Question about .308 and 7mm-08 barrels

[bydhrpr]

What can one expect in the way of bullet velocities when comparing 22 inch and 24 inch barrels in both .308 and 7mm-08? Is it worth going for the longer barrel?

What about Encore barrels? What type of accuracy can one expect from an Encore in each of these calibers? I am also considering a Remington model 700.

I would appreciate your thoughts as I am looking for an accurate "carry gun" that is effective on deer out to 500 yds. I plan on topping my new rifle with a Leupold 4.5 x14 50mm. I would love to hear what anyone else may use, as a compact and light set up for deer sized critters out to this range.

 

[bastover]

Well every barrel is different. Rule of thumb is 40-50 fps per inch of barrel loss. example 24 in barrel 2900 fps. 22in barrel 2800 fps. Like I stated before all barrels are different though. To me a good carrying deer rifle for 500 yd shots would be a 7mm-08 with a #5 fluted barrel at 23 inchs long 1-9 twist in a htg mcm stock or a b&c medalist stock. I tend to lean toward a heavy rifle. Thats just me. 308 has killed a many of deer and I have a good friend who hunts with one along with my dad. I would stay with the same set up as well. Encore barrels I would not shoot past 100 yards never had one that would shoot good. Hinge pin shifts in the frame causing point of impact shift.

 

[Bart B]

Well every barrel is different. Rule of thumb is 40-50 fps per inch of barrel loss. example 24 in barrel 2900 fps. 22in barrel 2800 fps.

That's a different "rule" than I've heard of. SAAMI states that for two barrels whose bore and chamber have identical dimensions and shooting the same lot of ammo in barrel lengths from 20 to 26 inches, the differences are:

Muzzle velocity from 2000 to 2500 fps, 10 fps per inch

Muzzle velocity from 2501 to 3000 fps, 20 fps per inch.

I've seen about 30 fps per inch between barrels with the same bore and groove dimenions chambered with the same reamer shooting the same .308 Win. load in 26 to 32 inch barrels at muzzle velocities from 2800 fps to 3100 fps.

 

[bastover]

Yea every barrel is different. I guess it depends on where you live and atmospheric pressures and humidity.

 

[Bart B]

Yea every barrel is different. I guess it depends on where you live and atmospheric pressures and humidity.

Those two variables have virtually zero effect on muzzle velocity. Neither effect internal ballistics in any way that would be measureable.

 

[bastover]

If you say so.

 

[Bart B]

If you say so.

Well, SAAMI says so. I just echoed what they state. That aside, all the atmospheric conditions effect how the bullet flies down range.

Stop and think about how there's any way the geographic location, barometer reading and humidity could effect how powder burns inside a virtual air-tight container. Then try to find any reference from any source that states there is an effect. Powder temperature will definitely make a difference, but smart people make comparisons with powder at the same temperatures.

The following SAAMI document lists the conditions for testing ammunition for pressure and velocity:

http://www.saami.org/specifications_and_information/publications/download/206.pdf

Page 94 and 95 lists the conditions for testing ammo. The only environmental condition is that ambient temperature be from 60 to 80 degrees F. Nothing about geographical, barometric or humidity requirements.

That whole document's got information that usually surprises folks.

 

[bastover]

Guess my chrono was lying to me. Guess Dan Liljas article about the Ballistic Effects of Altitude Tempature and Humidity is useless as well

 

[Scout1]

Guess my chrono was lying to me. Guess Dan Liljas article about the Ballistic Effects of Altitude Tempature and Humidity is useless as well

Thats EXTERIOR BALLISTICS not interior ballistics which is what we are talking about here. Barrel length, powder burn rates, and chamber pressures and ambient (POWDER) temperatures are directly related to bullet velocity.

Do yourself a favor a Google Density Altitude

 

[bastover]

What we are talking about is 7mm-08 or 308 rifle barrels and what lengths. I simply stated that a rule of thumb if you will was 40-50 fps per inch of barrel loss. A gentleman stated it was different that SAAMI states for a rule of thumb. Well I reposted that it may just be difference in atmospheric conditions and humidity causing the difference In the vel. All this inside ballistics come from him. I know we are not reading the vel. inside the barrel the bullet comes out of the barrel. I read SAAMI and right off the bat they state depending on componets equipment TEST CONDITIONS may cause different results. You gentleman have a nice day.