QL Results Discrepency

[snakeman]

 

The below images show data for 30cal (.308) 155g Sierra MK (#2155)

Vhit's website data for this bullet shows 46.5g of N150 but does not show it as a compressed load

Conversely, I have mirrored Vhit's data onto Quickload and the powder quantity when entered onto QL shows a significant increase, being a compressed load with a fill-rate ratio of 106.4g.....(does QL use Lapua cases?) 

(On Vhit's webiste only N550 shows a compressed load)

6.4g over seems significantly 'over'

Any idea what I'm missing here?

Cheers

 

[Gandy]

Is the seating depth correct can’t see well as using my phone but has a direct impact on case capacity / compressed load. 

[Laurie]

Viht's data frequently, more often than not I'd say, omits the 'compressed load' notation. That's not to say QL's calculation is correct, and the type of powder funnel you use and the charge pour speed/method you employ also have a marked effect on how the powder kernels lie in the case, hence how much room they take up.

The QL default 308 Win case water capacity of 56.0gn is IME very close to what my Lapua and RWS cases hold on firing in a minimum SAAMI chamber.

Remember QL is simply a model, not an oracle. It relies heavily on basic data supplied to it by powder manufacturers to obtain the key default values and the old computer rule of GIGO (garbage in = garbage out) applies as those data are often incorrect - and manufacturers don't use any industry wide indexing to relate their products' characteristics to those of others. This applies particularly to the key metric of burn rate where, for example, many Viht powders' values have been advised to QL's compiler as being much 'slower' than appears to the case in practice. (Precisely the same incorrect relationships appear as  a result in the various powder manufacturers' printed burn-rate charts, no doubt based on the same incorrect base data. QL does upgrade such default values every now and then on the basis of user feedback - N160 is a case in point having been changed in the last couple of years to have a much 'quicker' default. Case-fill depends on the bulk density figure supplied by the manufacturer, and is often a bit, or more than a bit, 'out'. 

The program is valuable in many respects, but should never, repeat never, be treated as 'gospel' which it's easy to do on the basis of calculations to two or three decimal points giving it an appearance of spurious precision. To me, its main value lies in determining possible good matches between components and likely starting loads, working from there. Also, where there is no factory data for whatever reason. In any event, I do an incremental charge weight vs pressure/MV run, print it, and then compare actual MVs against predictions during the range testing session. MV change = pressure change, only there is a multiplier of three or four so any significant MV error is considerably greater for pressure. N150 tends IME to produce higher MVs (hence pressures) than QL predictions, and N550 is far, far worse! As QL itself says as you boot the program up, results must be checked out using the manufacturer's data where available. 

[snakeman]

Many thanks for the pointers, Laurie

I'm inclined to follow Viht's published data before depending on QL results, and 'feeling' what the chamber of the rifle reveals to me upon firing incremental charge weights

Think I'll do a drop-tube funnel test with this. If nothing else it'll be intersting to see the disparity

Gandy - seating depth on QL is entered as Vhit's COAL at 2.795in on their website

Glad I asked this question

Thanks again guys

ATB

[Laurie]

19 hours ago, snakeman said:

Think I'll do a drop-tube funnel test with this. If nothing else it'll be intersting to see the disparity

 

See my piece on compressed loads here:

 

https://www.targetshooter.co.uk/?p=3543

 

and the pic of 27gn N150 in Lapua 223 Rem cases, one a straightforward vertical fast-pour through a conventional powder measure; the other using the Forster universal funnel with its narrow bore 5.25-inch drop tube allied to a slow, angled 'swirl' pour. 

[snakeman]

 

Thanks for the info, Laurie

Fascinating reading ...

I completed a test using the toothbrush method. Whilst the charge (amount) was reduced to some degree it was still showing a smidging (maybe 1 thou?) above the shoulder/neck juncture with 46.5g

It remains to be seen if there will be any further reduction when using a drop tube?

Still, all pertintent information and wisdom for my (growing) memory bank 👍

Many thanks again

ATB