velocity drop in going from 20" to 18" or 16" barrel in 308?

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Sheepdog1968

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Its for a hunting rifle. Longest shot I would ever need is 200 yards. Given max shot range, I'm happy to sacrifice some velocity for a more handy rifle. I have other hunting rifles with full length barrels. Anyone have any velocity data or an estimate. If an assumption on cartride, assume the 180 grain Rem CoreLok. Many thanks for the help.
 
If all you are going to shoot to is 200 yards, don't even worry about barrel length. A 16" would give you more than enough velocity. The main drawback of the shorter barrel is at ranges out past 500m. When you get that short you start running into issues of muzzle flash/blast, but probably not a huge deal in the context of firing a single shot at a deer.
 
I'll tell you this, I picked up 200+fps going from a 20" to a 26" in my .308........You may loose 30-40fps per inch, going backwards.
Click to expand...

This doesn't seem like a valid comparison, it's highly unlikely that you took a 20" bbl and stretched it to 26 inches so I have to think you used an entirely different barrel. We all are aware that each barrel is different unto it's self.


I have personally taken 2 different 26" 308 win chambered barrels and cut them down to 20 inchers and they lost an average of 70fps. The 308 is a fairly efficient and forgiving cartridge and does well in the shorter tubes. You can also taylor your hand loads for a short tube by using a faster burning powder.


The bottom line is yes you will lose some speed with a shorter barrel. How much ? Who can say for certain. Some barrels are faster than others given the same length.
With your maximum 200 yd limitation I wouldn't worry about it, go with whatever feels best as in balance point,weight etc.
 
Sheepdog1968 said:
Its for a hunting rifle. Longest shot I would ever need is 200 yards. Given max shot range, I'm happy to sacrifice some velocity for a more handy rifle. I have other hunting rifles with full length barrels. Anyone have any velocity data or an estimate. If an assumption on cartride, assume the 180 grain Rem CoreLok. Many thanks for the help.
Click to expand...
IMHO i think your choice of ammo has more effect than barrel length...i'am a big fan fan of short barrel rifles...years ago and many deer later my 18 1/2" Rem 742 with CoreLock's proved to me that with the right ammo short barrels will do the job out to 200 yards..hunting from ladder stands,climbers and ground blinds i find a short barrel for me is the way to go..every year for 10 year's i purchased the latest whiz bang ammo for my 30 caliber rifles (308,30-06 and 300 mag)..i even had some of reloading friends to load some of the pet loads to try in my hunting rifles...mind you some of these loads were very accurate , but they did not perform as well as corelock's on deer..what i did learn after many years using short barrels was that i had better performance using lighter bullet's (150-165 grain)...i even had my 300 mag cut dowun to 19"...yes i know that corelock's separate ,but that seems to aid in a quick kill....CORE LOCK'S rule..
 
I have a 24" Rengton 700 and a 16.5" AR both in 308. Both have 5R rifled barrels. The velocity difference between the two is just a hair over 200 FPS across all bullet weights from 110 grain Vmax to 175 grain VLD's. I wouldn't hesitate to take a shot on a deer or hog within 500 yards with either one. Even the 16.5" barrel will hold 1000 ft/lbs of energy out to 500 yards with any bullet over 150 grains.

The muzzle blast is much more pronounced in the 16.5" tube, but even with a muzzle brake blasting it out the sides it's not intolerable. I find my father in law's 20" 243 to be more bothersome. His is a 700 VTR with the top ports, LOUD!!!

If it mean anything to you I think 18" is the sweet spot between velocity and handling. POF*USA doesn't offer 18" barrels or that's what I would have gone with.
 
I say that going from a 20 to an 18" barrel will result in a negligible loss. Going from the 20" to the 16" will probably cost you something around 100 fps. Barrel length is only one factor in the velocity that a barrel will deliver. The chamber and throat cut will also contribute to velocity.

