[Brutus]

I've got an FAL (.308) that I've been thinking about getting shortened a bit. I think it currently has about a 21" barrel plus muzzle brake. I'd like to get it whacked back to maybe 18" plus flash suppressor.

I know that the M-1A's are made all the way down to 16", but I don't want to go that short anyhow - just personal preference.

Question:

How much velocity do you give up in .308 to go from a 21" barrel down to an 18" barrel? Is there an ideal for .308 rifles, i.e. -- shortest length without giving up significant velocity?

Thanks.

:tophat:

 

[nonnieselman]

I dont think there is gonna be much diff with a 308, some of the long range guys are using a 18" barrel in 308.

 

[captain-03]

Don't really know about the .308 -- a buddy of ours and I did do some testing using .223 ARs with 2 different barrel lengths with identical handloads .. we only lost about 200fps going from a 20" to a 16"

 

[mikey67]

I'm more familiar with CETME than FAL but I believe my CETME was a bit shorter(2") than my FAL and there was no difference that I could see. Don't think you would lose much velocity!

 

[X-Ring]

A .308 is about 35 fps differance per inch of barrel.
A buddy and I had Remington .308's both with the same twist rate.
His was a 20" and mine a 24". We shot the same loads through the
chrono to see what the differance was and 35 fps is what it average out to be.

 

[Brutus]

Thanks, all.

:tophat:

 

[DBChaffin]

A little late, but here are some links that I thought might be of some interest. The first is largely theoretical with formulas and such. The latter is more real world with actual .308 barrels cut down and chronoed inch by inch:
http://www.loadammo.com/Topics/October05.htm
http://www.tacticaloperations.com/SWATbarrel/

The loss will be at least slightly affected by the particular powder and load, as some will burn more quicky than others, and it very likely won't be consistent - meaning the loss per inch will likely be greater the shorter the barrel gets. So the difference from 20" - 16" will most likely be more than from 28" to 24", for example.

And finally, the below was taken from: http://www.chuckhawks.com/rifle_barrel.htm and has numerous internal sources:

The 2001 Edition of the Shooter's Bible states, in the introduction to the Centerfire Rifle Ballistics section, "Barrel length affects velocity, and at various rates depending on the load. As a rule, figure 50 fps per inch of barrel, plus or minus, if your barrel is longer or shorter than 22 inches." However, they do not say what category of load to which this 50 fps average pertains.

Jack O'Connor wrote in The Rifle Book that, "The barrel shorter than standard has a velocity loss which averages about 25 foot-seconds for every inch cut off the barrel. Likewise, there is a velocity gain with a longer barrel." He went on to illustrate this using a .30-06 rifle shooting 180 grain bullets as an example, so his estimate was obviously for rifles in that general performance class.

Other authorities have tried to take into account the different velocity ranges within which modern cartridges operate. The Remington Catalog 2003 includes a "Centerfire Rifle Velocity Vs. Barrel Length" table that shows the following velocity changes for barrels shorter or longer than the test barrel length:

MV 2000-2500 fps, the approximate change in MV per 1" change in barrel length is 10 fps.
MV 2500-3000 fps, the approximate change in MV per 1" change in barrel length is 20 fps.
MV 3000-3500 fps, the approximate change in MV per 1" change in barrel length is 30 fps.
MV 3500-4000 fps, the approximate change in MV per 1" change in barrel length is 40 fps.

The 45th Edition of the Lyman Reloading Handbook also has a table showing Center Fire Rifle Velocity Vs. Barrel Length. Their figures apply to barrels between 20 and 26 inches in length and agree with the Remington figures. The Lyman table shows the following approximate velocity changes:

For rifles with muzzle velocities in the 1000-2000 fps range, the change in velocity for each 1" change in barrel length is 5 fps.
For rifles with muzzle velocities in the 2001-2500 fps range, the change in velocity for each 1" change in barrel length is 10 fps.
For rifles with muzzle velocities in the 2501-3000 fps range, the change in velocity for each 1" change in barrel length is 20 fps.
For rifles with muzzle velocities in the 3001-3500 fps range, the change in velocity for each 1" change in barrel length is 30 fps.
For rifles with muzzle velocities in the 3501-4000 fps range, the change in velocity for each 1" change in barrel length is 40 fps.

