24" vs. 20" barrel for target shooting

[peacebutready]

In a caliber like .308 for example, a rifle with a 24" barrel will reach out further than one with a 20" barrel. How much difference in yards would that be assuming all else is equal?

How much more distance does one lose if barrel length goes down to 18"?

 

[Sam1911]

It's a velocity change, not a distance change, and the distance you can accurately shoot with a bullet that started at 3,000 fps from the 24" barrel vs the same bullet that started at 2,900 or 2,800 fps from the 18" barrel is going to depend on a lot of factors related to your ability to accurately figure the range and dial in your scope.

Just about impossible to say at what range you may no longer be able to hit a target, simply because of the velocity drop going from one barrel length to another.

Said another way, if you can hit it with the 24" barrel you can with the 18" one too but you'll need to dial a few more clicks up to compensate for the lower velocity.

 

[horsey300]

In a caliber like .308 for example, a rifle with a 24" barrel will reach out further than one with a 20" barrel. How much difference in yards would that be assuming all else is equal?

How much more distance does one lose if barrel length goes down to 18"?

I would include that a 20" bull barrel will steady better than a 24" pencil barrel, weight, balance, and heat (on an imperfect setup) play a larger role than barrel length, rifleshootermag is good about posting velocity vs barrel length on various cartridges for reference points, but honestly, especially handloading, the actual difference in achievable yardage within the same cartridge is rarely enough to matter and often most discernible by the trigger man's capabilities in dealing with the extra blast.

 

[GooseGestapo]

All things equal, the 20" bbl will be stiffer, likely giving slightly greater precision (i.e: tighter groups). However, the longer barrel with higher velocity may be better at longer ranges due to slightly less wind drift.

Bench rest shooters popularized the 20" bull barrels to take advantage of slightly greater stiffness. However, before F class (bench rest "from the grass"), most competitions were 300yds or less.

So; my "unqualified" opinion is that for 300yds or less, or from a tree stand or such for hunting, the 20" is the best choice, for 500yds and over, 26-27" or longer is preferred. 400-600yds, whatever floats your boat!

My "service rifle" AR15 wears a Wilson stainless 20" bull barrel in keeping with CMP and NRA rules. In practice, I've Shot 100/10X on a 600yd target at CMP Talladega. However, this is on electronic targets with "spotter" shots and a not particularly challenging range as far as windage is concerned.
YMMV.

 

[Llama Bob]

In a caliber like .308 for example, a rifle with a 24" barrel will reach out further than one with a 20" barrel. How much difference in yards would that be assuming all else is equal?

How much more distance does one lose if barrel length goes down to 18"?

"Reaching out" means different things to different people. Just to give you an example, let's do a .308 with a 168gr tipped match king loaded to SAAMI max length and pressure with 44.1 grains of IMR 4895. This is reasonable but not super high tech long range load. Velocities:

24 inch: 2790 ft/s
20 inch: 2690 ft/s
18 inch: 2630 ft/s

Now, as far as reach, the first reasonable metric is max point blank range - this is how far you can "reach out" without requiring POA adjustments. For a +- 3in MPBR:
24 inch: 294 yards
20 inch: 284y
18 inch: 278y

Another metric would be supersonic range:
24 inch: 1200 yards
20 inch: 1150y
18 inch: 1100y

Yet another metric would be windage per 10MPH of cross wind at 1000y:
24 inch: 88 inches of windage per 10MPH crosswind @ 1000y
20 inch: 93in
18 inch: 97in

As you can see, the differences are pretty subtle. Certainly one would happily take a 10% reduction in windage moving from a 18 inch to 24 inch barrel, but it's not THAT big a deal. Similarly, there's some extra supersonic range but it's out past the ranges most people have access to shoot. So if you have other reasons for wanting a short barrel there's generally not much downside to it.

 

[Bart B.]

When rifle shooters finally realize that free floating barrels of any length, weight and profile all whip and wiggle exactly the same from shot to shot moreso than any other part of the system, they'll know that long skinny barrels cluster bullets as tight as short fat ones. We all shoot only one barrel per group, don't we?

