Powder charge margin of error

[omnimedic]

Ok, my split personality is fighting and needs a tie-breaker with regards to powder charge measurements and margin of error. How close to the data do I need to be?

The "close is good enough" fireman in me says that getting within 1 grain is good enough.

The pre-med student that works in a chemistry lab and measures stuff says "you have to be as accurate as your scale"... I.e. if the charge calls for 46.1 grains of powder, 46.0 is too light and 46.2 is too much.

What say ye on margin of error? 1%? 1%?

[MEATSAW]

With rifle loads, I load for accuracy/consistency. So I measure every charge and I make sure every single one is the same. My scale measures to 0.1 grains. With pistol ammo I measure every 10-15 rounds and I make sure I'm throwing the same charge. With a good metering powder (I use #5) and my lee pro auto-disk it really never has been off.

[CrustyFN]

With rifle and pistol I don't want the charge to be off more than .2. So far with my Lee pro auto disk and Dillon powder measures they have never been off that much.

[xLPlushy]

With rifle I weigh every charge and they're all equal weight. With pistol, I'll check every 5th-10th charge out of my Lee PPM. When I'm working a new pistol load, I weigh every charge out of my RCBS ChargeMaster1500.

[Gster]

Rifle loads I make exact. Pistol, I use Titegroup and load .1 up from starting charge. Not a very big window with Titegroup and have never been off more than .1 either way.

[William T. Watts]

I hand weigh both rifle and pistol, I do not load more than 500 rds yearly so hand weighing doesn't take a great deal of my time. I use a RCBS 1500 Chargemaster, then confirm with a RCBS 505 scale! William

[Bart B.]

Benchrest winners and record holders shooting groups up to 300 yards meter powder. They see no need to weigh each charge to exact amounts. Up to 600 yards, they'll weigh to a 2/10ths grain spread and that's gonna do just fine. 1000 yards downrange, benchresters will weigh each charge to the nearest 1/10th grain; that does make a difference that far away with super accurate rifles shot by very good shooters.

Sierra Bullets meters all powder charges testing their stuff for accuracy. They don't even work up loads when changing component lots. Their best match bullet shoot 1/4 MOA in their 200 yard indoor range.

Federal's Gold Medal Match ammo in .308 Win. will shoot about 1/2 MOA at 600 yards in a good bolt action match rifle. The powder's metered, not weighed, put in brand new cases and bullet runout's up to .004". It'll shoot about 1/4 MOA at 100 yards.

Arsenal .30-06 and 7.62 NATO match ammo metered IMR4895 to about a 3/10ths to sometimes 4/10ths grain spread. With FMJBT match bullets not quite as good as Sierra match bullets and bullet runout up to 5, sometimes 6 thousandths, good lots of ammo would shoot 6 inches or better at 600 yards. They shoot a couple hundred shots per test group. M72 and M118 match ammo would shoot 1/3 MOA at 100 yards in semiauto service rifles.

The above aside, shoot a 30-shot group with exact charge weights and another 30-shotter with metered charges, use the method that produced the smallest group. I think most folks will be surprised.

[James K]

The replies seem odd to me. In most cases, small deviations in rifle cartridges are less likely to affect either accuracy or safety than in pistol cartridges, for the simple reason that a, say, .2 grain variation in a 50 grain charge is less percentage of deviation than the same .2 grains in a 3 grain charge.

Jim

[SL1]

In a rifle cartridge that takes something like 55 grains of a specific powder, a difference of 0.4 grains is not likely to make a big difference in accuracy IF IT IS ± 0.2 GRAINS AROUND A GOOD ACCURATE LOAD. And, 0.4 grains over max will probably not damage a good rifle, even nif it does give some pressure signs. (Of course, that is assuming that you worked-up to the max charge without getting any pressure signs.)

BUT, in a pistol cartridge with a heavy bullet and a fast powder, where max charge can be 4.0 grains and the start charge is 3.6 grains, that 0.4 grain spread can make a lot of difference in accuracy. And a 4.4 grains charge might put you 20% over SAAMI pressure limits.

So, how closely you need to measure your charge depends on what cartridge, bullet and powder we are talking about.

SL1

[jersurf101]

I agree that pistol caliber has the least room for error. Especially fast burning/low volume powders. Being within .1 grains seems fair to me. I weigh every charge. Especially with powders like unique.

The reason to weigh charges for rifles is different although no less important. like to hit what I am aiming for.

[math teacher]

+1 for Bart B. He nailed it.

[MEATSAW]

It may not make a difference being exact but I like making the best ammo I can. It's a pride thing I guess and I only load 50 or so rifle rounds at a time in the evenings, so the few extra minutes are of no matter.

[Newton24b]

it does but it doesnt. do you really think that the bulk box of 45 acp fmj you bought was weighed down to .04 grain deviation per cartridge? i think not. a generalized range is OK from what ive seen. its why if you deal only with pressure, and your not playing with a compressed charge you should have no real issues.

example, if im not crazy.

if your using a 148 grain wad cutter in a 38 special, and the powder your using calls for a 3.1 to 4.1 grain charge, and your particular gun shoots best with 3.2 grains, a 3.1 to 3.3 grain charge isnt actually going to do anything to you.

on the other hand, how inaccurate is your powder measuring/dispensing system. its not UNUSUAL for a black powder spout to be 10 % off of what its listed as when you switch granulations of powder.

