Warning

 

Close

Confirm Action

Are you sure you wish to do this?

Confirm Cancel
Member Login
Posted: 9/11/2010 2:08:37 PM EDT
All,

I picked up a buddies project. A "Scout" rifle made from a Savage .308 bolt gun. The barrel was cut down to 16" and recrowned. The smith did a good job on it.

I was wondering what the ballistics would be vs a normal 20" barrel say at 100, 200, 300 and 500 yards. Anyone have a guess?

J
Link Posted: 9/11/2010 2:13:26 PM EDT
Link Posted: 9/11/2010 2:15:01 PM EDT
I couldn't tell you. But I am curious about the same thing as it pertains to .223.

I have one of those "ballistics compensating" scopes designed for .223, and I'm curious what barrel length it was intended to be used on. IOW, with a 16" barrel, will the range markings on the scope turret be correct, or would it require a 20" barrel?
Link Posted: 9/11/2010 2:21:57 PM EDT
Originally Posted By AeroE:
The muzzle velocity will be reduced about 100 fps.

This is where you get into a ballistics program to answer the rest of your question on your own. There's a very nice one at www.hornady.com.



Thanks!
Link Posted: 9/11/2010 2:24:53 PM EDT
i am also interested. I have the redfield revolution with the accu range reticle on my 16" I wonder how close the actual POI at the different ranges is to the estimated POI on the reticle.
Link Posted: 9/11/2010 2:28:10 PM EDT
[Last Edit: 9/11/2010 2:29:13 PM EDT by MK4Mod0]
On a bolt gun you lose about 15FPS per in of barrel............got that off one of the sniper sites..........not sure if it would hold true for an AR.
Link Posted: 9/11/2010 7:17:21 PM EDT
Originally Posted By MK4Mod0:
On a bolt gun you lose about 15FPS per in of barrel............got that off one of the sniper sites..........not sure if it would hold true for an AR.






No, it won't. A rifle loses around an average of 100f/p/s per inch of bbl loss from a 20/22" to a 16" bbl.

A handgun loses an average of 50f/p/s from a change of a 4/6" bbl to a snubbie.
Link Posted: 9/11/2010 7:19:52 PM EDT
Originally Posted By BobCole:
Originally Posted By MK4Mod0:
On a bolt gun you lose about 15FPS per in of barrel............got that off one of the sniper sites..........not sure if it would hold true for an AR.






No, it won't. A rifle loses around an average of 100f/p/s per inch of bbl loss from a 20/22" to a 16" bbl.

A handgun loses an average of 50f/p/s from a change of a 4/6" bbl to a snubbie.


Really

Someone needs to tell ATK

Recent Lake City M855 testing by me
24" Bolt gun - Avg 3158
20" AR - Avg 3118
16" AR - Avg 2945

Checked on 2 Chronographs
Link Posted: 9/11/2010 7:22:04 PM EDT
I seem to recall FALs cut down to 16" lose at least 200fps, if not more. And they throw a huge fireball.

Eighteen inches seems to be the sweet spot for carbine-length .308s.

I have two 16.25" FALs and thinking back, I should have had them cut to 18". Live and learn.
Link Posted: 9/11/2010 7:30:41 PM EDT
Originally Posted By BarryTolar:
Originally Posted By BobCole:
Originally Posted By MK4Mod0:
On a bolt gun you lose about 15FPS per in of barrel............got that off one of the sniper sites..........not sure if it would hold true for an AR.






No, it won't. A rifle loses around an average of 100f/p/s per inch of bbl loss from a 20/22" to a 16" bbl.

A handgun loses an average of 50f/p/s from a change of a 4/6" bbl to a snubbie.


Really

Someone needs to tell ATK

Recent Lake City M855 testing by me
24" Bolt gun - Avg 3158
20" AR - Avg 3118
16" AR - Avg 2945

Checked on 2 Chronographs


Was that checked near the muzzle, or down range at least 100 yards? I've most always read an inch = on avg 100fps. Perhaps that is at distance, if that would matter.
Link Posted: 9/11/2010 7:33:42 PM EDT
It was 25 meters approx from muzzle
Link Posted: 9/11/2010 7:40:37 PM EDT
Originally Posted By BarryTolar:
It was 25 meters approx from muzzle


Well that's not near the difference I would be expecting. That's the whole reason I went with a 24" barreled upper when I built my dedicated bench/varmint rig, was more velocity. Those numbers don't show near enough difference to get excited about so I would be better off replacing the barrel with something shorter and lighter.
Link Posted: 9/11/2010 7:42:55 PM EDT
Also the 24" Figure it from a bolt gun

Got the numbers from a 20" bolt gun we ran today but not on this comp

I'm having beyond hell duplicating that load

but yeah there isn't really enough difference to warrant the longer tube

at least on M855 - do not know about 77gr stuff - yet
Link Posted: 9/11/2010 7:43:05 PM EDT
Link Posted: 9/11/2010 7:45:23 PM EDT
Not really one rifle

yeah 1 24" and it was a bolt

3 20" Guns (AR, Aug, Single Shot)

4 different configs of 16" guns

it's NOT 100fps per inch for current production M855
Link Posted: 9/11/2010 7:49:25 PM EDT
The only way to tell is to test the actual loads that will be used with a chronograph. Different loads will "react" differently to different barrel lengths.
Link Posted: 9/11/2010 7:54:06 PM EDT
Originally Posted By BobCole:


No, it won't. A rifle loses around an average of 100f/p/s per inch of bbl loss from a 20/22" to a 16" bbl.
.


