Thread: Optimal Barrel Time (OBT) - anyone else use it?

Anyone else here also use Optimal Barrel Time and Quickload with load development? I’ve attached a link for the guys potentially interested in it.Optimal Barrel Time Concept . Although referred to as a theory, I’ve used it with great success in the past. As a example, the Barnes X group was the second load I tested in my 375H&H and the Nosler also the second or the third load tested.

Yeah I've used it but my experience was that it only "works" about 50-60% of the time. My latest effort with it in a 6mm CM (using the app in Gordons Reloading Tool) was an epic failure. I'm in the early stages of trying to work out why.

Yep it’s how I’ve done all my load development the last few years. I’ve found it very accurate and have saved a lot of time and money. The theoretical optimum speed and best accuracy is usually within about 20-30fps Haven’t tried the other program mentioned just qload and the btt spreadsheet

https://www.nzhuntingandshooting.co....76/index2.html
My thoughts on OBT in post #24

I know some guys are of the opinion that longer barrels are sometimes challenging. Are you able to calibrate Gordons reloading app? The approach has only failed me in the past as a result of some error on my side.

I've used it as a tool or ballpark target but always find the velocities either to low or just out of reach

Sort of worked for me with my old rifle that had a 24" barrel and no suppressor (i.e got within .4 of a grain or so).
With my new Tikka and a 20" barrel and suppressor I can't even get close. As with Noswai I found the speed at each nod to be either to slow or over pressure.
Now I just work up a load with a low SD, then adjust the seating depth to get the accuracy

I reckon its close but perhaps its for uniform barrels harmonically. Mine it turned down to take a half back fwd suppressor and it is really tuned atm. But i put my load into the GRT program and i noticed that OBT figure was off.

Giving this a go in my Kimber (OBT). You can use seating depth to tweak barrel time (see 46gn vs 46.5gn).










So both these loads sit nicely on Node 5 based on a Lab Radar measure of velocity. Hopefully one or other or both shows some accuracy...

It's a bit of a dark art. It seems to work well for me in most cases but like has been said, it's often off by a little bit.

I do wonder if little things like a concaved crown might mean that the true length needed for the calculation is like 19.9" rather than 20".

Pommy, the job that I’m trying to fund my passion with includes a lot of modelling, specifically flood (hydrology and hydraulics) modelling. In my experience like any other modelling Quickload should be viewed as a relatively close approximation (almost crude) of reality and in this case of internal ballistics. There are just too many unknowns that can not all be accurately factored in. The trick with QL is further knowing what to change in order to increase (almost calibrate) the confidence in QL for the setup you are modelling. My rule of thumb is to populate QL with as many as possible knowns. I measure barrel lengths by means of inserting (very carefully) a cleaning rod from the muzzle until it reaches the boltface and then mark the rod where the crown touches the rod (masking tape around that point helps as well) and the measure that length. So yes I measure my barrel length based on the crown and provides me with a little more confidence but the question does that few mm make difference. Perhaps not.

Before I started using chronographs, I would run QL and then load one load on OBT and then load 2 more batches, one .3gr above and the other one .gr below OBT load. The 375 loads above was done this way. My approach these days is to research what sort of jump the guys are getting accuracy with, load 3 rounds on OBT with that jump, measure velocities with that load, “calibrate” QL with that data and still do the same. The only thing thing that I have changed is that I build a mobile reloading box and with prepped and primed cases I start searching around the OBT load while on the range. I therefore use it more as a guidance on where to start searching for a load and use the target as my final guidance.