OCW and OBT Load Development

[NYDAN]

Last week Ridgerunner665 made a comment abut OCW and OBT load development. I didn't recognize those terms so I googled them last night and read up on the concepts of:

Optimal Charge Weights by Dan Newberry http://optimalchargeweight.embarqspace.com/#

and Optimal Barrel Time by Christopher Long http://www.the-long-family.com/OBT_paper.htm .

If I understood the concepts correctly, OCW is a purely emperical method of developing an optimum charge weight to minimize changes in POI and then fine tuning the load with seating depth changes to reduce variations in velocity and group size.

OBT accomplishes a similar result by using a model to predict an optimum barrel time and using Quickload to find a powder combination with the desired barrel time. Then adjusting the seating depth to fine tune the load. A reloader can fine tune Quickload predicitons to match his/her rifle by adjusting a couple of variables within Quickload.

I am guessing that these methods work quite well and that I should get a Quickload program so I can satisfy my curiosity and further my knowledge/understanding of reloading.

Based on prior comments I have seen posted on this forum I am guessing that some of you are using these methods. At the very least, these methods would give a person a starting point in load development. Any comments?

Dan

 

[joelkdouglas]

Dan, I played around a bit with OCW and OBT load development, but the more I reload the more I believe there are several considerations for load development/accuracy. Bullet concentricity, pressure in the chamber (many powders and loads perform better above a certain pressure threshold), bullet choice, etc.

Given all the above are near perfect, or as good as you can get, OCW and OBT might improve a group slightly. But even with Quickload I can't figure out the OBT for some loads, like 57.0-57.5 grains IMR4350 with a 165 grain bullet in a 30-06. It just shoots well, and I've never been able to line up the optimum OBT and OCW for it.

 

[Ridgerunner665]

Joel,
1.12 milliseconds (OBT)....IIRC, going from memory...thats the 30-06 load you mentioned in a 24" barrel.

OCW and OBT don't always match...there is a time and place for each method...either method will generally produce far more consistent accuracy than loads developed without it.

OCW is easier for most folks to do....all you need is a 100 yard range.

Changing seating depth IS changing the barrel time...

The OBT charts are pretty consistently accurate...to within 3 percent or so.

Ladder testing can be useful...but a 300 yard range is difficult for some to find.

 

[Ridgerunner665]

Just realized...I'll be rolling right through Campbell, NY tomorrow...on my way up to Henrietta.

 

[Dwh7271]

I use OBT as a starting point along w QuickLoad. I try to find a powder at the speed I'm roughly going for with a bullet I want that hits close to OBT. Sounds a lot more complex than it is. I.e.- if I want close to 3000 fps from a 24" barreled 25-06 w a 115 BT , I choose the cartridge, bullet, and run a powder comparison. I hopefully find one I like near the OBT and do a run of that powder etc. fine tune to gr to get OBT, generally start at book COAL, and start there.
Worked for three rifles thus far without having to blast 20 or so rounds at varying charges down the barrel.
Is it the one solution? Nope, don't think so. It's not perfect but seems to work for me. :grin:

 

[NYDAN]

Just realized...I'll be rolling right through Campbell, NY tomorrow...on my way up to Henrietta.

RR, PM sent.

Dan

 

[Wyo7200]

I ran across the OBT a while ago and disregarded it because I didnt have a way to measure the barrel time. I forgot about it after I got quickload- until this thread reminded me. So I checked my loads against an adjusted powder burn rate in QL and the table of OBT nodes. Quite surprising results that adds to the OBT theory I guess. I am "on" a node for several loads while I am almost there with the others that I'm not 100% satisfied with. Switching powder or bullet weight will get me there. Aggregating pet load data from the interweb for my new project, puts the charge on a node. I think I'd try to compare the method against the identified most accurate loads Nosler lists in its published data and see what it comes of it. Either way, I'm changing my method to be similar with what dwh mentioned above. All I need is to find a flux capacitor.

16 inchers:
62gr Nos Varm, 5.56, W748, hits node 5, .8232
64gr Nos Bond, 5.56, AR-Comp, hits node 6, .8821
110gr Amax, .300 blk, H110, hits node 6, .8821
125gr Btip, .300 blk, H110, hits node 7, .9585
168gr CC, 7.62, Varget, hits node 7, .9585- OLD LOAD that I PULLED...

22 inch barrels:
60gr Partition, 22-250, R15, near node 4, 1.0126. (can drop to 34.3 grains (-.7) to be on or change powder to R17 to be on 1.0126 with less pressure.

24 inch barrels:
6.5 Creedmoor, 123 gr Amax, R17 hits node 5, 1.2282 (proposed) based off interwebs 41.5 gr IMR 4350 node success reports
6.5 Creedmoor, 140gr Amax, R17 hits node 6, 1.3084 (proposed)
110gr AccuBond, 25-06, IMR4831, hits node 6, 1.3084 (drop load 1.1gr)
110gr AccuBond, 25-06, R25, hits node 5, 1.2282.

26 inch barrels:
160gr AccuBond, 7mm Rem Mag, R22, just above node 5, (drop load .5 grains) 1.3295
160gr AccuBond, 7mm Rem Mag, R22, node 5, (64.5gr) 1.3295
40gr Varmeggedon, .223 sps, H335, hits node 2, .9661

__________
changed to reflect load adjustments based on QL&OBT estimates

 

[NYDAN]

Thanks for the feedback. You have really got my interest piqued.

