Optimal Barrel Time?

[Dwh7271]

I was glancing at 7025-06's post on his results with his 25-06 and the Sierras.
I saw the reference to optimal barrel time.
I downloaded the Excel calc for this a while ago and have played around with it but not gotten very deep.
Any of you had experience with this?
Pros? Cons?
And does this potentially have a value in determining a bit quicker where an optimum load for your barrel may be?
Thanks!

edit: Here's the link to the paper I read.
http://www.the-long-family.com/OBT_paper.htm

 

[Darkhorse]

I just read through that explanation and at first read it seems overly complicated to me.
It will take some deeper reading and thinking on my part.
A couple of things got me thinking;
I'm unclear on how to take the barrel times and apply it to a load. Like where do I measure from and when. I don't like long formulas.
After a career working with multiple materials in the aircraft industry, I have a problem with the idea that the muzzle will change diameter during this process.
I just think it's simpler than all that and that barrel harmonics are pretty constant, and what we are dealing with is the location of the bore upon bullet exit and not the size of the bore.
Just first thoughts.

 

[rodell]

I've played with the model. I do believe there is truth to the theory about a second type of wave that travels the barrel besides a longitudinal flex. The analysis supports it. The question is whether or not it matters enough to worry about and empirically, it matters to some degree.

You are playing with OBT when you change seating depth.

 

[Guy Miner]

Yeah... I'm probably too dense to understand it.

I just loaded what the other long-range high master competitors were loading, and used it to shoot some pretty danged good scores. Won a few matches doing so. Lost some more when I didn't read the wind properly.

I dunno. Didn't then. Don't now.

If it makes you happy, then by all means pursue it!

Regards, Guy

 

[mustanggt]

Ouch. That makes my head hurt. It's enough for me to just try and do things consistently vis a vis the reloading manuals I've learned from. I've learned so much by just burning powder that if I tried to apply any of that it would be like when Mickey Mantle talked with Ted Williams during an All Star game and Ted being a very cerebral hitter asked Mick all kinds of questions about how he hit and after that Mick went into a slump because he tried to do things Ted talked about. That's what would happen if I tried to make sense of all that stuff in that article.

 

[Ridgerunner665]

Science supports it, experiments done support it, and it all makes sense to me...so I support it.

I think a lot of people use OBT loads, even though many of them don't realize it...and they found them by accident.

A recent example...the load for my wifes 270 that I came up with, that one shot REALLY good...was found using this method...the barrel time, according to QuickLoad, is within 3%.....22" barrel OBT is 1.030 milliseconds, the 270 load is 1.059 milliseconds...

The only load work I done was to find the max for that rifle...the chosen load was derived from QuickLoad and OBT...without a single round fired at a target before the range session I posted here.

It took me some figuring though, being new to QuickLoad, to get everything matched up...honestly I'm not sure how or why it worked that time, but it did.

Also...a popular 30-06 load, 168 grain BT's under 57.5-58 grains of H4350 (depending on case capacity)...24" OBT is 1.120....the barrel time of that load in a 24" barrel is 1.120 according to QuickLoad...that load shot .2" in my 30-06....CONSISTENTLY! That same load...shoots almost as good in my sons 30-06 (his is all factory, mine had the glass bedded McMillan stock)...I found this load without QuickLoad, as have many other people...

Another example....JD338's 160 AccuBond load for his 280 Ackley...I don't know the OAL legth of his loaded rounds, but when I run it at 3.34"....the barrel time in QuickLoad is real close to the OBT.

Looking forward to driving a 150 ABLR through mine...if pressure doesn't max out before I get there....that bullet shows a barrel time of 1.123, with a max load of MRP...

 

[Oldtrader3]

Either OBT or a device such as the BOSS system which helps by lengthening or shortening the barrel harmonics.

 

[rodell]

Interestingly enough, the B.O.S.S. doesn't affect OBT. It does tune the barrel longitudinal wave to a quiet point.

Essentially, the OBT model shows a doughnut of constriction that travels up and down the barrel. If you can get the bullet to exit when the muzzle is quiet from flex and the doughnut at teens you will have the most accurate load.

 

[Oldtrader3]

By changing the length to coincide with a OBT barrel length! Length changes equal barrel length and therefore time changes! That is, given a small differential projectile speed change and larger weight change with BOSS.

 

[Ridgerunner665]

When you think about it...all those weird things barrels do when you cram a bullet through them with upwards of 60,000 psi of pressure explains a lot of things...secondary pressure spike for example, bullet catches a constricted bore at just the right time...err,wrong time...in the powder burn.

That would explain how you could blow the last few inches off a barrel with a really heavy dose of slow powder...somebody did that, read about it on 24hr campfire...forget the exact round and combo, it was a magnum of some sort.

 

[Guy Miner]

Yeah. I'm old fashioned. I just go for the best grouping load.

And often rely on loads that others recommend, like Sierra, Nosler, other top notch match shooters....

Guy

 

[Ridgerunner665]

Yeah. I'm old fashioned. I just go for the best grouping load.

And often rely on loads that others recommend, like Sierra, Nosler, other top notch match shooters....

Guy

Ain't a thang wrong with being old fashioned...matter of fact, its commendable...if it ain't broke, right?


But your post appealed to my curious nature...I just ran a few of Nolsers 280 AI "accuracy loads" in QuickLoad...hadn't done this before...every one is close to (within 3%) one of the nodes mentioned in the article, when you match up the velocities...not the powder charge (too many unknown variables...case case capacity, burn rate variations, etc.)

