this AR15 is someone's attempt at combining DI AR15 accuracy with FAL or even AK simplicity and reliability. The net result is a simple to operate, highly accurate, and 100% reliable rifle. It lacks customization capability, but for someone wanting a KISS Piston AR this is definitely a "best buy".