Quickload setting

[Brillo]

Here's a question for those of you who use Quickload, when you set the COAL, do you enter the chamber measurement or the COAL you're actually shooting with?

[blackburnbuccaneer]

The one you have loaded to / intend to load to - this way it knows how much space there is in the case under the bullet.

[furrybean]

Don't agree. I enter max oal and seems to work well.

[sandyb]

The one you have loaded to / intend to load to - this way it knows how much space there is in the case under the bullet.

This is correct, not the post that follows.

 

Having measured the case capacity using a fired case filled with water, first measuring the brass empty, then again filled with water, the difference being the case capacity.

From the bullet chosen the software knows the bulletts length, and so depending on the kength and thus the COL, the longer the COL, the less the bullet is seated into the brass leaving more capacity for powder. This also has a bearing and a factor on the pressure as calculated for a round of the same charge.

[Laurie]

Think about what happens when ignition takes place. Primer ignition alone usually generates enough pressure to displace the bullet into the lands - as those who have forgotten to put a charge in generally discover.

 

The charge starts to burn generating pressure and the case-walls obturate in the chamber making them grip it. Although pressure rises very rapidly to its peak, it is not an instantaneous increase to the PMax value - if it were, it would be detonation and goodbye intact firearm and maybe owner too!

 

The bullet moves into the lands long before PMax is achieved and there it receives a check. That point in effect determines the combustion chamber volume that applies as pressure undertakes most of its build-up. The check means that pressure rises more rapidly as nitrocellulose propellants' burn speed is affected by pressure. Once the bullet starts moving to any extent further down the barrel, the combustion chamber volume is again increasing, but for a very short period the rate of gas production exceeds the rate of chamber volume increase, so PMax occurs maybe around the two inches of bullet movement mark. After there, the bullet is accelerating quickly so combustion chamber volume increases quickly too, but in any event gas production has peaked and its rate now starts to decline rapidly long before the bullet reaches the charge all-burned point. Bullet weight and shank length affect things as a heavy long bullet accelerates more slowly than a light short one so PMax occurs with considerably less movement unless a slower burning powder is used in compensation - as it often is for large increases in bullet weight.

 

If it were purely the combustion chamber volume as determined by the round as loaded into the chamber and as yet unfired, ie the amount of space under the bullet base inside the case, then the loaded COAL v actual freebore / jump would have no effect on pressure; also a round with a given standard COAL as in factory ammunition fired in two rifles with the same make / length / chamber / freebore when new barrels would produce the same pressures (ergo MVs) irrespective of barrel of round count / throat erosion.

 

You don't need QuickLOAD to tell you that a 308 Win TR rifle with 5,000 rounds down it and 2 or 300 thou' throat erosion say produces considerably less pressure and lower velocities than the identical new only just run-in set-up with a nearly zero freebore chamber.

 

For single-loaded rounds with bullets seated to just short of the lands, the difference is neither here nor there. For long FB chambers but where some rounds are loaded short giving substantial jumps into the lands to fit magazines - eg 77s loaded to 2.25" COAL in 223 but fired in chambers that are optimised for an 80gn bullet at a much longer COAL, it does make a considerable difference to QuickLOAD's accuracy.

[Brillo]

Many thanks for the comprehensive reply Laurie.

[Webby]

This is interesting! especially Laurie's comments. I believe that Quick Load uses the COL entered and the case/bullet length to calculate the case volume (given an accurate starting case capacity measured by water) also calculating for tapered base it seems. Quick Loads projected pressure curve does not look anything like the actual pressure curve produced by my rifle. (I have a strain gauge attached to my barrel for what its worth!) I am interested in the OBT theory which suggests that there are optimal bullet exit times for accuracy nodes. Quick Load gives barrel exit times, however they will be incorrect if the pressure curve prediction is as far out as it seems to be compared to my strain gauge produced curves which back up what Laurie says. Ie. The moment of primer firing produces pressure which then levels out for a few millisecs(I assume as the bullet moves forward to contact the lands and as the powder ignites) before the main charge fully goes off. It then climbs steeply before dropping sometime before the bullet exit. The software purchased with the strain gauge also gives barrel exit times along with suggested accuracy nodes. These differ somewhat from quick loads prediction however they are still a calculation based on the curve to predict the exit time. Whilst the actual pressure curves show how good your reloading consistency is (and is v useful for that) it seems that bullet impact data is still required to find actual accuracy nodes.

I enter actual cartridge length. However to get meaningful results it is also necessary to calibrate the powder burn rate in QL to produce MV's that match with actual data from the field.

[pengo]

This is correct, not the post that follows.

 

Having measured the case capacity using a fired case filled with water, first measuring the brass empty, then again filled with water, the difference being the case capacity.

From the bullet chosen the software knows the bulletts length, and so depending on the kength and thus the COL, the longer the COL, the less the bullet is seated into the brass leaving more capacity for powder. This also has a bearing and a factor on the pressure as calculated for a round of the same charge.

Hi Sandy B,

 

Sorry to question your statement regarding finding the case volume using water, but should this not be done using a full length sized case, rather than a fireformed one?

 

The reason I think this, is because if you measure a fireformed case, surely it would be bigger (having expanded upon firing), therefore when you have full length resized your case the capacity would be less, which means if you have loaded to a fireformed capacity you will be more likely to have increased the pressure, unwittingly.

 

This is only my thoughts; and no doubt there a much more knowledgeable people on here, that may be able to confirm either way.

 

I am by no means a reloading guru, so I'd be just as curious to find out if my suggestion is actually correct (always happy to learn).

 

Please don't take any offence at my comment, as it is purely an observation on my part.

 

Cheers

Paul

[Laurie]

No, fireformed is the correct option - the case in this form again mimics the case as it is when pressures are in the early stages of rising, therefore that's the actual combustion chamber volume which the program needs to know.

 

In fact it will marginally understate the combustion chamber volume as a fully obturated case will have fractionally more volume, but it is liskely so mall a difference as to be unimportant.

[pengo]

No, fireformed is the correct option - the case in this form again mimics the case as it is when pressures are in the early stages of rising, therefore that's the actual combustion chamber volume which the program needs to know.

 

In fact it will marginally understate the combustion chamber volume as a fully obturated case will have fractionally more volume, but it is liskely so mall a difference as to be unimportant.

Thank you for putting me right on that point Laurie.

 

I really appreciate the knowledge that is shared on here; and yet again, I can look to moving forward with my load development. Who says you can't teach an old dog, new tricks.

 

I suppose that's the next few nights taken up readjusting my loading data.

 

Cheers

Paul