Quickload

[furrybean]

Hi all,

Ive been playing with QL for the 6x47 and been using the normal seating depth defaulted by the program.

Im looking at a load for the 105gr Amax and the default gives OAL of 2.800 and my max is 2.608

The pressures go through the roof at that OAL compared with default

I used default with the VLD and worked up and they were great.

Ive adjusted the H2O value also up 0.7gr

Anyone with any thoughts?

[DaveT]

I have no experience of this specific calibre (I do note that you have chosen a heavy for calibre bullet) but if you are saying that your chamber will only accommodate a max COAL which is 2/10" less than Q/L is expecting then I am not surprised that pressures are elevated.......from your post it sounds like you are reducing case capacity by seating the bullet very deeply.

[Brillo]

First of all you need to recognise that QL is a database of all known data or the cartridges within it.

Some cartridges need a bit of adjustment and one of those is the 6mm BR. I suggest that your first port of call is the actual H2O capacity and take it from there. Then measure the real bullet length.

Tweek those and note the pressures.

[furrybean]

Cheers for the replies.

I've put in the actual h2o and oal and that's what lead me to the question.

It was surprising how much the decrease in oal increased pressures and as I develop my loads powder first and then oal, if the best accuracy comes from near max then adjusting the oal (which I normally start long and work increasing the jump) will increase pressure further.

[Laurie]

This applies to any small case-capacity design as any change to the effective case capacity has a large effect on the pressure that any given charge weight produces. It's partly about changing the ratio of combustion chamber volume to bore area, partly about the change it makes to the fill-ratio as a charge that fills the case fully or is compressed behaves differently to a charge of the same powder that uses say 90% of the available space in a case.

 

One thing that many people don't recognise here though is that it's not so much COAL as loaded, rather the available COAL if the bullet is seated to just short of the rifling. This may be the same value, but not always. If a chamber's throating is such that a 308 Win say could have a bullet seated at 3.000 inches, but the user seats it at 2.800 for magazine feed, I'd use the former figure in the program. Even if seated at the shorter length, the bullet will move forward into the rifling before charge burn gets fully under way, so it's the longer length that reflects the intial combustion chamber volume.

 

There is a related aspect where I sometimes find myself disagreeing with QuickLOAD - the additional recommended shot start pressure that's advised when the bullet is seated into the rifling. Perhaps because I normally use light neck tension which comes close to producing 'soft seating', I find that increasing the value by the recommended additional amount of 7,600 psi taking it to 10,826 sees a higher pressure / MV prediction than I actually encounter in practice. So, I usually leave this value at the default setting irrespective of whether my rounds are making a small jump to the rifling, or are gently seated into the lands. Lots of neck tension allied to a significant 'hard seating' into the lands may be a very different matter.

 

To quote an example from 6.5X47L and a load that I tried on the range yesterday, QL predicts 59,817 psi PMax with the default shot start setting of 3,626 psi, but move the bullet forward marginally into the lands and add the recommended 7,200 psi to take it to 10,826 and the pressure peak rockets to 70,176 psi. If correct, I'd have to reduce the charge weight by two full grains from 39 to 37.0 to bring it back to the original pressure level.

[furrybean]

 

One thing that many people don't recognise here though is that it's not so much COAL as loaded, rather the available COAL if the bullet is seated to just short of the rifling. This may be the same value, but not always. If a chamber's throating is such that a 308 Win say could have a bullet seated at 3.000 inches, but the user seats it at 2.800 for magazine feed, I'd use the former figure in the program. Even if seated at the shorter length, the bullet will move forward into the rifling before charge burn gets fully under way, so it's the longer length that reflects the intial combustion chamber.

Brilliant. Thanks a millions, that is the information I was wanting. Such great knowledge!

[henryo]

Here are some examples I chronographed (only thing varied is seating depth - averages):

 

Load A: 10 thou Jam - 2356 fps

40 thou Jump - 2314

80 thou Jump - 2325

120 thou Jump - 2337

 

Load B: 10 thou Jam - 2407 fps

40 thou Jump - 2371

80 thou Jump - 2397

120 thou Jump - 2384

 

Load C: 10 thou Jump - 2501 fps

50 thou Jump - 2459

90 thou Jump - 2450

120 thou Jump - 2486

 

A fairly small difference - probably not enough to worry about.

They all seem to follow a trend though.

Compared to a slight Jump:

Jamming increases velocity slightly

Seating deep increases velocities slightly

 

I've also tried going from a mild primer to a magnum primer and it made no difference whatsoever.

[Laurie]

henryo - very interesting results and thanks for posting them. I've seen similar effects reported before but not with so much detail that shows a pattern.

[henryo]

I should mention the sample size was fairly limited in this case so the conclusion I drew isn't incredibly scientific.

Might be worth doing 10 shot averages in a low ES round some point in the future at more seating depth intervals.

[Brillo]

There's some interesting stuff here about QuickLoad, especially Laurie's second paragraph in his first response. Up to now I have always adjusted my powder charges according to the variations in seating depth. For example, I'll use QL data to ensure a new load is safe. Once I've found a potential sweet spot from that load I'll then vary the seating depth and alter the charge upwards or downwards depending on increasing or decreasing seating depth to keep the velocity the same in the QL results and then develop further depending on group size and actual chronograph results.

The part about using the maximum possible COAL as the basis for all loads of that particular calibre now leads me to believe I'm trying being to precise.

 

One thing is for sure. Although I use QL extensively and find it an extremely useful tool, and a brilliant aid to load development, I won't follow it blindly.

[furrybean]

In a similar vein, if you know your water capacity of a fired case, can this value be used for all calculation even if using new brass of the same lot etc as ultimately it will expand to the same volume?

[Laurie]

In a similar vein, if you know your water capacity of a fired case, can this value be used for all calculation even if using new brass of the same lot etc as ultimately it will expand to the same volume?

 

Yes, absolutely right. The case starts to expand to fit the chamber through primer induced pressure alone and is a near perfect fit as peak pressure is achieved. So it doesn't matter if the case is new or has been full-length sized.