Of course, heavier rifles hold steadier and their point of aim will wander around in a smaller area about the target. But the shots cluster about the place on target where the sight was when the rounds fire. A poor marksman shooting a 1/2 MOA rifle-ammo getting all shots aimed inside a 3 MOA area on target will shoot a 4 MOA group. Had he got those shots off in a 1 MOA area, the group would be 2 MOA.

I've seen nothing that proves flimsy rifle barrels are less accurate than stiff ones. Besides, a 22" featherweight, 26" varmint and 30 inch heavy match barrel can have the same stiffness and vibrate at the same resonant frequency.

 

[WestKentucky]

Your consistent accuracy will depend more on the rounds chambered than the barrel length. Loads optimized for each barrel length will shoot better than random off the shelf ammo, especially if your bullet starts slowing down while still in the tube like is common with .300bo guns.

 

[Llama Bob]

When rifle shooters finally realize that free floating barrels of any length, weight and profile all whip and wiggle exactly the same from shot to shot moreso than any other part of the system, they'll know that long skinny barrels cluster bullets as tight as short fat ones.

Where do you get that they wiggle "exactly the same"? If I remember right the deflection of a cantilevered beam is proportional to the cube of the length.

 

[Bart B.]

...exactly the same from shot to shot... for each barrel and a given load. Different barrels can vibrate at different frequencies. A given barrel vibrates the same amount (amplitude) and direction for each shot in the same rifle configuration. The amount and direction can change as rifle configuration changes for a given barrel.

 

[jmr40]

Every rifle barrel is different. A 24" barrel on rifle "A" isn't necessarily going to shoot faster than a 20" barrel on rifle "B". A difference of 25-50 fps between 2 different guns with the same barrel length is common and over 100 fps isn't unheard of. I've seen individual guns with 20" barrels match or beat the speed from individual 24" guns. I've also seen some 20" guns shoot 150 fps slower than some 24" guns. But the difference is in the individual barrels, not the length.

There are dozens of folks who have taken a longish barrel, measured velocity and cut the barrel shorter in 1" segments and measured velocity as they go and have posted the results. With 308 class cartridges 10-20 fps/inch of barrel is the norm. Depending on the powder and bullet used this can vary some. Heavier bullets tend to show more velocity loss from short barrels than light bullets in my observation. But that number is only valid if you start with a known speed and cut the same barrel down. FWIW my 18" 308 shoots the same loads about 60 fps slower than one of my 22" guns. About 40 fps slower than the other. Unless you are planning on 1000 yard shots an 18-20" barrel should be enough. For 1000 yards you probably need more than 24".

The deciding factor should be how compact you want the rifle, how it looks and balances, and how much noise you want to deal with. Shorter barrels are louder. For a target rifle fired from a rest there isn't much downside to going with a longer heavier barrel. If you need to carry it in the field, get it in and out of vehicles or fire from enclosed spaces such as box blinds while hunting then shorter barrels are a plus.

 

[Bart B.]

22" skinny M14NM barrels have shot virtually as accurate as 26" heavy bolt gun barrels in 1000 yard matches. Limited mostly by the M14's 4.5 pound trigger pulls and a post front sight. Both shooting 308 Win hand loads.

 

[Bart B.]

Here's SAAMI's test results cutting an inch off the same barrel using the same ammo so only barrel length was the variable for the different cartridges used

 

[Bart B.]

Delete

 

[salt&battery]

I realize shorter barrels are stiffer but for me I always seem to shoot a 24" bolt gun better then other lengths. maybe I can steady them better

 

[Newtosavage]

My most accurate rifle ATM is a Ruger Hawkeye 77 with an 18.5" pencil barrel (a 7x57 RSI dropped in a synthetic stock). It weighs 6.75 lbs., scoped.

Just shot a 2" group at 300 yards on Sat. morning with it (2-7x scope), and have fired many sub-MOA 5-shot groups with that rifle of late... One you could have covered with a nickel.

Go figgr.

I have a Savage 12 FV in .308 on the way that should give it a run for it's money though. 26" heavy barrel. We'll see what it can do.

 

[Bart B.]

Newtosavage, Whats the size of the biggest groups? All groups count in accuracy assessment, don't they?

I can imagine a benchrest competitor shooting several groups for a 5-shot match but submitting only the smallest one as his entry.

