Varations In Powder Lots

[Funshooter45]

Some of the above points are very good. If indeed, it was common for powders to vary by 10%, then it would be impossible to find a sweet spot and then duplicate it without resorting to the whole load workup scenario. That's why I mentioned that in my experience, the powders don't really seem to vary much. Sure, it's wise to be careful. If I start out with a new jug of powder, I might load 5 or 6 test rounds, starting 2 or 3 % below my favorite, assuming that favorite load was not pushing the max before in my rifle. I'll fire those just to make sure they don't show any high pressure signs. So far, I haven't noticed any big changes. The favorite charge weight still works the same usually.

However, that is one of the reasons to buy big jugs of powder for rifles. Besides getting a cheaper price per pound. For rifles, it's typical to get only 100-150 loads per pound. So if you find the magic load you like, if you have an 8 lb jug, then you know you're good to go for 800-1000 rounds or so.

But it's not wise to rush out and buy 8 lbs until you decide it's what you really want. For your 22-250, Varget could well not be the best choice at all. Something might work better. I'm like you also in that if My first 20 loads with a given powder, bullet, cartridge look really promising, I'm likely to go out and buy another 1 lb jug and start mixing them together, just to be safe that any favorite loads I get from then on will easily apply for the next 200 rounds or so. I don't have any problem mixing the same powder from different lots. Heck, I've even mixed W-296 and H-110, same thing mixing HP-38 and w-231.

 

[MEHavey]

A chronograph only tells what the average pressure that drove
the bullet down the barrel is.

It does NOT supply information about the peak pressure.

Cartridge + Case + powder type/weight + bullet type/weight + OAL + Internal Ballistics program will give you a pretty good idea of the velocity expected for a given pressure curve.


From the velocity observed, you can then extrapolate an approximation of the actual pressure (for example by cubing the velocity ratio).

Nothing in life is "exact," but at squinting with one eye open is a whole lot better than flying blind.

 

[kingmt]

This is what I was told by a company that buys large containers that has been blinded by the manufactures & resales it in smaller containers. The reason for the 10% or go back to the starting load whichever is less is 2 part. 1st is a company my change the powder & not the name. He said it is best to use load data for the same period of the powered. He gave an example of Alliant & Promo but I don't remember the exacts. 2nd part being the powder isn't always what they say it is. He then gave an example of company X sent a batch of product A but it didn't look like A so he tested it & it burnt way to fast for A. So he called company X & gave them the lot number & explained what he found. They checked into it & found that when they went to blend 2 lots together they actually had 3 different lots.

All of this is not something I want to put out as gospel so I leave the names out to protect the company from slander if it is not the truth.

This is possible & is the reason I repeat it.

 

[brickeyee]

From the velocity observed, you can then extrapolate an approximation of the actual pressure (for example by cubing the velocity ratio).

You are still at the mercy of the powder burning model in the SW.
As you get further from the conditions used to develop the model, the less reliable it becomes.

All the SW is doing ti estimate velocity is integrating under the pressure curve with a set of parameters.
Bullet bore friction, the burning behavior of the powder (it is a function of the pressure the powder generate burning), jump to rifling engraving, engraving force, etc.

There are very good reasons we still use pressure barrels and systems to actually measure the pressure when we need to know what it is for sure (and even those tests cannot catch every possible combination of parameters).

No model has yet accounted for secondary detonation.

We know it happens, but no hard idea why (though a leading theory is that the bullets actually stops momentarily leading to bore obstruction type behavior).

All models are wrong.
Some models are useful.

 

[MEHavey]

As before, Nothing in life is "exact," but at squinting with one eye open is a whole lot better than flying blind.

Neither I nor anyone else should rely exclusively on even the best of theoretical models for exact pressures. For that matter, you can't rely on data from someone else's pressure-gauged barrel either as the data is good only for that chamber, that barrel, and that day's firing environment ....all of which can be dramatically different from your barrel, your chamber, and your firing environment.

Models are guides. Models allow the experimenter to predict results which must be compared against actual data. Models permit better understanding of what the key factors are which affect that actual data. Good models allow the competent experimenter to fit those factors to actual data and then compare against new data in a changed loading regime -- and to do so w/o flying blind.

Moreover, good models allow you to cross-correlate between very different load recommendations for the same cartridge found in different manuals. Without that ability, you don't have a clue who is right, or why.

