308ar Barrel length question

[wildfowler]

Using reloads and a suppressor could someone give me an approximation of how much barrel length it takes to get a typical 168 grain hunting bullet up to 2600 FPS.

I know it won't be exact and your results will vary from barrel to barrel, ect.

I'm just curious to know what might work. Thanks.

 

[FMJBT]

Should be able to hit 2600 FPS out of an 18" barrel. Possibly a 16", but the loads will have to be pretty hot. If you can find some Hodgedon CFE-223, that will give a bit more velocity than most other popular powders for 308 like Varget or 4895.

 

[wildfowler]

Thanks.

The only thing I've got to go on is Federal gold-medal match 168 out of a 16 inch DPMS. Only got 2350-2400 from that factory ammo.

I don't know why, but I was thinking it might take over 20 inches plus suppressor to do this.

 

[FMJBT]

Wow, that's really slow even for FGMM. My 16" 308 AR is pushing the heavier 190 Nosler CC's at around 2500 FPS using CFE-223.

 

[wildfowler]

190 at 2500. Compared to my results your barrel must be really fast?

Thanks.

 

[BCP]

My DPMS SASS barrel was slow as well. I had to load very hot to get a 168 near 2600fps

If velocity is an issue switch to a different bullet. You can gain some speed with a lighter bullet or have a heavier higher BC bullet going 'slow and steady'

Also your chrono readings could be off. I would not take them as gospel until you get on the range and measure your drops to say 400 or 600 yards if possible

 

[FMJBT]

190 at 2500. Compared to my results your barrel must be really fast?

Thanks.

I calculated mine using the drop I was getting at 650 and 1000 yards, pretty sure it's accurate to within about 50 FPS. My barrel is a Rainier Arms Select, which are made by Black Hole Weaponry. I would imagine that their 3 groove polygonal rifling probably contributes to that velocity. The Hodgedon CFE powder is known for getting higher velocities than most other powders as well.

 

[Three57]

I got a 15 round average of 2558 with HSM 175 SMK M118LR equivalent with my 20" KAC ER. I also got roughly the same with my reloads with hornady 178 BTHP and ramshot tac. 168s should be quite a bit faster than 2600 with a 20" barrel. Sorry, but I haven't shot or tested any 168s. Hope this helps.

 

[Howa4AU]

My 20" Lilja barrel gets just over 2,600 with 168 FGMM.

 

[wildfowler]

Thanks guys. I have a future purchase in mind and trying to consider a few things ahead of time.

 

[wildfowler]

I would imagine that their 3 groove polygonal rifling probably contributes to that velocity.

That's interesting. Does this imply that there are certain types of rifling that are going to produce higher velocities?

Does anyone know if there are certain rifling types that are known to lower velocities?

Thanks.

 

[Jrb572]

This is a good article about barrel length.


SWAT Article BARREL LENGTH

 

[Cold_Bore_88]

My SIG 716 gets them out pretty quick 2600+. It has a 16". I just shoot hornady match 168 BTHP or AMAX.

 

[Cold_Bore_88]

I calculated mine using the drop I was getting at 650 and 1000 yards, pretty sure it's accurate to within about 50 FPS. My barrel is a Rainier Arms Select, which are made by Black Hole Weaponry. I would imagine that their 3 groove polygonal rifling probably contributes to that velocity. The Hodgedon CFE powder is known for getting higher velocities than most other powders as well.

I think the rainier arms barrels are very under rated. I have gotten sub MOA groups with 62 gr XM855 out of my 10.5" SBR.

 

[stu2]

I agree. I get same results. I also get sub moa with 55gr xm193 ammo.

I think the rainier arms barrels are very under rated. I have gotten sub MOA groups with 62 gr XM855 out of my 10.5" SBR.

 

[redhooker]

With a 16 inch CL bbl my LMT runs ~2550 with the 175smk 118LR as well as my hand loads. No pressure signs I believe I could easily hit 2600 without issue if I wanted to. 168s should be easier to hit that speed. That was chrono'ed as well as confirmed at distance of 850 yards with a 9.3 mil come up. So I would say 16 inch would do what you need it to.

 

[Unknown]

Some barrels are simply faster than others. Even when coming out of the same factory, on the same series of rifles, there can be a variance.

I have a DPMS LR308 with a 24 inch barrel having a Miculek flash suppressor on it, and it generates about 25 fps more velocity than a 26 inch bolt gun (TRG22) does, when using the same ammo. If you would have asked me to guess before shooting them, I would have bet money that the longer bolt gun would have generated more velocity. Twist rate is about the same for both rifles, but the TRG has a chrome bore. I always thought Chrome bores had less friction..maybe less friction builds less pressure, hence less velocity. It will take someone with greater understanding of all this than I have to figure it all out. I just accept it and deal with it.

 

[JR1]

I get just under 2500fps with 168 FGMM from my SOCOM 16.

My 18.5" gas gun with a 762SD only gives me 2535.

My Rem AAC-SD gave me 2660 with the same can (back when the barrel was 20").

I just chalk it up to each barrel being different.

 

[wildfowler]

I wound up buying a 20 inch black hole weaponry 308 barrel. I'm using a Lapua brass with 165 grain Barnes TSX hunting bullet and CFE223.

My initial (but not yet confirmed) OCW testing is showing an accuracy node at 47.5 grains with chronograph readings just under 2800 ft./s.

CFE223 must be temp sensitive because I got just over 2800 last week when the temps were a little warmer.

I've got to say this has exceeded my expectations greatly.

Hogs, consider this your formal notice.

Thanks for the suggestions on barrel type and powder.