I suspect that JD went from a stock barrel to a custom barrel that had a tighter chamber. I'd say that about half of his velocity gain was due to barrel length and the other half of the gain was due to the better/tighter chamber.

Last year, I replaced the 20" barrel on my SPS Tactical with a 22" Krieger that had a chamber cut specifically for 168 SMKs. The chamber was so tight that when full length sizing the brass, it felt also as though there was no brass on the holder. All I was doing was bumping the shoulder back a little. I gained over 100 fps in velocity and I doubt that 2" of barrel alone would account for the gain.

What I'd do to minimize the velocity loss, depending on the profile of your barrel, is see if your smith can take enough length off of the breech end to rechamber the barrel and then take the rest of the length off of the muzzle end.
 
I suspect that JD went from a stock barrel to a custom barrel that had a tighter chamber. I'd say that about half of his velocity gain was due to barrel length and the other half of the gain was due to the better/tighter chamber.
Click to expand...

This is true....

I seen an artical online, where A guy started out with a long factory barrel, and cut an inch off at a time until it was only a few inches long. Wish I could find it!! Velocity, accuracy, with the same load was recorded along with working up new loads as it was cut. Was a ton of info, and very well writen.
 
Well I cannot say what the actual "drop" in velocity is, as the only rifle I have in .308 sports a 16.5" barrel. I for the most part have used plain ol 150gr Remington CL's in their standard cheap loads, since I got the rifle. I have clocked them at just over 2600fps on average.

This said, I have used this short little Ruger to reach out and drop plenty of feral hogs to ranges past 400yds with one shot. I personally like the little Compact as it seems it was built just for tucking into the bend of your arm and slipping through the brush. I have not had any issues what so ever with the 150gr CL's not preforming like they should. In fact most of the hogs pictured in the below photobucket link and albums, were taken with this rifle and the Remington CL's.
 
What I have found is there is minor velocity changes and that differing bullet types and weights will have more effects on realized velocities. Longer barrels give greater velocities, but not a great amount.

Weapon 1 - Remington Model 600 .308 Win, 18 1/2 inch 1 in 10 twist.
Weapon 2 - Springfield Armory M1A .308 Win, 22 inch 1 in 11 twist.

Firing the same rounds from each. Velocity at 10 feet.

150 grain flat base: #1 - 2335 FPS #2 - 2570 FPS = diff 245 FPS
150 grain bt: #1 - 2381 FPS #2 - 2502 FPS = diff 121 FPS
110 VMax: #1 - 2961 FPS #2 - 3105 FPS = diff 42 FPS

I can't explain why the fb and bt have that great of velocity change with the only variable being the change in bullet type. I was looking for the best accuracy with a common loading. These tests have been repeated several times and have the same results (with in 10FPS) each time.

The point is the velocity change between a 18 1/2 and 22 inch tube.

OSOK
 
If 200 yards is max, why the .308 at all? The .30-30 or 6.8SPC would be more than adequate, and still have another 50-100 yards with power levels over 1000 ftlbs of force.

Take an intermediate caliber rifle and enjoy the reduced recoil, minimal muzzle flash, and lighter weight.
 
I'll tell you this, I picked up 200+fps going from a 20" to a 26" in my .308........You may loose 30-40fps per inch, going backwards.
Click to expand...

How did you add length to your barrel?

Velocity is determined by several factors. #1 the load you are using. #2 the quality of the barrel. #3 the length of the barrel.

Comparing the velocities of different guns is useless. I've seen 100 fps difference between 2 different guns with equal length barrels with ammo from the same box. Seen 20" barrels shoot the same ammo faster than another gun with a 22" barrel. Quality barrels barrels tend to shoot faster than average barrels.

The only fair comparison is to research folks who have started with a longish barrel and chrongraphed the same loads as they gradually shortened the barrel. For a 308 this means 10-20 fps/inch most of the time.