[Qtiphky]

I really think it depends on what you are talking about. I agree that if you are loading for rifle and your load is 23.6 grains and you go through and weigh each charge that is thrown, you will probably get a slight variation. I don't typically load more than 50 per session as my ADHD kicks in and I don't want any mistakes. Repetitive work for me is very boring. I weigh every charge and those that are under, I throw back, those that are over I hand dump some back in until it is right. As for the 50, once I get my trickle charger dialed in, I have maybe 2 that will need to be thrown back or hand lowered. Not that I am afraid of being over the charge by 1/10 or 2/10, but the charge is the charge that works in that rifle. During testing I already tried above and below that charge and found that the 23.6 works the best out of that particular rifle. Will it still hit a tennis ball sized target at the distances that I am shooting, yes, but like you I believe that the measurement and the load is the measurement and the load.

As for pistol, once I get my powder dump dialed in, I don't check but maybe every 10th round. I visually inspect each load to ensure that the level of powder appears to be the same and keep loading. I'm not worried so much with pistol rounds as I don't shoot matches or the like, just defensive skills work and family fun at camp. At the 7-20 yards we shoot at, I haven't noticed any accuracy changes.

[thump_rrr]

Ok, my split personality is fighting and needs a tie-breaker with regards to powder charge measurements and margin of error. How close to the data do I need to be?

The "close is good enough" fireman in me says that getting within 1 grain is good enough.

The pre-med student that works in a chemistry lab and measures stuff says "you have to be as accurate as your scale"... I.e. if the charge calls for 46.1 grains of powder, 46.0 is too light and 46.2 is too much.

What say ye on margin of error? 1%? 1%?

In a reloading manual you will never see a particular charge being called for.
There will always be a starting load and a maximum load.
That is also dependent on the firearm they used to develop the load.
Always start with the starting load and develop it to your wants and/or needs.

A good load should maintain accuracy +- a few 10ths of a grain.
If you are loading maximum power loads that are cratering the primers, sticking bolt handles etc. then a few tenths more may mean disaster.

Personally I spend the time to maintain 0.1gr consistency for my bolt action rifle loads and 0.2gr accuracy for semi-auto rifle and pistol loads.
Then again none of my loads are +P loads.

[Nathan]

Pistol. . .I try to dial in my charge so the average throw meets my load I want. On small charges, I like to keep throw variation +/- .1 on my lot control data. Check 1 in 10-50 rounds. On larger pistol charges +/- .2

Rifle. . .Ball - +/- .2 Stick. . .Weigh each one for +/-.1

Frankly scale accuracy probably adds another .1 in there.

[William T. Watts]

If I were not going to weigh ever charge I would probably go to the local Walmart and pick up Remchester ammo and call it good to go. The ammunition will function thru virtually ever type of firearm made, the rounds will fire, they will kill game, they will not shoot the smallest groups. There are those of us who weigh every charge, I say try weighing, then try throwing, make up your own mind which you prefer. William

[Unclenick]

Omnimedic,

I'm going to avoid the whole name-a-grain issue. There is an old rule of thumb that if you see a load produce a pressure sign, you should reduce it 5% and call that your maximum load. A charge reduction of 5% will usually produce between 8%-15% decrease in peak pressure, or roughly 12% on average, depending on the cartridge and powder and pressure level and how much empty space is in the case. Generally, to play safe, one tries to keep within half that much change in incrementing a load to approach a maximum charge level, so as not to overshoot it. Richard Lee recommend 2% charge increments for load workups, for that reason. These will produce between 3.3% and 6.3% peak pressure increase, depending on the cartridge, but around 5% average peak pressure increase for all cartridges.

So, I think from your "good enough" standpoint, a ±2% charge weight precision will be safe and should continue to function in most guns. For accuracy loads in a rifle you will want to do better, and ±1% is often fine for a "good" rifle accuracy load. Some loads are touchier than that and want tighter charging. I've build a number these over the years. I always reject them. The reason is that a load that touchy is not going to behave well if ambient temperatures change much and particularly not as barrel temperature increases during any sort of sustained fire situation (rapid fire phase of a match, for example). You always want to look for a rifle load that starts out able to span at least 2% (±1%) of charge weight without changing point of impact appreciably in your rifle, and will do it at longer ranges, and not just at 100 yards.

So now you run into another problem. Those percentages are too small to hold for many pistol rounds. 2% of 5 grains is 0.1 grains, and that's about as tightly as you can measure. Fortunately (or not, depending on how you look at it) most handguns don't shoot with the range or accuracy asked of a rifle load, and so we can afford to be less precise. The way to handle that is to see what your powder measure dispensing span precision is, then subtract half that amount from the maximum load we expect to approach and don't pass that point. If you shoot reduced pressure target loads, that also gives you more safety leeway. With very small capacity cases, like .25 Auto, 0.1 grains can be 10% of the load. For those I suggest making a custom powder scoop. Search the board and you'll find threads describing how to make these from .22 rimfire cases.

[BumbleBug]

Originally Posted by James K

The replies seem odd to me. In most cases, small deviations in rifle cartridges are less likely to affect either accuracy or safety than in pistol cartridges, for the simple reason that a, say, .2 grain variation in a 50 grain charge is less percentage of deviation than the same .2 grains in a 3 grain charge.

The replies seem odd to me too. I think it is right to think of a maximum allowed variation in terms of percentage, but I also believe there should be limits. The lowest limit of variation should stop at .1gr and maximum limit should stop at 1gr. The actual percentage should be less than 1% in my opinion. I use .6% variation as acceptable for standard ammo.

FWIW...

...bug