 

[Dr. Vette]

How do you choose which node to use with the OBT method?
Or do you run calculations for 8 nodes to see if you hit one?

 

[Ridgerunner665]

Myself....I use the fastest (MV) one I can hit with slowest powder I can use with a given bullet weight.

Example....

280AI, Norma MRP, 150 grain ABLR...node 4 for a 24" barrel is around 1.12 milliseconds...give or take 3 percent.

According to QL...I might be able to reach that one....with a little over 3,100 fps...if not, I'll have to drop back to around 2,950 fps....or switch to a faster powder and hit it at 3,000-3,050 fps.

Something I've noticed....most all published load data puts its max at 10% below true max pressure (a little over 58.5k psi for a 65k psi round), some are 15% below...this is a SAAMI recommended safety net...QL also uses it...

Load data also often stops just below the next node...not necessarily because the next node is over 65k psi...I'll gladly push on to within 5 percent of true max, or around 61,000 psi....thats about as far as you can go without really leaning on the the brass and its longevity.

SAAMI has some terms it uses: (http://www.saami.org/specifications_and ... re_CfR.pdf )

MAP (maximum average pressure)= just what it says, maximum average pressure of the rounds tested in a lot.

MPLM (maximum probable lot mean)= maximum likely to be encountered due to variables

MPSM (maximum probable sample mean)= maximum allowed or expected for any individual round for any reason...you'll notice that for 65k psi rounds it is just below 70k psi, the yield strength of brass

In a nutshell...carefully sneaking up to and over published max can be done...the key word is CAREFULLY...and the point is, the next node just may be within reach, or it may not...only one way to find out...CAREFULLY.

If that next node is over 63,000 psi...I'll settle for less speed, either with less powder or a different powder....brass is too expensive, and ONLY Lapua brass can take a full 65,000 psi and still give decent service (8-10 loads)

The above is true for modern rounds in modern rifles...DO NOT misinterpret what I said and try to load your small ring Mauser conversion (308 Win for example) or you old Marlin 1895 up to 69,100 psi....it will end badly, very badly....a certain level of common sense and knowledge of the limitations of certain firearms is required...brass yields at 70k psi...small ring Mausers and other old firearms will explode like a grenade well before 70k psi....the brass is only a "gasket", the firearm has to hold in order for the brass to do its job.

 

[Wyo7200]

Looking over my previous loads QL data, seems that there are two b_times in QL that will coincide with two obt nodes, the third node being well into the red. I think I'll start with the QL b_times for each powder and see which will give me a good velocity and psi without getting into the red.

 

[Ridgerunner665]

Which OBT chart are you going by...there are a couple different ones floating around.

 

[Wyo7200]

I'm using the table that best matches my loads of course! just kidding. I am using the one linked here in the .pdf Do you have a better source/ table?

http://www.the-long-family.com/OBT Table.pdf, found in the webpage http://www.the-long-family.com/optimal barrel time.htm

Thanks for the explanation Ridgerunner. Some of my loads (25/06, 7mm, and 22-250) have been above published max. I attribute it to having larger case capacities than what was used in the lab tests.

However, I'm perplexed at one load I tested with R22 and IMR4831 w/ 110gr AccuBond, which caused me to purchase QL. My logs show I went up to 56 gr. with no pressure signs on the brass. Second loading at 53.4gr I got full ejector marks and sticky-heavy bolt lift. Went up to 54.1 gr of IMR4831 (best group ever out of that rifle) without p signs. Second loading I saw p signs at 53.1gr. I really think I got a bad batch of Nosler brass. It's 12-13gr lighter than my RP and converted Lapua, and has 2gr avg more than RP and Lapua. Tarnishes extremely fast too. Different concern, different thread though.

 

[Dr. Vette]

OK. I can see that without having Quickload here to play with some of this info makes no sense when taken out of context. Still trying to decide if it's worth the $ or not. I know that they let you download a trial copy - does anyone know what parameters are limited in a trial copy?

Thanks.

 

[Ridgerunner665]

Very limited....

 

[Ridgerunner665]

Dr. Vette...

Give me some load and rifle info for one of your known good loads.....powder charge, bullet, oal, barrel length, and chrono'd muzzle velocity....and I think I can show you what you want to see.

Or it can be a known bad load....just any load, with a measured muzzle velocity.

 

[Wyo7200]

I think you can look at a .308 Win and 5 powders. Don't think you can change anything either so all you can do is see how the windows look. I don't mind running estimates either.

 

[DrMike]

OK. I can see that without having Quickload here to play with some of this info makes no sense when taken out of context. Still trying to decide if it's worth the $ or not. I know that they let you download a trial copy - does anyone know what parameters are limited in a trial copy?

Thanks.

Drop the coin; it's worth the investment. The money spent will serve the serious shooter very well.

 

[Ridgerunner665]

OK. I can see that without having Quickload here to play with some of this info makes no sense when taken out of context. Still trying to decide if it's worth the $ or not. I know that they let you download a trial copy - does anyone know what parameters are limited in a trial copy?

Thanks.

Drop the coin; it's worth the investment. The money spent will serve the serious shooter very well.

+1

 

[SJB358]

OK. I can see that without having Quickload here to play with some of this info makes no sense when taken out of context. Still trying to decide if it's worth the $ or not. I know that they let you download a trial copy - does anyone know what parameters are limited in a trial copy?

Thanks.

Drop the coin; it's worth the investment. The money spent will serve the serious shooter very well.

+2. You'll love it Dr Vette.