I've done a fair amount of research on this and found the most accurate predictor is to expect somewhere between .5% to 1% difference in velocity for each inch you change barrel length. If the book says your cartridge should be getting 3000 fps then expect velocity to change 15fps-30fps for each inch you go shorter.

The length also matters. A 308 is pretty efficient at 20". As you go longer the increases in velocity tend to get smaller and smaller as you go. If you go shorter than 20" the losses tend to become greater as you get shorter. Even this is just an educated guess since every barrel and gun are a bit different

Here is a good read:

http://www.tacticaloperations.com/SWATbarrel/
 
Chronographing a 16" vs. a 20" (both RRA LAR-8s) showed us a fairly consistent 150fps drop in the shorter barrel with several different factory loads and handloads (mostly loaded with H335 IIRC) from 147gr up to 168gr.
 
Well, in any case, if 200 yards is the longest shot that you'll ever take, I'd go as short as I'm comfortable with. Just be prepared for the noise. Most that go that short, do so in order to be able to run a suppressor without getting inordinately long.

In my experience, the noise level gets to an uncomfortable level at under 20". To me this means that I can't just wear plugs. I have to be wearing muffs.
 
It should not matter at your ranges, but a shorter barrel with be harsher on you for sequential shots, noise, and recoil. Pick what you please.
 
oldpapps: that is an interesting result!

I would have expected less difference with the heavier loads (less powder to burn and more bullet dwell time in the barrel to burn it, so shorter barrel would make less difference is what I was thinking), but it was the lighter load with the least difference. Do you recall the powders used in your loads? Faster powder in the lighter bullet load maybe?
 
If 200 yards is max, why the .308 at all?
Click to expand...

What are you hunting?

I've clocked approximately 2600 FPS out a 16" S308 with brown bear 145 grain ammo. I've never had occasion to shoot a 20" gun over a chronograph, sorry.
 
My test results:

I used my new Browning X-Bolt Medallion as a comparitive rifle to see what measured difference in muzzle velocity there is between the two. The chronograph used is a Chrony F-1. Ammo was Winchester 7.62 white box factory ammo, 147 grain FMJ Q3130.

The M1A has a barrel length of 18", the Browning 22", a difference of 4".
The chronograph was placed about 10' in front of the muzzles of both rifles.

Results:

1) Browning X-Bolt:

-2781 fps
-2764 fps
-2799 fps
-2759 fps
-2789 fps

Average = 2778 fps

2) Springfield M1A:

-2732 fps
-2789 fps
-2773 fps
-2760 fps
-2740 fps

Average = 2758 fps

Difference in average between a 22" barrel and 18" barrel = 20 fps.

In addition, the Browning is a bolt action (obviously) and the M1A is semi-auto (again, obviously).

So, it looks like the ballistics are almost identical between the two. The gas system doesn't seem to rob anything from the MV and the barrel length only takes 20 fps.
Dan
 
"oldpapps: that is an interesting result!

I would have expected less difference with the heavier loads (less powder to burn and more bullet dwell time in the barrel to burn it, so shorter barrel would make less difference is what I was thinking), but it was the lighter load with the least difference. Do you recall the powders used in your loads? Faster powder in the lighter bullet load maybe?" from Random Discharge

The 150 grain loads were 42.2 grains of 748 (both the BT and FB). The 110 grain VMax were 41.5 grains of H4895. The 748 burn rate is just a tad faster than the H4895.
The 150 grain BT bullet loads are a little more accurate than the FB bullets in both weapons. The short 110 grain VMax bullets love the Remington 600 and it's shorter barrel.

OSOK
 
Thanks to all. This has been helpful. Just to answer a few questions in the responses. It will be used primarly to hunt black bear, deer, and hogs. As for hunting rifles, I already own a 30-30 (its my favorite) and 30-06. I just want another hunting rifle and figured a 308 with a shorter barrel would fit the bill. Just was curious how much velocity I might loose. Doesn't sound like much.
 
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