They stopped just short of the next node on many of the loads...the 160 AB and Reloder 22 being one of them.

 

[Elkman]

I am math challenged, if I can't do it in my head, it's over. Well beyond the abilities of my pea sized little brain.

 

[SJB358]

I am another that believes the OBT is pretty accurate, but reaching some of the timing nodes it calls for are tough to attain. It seems like alot of the nodes sit on the low side in one spot and the high side (FPS) in the next highest node. I use it to a certain extent, enough to know it makes sense and works, but I don't think it will stop anyone from still doing the leg work to find a load. It does minimize the amount of shooting you might have to do in some cases though.

I will usually look and compare it when I am working with a new bullet/cartridge combo, and start with it, but I almost always end up varying from exactly what I "should" be seeing to a certain extent.

It is cool stuff though. I would be if alot of you all gave the guys with QL your exact load, with H20 capacity, OAL, powder and such, and ran against OBT, you'd probably be sitting close to what they predict. Maybe not right on, but I'd bet your close.

 

[SJB358]

Here is an example of mine. I am not saying it isn't completely lucky, but just how it lines up for me..

Here are the barrel times that OBT says should be nodes..


Barrel Node Node Node Node Node Node Node
25.0 0.8489 0.9305 1.0639 1.1461 1.2788 1.3617 1.4938


Cartridge : .338 Win Mag.
Bullet : .338, 225, Nosler PART SP 16336
Useable Case Capaci: 75.325 grain H2O = 4.891 cm³
Cartridge O.A.L. L6: 3.330 inch = 84.58 mm
Barrel Length : 25.0 inch = 635.0 mm
Powder : Alliant Reloder-17

Predicted data by increasing and decreasing the given charge,
incremented in steps of 2.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step Fill. Charge Vel. Energy Pmax Pmuz Prop.Burnt B_Time
% % Grains fps ft.lbs psi psi % ms

-20.0 79 57.20 2385 2841 32568 8329 97.8 1.565
-18.0 80 58.63 2442 2978 34770 8522 98.5 1.523
-16.0 82 60.06 2498 3118 37149 8697 99.1 1.481
-14.0 84 61.49 2554 3260 39680 8854 99.5 1.436
-12.0 86 62.92 2610 3403 42386 8992 99.8 1.393
-10.0 88 64.35 2665 3549 45285 9110 100.0 1.351
-08.0 90 65.78 2720 3695 48389 9208 100.0 1.311
-06.0 92 67.21 2774 3843 51717 9298 100.0 1.273
-04.0 94 68.64 2827 3993 55290 9385 100.0 1.236 ! Near Maximum !
-02.0 96 70.07 2880 4143 59127 9469 100.0 1.200 ! Near Maximum !
+00.0 98 71.50 2932 4295 63250 9551 100.0 1.166 ! Near Maximum !
+02.0 100 72.93 2984 4448 67691 9630 100.0 1.133 !DANGEROUS LOAD-DO NOT USE!
+04.0 102 74.36 3036 4604 72478 9705 100.0 1.101 !DANGEROUS LOAD-DO NOT USE!
+06.0 104 75.79 3087 4760 77641 9777 100.0 1.070 !DANGEROUS LOAD-DO NOT USE!
+08.0 106 77.22 3138 4919 83222 9845 100.0 1.041 !DANGEROUS LOAD-DO NOT USE!
+10.0 108 78.65 3189 5080 89235 9909 100.0 1.012 !DANGEROUS LOAD-DO NOT USE!

Results caused by ± 10% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 10% relative to nominal value:
+Ba 98 71.50 3027 4577 77172 9190 100.0 1.085 !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba 98 71.50 2785 3875 50948 10003 99.4 1.274


So you can sorta see where my most accurate load lined up with the barrel timing. Not perfect, but close enough when you take into account my barrel probably isn't exactly 25" (depending on how it's measured) and all of the other factors involved.

Just food for thought. It isn't super hard to figure out, but you need to have some decent inputs in order to get useful outputs from the program and OBT. I still think there is some withcraft involved, but I do reference it still.. :lol:

 

[JD338]

I too am old fashioned and haven't looked at OBT. almost 40 years of loading with a funnel and a ball peen hammer.
Guess I will take a closer look.

JD338

 

[SJB358]

Jim, chances are you'll end up at the same spot most of the time, I did and never realized it. This just cuts a little part of a corner. If any of you all ever wanna try it out, just for grins, please hit me up, I'd be glad to run the data and see what comes from it.

Like I said, there are alot of other variables working, so this is just one aspect of it.

 

[Ridgerunner665]

That goes for me too...I'll just be sitting here in MD until Monday morning...all kinds of time to play on QuickLoad if anybody needs or wants me to....

 

[Guy Miner]

I too am old fashioned and haven't looked at OBT. almost 40 years of loading with a funnel and a ball peen hammer.
Guess I will take a closer look.

JD338

Jim... What are you doing with the hammer? :grin:

 

[SJB358]

I too am old fashioned and haven't looked at OBT. almost 40 years of loading with a funnel and a ball peen hammer.
Guess I will take a closer look.

JD338

Jim... What are you doing with the hammer? :grin:

That's how he cycles and opens the bolts on them old Remington's... :grin: