Perfect SBR length
 

Hypothetically speaking, if a guy was going to cut down an AR barrel and do a SBR, about what length would be desireable? Then end result would be something I would want to use for out to 100 yards, subsonic with the can.

I see some others that are about 10.5" here on the board, but want some imput as to how those guys feel about them, if they would have gone longer or shorter if they had it to do over again.

While I can't speak for the AR crowd I can say that my SIG 552-300 with a 9" barrel is quite nice. I'm not sure how much difference the barrel length will make if you do your own loading. You can tailor the load to fit the barrel length by using faster powders for shorter barrels. The most likely way to figure out whats best is to see what sort of accessories and handguards you will have and fit the barrel to them. . .

Frank

Hi. I'm new to this forum but have been experimenting with subsonics in various rifles and assembling asorted calibers of AR-15 for several years. Recenetly M1S shipped me a custom 300-221 (300 fireball chamber) 10" long, 1-8 twist pistol barrel with a standard pistol gas port location. After running Quickload calculations I had concluded that was close to ideal for 200-240 grain bullets at 1000 fps muzzle velocity and still cycle an AR-15 action. For most reasonable propellants with uncoated or moly coated 200 to 240 grain jacketed bullets in a 300-221 bullet velocity peaks between an 8" and 10" barrel length requiring more propellent for a shorter or longer barrel. I chose 10" since I can cut it down more if I want but can't extend it. Having a barrel longer than where the bullet achieves peak velocity does allow more expansion and less muzzle blast, but it can't help velocity consistancy due to bore friction and that has to hurt long range accuracy from vertical stringing. Shorter would give more muzzle blast and makes it more difficult to time and cycle the action with no other benefit than being short.

I can't say I'm an expert. This is my first 300-221 build. I have an MIS 16"1-8 Fireball carbine which shoots pretty well with Corbon 220 gn subsonics. The Corbon ammo appears to be designed for a 16" carbine. . The pistol is still under construction so I can't prove any of the above even to myself. I expect it though to give a little better accuracy than the 16" barrrel using lighter loads and still cycle an AR-15 action ok. I wouild not expect a 10" or shorter barrel to give as good of performcane as a 16" with lighter supersonic bullets.

I love my 10.5 but like amafrank said. Whatever works best for you. A subsonic 220-240g bullet dosent require much brl. I did a 9" brl for someone the other day. It worked best with his freefloat & supressor.

What kind of effective range should an owner expect from a 9"-10" barrel with heavy subsonics and a supressor? I'm looking for 100 yards on in, but after that would be a bonus as far as I am concerned.

Its subsonic no matter what the brl length is. The post below(max range 300W) should answer your Q.

What sort of effect are you looking for???? Effective range is a pretty ambiguous question and impossible to answer unless you give a few more details about what you want to do...here are a couple details that illustrate this problem...

Max range of the 220gr sierra match king slug fired at an intial velocity of 1050 fps is given by the JBM calculator as over 3000yds with a velocity of 603 fps even at that range. Would that vel be lethal with that size bullet?? I think its very possible. So we could say that the round would be effective at killing something(one) at 3000 yds. However when we look at the other figures....drop for instance, we see that at 3000yd the drop is 24,567" or 2047 feet so your angle of fire is going to be pretty critical and hitting the target at that range nearly impossible without electronic aids. So I'd say this is not an effective range for this round in reality. .....

The ballistic computer is found on the JBM site at http://www.eskimo.com/~jbm/ballistic...raj_basic.html

To further add to the confusion, I've fired my SIG and the 799 remington at 250yds with the whisper and find that range to be easily reached accurately. I think the round is capable of 300-500yds in the right hands with the right weapon. My opinion of course....

Hope that sort of answers the question.

Frank

I have a 10.5" on an AR pistol, I think its a great length for that. With pretty much any barrel length you should be able to push a 220 out to 1050fps.

Frank, you mentioned a 220gr being lethal at 650fps, a 45ACP isn't going a whole lot faster.


Jon

You are absolutely right Jon, a 45 is only doing around 850fps at the muzzle....it has a "slightly" larger footprint than the .30 cal but the same weight. I'd hate to be hit with either one of those at any range.

I've seen a number of posts on different boards in the last week or so asking questions about the "effective" range of a particular round and it got me thinking....what effect are they after and how do you rate the round. The point I was trying to make with the previous post is that the bullet from the whisper is capable of killing even at its max range but is that an "effective" range when you need radar to guide it? I see from the JBM site that the drop with the 220 SMK at 500yd is over 300 inches so we are starting to see a mortar like trajectory forming and chances of hitting are getting smaller so would 500 be a good "effective" range?

I hope it doesn't look like I'm picking on anyone....not intended that way, just wondering how to answer some of these more ambiguous questions.

Frank

The HUGE advantage of a .308 - 240g bullet vs a 240g - .45 is it's ballistic coefficient.
It's by no means flat but it's a LOT flatter shooting than the other heavy bullets.
Also easier & more efficient to suppress a .308 pistol discharge than a .45 discharge @ same velocity.