Barrel length and "effective" barrel length

[GhengisAhn175]

I was doing some barrel measurements to send to someone for a mirage when I noticed I didn't have "26" barrels.

i checked 4 barrels j have where I thought they were supposed to be 26".

Technically they are, from muzzle to nearly the end of barrel threads. They're actually closer to 24.5" - 25" from the front of the action.

So I'm wondering when we're entering in barrel length in our ballistic solvers , quick load or when posting load data, how much is off?

im assuming "effective" barrel length as far as velocities go should be from the case mouth forward when inside the chamber. In that case it's damn near 23"

anyone got an answer for this?

 

[spife7980]

That's a good question. I guess technically it should be length of the rifling but velocity is independent of length so as far as solvers go it's a moot point. Muzzle velocity is muzzle velocity. For quick load though it could make a good bit of difference. I wish I had quickload.

 

[TonyTheTiger]

The ATF tells me to measure barrels from the bolt face, and all the barrels I've measured this way are the advertised length.

 

[samb300]

The ATF tells me to measure barrels from the bolt face, and all the barrels I've measured this way are the advertised length.

This ^^^

If you measure a factory AR barrel listed at 16", it will be 16" from the bolt face to the muzzle. It's interesting though, because yes, on a 308 barrel the actual distance the bullet travels down the barrel is about 3" less than the barrel length.

To the original question though, I'm not sure what Quick Load uses for the barrel length.

 

[AIAW]

QuickLoad compensates for bullet travel versus barrel length. Hovering over the barrel length box will tell you this.

QuickLoad uses the case length and seating depth to determine what the actual bullet travel will be (bullet specs must be pulled from the database or entered manually to determine ogive to base of the bullet in use).

[IMG2=JSON]{"data-align":"none","data-size":"full","src":"https:\/\/s11.postimg.org\/uotnlfkhv\/image.jpg"}[/IMG2]

 

[GhengisAhn175]

Thanks for the replies guys.

Good to know quickload accounts for that.

I wonder if it matters for ballistic solvers as far as amount of twist the bullet receives or if that even matters

 

[AIAW]

No problem! Twist rate and direction (as far as a ballistics calculator is concerned) should only affect spin-drift calculations.

The stability factor will remain the same on any barrel length, but the bullet specs combined with velocity and twist-rate affects the stability factor overall. In essence, a shorter barrel will natively have a lower stability factor. The solver wouldn't use any stability/gyroscopic factors or barrel length for any ballistic calculations, at least not external ballistics.

 

[Hawk in WY]

From the bolt face it is.

For QuickLoad, how do you deal with a muzzle brake or compensator? From the bolt face to the muzzle or to the end of whatever is attached?

I would assume muzzle but suspect whatever is attached would affect harmonics.

 

[ballison]

From the bolt face it is.

For QuickLoad, how do you deal with a muzzle brake or compensator? From the bolt face to the muzzle or to the end of whatever is attached?

I would assume muzzle but suspect whatever is attached would affect harmonics.

Can't remember where I read it, but you DO NOT include the brake. The easiest way I've found to measure barrel length for QL is to close the bolt and insert a cleaning rod from the muzzle (w/o brake).

 

[918v]

You don't include the brake because while brakes affect point of impact they do not affect accuracy (group size). In theory, the only aspect of barrel harmonics that affects group size is the expansion and constriction of bore diameter at the muzzle while the barrel oscillates.

I ran two kown loads through QL that whose barrel time in James' "effective barrel length" matches Chris Long's OBT: 300WM 208 Amax/77.4 gr H1000 and 308 175SMK/41.8gr 4064. I also ran 175/44Varget but it did not match. 43grs of Varget does match although in my testing the 44gr load is more accurate.

 

[AIAW]

From the bolt face it is.

For QuickLoad, how do you deal with a muzzle brake or compensator? From the bolt face to the muzzle or to the end of whatever is attached?

I would assume muzzle but suspect whatever is attached would affect harmonics.

Take a look at my picture that I posted above and it tells you where the measurement should be between.

QuickLoad is an internal ballistic application only. Internal ballistics cease to exist any longer at the crown, so no brake included in the measurement.

 

[Hawk in WY]

Thanks guys.

My copy of QuickLoad arrives this afternoon.

I'm looking forward to comparing know accurate loads with what QuickLoad tells me.

One load shoots great in a .243, 7 twist AIAW coincidentally.

Expect to learn I'm close but could improve things with some fine tuning.

Then off to test and load a bunch.

 

[AIAW]

Cool. Just be sure to enter as much cartridge data as you can. Building rifle profiles also helps. You need to be pretty anal with the case capacity and other measurements.

If you have a known, verifiable load that you can input then you can see what muzzle velocity QuickLoad is predicting for that load - a good way to verify that your data is in sync and QL isn't spitting out trash!

 

[Hawk in WY]

QuickLOAD program arrived this afternoon. Very cool.

Weighed cases for H2O capacity.

First known accurate load checked was slightly over pressure.

Optimal Barrel Time was 0.3 grains lower and within SAMI max pressure which is good.

Will try that and see if that new load shoots as well as the original load which shot less than 0.250 moa..

Dakota .223 rifle with 24 inch Lilja 1:8 twist barrel. 75 gr Amax.

Will check velocity and see if I can make actual match estimate by adjusting burn rate.

Off to the range tomorrow.