Barrel length and velocity.

[bewsher500]

I have a 20" and soon to add to that a 18" .222
The 20" hasn't lost any of its potency out past 200yds

MV is not really of interest to me
Terminal Velocity and more importantly Terminal Energy is
That comes from bullet choice as much as barrel length


I also have a 30" 308
now the potential for running higher MVs to maintain supersonic speeds at 1000+yds is much higher
but as I am no FTR shooter it is of little real relevance
even less relevance to a stalker shooting 100% inside 300yds and 95% of that within 150yds

 

[JabaliHunter]

Unless the barrel is an un-turned blank or a heavy varmint profile how much weight does that 2" add? Not much, certainly not enough to make up for the loss of velocity and the increase in muzzle blast and noise.
A far better option would be to go with a light sporting or even ultralight profile barrel and keep those inches.
My experience of 'drinking straw' barrels is that they shoot straight for long enough to get what you are shooting at. Just not so good on a range after 20 rounds in succession.
If weight is a problem, resist the temptation to put a massive over powered 'Tactical' scope on it.

Its not usually about weight though, more trying to solve the problem of waving an unwieldy pole about once you factor in the extra 4+in of moderator stuck on the end.

 

[hybridfiat]

Its not usually about weight though, more trying to solve the problem of waving an unwieldy pole about once you factor in the extra 4+in of moderator stuck on the end.

True, I tend to overlook the moderator as they are totally illegal in Australia due to their ability to turn a mild mannered hunter into a rabid, cold blooded, Mafia hitman overnight (known fact, just ask the police).

 

[jamross65]

SWAT Article BARREL LENGTH

above article is is a good read on this subject.

If anyone has access to a Quickload programme, it will show that the effect of shortening a barrel on MV can be lessened by the use of different powders...

 

[ofbiro]

Calculate with the following procedure

Step 1: Calculate the ratio "bullet run with short barrel/bullet run with original barrel"
The "bullet run" is the barrel length minus case length minus bullet depth into the case
The “bullet depth” can be measured unloading a cartridge, or assumed to be 1.5 X bullet dia.

Step 2: Extract the square root of the ratio above. The operation is possible with any pocket calculator
Step 3: Extract the square root of the result of Step 2. If you are familiar with math you can extract the fourth root of the result of Step 1 or elevate the result of step 1 to .25
Step 4: Multiply the result of Step 4 by the MV with the original barrel.

Example
Caliber .222 Rem: MV 3182 fps with a 28” barrel. What is the expected MV with 20”?

a) Calculation of the “bullet run” with original barrel (28”)
The case length is 1.7”. The bullet depth is .336”
The bullet run with original barrel is:
28-1.7-.336 = 25.964”
b) Calculation of the “bullet run” with short barrel (20”)
The case length is 1.7”. The bullet depth is .336”
The bullet run with short barrel is:
20-1.7-.336= 17.964”

Step 1: 17.964/25.964=. 691
Step 2: Square root of .691= .831
Step 3: Square root of .831= .912
Step 4 .912 X 3182 = 2902 fps

For math friends the form is:

MV[SUB]sb[/SUB] = MV[SUB]ob[/SUB] x (BR[SUB]sb[/SUB]/BR[SUB]ob[/SUB]) [SUP].25[/SUP]
Where:

MV[SUB]sb [/SUB]= Muzzle velocity with shortened barrel
MV[SUB]ob[/SUB] =Muzzle velocity with original barrel
BR[SUB]sb [/SUB] = Bullet run with shortened barrel
BR[SUB]ob[/SUB] = Bullet run with original barrel

This is not my invention but an expression found by a German ballistician named Weidel.

However, this is pure theory. In practice, shortening the barrel could result in “amputating” a badly machined portion of the barrel (the bore was not perfectly concentrical, the rifling was rough a.s.o). In this case the actual MV with a shorter barrel could be slightly less than before the “amputation”.
Paradoxically, if a very short “bad section” of the barrel is removed, the MV with a shortened barrel could be even higher than with the original barrel.
The form above is just a guideline to help in comparing the behavior of two “perfect” barrels.

Warning! In certain countries (e.g. in Italy where I live) shortening the barrel is a major modification, involving sending the rifle back to the proof. Otherwise the possession of the modified rifle is illegal.
No liability accepted for the above a.s.o.

 

[MARCBO]

Buy a chronograph.

SS

 

[ofbiro]

Marcbo, if somebody already has the rifle the chornograph is of unvaluable help. But if somebody is planning to buy a rifle, no chronograph in the world can measure the MV of a rifle still standing in the gunshop rack.

 

[Brandlebracke]

To be honest that's a pretty good retention of velocity. It's only 43.75 fps/inch loss.

More overbore cartridges such as 22-250 would do much much worse.

If you compare two cartridges from the same 'family' such as 243, 308 and 358 the velocity drop per inch lost is less in the larger calibres as the cartridge is less overbore.

Here is an interesting article where they chop a 308 barrel down from 26" to 13.5" and they get a 25 fps/inch loss
The Truth About Barrel Length, Muzzle Velocity and Accuracy - The Truth About Guns

interesting read

 

[Druid]

Unless the barrel is an un-turned blank or a heavy varmint profile how much weight does that 2" add? Not much, certainly not enough to make up for the loss of velocity and the increase in muzzle blast and noise.
A far better option would be to go with a light sporting or even ultralight profile barrel and keep those inches.
My experience of 'drinking straw' barrels is that they shoot straight for long enough to get what you are shooting at. Just not so good on a range after 20 rounds in succession.
If weight is a problem, resist the temptation to put a massive over powered 'Tactical' scope on it.

Very wise! That's why when getting my .243 threaded I chose not to chop any length off the 24 inch fluted barrel even though the short, handy feel of a 20" barrel appealed to me.

 

[bewsher500]

more trying to solve the problem of waving an unwieldy pole about

daily problem......

 

[Greener Jim]

You a scaffolder are ya bewsh