barrel lengths per cartridge decisions

[ARlife4me]

Don't think i ever said cooler powder wouldn't give you better barrel life. My post isn't about powder burn rates. Again, I don't care about burn rates with regards to different barrel lengths in the same chamberings. Certain powders shoot well in certain chamberings. I've found they shoot well no matter what length barrel. I don't know where all this other stuff you're talking about fits in hahah.
H1000 shoots really well in 300wm...throated correctly it will push a 200 gn berger over 3000fps in a 26"....it just so happens that h1000 ALSO shoots really well in a properly throated 300wm with a 22" barrel. It won't do it over 3000fps which is why I would CHAMBER UP to maybe a 30noz if I wanted to run that same 200 over 3000fps. My posts said that I chamber and choose barrel length based on what bullet I want to use and the type of performance I want out of it. That's all.

Chambering up is why I have 3 different 30cals and 5 different 26cals in various barrel lengths to boot. Not to save weight but just maneuverability with shorter barrels. If I want more velocity I go up in cartridge size and/or go longer. I have limits on what cartridge I'll use (i.e., longer 264wm barrel vs 26nos/6.5-300wby).

 

[MagnumManiac]

Using the Pressure Trace to get real world data was THE biggest eye opener for me. I had QL and ran the numbers side by side, what it showed me was this.
For my wildcats based on the 416 Rigby Improved (not AI) case, I required a barrel of 30" minimum and optimum lengths ran into these lengths: 30 cal = 34", 33 cal = 32" & 37 cal = 30-31". I dabbled with .408 cal and it said optimum was 31-32" which I questioned, but the bore size fell off sooner than the others.
Now, taking all that into consideration, and ease of implementing blank sizes, I erred on the shorter lengths because getting blanks to finish at 34" here is a pain.
So, my barrels run, 32" for 30 cal with 35° shoulder, 32" for 33 cal, and a 30" barrel for 33 cal 45° shoulder & 30" for 37 cal 40° shoulder. Twists run 10" for 30 cal, 9" for 33 cal & 10" for 37 cal which is super fast I discovered. The 300g SMK didn't like this twist…
The only known cartridges to me that up this performance, are the Allen Magnums based on the 408 CheyTac case, which is essentially the altered 505 Gibbs case, which I had one for several years. Unbelievable cartridge pushing 600g pills at 2500fps, if desired, I did it once! Never again in a 9lb rifle.
Anyway, if you want the utmost performance, long barrels are required to burn the powder and to get the desired velocity.

Cheers.

 

[Mikecr]

Pretty sure pressure trace will also show that a barrel grossly too short for the charge can cause secondary pressure spikes, which can even exceed the primary pressure peak. While this is not predicted, I think minding muzzle pressure would mitigate the chances of it.
That is, when muzzle pressure as predicted exceeds 12kpsi, you're likely dumping a lot more than predicted.
What are your thoughts on this MagnumManiac?

 

[akmtnhnt]

Pretty sure pressure trace will also show that a barrel grossly too short for the charge can cause secondary pressure spikes, which can even exceed the primary pressure peak. While this is not predicted, I think minding muzzle pressure would mitigate the chances of it.
That is, when muzzle pressure as predicted exceeds 12kpsi, you're likely dumping a lot more than predicted.
What are your thoughts on this MagnumManiac?

I remember reading something on this as well, but wasn't it in relation to having unburned powder coming out the end?

 

[Mikecr]

I remember reading something on this as well, but wasn't it in relation to having unburned powder coming out the end?

It may be a combination of things.

Many factory designs use relatively narrow, high taper cases, with low shoulder angles. Good funnels.
This leads to a big wad of unburned powder traveling down the bore with bullets, adding mass, recoil, and pressure.
But the pressure is not in the chamber here. And the shorter the barrel, the less time for that slug to burn off -somewhere inside the barrel.

An improved case design reduces body taper of larger diameter shorter cases, and adding high shoulder angles.
This holds the powder back to burn more in the chamber, similar to front ignition.
It lowers muzzle pressure.

 

[MagnumManiac]

Pretty sure pressure trace will also show that a barrel grossly too short for the charge can cause secondary pressure spikes, which can even exceed the primary pressure peak. While this is not predicted, I think minding muzzle pressure would mitigate the chances of it.
That is, when muzzle pressure as predicted exceeds 12kpsi, you're likely dumping a lot more than predicted.
What are your thoughts on this MagnumManiac?

You are correct, however, my understanding of this is a perfect example of bore ratio. The only time I personally saw this was with the 338-416 Rigby Improved 45° using RE25 in loads above 118g with a light 285g bullet. Pressure reached max and then at bullet release there was a jump up to 100,000psi. I recall the muzzle flash was extremely large also. I used to have that graph, but haven't used that laptop since closing the gunsmithing business and my divorce.
Very interesting results.
I think that muzzle pressure is a direct relationship to bore ratio and you can't get around it unless you increase barrel length to match.
Still haven't tested the 300RUM, but believe this is a very good candidate for muzzle pressure issues.

Cheers.

 

[FireFlyFishing]

Sigh…

Short barrels are en vogue due to suppressors.

I will say though…I have a 20" .308 Tikka CTR, suppressed (7"can) shooting 24" velocities as posted by loading manuals tested at sea level. My range is 3400'. My hunting grounds are 5000-8000' elevation. All good in the neighborhood from my perspective. Gives me wiggle room.

 

[Mikecr]

A 308 works with very short barrels because it's capacity is small for cal (an underbore).