Barrel length and velocity

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TonyAngel

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Hey guys,

I'm shooting an SPS Tactical in .308 right now, and over the course of the last 1500 or so rounds it has gone from being a one hole tack driver to being just a sub MOA shooter. I don't know if I burned something out or what. Maybe I just got overly zealous in trying to get all of the copper out of the barrel. In any case, I have a Krieger barrel coming in. It is a 26" blank, so I can have up to a 25" barrel.

I'm thinking that I'll probably go longer than 20". The question is how much longer. With my 20" tube and a load consisting of a 168gr SMK and 42gr of RL15 or Varget, I'm getting right at 2400fps in Winchester brass and 2450 in Lapua brass. The longest that I'll probably ever be shooting is 600 yards.

Is it reasonable to say that you will get around an additional 50fps for every extra inch of barrel? I'm asking because what I'd like to get is a 22" as a good compromise between being compact and getting decent velocity....or should I just go for the 24" tube. I definitely don't want anything longer than that.

I know that I can hotrod my loads, but I've been there and it's rough on the brass, generates a lot of heat and is rougher on the rifle. I'd like to keep things tame, but wind up at about 2600fps with the 168 SMKs.

Any opinions?
 
Every barrel is different velocity wise. A rule of thumb for the 308 is about 40 fps per inch.

I'd get it as long as it'll go after chambering and crowning. Then when you burn the throat of this one you can just have it set back a inch or two.
 
You do get more velocity with longer barrels. I'd say 22 is minimum in your scenario. Why not built it 24" and see how you like it. If it's too forward heavy, you can always trim it later and recrown :)
 
Yeah, even if I only get 40fps of extra velocity, at 24" that gives me as much extra velocity as an extra 1.5 to 2gr of powder. I'm gonna go with the 24" to start. That isn't overly long anyway.
 
My 308 bolt guns are both 26 inch, Rem 700 VSSF and REM 40X. They're not too long for me.

M
 
Personally I would go with 25" after all you paid for every inch of that tube, so you might as well use it!

I doubt you'll see huge velocity gains over a 22" though, since .308 is nowhere near overbore and doesn't need a long barrel to achieve near maximum velocities with most standard rifle powders.
 
I have several 308's. one with a 20" barrel, the others with 22" barrels. I've never gotten more than 30fps more velocity from the 22" guns and some loads actually shoot 5-10 fps faster from the 20" barrel.

Individual guns vary. I have a Winchester in 280 as well as a Ruger in 280. No matter which load I try the Ruger is always 75 fps faster than the Winchester. Both have 22" barrels.

The 308's sweet spot on barrel length seems to be about 20-22". Going shorter may make a big difference. Going longer is not of much help. You will have to go 26"-28" to see any noticeable gain.

Here is a good read http://www.tacticaloperations.com/SWATbarrel/ Google velocity and barrel length. You will find more info than you can use.
 
Well, I'm 5'2" tall, and what may not be too long for most can easily be too long for me. I like to keep things easy to handle, although weight isn't much of a concern.

jmr40, you're really giving me the ammo to do what I want, which is to keep it short. My initial wish was to go with 22". What you are saying pretty much duplicates what my gunsmith told me, for a .308 anyway. I just don't want to cut it short and then wish that I hadn't. 22" sure would make for a sweet rig for me.

I already have the barrel coming. I'm shooting a match this weekend, weather permitting, and I'm going to be shooting a slow load. 2450 out of my 20" tube and I'll see how much more velocity would have helped, if any. If it turns out that it isn't such a big deal, I'll just go with the 22" tube and find a good 2600fps load for it. I should be able to do that without having to get to heavy on the powder.
 
Is it reasonable to say that you will get around an additional 50fps for every extra inch of barrel?
Click to expand...

No way of knowing. I've got two match rifles, both with 26" barrels, and with the same exact load, one gets 75fps more than the other. Personally, I would go with 24", but certainly not shorter than 22". Krieger and other custom barrels tend to be fast, and it would be a shame to inflict a self-induced velocity reduction on yourself.

Don
 
I'm partial to 24" barrels. Unfortunately most of mine are 26". But I feel more at home with the 24". On the other side I've never owned a 22" so can't say how they are. I've owned 1 20" and didn't like it.
 
It's more like 25fps per inch with a .308.

At any rate I can get over 2700fps from my 24" w/168gr SMK, but it hurts my shoulder. And it shoots just as well at 2550 fps.

A 20" barrel will be stiffer. If you're not shooting past 300 yards, it will be fine. Past that and I would consider 24", and since the extra inch is free, go 25"... then you can always rechamber when the throat is eroded and have a 20" or perhaps 22" and a new chamber and a new crown.
 
From 20"-24" the velocity difference is pretty insignificant unless you are pushing the round to the fringes of its abilities. I don't think you will ever notice the difference at 300-400 yards. At 600, maybe, I'll leave that up to some long range shooters who know more than I do.

To me it comes down to how each feels and balances. As well as how much muzzle blast I'm willing to put up with. I'm a hunter, not a long range target shooter. But I do practice out to 300-400 yards. For me the 22" barrel , at least in a sporter weight gun just feels and balances better.
 
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