Velocity Loss with Shorter Barrel - .308 vs. '06

[ArmedBear]

I'm contemplating a second hunting rifle. My .30-06 with a 24" barrel shoots well and will do anything I want it to, shooting-wise, but doesn't carry all that well in heavy brush and steep terrain.

With a shorter barrel, is there a difference in velocity loss between the '06 family and the 08 family (.270 vs. 7mm-08, .30-06 vs. .308, etc.)?

Does the different powder used affect this? Or will both short and long cartridges in these velocity ranges lose roughly the proverbial 20 fps per inch?

 

[rangerruck]

more like 30 plus, depending on cartridge, powder, etc., a 4 inch shorter bbl, will make very little difference insid of 300 yds, use the same poi.

 

[ArmedBear]

What about 16.25" (Ruger Frontier and Compact bolties) or 18.5" (Remington 750)? Seems like, at some point, a 20" .30-30 with the new Hornady ammo would be about the same, especially if you lose 250 fps from .308, which is already a fair amount slower than '06 in factory loadings.

Some real-world testing I read says 15 fps per inch, but I have no idea what powder they used.

But is there an inherent difference between, say, .30-06 and .308, since they use whole different classes of powder at similar velocities?

The Frontier in 7mm-08 is awfully tempting, but I'm not so sure about a 16" barrel. It's pretty pricey for what it is, though, especially if it doesn't shoot much different from a 336 with an IER scope on it (another attractive option).

 

[351 WINCHESTER]

Everyone's mileage may vary. Most of my rifles are carbines and have never found them lacking for power or accuracy.

 

[Vern Humphrey]

The rule of thumb is 25 to 50 fps per inch of barrel. And that's about as right as any other SWAG. The cartridge doesn't seem to make much difference, except at the extreme ends of the spectrum. A .22 LR, for example, will usually develop max velocity around 14" to 20", while a centerfire magnum with a huge case may lose a bit more than the rule of thumb indicates.

 

[R.W.Dale]

According to Hodgon a 308 WIN loaded with Varget and a 165grn bullet is good for...... GET this

2576 FPS in a 15" handgun barrel
VS
2773 FPS in a 24" rifle barrel

So in 9" you lose 197 fps or a whopping 21 fps per inch



Now for 30-06 , same bullet and powder

15" handgun 2534 FPS
VS
24" rifle 2873 FPS

in 9" of barrel you lose 339 FPS or 37 fps per inch

I'm gonna guess that 308 bests 30-06 in velocity loss due to it's higher pressure rating.

If you'll notice at no point will a 20" 30-30 become the equal of 308/30-06 in fact given how little velocity you lose I'm suprsed carbines in these two rounds aren't more common. There literally is no point to carrying a barrel longer than 18" for deer or paper inside 300yds

 

[erict]

I've been looking around for a .308 and found similar info to krochus's post. Now my search has started for my next rifle and I narrowed it down to the Remington SPS Tactical with the 20" heavy barrel and Hogue stock. The 20" should do fine and I'll never shoot past 300 or so yards anyway. If only I could find one IN STOCK anywhere at a decent price.

 

[miko]

According to Hodgon a 308 WIN loaded with Varget and a 165grn bullet is good for...... GET this

2576 FPS in a 15" handgun barrel
VS
2773 FPS in a 24" rifle barrel

So in 9" you lose 197 fps or a whopping 21 fps per inch

While technically correct, that may not be practicaly-useful info. The range is just too great.

Sure, there is 200 fps gain going 9" from 15" to 24" with .308
However, I am pretty sure that at least 150 fps of that is gained in going 3" from 15" to 18".
The extra barrel length (beyong 18.5" for .308, 20" for 30-06) might be worth it to extend the front sight or as weight to reduce recoil, but trading handiness for relatively small increase in power...

Remington sells a popular 7600 Pump in 30-06 in 18 1/2 carbine - a great combination that works just fine, even though 30-06 would likely gain more from extra inches than .308
Unfortunately, they do not sell any other calibers in carbine length, except for 7600P in .308 that has 16 1/2 barrel (and receiver-mounted ghost-ring rear sight).

I've got the 7600P and after playing with it and looking at ballistics, I have decided to have the barrel of my other 7600 in .243 cut to 18.5", maybe even 18".

miko

 

[miko]

^^^
I have composed a spreadsheet for this particular case.
I assumed that the powder has burned completely by the time the bullet passes 15 inches, so the pressure drops proportionately to the increase of the barrel length (actually less due to chamber length but also more due to heat transfer, etc.)

The energy increase per inch is proportional to pressure (force multiplied by distance) while the velocity increases as square root of energy.

The columns are: barrel length, velocity, velocity gain over the last inch.

15 2576 0
16 2604 27.8
17 2630 25.9
18 2654 24.2
19 2677 22.7
20 2698 21.4
21 2718 20.2
22 2737 19.2
23 2756 18.2
24 2773 17.4

Seems kosher to me.

miko

 

[rcmodel]

More info:

http://www.loadammo.com/Topics/October05.htm

http://findarticles.com/p/articles/mi_m0BQY/is_1_50/ai_110470564/pg_2


rcmodel

 

[Omnivore]

Unless you're pushing the range/power envelope, like shooting Moose at 600 yards, or you're going for 4" targets at long range and you have to eek out every last quarter minute of angle accuracy in the wind, simply buy the rifle you like the best-- the one that speaks to you and says, "take me home, baby". Most game animals are terrible at math and won't notice the small differences in KE.