The 43rd edition of the Lyman reloading Handbook gave some concrete examples of velocity loss for specific calibers and loads. The Lyman technicians chronographed some high velocity cartridges in rifles with barrels ranging in length from 26 inches down to 22 inches with the following results:

The average loss for the .243 Win./100 grain bullet was 29 fps per inch.
The average loss for the .264 Win. Mag./140 grain bullet was 32 fps per inch.
The average loss for the .300 H&H Mag./220 grain bullet was 25 fps per inch.

For standard high intensity cartridges in the same test, the Lyman technicians chronographed the cartridges in barrel lengths ranging in length from 24 inches down to 20 inches with the following results:

The average loss for the .270 Win./130 grain bullet was 37 fps per inch.
The average loss for the .270 Win./150 grain bullet was 32 fps per inch.
The average loss for the .300 Sav./180 grain bullet was 17 fps per inch.
The average loss for the .30-06/180 grain bullet was 15 fps per inch.
The average loss for the .35 Rem./200 grain bullet was 11 fps per inch.

After a bunch of disclaimers, the Lyman people concluded, "The rule of thumb is that high speed, high pressure cartridges shed more speed in short barrels than do the low speed, large bore types." It's funny, but that is what I had suspected all along!

Most importantly, if you make the change, let us know what the actual numbers turn out to be if you don't mind.

 

[nonnieselman]

Mike at TacOps called me last week and he guarantees every rifle that comes out of his hands are capable of 1/4MOA. And the majority of those are with a 18" barrel.

This right here kinda shows that
"fired a three-shot group at 700 yards that measured just under two inches center-to-center. Colleli also fired a sub-1/4- inch group at 200 yards. The target is now framed and hanging in his lieutenant's office."


He suggested i go with a 24" barrel on my 300WM if i handload.. but for factory ammo use a 26"..



Now the important part,, how well with the rifle cycle with the barrel being cut down some? or does that matter?

 

[DBChaffin]

Now the important part,, how well with the rifle cycle with the barrel being cut down some? or does that matter?

Holy smokes, I completely ignored that part! I am not sure being it is a gas-piston operated FAL, but I know of an AR10 that an owner ruined by cutting the barrel down. It flat wouldn't run. Ok, "ruined" was too strong of a term. Ruined the barrel, how about that? It now wears a Krieger barrel and runs just fine and is probably more accurate too. I heard it was for sale, for what that is worth.

 

[nonnieselman]

Now the important part,, how well with the rifle cycle with the barrel being cut down some? or does that matter?

Holy smokes, I completely ignored that part! I am not sure being it is a gas-piston operated FAL, but I know of an AR10 that an owner ruined by cutting the barrel down. It flat wouldn't run. Ok, "ruined" was too strong of a term. Ruined the barrel, how about that? It now wears a Krieger barrel and runs just fine and is probably more accurate too. I heard it was for sale, for what that is worth.

I just remembered a guy at the range having all kinda problems with his M1A scout with the shorty barrel. it wouldnt cycle but every other round.

 

[Brutus]

A little late, but here are some links that I thought might be of some interest. The first is largely theoretical with formulas and such. The latter is more real world with actual .308 barrels cut down and chronoed inch by inch:
http://www.loadammo.com/Topics/October05.htm
http://www.tacticaloperations.com/SWATbarrel/

The loss will be at least slightly affected by the particular powder and load, as some will burn more quicky than others, and it very likely won't be consistent - meaning the loss per inch will likely be greater the shorter the barrel gets. So the difference from 20" - 16" will most likely be more than from 28" to 24", for example.

And finally, the below was taken from: http://www.chuckhawks.com/rifle_barrel.htm and has numerous internal sources:

The 2001 Edition of the Shooter's Bible states, in the introduction to the Centerfire Rifle Ballistics section, "Barrel length affects velocity, and at various rates depending on the load. As a rule, figure 50 fps per inch of barrel, plus or minus, if your barrel is longer or shorter than 22 inches." However, they do not say what category of load to which this 50 fps average pertains.

