Longer barrel lengths for longer ranges

D

Doub

Guest
I'm relatively new to F-class shooting, I've been practicing for 2 years with a club rifle. I'm now considering having a rifle built, but I'm getting a bit confused. When asking my fellow club members I often get pre-formatted answers, but nobody can really explain the why. And the Internet is as inconsistent on that topic as on any other. So everybody around me is using 30-32 inches barrels, but I'd like to know what my leeway is.

My objective is to be able to shoot 308 Winchester club ammunition (155gr Sierra & ~45gr load) at up to 1200 yards.

If I understand correctly that bullet can go trans-sonic at that range without a high muzzle velocity, and the longer the barrel the higher the muzzle velocity. I understand that the longer the barrel, the more it can flex and bend, but that should be relatively consistent if the ammunition is. And also the longer the barrel, the heavier it is, so there is a weight limit.

Is there something else important I'm missing? Would it be reasonable (if not a little eccentric) to add 2, 5, 10 inches to the usual 30-32?

And maybe a more fundamental question: is there a way to estimate muzzle velocity based on ammunition and barrel characteristics?
 
It's all about diminishing returns. The longer you go the less fps you gain per inch. 30-32 pretty much gets all you can use within reason. Unless your shooting a larger magnum size case to take advantage of the longer barrel but then you run into heat issues over long strings along with short barrel life. The long strings in F are a double edge sword as far as large capacity cases go. A 7 Ultra Mag with 195 Bergers would probably take advantage of of a 36" barrel nicely and have incredible performance but by the end of a 20 shot string the muzzle would probably be in the dirt from melting in half ;)
 
Doub said:
is there a way to estimate muzzle velocity based on ammunition and barrel characteristics?
Click to expand...
Speculation comes in handy.

Real life situation: Two barrels same specification, within 3 serial number range of each other, gunsmithed for two people with the same reamer. One shot 150 fps slower than the other with the same load both had commonly used for a better return.
 
Don't get carried away here....

Figure out who wins the most and ask how long the winning barrel is. Doesn't matter why!!
 
Wilbur said:
Figure out who wins the most and ask how long the winning barrel is. Doesn't matter why!!
Click to expand...

I get your point and it's a good one. But sometimes the "why" can make a difference.

When you're new to a competitive sport, it's often wise to see what the winner uses and copy his gear pretty closely until you gain the personal knowledge needed to improve on that formula.

But don't be fooled by the one local hot-shot who wins each month with a 28" barrel. Who knows? The winner may be shooting a 28" barrel because his dad wore out the throat on a really great 30" barrel, had it rechambered, and passed it down to his talented son who doesn't have two dimes to rub together.

Shooters are generally more knowledgeable about their equipment than some other sportsmen, but not always. Plus myths abound when it comes to accuracy/precision.

Following in the footsteps of a winner is a good idea, but make sure you pick the right winner to copy and be sure you're doing it for the right reasons.
 
As a rule of thumb for .308, you will gain about 100 fps for every 3 inch increase in barrel length.
Most guys I compete with are using a 30 inch barrel with a 1:10 to 1:12 twist and the majority are shooting a 175 grain bullet or heavier. The trend is to go heavier (200+ gr.) now but many are still using the 185 Juggernauts; The idea is to have a high BC bullet that does not get blown off course as easy as the lighter bullets with a corresponding lower BC.
A chamber with a longish throat will allow you to seat the bullets out further, thus allowing room for more powder without driving up the pressure.
 
308 for 1000 yards in F-Class

Palma International rules require a 155-156 grain bullet.

F-Class has no bullet weight restrictions.

155-156 grain bullets have a much shorter bearing surface than the longer 185-215 grain 308 bullets.

The 155-165 grain bullets to achieve velocity need a slower twist 1:12-1:13.5 and a tighter bore .297-.298.

The 185 to 215 grain bullets like a looser bore .3000-.3008 and a faster rate of twist 1:9-1:10.

You will achieve better velocity with a 30-32 inch barrel.

Don't handicap yourself with the wrong combination.

Nat Lambeth
 
alinwa said:
1 test is worth more than all the innernet speculation in the world, ever

http://riflebarrels.com/long-barrel-velocities/
Click to expand...

Al, that is a commendable effort by Dan, but do keep in mind, he was using a 338/378, with a capacity of well over 110 grns of suitable powder.

I have been to quite a few 250 to 600 yard Clay Break Matches this year, and I have not seen anybody shooting anything with more capacity than a typical 284 Improved Chamber that has a capacity of about 60 grns of suitable powder.

Since I am a Novis at Long Range Shooting, that is the only comment I have at the moment.
 
jackie schmidt said:
Al, that is a commendable effort by Dan, but do keep in mind, he was using a 338/378, with a capacity of well over 110 grns of suitable powder.

I have been to quite a few 250 to 600 yard Clay Break Matches this year, and I have not seen anybody shooting anything with more capacity than a typical 284 Improved Chamber that has a capacity of about 60 grns of suitable powder.

Since I am a Novis at Long Range Shooting, that is the only comment I have at the moment.
Click to expand...

All's I'm saying is......exactly what Dan was testing.

Velocity.

Dan showed that even with the huge 338-378 case there's a point of diminishing (null) return. Dan showed that velocity DOES NOT just keep going up with length, that beyond 40" the big case flatlined......

Size of the case is irrelevant (altho myself and others have done the same thing with 6BR and 308) except to prove that we are near max attainable velocity with the stuff we can buy off the shelf. I routinely chamber up the longest blanks I can get, even shoot thru the lapping bell a few times to get a velocity reading, right out the raw blank....

IMO the bestest way to soup up a 308 is YES start with a long blank but more importantly use 308 Palma cases and ramp the pressure up to PPC levels.

I have my own recipe for this and it DOES work. Provided you don't use the typical tight-butted Palma Match reamer. Taper, shoulder angle, neck/throat/leade are all up for grabs but I will state as FACT that a tight chamber will start clicking-and-sticking long before MAX velocity is reached. By MAX velocity, I mean a velocity which, while HOT, will allow one to load a case 30-50 times before it's trashed. A velocity so far "out of the book" that the book is just a starting point, but completely SAFE as long as one is careful.

But I'm done arguing the point. Y'all can go test it yerownselfs :) I've been called out enough for one lifetime. By people who REFUSE to test.....

"Never Let The Facts Mud Up A Good Theory"

LOL

al
 
jackie schmidt said:
Al, that is a commendable effort by Dan, but do keep in mind, he was using a 338/378, with a capacity of well over 110 grns of suitable powder.

I have been to quite a few 250 to 600 yard Clay Break Matches this year, and I have not seen anybody shooting anything with more capacity than a typical 284 Improved Chamber that has a capacity of about 60 grns of suitable powder.

Since I am a Novis at Long Range Shooting, that is the only comment I have at the moment.
Click to expand...

I guess it's kinda' like a big lathe.......you can make bigger chips than me but in the end the same rules apply, "keep the heat in the chips"


Just like with a lathe, the big 338-378 case follows the same rules as a smaller case
 
You must log in or register to reply here.
Back
Top