Cameron,
Just some food for thought:
Barrel length has nothing to do with accuracy. Depending on ammo, etc. the difference between a 16" barrel and a 20" barrel is only around 100 feet per second.
Velocity with 3 different barrel lengths
using 5.56 M193
55 grain ball
14.5" barrel - 3064 feet per second
16" barrel - 3132 feet per second
20" barrel - 3259 feet per second
With this ammo, chrome lined barrels, the velocity gained from a 16" barrel to a 20" barrel is 127 feet per second......
for each inch of extra barrel you are gaining 31.75 feet per second in velocity. The velocity gain isn't as great as many may have thought.
18"
-You can use a rifle length gas system on a 18" barrel (slightly smoother than a mid-length gas system). Some companies use an intermediate gas system (between a mid and rifle length gas system on 18" barrels)
-Slight velocity gain (approximately 50 - 75 feet per second - depending on barrel, ammo, etc.) at the cost of added length and added weight (on most stainless barrels a 18" barrel will weigh 6 to 8 ounces more than the exact same 16" barrel)
16"
-Shorter, lighter, more compact, thus making it a little easier to shoot from unconventional shooting positions.
-Most will use the mid-length
-Slight loss in velocity
When talking about the different gas systems on a 18" barrel, think about the distance from the gas hole to the end of the barrel. The longer that the bullet is in the barrel
after the bullet passes the gas hole, the more gas that is getting pushed back through the gas tube. The end result is a sharper recoil impulse.
This is why on a 16" barrel, a mid-length gas system is slightly smoother than a carbine gas system.
A mid-length gas system on a 18" barrel is much like a carbine gas system on a 16" barrel, the recoil impulse is going to be sharper due to the longer dwell time. The distance from the gas hole to the end of the A2 flash hider on a
18" barrel with mid-length gas system is approximatley
9.5". The distance from the gas hole to the end of the A2 flash hider on a
16" barrel with carbine-length gas system is approximatley
9.5".
A intermediate gas system on a 18" barrel is simular to a mid-length gas system on a 16" barrel. The distance from the gas hole to the end of the A2 flash hider on a
18" barrel with intermediate-length gas system is approximatley
7.5". The distance from the gas hole to the end of the A2 flash hider on a
16" barrel with mid-length gas system is approximatley
7.5"
The rifle length gas system on the 18" barrel will be the softest shooting of the 3 gas systems listed. You will find that most run and gun rifle competitors and 3 gunners prefer the rifle length gas system on 18" barrels because of it's softer recoil impulse which aids in faster follow up shots.
Give me a day or two and I'll post an article that has the weight of several stainless match 16" and 18" barrel weights, if you're intrested in them.
As gotM4 already pointed out, take a hard look at the BCM SS410 stainless barrels (they come in 18" rifle length gas system and 16" mid-length gas system and are 1/8" twist). I'm currently running a BCM 16" SS410 on my run and gun carbine.
You had mentioned White Oak Armament SPR profile 18" barrel. I used one on a competition gun several years ago. Great barrel, but it was on the heavy side (for my preferences, based on my body size and shooting style) and went back to a 16" barrel:
http://www.m4carbine.net/showthread....ighlight=White
Some good info on 1/7" vs. 1/8" twist rates can be found here: http://www.m4carbine.net/showthread.php?t=29302
As Failure to Stop already pointed out, the PWS is an excellent comp. There are better comps on the market, but they come at the cost of added length, added noise, added blast, etc. I've been running the PWS FSC556 and DNTC comps on my work and competition gun for the last couple years. The FSC556, DNTC, and Todd's Tiny One all have identical blast chambers and have identical performance in reference to reducing muzzle flip. Here are a couple articles on the PWS DNTC and Todd's Tiny One:
03designgroup |
Primary Weapons System Todd's Tiny One Compensator 
03designgroup |
Primary Weapons System (PWS) Custom DNTC Compensator
The Surefire 556k muzzle brake is an excellent brake and does a slightly better job at reducing muzzle flip. Down side is that it adds approximatley 2.25" to the overall length of the barrel and it's noticeablly louder than the PWS comps. I use the Surefire 556k on guns that I use my 556k suppressor on.
You mentioned using the the rifle matches and 3 gun competitions and using the Leupold Mark 4 3.5-10x40mm LR/T M3 Illuminated Scope. I like this scope on a bolt gun, but I have found this scope is long, heavy, and cumbersome on an AR that is used for run and gun competition. If you are wanting to get up around 10x you may want to consider a shorter and lower profile optic like the Night Force 2.5 - 10x, Leupold MKIV 2.5 - 8x (same scope that edwin907 has on his rifle .... Leupold makes the same scope in a 3-9x, I would not recommend this scope due to it's shorter eye relief), or simular optics.
Hope this helps
Happy Holidays
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Trying to make a decision about an 18" SPR barrel
FFL/SOT armorer
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