400 fps in 4" no way
'

from my own test

70 degrees, no wind 3200 msl

all AR10's 147 gr

16" barrel/ML gas

2605 avg

18" barrel/rifle gas
2629avg +24

20" nm ss barrel
2673avg +44, +68

2" added, 24fps, 4" added 68 fps

nearly double the jump from 18" to 20" (44fps) versus 16" to 18"= (24fps)
Link Posted: 9/11/2010 8:20:18 PM EDT
Link Posted: 9/11/2010 8:25:40 PM EDT
Originally Posted By AeroE:
Originally Posted By BarryTolar:
Not really one rifle

yeah 1 24" and it was a bolt

3 20" Guns (AR, Aug, Single Shot)

4 different configs of 16" guns

it's NOT 100fps per inch for current production M855


Or any other ammunition.

The speeds will vary from about15 to 35 fps per inch in the range of lengths of rifle barrels. There is no set answer, the barrel, bullet, and gunpowder all affect the loss.





Dude I agree with that it's 15 to 35

but it's NOT 100

I've always read it's 100

but it's not

at least not NOW

and yeah I didn't test anything other than M855

that's all I'm shooting (well 62gr anyway)

I'm just saying that the 100fps per inch is not true
Link Posted: 9/13/2010 1:14:20 PM EDT
[Last Edit: 9/13/2010 1:16:57 PM EDT by MK4Mod0]
I copies this from here http://www.sniperschool.com/sniper-rifle-barrel-length

I'll try to find the article that quotes 25FPS per Inch..........

This article does not adress the FPS issue, but I thought it would be some good info to pass along.

Sniper Rifle Barrel Length
Print PDF

“All Great Truths Start as Blasphemy” -George Bernard Shaw

Appropriate barrel length for sniper rifles has been debated at length in tactical communities and online forums alike. In the spirit of GPS Defense’s teaching principle of deciphering the truth out of the piles of opinions by testing a theory and seeing the results first hand, we decided to put the barrel length issue to rest.

As our previous students can attest, and as you will experience in any of our classes, we often choose to prompt our students to figure out the answer to a question or previously held belief on their own. Chances are, we have encountered their question or opinion many times before and we have learned that the reason they are led to believe a certain point is simply because somebody else told them it was so. If we do the easy thing by simply telling them the correct answer, the truth we tell them will have no more weight in their mind than the possibly incorrect information that has been unquestioned and passed down from person to person.

Simply put, barrel length (within reason) does not affect accuracy within a manner many people believe. My personal rifle, based off of a Remington 700 action, has an 18″ .308 barrel. When people see my rifle, they often ask, “How much does that affect the accuracy?”

Their question, although a valid one, is usually asked in such a way that assumes accuracy must have been compromised in order for the barrel to be so short. The exact opposite is true.

My rifle came from the factory with acceptable sub minute of angle (less than 1″ group per 100yds) accuracy out of a 26″ barrel. I had my barrel cut down to 18″, took it out to the range and was pleasantly surprised to see the accuracy improve to a 1/2 minute of angle. Yes, you just read that right… the shorter barrel was more accurate.

When I dropped off the rifle to have it cut and re-crowned from its factory length, the gunsmith asked how short I wanted the barrel to be, and when I told him 18″, he tried his best to talk me out of it. He explained to me that 20″ is a “safe” length and about as short as he has seen people go while maintaining accuracy. I decided that since I was cutting the barrel to create a more manageable and compact shooting platform and partly to prove a point, I shouldn’t go to a “safe” length…. I should go shorter.

A common argument I hear from disbelievers revolves around some sort of belief that the twist rate must relate to the barrel length. This fallacy tries to say that since the twist rate of my .308 700 PSS is 1 in 12″, the barrel must be cut to a length in multiples of 12 inches in order for the bullet to spin properly. This is absurd. If this was true, Remington would never ship the PSS from the factory with a 26 inch barrel. And for that matter, a 1911 style .45 with a twist rate of 1in 16″ would have a 16″ barrel in order to be able to hit the target.

So, if a bullet from my barrel is spinning at a 1 in 12″ rate regardless of the length, why did cutting it down increase the accuracy? The answer lies in the effect of barrel stiffness. We all understand that a thicker bull barrel will provide better accuracy than a thin sportster style barrel. From this we know that a stiffer barrel helps increase accuracy by negating excessive barrel flex and vibration. The only way to stiffen an already stiff bull barrel from the factory is to shorten it. Let me explain….