I figgr all groups range somewhere between zero and some units of measurement. That ain't hard to figgr; it's reality. Celebrating small groups is popular, but they're only about 10% of what happens. Big groups happen just as often.

 

[stoky]

I got pretty close to 40fps/inch with 150gr .308s cutting a Savage barrel from 22" to 18".
didn't do it an inch at a time

 

[Newtosavage]

Newtosavage, Whats the size of the biggest groups? All groups count in accuracy assessment, don't they?

I can imagine a benchrest competitor shooting several groups for a 5-shot match but submitting only the smallest one as his entry.

I figgr all groups range somewhere between zero and some units of measurement. That ain't hard to figgr; it's reality. Celebrating small groups is popular, but they're only about 10% of what happens. Big groups happen just as often.

What I meant were larger groups from different loads. The sub-MOA groupings are easy to repeat if I use the same loads. I have no idea why I'd want to use the poorer grouping loads once I've determined what they are...

With my best hand loads, MOA is not cherry picking at all. It's routine.

 

[Newtosavage]

I got pretty close to 40fps/inch with 150gr .308s cutting a Savage barrel from 22" to 18".
didn't do it an inch at a time

Compared to published velocities, I'd say my experience is similar.

 

[salt&battery]

What I meant were larger groups from different loads. The sub-MOA groupings are easy to repeat if I use the same loads. I have no idea why I'd want to use the poorer grouping loads once I've determined what they are...

With my best hand loads, MOA is not cherry picking at all. It's routine.

he does not mean for you to use loads that group bigger he means your good loads that get small groups might shoot bigger groups. Bart B has tons of experience and has seen a lot to base opinion

 

[Gtscotty]

Recorded velocities for a .308 Win cut down from 28" to 16.5" :

http://rifleshooter.com/2014/12/308...ato-barrel-length-versus-velocity-28-to-16-5/

Whether the velocity loss matters depends entirely on your intended use. Long range shooting in high wind... It probably matters. For most types of hunting... I'd say a 20" barrel is about perfect for a .308.

 

[Bart B.]

he does not mean for you to use loads that group bigger he means your good loads that get small groups might shoot bigger groups.

I mean he will shoot bigger groups. Half are around average, one fourth are big and one fourth small.

The more shots in each group, the closer to one size they'll all be.

 

[Wreck-n-Crew]

I mean he will shoot bigger groups. Half are around average, one fourth are big and one fourth small.

The more shots in each group, the closer to one size they'll all be.

I have some questions on that and a bit of a revisit on the subject of shots in a group.

barrel: 24"
load: One set of test loads using a 10 shot group averaging 1.3"
notes: 7 of the 10 were within .65" and the remaining 3 being responsible for the larger group size/

Does the 10 shot group tell you more than 2 five shot groups? Or is one group (even though it contains more shots) still not enough to go on as far as figuring an average on that barrel in that gun? If not how many of what group size more reflect the capabilities of that particular barrel and gun as far as average groupings?

 

[Bart B.]

If one shoots 3, 5, 7 or 10 shots per test group, there's a 95% probability that all groups will be somewhere in the following percentage spread of what one group's extreme spread is:

3 shots, 41% to 244%
5 shots, 66% to 153%
7 shots, 74% to 134%

And you don't know if that single, few-shot group fired is at the large end of several or the small one. Ten or twenty shot groups are better:

10 shots, 81% to 116%
20 shots, 89% to 112%

If you've ever seen the results of a 100 yard benchrest match on a weekend, you'll note each person shoots 5 to 10 five-shot groups per day. There's a 5X or more spread from the smallest to the largest group shot by each of the top ten on the score board. Bigger spreads for the ne'r-do-wells. The first group shot each day per competitor is seldom his smallest; largest, either, for that matter. Single group records are under .03" but record aggregates (average) for several groups have biggest ones in the .200" to .300" range at 100 yards. These rifles are shot free recoil virtually untouched by humans.

Group shooting equates to rolling a pair of dice. Simple statistics. Odds of getting a small number are the same for a big one. How often do you get snake eyes? Or a double Duce?

If you're holding the rifle against a shoulder to test from a bench, 25% to 50% of the group is the rifle and ammo; you're the other 75% to 50%.

 

[peacebutready]

Thanks for the replies.