thoughts on velocities for 22 in barrel .308

[cacoltguy]

My rifle is a Weatherby Vanguard Sub-MOA in .308 Win with a 22 inch barrel (1 in 10 twist). I've been reloading for this rifle for about 6 months now with decent results out to 300 yards (1/2 MOA if I do my part) I'm using Nosler brass, 175 gr Sierra Match Kings, Fed Match primers and 42.7 gr of IMR 4895. Soon however I intend to shoot this rifle out to 800 yards and participate in some long range matches with my local club. My question is regarding what kinds of muzzle velocities should I be getting out of this barrel to effectively shoot at these longer ranges. I realize that a 22 inch barrel isn't what most people would consider ideal for 800+ yard shooting with a .308, but it's what I have at the moment. Right now with my loads, I'm getting around 2590 fps muzzle velocity. Just curious if some of you more experienced shooters think this is adequate to send a 175gr bullet out to those ranges with a 22 in. barrel.

 

[briang7511]

A friend of mine uses a savage mod 16, 24in stainless med weight barrel and by no means is he an experienced shooter (first time at this distance) but with a spotter to see where you are hitting we had him hitting the 1000yd gong. he was using Fed GMM 168gr factory ammo not the best ammo at that distance. My gun likes the 155gr amax, which is my suggestion and what i shoot at 1000yds, to get some more velocity out of that short barrel. It appears from the groups you are getting now you have found a load your gun likes before changing to a different load its worth trying them out at the longer distances.

 

[Slamfire]

I was squadded next to an Army Reservist who was shooting a short barreled M700 (I think it was 22 inches) and current Army Longe range ammo loaded with 175 SMK's. This was at 600 yards.

He was not happy about the low velocities and thus wind sensitivity he had on target.

You can still shoot very well but expect more left to right movement due to wind changes.

I have shot 175's at 600 yards and 1000 yards with 22" M1a's. Good shooters can shoot outstanding scores with 22" barrels, I have seen it. I can no longer see a post well enough to shoot HM at long range with the things, but it can be done.

 

[cacoltguy]

That's my concern Slamfire (Wind and big time bullet drop) I wasn't too worried about the velocity since my loads are pretty close to Federal Gold medal Match in terms of velocity (about 20 fps slower) However it seems like everyone shooting .308 long range is doing it out of 26 inch barrels and getting around 2800 fps. I certainly believe my setup is capable of doing well but I still wonder if I need to squeeze out more muzzle velocity somehow.

 

[briang7511]

http://www.snipercentral.com/boltdmr.phtml

read this article, i remembered reading it about a year or so ago. they build a rifle and cut the barrel to 16.5 in and only lose about 70fps from factory stated 2875fps hsm ammo. not sure what barrel length hsm used to get the velocities but 16.5 is short.

 

[jmr40]

According to my load manuals that is a pretty light load. That is max for H4895, but IMR 4895 shows 45 gr as max. They show 2647fps as the velocity you should be getting from a 24" barrel so you are pretty close to what the book says you should be. You should be able to get pretty close to 2700 fps with a max load or IMR-4895. In a 308 you'll only gain or lose 15-25 fps for each inch of barrel you lose or gain.

Another thing to remember is that no 2 barrels will shoot the same. I've seen 130 fps difference between 2 guns with equal barrel lengths when shooting ammo from the same box. You're about 60 fps slower than what the book says. If you allow for 2" less barrel it appears that your barrel is shooting to almost exactly the speeds it should be.

If you don't already use this site it is a good source for loads

http://hodgdon.com/basic-manual-inquiry.html

You might also want to try another powder, some of the Alliant powders have a good reputation and they show some 175 gr 308 loads at 2700+ fps.

http://www.alliantpowder.com/reload...?gtypeid=2&weight=175&shellid=80&bulletid=251

 

[jmr40]

Here is a link I just found on another site this morning. A very good read on loading the 308 for long range shooting

http://www.6mmbr.com/308Win.html

 

[HoboCoastie]

I read an article somewhere that said you lose about 20-25fps mv for every inch of barrel you lose. Most ammo I believe is tested using a 24" barrel?

Now I've heard that when the bullet drops below super sonic speeds (1129fps at sea level and 70°F), it causes it to de-stabilize and wobble and severely affects accuracy...so the theory is you want to know that your bullet will still be exceeding super-sonic speed at impact.

Using this as a quick guide (.308 on Page 3)...

http://www.hornady.com/assets/files/ballistics/english-ballistics-chart-2010.pdf

Now this is VERY rough math, but you can see the 178gr is down to 1558fps at 500yds which puts you at about 1508 or so with the 22" Going from 500 to 800 yards you're going to lose another 500-600fps with a normal barrel, so that's definitely going to have you de-stabilizing before impact. And also notice that the Hornady bullet is about 500fps faster at the muzzle than what you're getting with your load.

The best I could tell you is try it...but I think you're going to find poor groups for target shooting at those ranges.

 

[briang7511]

http://www.hornady.com/ballistics-resource/ballistics-calculator

as long as you know your muzzle velocity you can use this ballistics calculator to see if you are still above super sonic speeds

 

[cacoltguy]

Thanks for the info guys. I did plug my data into the JDM ballistics calculator and I am getting close to sub-sonic at 800 yards. My current load seemed to give me the best group at 100 yards but honestly groups with loads 1 grain hotter didn't seem to be much worse. Perhaps some retesting is in order.....

 

[Haxby]

Might want to run those numbers again. That load should be well above the speed of sound at well past 800 yards. As far as accuracy at that range, try it and see.

 

[cacoltguy]

Haxby I suppose your right but I guess I'm not sure what most people would consider well above speed of sound. At 800 yards my calculations give me 1384.2 fps, which seems adequate, but at 1000 its down to 1186.9 fps, which is barely above the line of speed of sound if I'm not mistaken. My first match will be 800 yards but I'm sure I'll be shooting 1000 eventually. I shoot at sea level and the temp is about 60 deg F. on average now. Some of the advice I have read and heard is that 1200 fps is a better cushion at this range. I agree that the only way to know is to shoot and see and I will definitely be doing that.