As to the simplified "(Vactual/Vpredicted)-cubed" pressure adjustment, it has proved quite useful over the years if the excursion from predicted isn't too radical. (If it is, look for a loading blunder or data-entry mistake before you blame the model.)

Case-in-point:
- QL predicts 2,800fps and 47,300 psi for a certain 150gr/IMR4064 loading .
- Actual velocity chrono's for the day out to be 2,870.
- The (Va/Vp)cube adjustment yields probable actual day's pressure to be close to be 51,000

.... and I'd back off a full 1.5gr (predicted) to get the originally-targeted pressure/velocity for my M1 that day -- regardless of any manual's listings.

 

[243winxb]

Varations In Powder Lots- Varget

Proof of Varations. Read first post @ Link http://benchrest.com/showthread.php?73272-Reloading-Question-things-gone-bad-and-can-t-find-a-reasonPost #20 >

Well, just got back from the range, and think I've found the problem, and not real happy with the cause. Seems there is a big difference between this container of powder from the first two I've used.
After the first pound of Varget, I decided I was going to stick with it so I bought five one pound containers of all the same lot/batch numbers in an effort to eliminate the problems you sometimes have between different batch's. Well, it looks like that plan backfired on me.

I started from scratch, loading new, unfired brass. I loaded two different bullets, 52 grain Sierra HPBT's and 50 grain Nosler Ballistic tips. I backed down to 36 grains of Varget with each and used BR2 primers for the first sets and then 36.6 grains for the second sets. I seated bullets for each set of bullets to jump .020", .010" and then touching the lands.

I set the Chrony up so I could check velocities on each load. My normal load of 36.6 grains of Varget and 50 grain Noslers were always in the 3,790 - 3,800 fps. I didn't have a records on the velocities for the 52 gr Sierra's.

The first loads I shot were the 52 gr Sierra's with 36.0 gr of Varget, since they didn't cause a problem last week. They were 3,700 fps average with not pressure signs.
Next were the 52 gr Sierra's with 36.6 gr of Varget. The were 3790 fps with slight flatning of primers.
Next was the 50 gr Noslers with 36.0 gr of Varget. The .020" jumps were 4,070 fps with flattend primers. The .010" were 4,054 fps with very flat primes and small craters. I decided not the shoot the one against the lands
Next was the 50 gr Noslers with 36.6 gr (was my normal load). The .020" jump were 4050 fps, flatnend primer with small crater and bolt face mark on base of brass. I didn't shoot the rest.

I have a 300 fps increase in this load with this recently opened container of powder and this is the second container I've opened from the same batch/lot number. This kinda pisses me off. The reason for buying so much powder at once was to keep this from happening. Since this was enough powder to last me several years for this rifle, I've got to dump it all into one container, blend it all together and start off all over buiding my load. That or switch over the to 52 grain Sierra bullets, since they are not giving me the problems and they do shoot very well in it.

Even the 36 grains of Varget is showing to hot for the 50 grain Noslers right now.

Well, I need to make a correction. The 52 grain Sierra's were having more pressure problems than they were showing in the primers. I just got through mic'ing the the bases on all that new, unfired brass I used to load with. I should have taken the mic with me. It's mic'ing as much as .002" - .003" larger than it did before I shot it. With what I ruined last weekend and that from this weekend, that's about 50 pieces of brass that's only good for scrap metal now. That's a lot of work down the tubes because all this brass has been fully prep'd and matched as if it was going to be used for benchrest.

 

[28lx]

Proof of Varations. Read first post @ Link http://benchrest.com/showthread.php?73272-Reloading-Question-things-gone-bad-and-can-t-find-a-reasonPost #20 >

Sorry to hear about your problems. As I stated before the Chrono dont lie.

 

[243winxb]

Not my problem, shows you did not follow the link

Sorry to hear about your problems.

Not my problem.

As I stated before the Chrono dont lie.

A Chrono tells us nothing about pressure.. It only confirms high velocity . The web area expanding is what shows high pressure. From post above>

I just got through mic'ing the the bases on all that new, unfired brass I used to load with. I should have taken the mic with me. It's mic'ing as much as .002" - .003" larger than it did, before I shot it.

This .002" to .003" is measured over the web area. :banghead: Firing 1 round would have shown high pressure.