10BA .308 Steath bullet weights

[CFJunkie]

Actually the single pass reflection time can be easily calculated if you know the speed of a reflection in steel.
Of course you need to know the length of the barrel.

If you know the steel in the barrel and the length of the barrel you can calculate the reflection time.

Savage 3% carbon steel reflects at 19,107 fps.
4150 or 4140 stainless reflects at 19,969 fps.
416R stainless reflects at 20014 fps.
Most materials handbooks list the speed but you would need to know the steel your barrel is made of.
As I mentioned, the % carbon might vary by steel lot, but the 9 Savage barrels that I have all seem to be very similar.
The exact lengths sometimes vary compared to the specs (a few are off by 0.125 or less) but by experimenting with the exit times by +/- 0.010 msec. you can focus in on the best exit time.

For exit time, you try to get the time for an even reflection, with the shock wave back at the chamber.
The reflection speed is much longer than the speed of the bullet as it starts from zero and accelerates down the barrel.
Each type of powder varies the acceleration and the exit velocity, so the exit time also varies.

Having muzzle brakes and flash hiders complicates the calculation.
The reflection moves along the barrel and through the attachments to it.
But the steel in the Muzzle brake/flash hider might not be the same steel as the barrel so that has to be figured into the equation.
Colt flash hiders are 4140/4150 steel.
Since flash hiders and muzzle brakes (and suppressors) don't have rifling, the bullet actually leaves the barrel at the last reflection minus one length of the barrel appendage.
That also complicates the calculation.

[Ted_Feasel]

Actually the single pass reflection time can be easily calculated if you know the speed of a reflection in steel.
Of course you need to know the length of the barrel.

If you know the steel in the barrel and the length of the barrel you can calculate the reflection time.

Savage 3% carbon steel reflects at 19,107 fps.
4150 or 4140 stainless reflects at 19,969 fps.
416R stainless reflects at 20014 fps.
Most materials handbooks list the speed but you would need to know the steel your barrel is made of.
As I mentioned, the % carbon might vary by steel lot, but the 9 Savage barrels that I have all seem to be very similar.
The exact lengths sometimes vary compared to the specs (a few are off by 0.125 or less) but by experimenting with the exit times by +/- 0.010 msec. you can focus in on the best exit time.

For exit time, you try to get the time for an even reflection, with the shock wave back at the chamber.
The reflection speed is much longer than the speed of the bullet as it starts from zero and accelerates down the barrel.
Each type of powder varies the acceleration and the exit velocity, so the exit time also varies.

Having muzzle brakes and flash hiders complicates the calculation.
The reflection moves along the barrel and through the attachments to it.
But the steel in the Muzzle brake/flash hider might not be the same steel as the barrel so that has to be figured into the equation.
Colt flash hiders are 4140/4150 steel.
Since flash hiders and muzzle brakes (and suppressors) don't have rifling, the bullet actually leaves the barrel at the last reflection minus one length of the barrel appendage.
That also complicates the calculation.Thats what I'm kind of getting at, is instead of relying on known reflections of steel (because even though the target amount of carbon may be 3% ,nickle 10% etc) it will be slightly different from batch to batch and maker to maker where as if on actually records the true pitch of the barrel it would allow for precision reflection calculations.. now possibly that would be splitting hairs or negligible in the difference it would make but thats just my brain at work lol

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[Robinhood]

Thats what I'm kind of getting at, is instead of relying on known reflections of steel (because even though the target amount of carbon may be 3% ,nickle 10% etc) it will be slightly different from batch to batch and maker to maker where as if on actually records the true pitch of the barrel it would allow for precision reflection calculations.. now possibly that would be splitting hairs or negligible in the difference it would make but thats just my brain at work lol

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Great conversation. Hopefully Jim will pull it out and make it it's own thread.

Now we introduce tuners.

[Ted_Feasel]

Great conversation. Hopefully Jim will pull it out and make it it's own thread.