Jack O'Connor wrote in The Rifle Book that, "The barrel shorter than standard has a velocity loss which averages about 25 foot-seconds for every inch cut off the barrel. Likewise, there is a velocity gain with a longer barrel." He went on to illustrate this using a .30-06 rifle shooting 180 grain bullets as an example, so his estimate was obviously for rifles in that general performance class.

Other authorities have tried to take into account the different velocity ranges within which modern cartridges operate. The Remington Catalog 2003 includes a "Centerfire Rifle Velocity Vs. Barrel Length" table that shows the following velocity changes for barrels shorter or longer than the test barrel length:

MV 2000-2500 fps, the approximate change in MV per 1" change in barrel length is 10 fps.
MV 2500-3000 fps, the approximate change in MV per 1" change in barrel length is 20 fps.
MV 3000-3500 fps, the approximate change in MV per 1" change in barrel length is 30 fps.
MV 3500-4000 fps, the approximate change in MV per 1" change in barrel length is 40 fps.

The 45th Edition of the Lyman Reloading Handbook also has a table showing Center Fire Rifle Velocity Vs. Barrel Length. Their figures apply to barrels between 20 and 26 inches in length and agree with the Remington figures. The Lyman table shows the following approximate velocity changes:

For rifles with muzzle velocities in the 1000-2000 fps range, the change in velocity for each 1" change in barrel length is 5 fps.
For rifles with muzzle velocities in the 2001-2500 fps range, the change in velocity for each 1" change in barrel length is 10 fps.
For rifles with muzzle velocities in the 2501-3000 fps range, the change in velocity for each 1" change in barrel length is 20 fps.
For rifles with muzzle velocities in the 3001-3500 fps range, the change in velocity for each 1" change in barrel length is 30 fps.
For rifles with muzzle velocities in the 3501-4000 fps range, the change in velocity for each 1" change in barrel length is 40 fps.

The 43rd edition of the Lyman reloading Handbook gave some concrete examples of velocity loss for specific calibers and loads. The Lyman technicians chronographed some high velocity cartridges in rifles with barrels ranging in length from 26 inches down to 22 inches with the following results:

The average loss for the .243 Win./100 grain bullet was 29 fps per inch.
The average loss for the .264 Win. Mag./140 grain bullet was 32 fps per inch.
The average loss for the .300 H&H Mag./220 grain bullet was 25 fps per inch.

For standard high intensity cartridges in the same test, the Lyman technicians chronographed the cartridges in barrel lengths ranging in length from 24 inches down to 20 inches with the following results:

The average loss for the .270 Win./130 grain bullet was 37 fps per inch.
The average loss for the .270 Win./150 grain bullet was 32 fps per inch.
The average loss for the .300 Sav./180 grain bullet was 17 fps per inch.
The average loss for the .30-06/180 grain bullet was 15 fps per inch.
The average loss for the .35 Rem./200 grain bullet was 11 fps per inch.

After a bunch of disclaimers, the Lyman people concluded, "The rule of thumb is that high speed, high pressure cartridges shed more speed in short barrels than do the low speed, large bore types." It's funny, but that is what I had suspected all along!

Most importantly, if you make the change, let us know what the actual numbers turn out to be if you don't mind.

Thanks for that, DB.

Very informative.

 

[Brutus]

Now the important part,, how well with the rifle cycle with the barrel being cut down some? or does that matter?

Holy smokes, I completely ignored that part! I am not sure being it is a gas-piston operated FAL, but I know of an AR10 that an owner ruined by cutting the barrel down. It flat wouldn't run. Ok, "ruined" was too strong of a term. Ruined the barrel, how about that? It now wears a Krieger barrel and runs just fine and is probably more accurate too. I heard it was for sale, for what that is worth.

I just remembered a guy at the range having all kinda problems with his M1A scout with the shorty barrel. it wouldnt cycle but every other round.

Good point, however.......

The FAL is a different beast altogether than an M-1A or an AR-10 type rifle. The FAL has an adjustable gas system that allows you to choose how much gas gets bled off, and vice-versa how much gets fed into the gas tube to cycle the rifle. You can adjust it all the way from a full load of gas to cycle which will throw the brass 20 feet, or you can adjust it all the way the other way where it won't even cycle and basically functions as a straight-pull bolt action. (That's actually a pretty handy function to have if you're bench shooting and don't want to have to chase down brass all over the place.)

8)