Inch per inch, the barrel’s stiffness has not changed. But when taking the entire length into account, the overall effect is a stiffer barrel. Think about a 2 inch stick that is just stiff enough to be unbreakable. Now, take a stick of the same diameter with a length of 12 inches…. it would be much easier to break. Each individual inch of the two sticks share the same rigidity, but the longer stick allows more leverage to be imparted on the stick and therefore nets less overall stiffness and more leverage.

So, by cutting the barrel, the twist rate was not affected and the barrel was relatively stiffer. The only other concern lies in whether or not the powder has enough time to burn before the bullet leaves the barrel. This should not affect accuracy since it should burn consistently whether or not it burns completely. The only problem will in fact lie in the change in velocity of the bullet.

At 100 yards, I found absolutely no change in the point of impact of the bullet from the longer 26″ original length to the new shorter 18″ length. I did, however find a significant difference at longer distances.

At our 920 yard target on our range, school rifles with standard length barrels are able to hit the target with a 34 minute of angle adjustment above their 100 yard zero. When I first shot my rifle to compare the bullet drop from my rifle with the short barrel to the school rifles, I was using 168 grain Federal Gold Match ammunition and recorded hits at 39 1/2 minutes up from my 100 yard zero. That translates into a little over 50 inches of difference between the barrel lengths at 920 yards!

After realizing that the powders used by Federal (ammo I used) and Black Hills (ammo the students use) may burn at different rates, I decided to re-test my rifle with the 175 grain Black Hills Match ammunition that our students use. When using the same ammo, my rifle only needed 36 minutes of elevation in order to hit the target. Based on changing the ammo, I had a 3 1/2 minute change at 920 yards! Using consistent ammo and consistent environments, my 18 inch barrel only requires two additional minutes of elevation to engage a target 920 yards away!

With a more manageable, compact, lighter, and more accurate rifle only requiring only 2 more minutes of angle at 920 yards, I see no reason to not cut down a barrel on a sniper rifle. Still don’t believe me? Enroll in a class and I will shoot my short barrel rifle next to yours and you can learn what happens in the manner we suggest the most… you can see for yourself.

–Ryan Cleckner
Link Posted: 9/13/2010 1:33:37 PM EDT
Originally Posted By BarryTolar:
Originally Posted By BobCole:
Originally Posted By MK4Mod0:
On a bolt gun you lose about 15FPS per in of barrel............got that off one of the sniper sites..........not sure if it would hold true for an AR.






No, it won't. A rifle loses around an average of 100f/p/s per inch of bbl loss from a 20/22" to a 16" bbl.

A handgun loses an average of 50f/p/s from a change of a 4/6" bbl to a snubbie.


Really

Someone needs to tell ATK

Recent Lake City M855 testing by me
24" Bolt gun - Avg 3158
20" AR - Avg 3118
16" AR - Avg 2945

Checked on 2 Chronographs


Facts in GD?! LIAR!!!!!
Link Posted: 9/13/2010 1:36:09 PM EDT
The amount you lose per inch increases as you get shorter, IIRC.
Link Posted: 9/13/2010 1:42:53 PM EDT
Originally Posted By MK4Mod0:
I copies this from here http://www.sniperschool.com/sniper-rifle-barrel-length

<snip>


I get funny looks and "that's not true" comments from "experienced" shooters whenever I mention that all else being equal, a shorter barrel is generally going to be more "accurate" than a longer barrel.

Even after explaining it in terms of barrel whip, etc., the usual response is that a longer barrel is still going to be more accurate because the higher muzzle velocity will translate into less wind drift. While that's true, I'm talking about accuracy, not necessarily ability to hit a super long range target in windy conditions. For that, heavier faster bullet from a longer barrel is probably going to be easier to get on target. That doesn't mean the longer barrel is more "accurate" in terms of consistency though.
Link Posted: 9/13/2010 1:51:40 PM EDT
I handload everything and like short bbl rifles. I tailor the powder and load to suit a specific rifle. It is possible to have a 400 fps difference from an 18" bbl to a 24" bbl, it is also possible to have an 18" bbl shoot only 100fps less than a 24" tube by changing powder specs. Factory ammo is a crapshoot but handloads are great. It is important to chrono everything and really shoot it at distance, not just rely on paper ballistics.
Link Posted: 9/13/2010 5:08:20 PM EDT
Link Posted: 9/13/2010 6:47:42 PM EDT
Find someone who has or maybe even get yourself a copy of quickload and really have fun playing with ballistics concerning loadings, barrel length etc.
It is a real eye opener.



Umm expensive too so you might want to find yourself a hardcore reloader who will let you play with his copy.
Link Posted: 9/13/2010 6:48:22 PM EDT
4" chop is about tree fiddy.
Link Posted: 9/15/2010 2:39:47 PM EDT
I found this here. http://www.chuckhawks.com/rifle_barrel.htm

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!

Again this is not specific to AR's.
Link Posted: 9/15/2010 2:47:48 PM EDT
I just had my 26" bolt .308 cut down to 18"... it was worth it just in maneuverability and weight savings.

Fortunately, .308 isn't nearly as velocity-dependent for its ballistic performance as .223
Top Top