Now we introduce tuners.Lmbo yup

Sent from my SM-N975U using Tapatalk

[CFJunkie]

Even though I love theoretical arguments, just to put the variation in steel reflection speed versus exit time in perspective:

For a 24-inch Savage barrel with no muzzle brake (19,107 fps reflection speed) with an normal exit time of 1.2561 msec., a change of 100 fps in reflection speed of the steel (1/2 way to old (1930s) barrel steel's reflection of 18.916 fps) changes the 12th reflection exit time by 0.0066 msec.
That much of a change in carbon percentage should be noticeable in quality control measurements of the steel batch.

Based on my measurements, that makes so little change in accuracy that it is lost in my shooter variation (even with over 100 measured groups). Anything less than 0.007 is pretty much masked by shooter induced variation.
I would, therefore, conclude that the theoretical concerns you have for steel variations, while valid and correct in theory, really don't make much of a difference in measurable accuracy, at least, for anything I have measured.

Most of my Savage barrels, of 24 and 26-inch barrel lengths, fit the calculation of exit time for the barrel length, and when I load for the calculated exit time, the long term group averages show the best overall averages for each powder and bullet type. The max difference in average group size between being within +/- 0.005 msec. of the calculated exit time and being close to the muzzle is about 0.090 inches on average.
Since my long term 5 round group averages range from 0.290 to 0.345 inches, depending on the caliber, that much difference is measurable so I make sure I load for accuracy and keep my exit times very close to the calculated exit times.

In contrast, the reflection speed of 4140 or 4150 stainless of 19,969 fps yields a 12th reflection exit time of 1.2019 msec. or a change of 0.0542 msec. That would move the shock wave about 60% down the barrel towards the muzzle and would show a change in average group size of about 0.030 to 0.038 inches based on my results. That indicates that it is important to know what the steel is in the barrel when you are calculating exit time.

Barrel length variations can also make a difference, but I have found those variations to also be relatively rare in my Savage barrels.
A change of 1/8 inch in barrel length for a Savage barrel changes exit time by 0.0065 msec. That's about the same difference as 100 fps in reflection speed.
I have one Savage barrel that is that far off the barrel spec measurements, but that has a Suppressor Ready (SR) barrel so the added length is in the screw-on thread protector. Most of the other 8 barrels are right on the specified length.

[Robinhood]

I found some articles that put that into some terms that a lyman like myself can understand. This one was nice and easy.

https://www.shootingsoftware.com/barrel.htm

[CFJunkie]

Robinhood

The basic explanation is a good one, but in 2003 -2004, the choice of barrel steels was still not broad.

Today, the reflection speed of a Savage barrel is about 900 fps slower than 416R steel. That amount of difference in a 26 inch barrel would put the reflection that was perfect for Savage barrel steel for an even reflection at the chamber, at the muzzle for 416R barrel steel. That would mess up the harmonic calculation if you had a SS barrel. The theory still works, but the results need to consider the type of steel in the barrel.

However, a small variation if the steel speed due to batch variations is like the difference that one additional deck chair would make on the weight of the Queen Mary.

[charlie b]

So is the exit time based on when the base of the bullet exits the barrel? If so, I would assume that is calculated when you set your OAL, ie, you know the length of the bullet and seat it accordingly? If it is a boat tail I would also assume it is when the last of the bearing surface exits the barrel?

Or is it based on the forward part of the bearing surface of the bullet?

[CFJunkie]

Your assumption is correct. The exit would occur when the last of the bearing surface of the bullet exits the barrel.

QuickLOAD has all the bullet dimensions for the bullets in its data base, including the dimensions of a bullet's boat tail, if it has one.
You also enter trim length of the brass and the O.A.L. before QuickLOAD preforms its calculations.
At 2700 fps muzzle velocity, a 0.2 boat tail (.264 or .30 Cal SMK) would reduce the exit time by 0.00617 msec. compared to a flat base bullet.
Smaller caliber bullets have smaller boat tail dimensions and the velocities are generally higher so boat tails would have a smaller difference.

[charlie b]

Thanks.