Powder Variances between lot numbers

[cgrivois]

Ive got a load that Ive been trying to get to run in my pistol, but the load is too weak to cycle the pistol. The load is run by many other people in the same pistol under the same weight bullet. Ive run the loads through a chrono and my velocities/power factors are way lower than others are reporting. Ive checked my digital scale against a balance beam scale and they both show the same results. Is it possible that there are variances in the same powder from different lots. The load is 3.6 grains of N320 under 180gr fmj bullet, oal 1.125. Others are reporting a power factor of 125 or better equating to velocity of 695 or better. My results over a chrono were 635fps for a power factor of 115. Even went as far as firing the same rounds through a gun of similar model, just a shorter barrel, and results were pretty much the same. What gives.

A side not, the chrono I used was brand new out of the box, all shots registered, granted it wasn’t the most expensive model.

[Larry Gibson]

New pistol vs broken in pistol, lot to lot powder variation, stronger spring in yours, etc. Lots of potential reasons why. What pistol, what cartridge? and why such a weak load? Simple solution is to up the powder charge until functional reliability is achieved. This assumes your loads are on the low end for the cartridge used.

Larry Gibson

[cgrivois]

New pistol roughly 1500 rounds, tried every spring down the weakest one they make, Glock 35. Weak load is I shoot IDPA, trying to get around 130ish PF. I realise the loads are week, just trying to figure out why they dont replicate other loads. I need to load 4.2gr to achieve the same numbers others are getting at 3.6.

[Larry Gibson]

Have you tried taking the weakest spring and cutting 1/2 coil off at a time until you get functional reliability?

Larry Gibson

[frnkeore]

My suggestion is to buy another can of powder. Make sure it does not have the same lot# on it and try it again.

My only thought regarding your gun not producing similar results is that it might have a longer or larger chamber. Check that out.

Frank

[leadman]

What about the primers? Do you have the same case neck tension as others using this load?
Sometimes jacketed bullets are a little undersized so if your sizing die is a little on the large size this may make it easy for the bullet to leave the case before full pressure has built up.

[Rocky Raab]

As to the original question about lot variation, the accepted SAAMI standard is that canister powders be within 5% of the specifications for that powder in lot-to-lot tests. Most companies better that and hold to a 3% variation.

That's for new powder. If your old can of powder has been around a while and frequently opened (as with most handgun reloading), it has probably dried and lost some solvent content a well. That means a given amount (volume) of it will weigh less than a sample of new powder would. Because we load by weight, that means you may actually have adjusted your charge upwards to "make weight" and are therefore using more of the old powder than you would with an equal volume of new powder.

You can test that by dispensing ten charges of old powder and weighing it, then WITHOUT CHANGING THE MEASURE SETTING weigh ten charges of the new powder. If the old powder weighs less, there's part of your answer. (Ten charges allow very small differences to become obvious.)

[cgrivois]

I dont think the issue is within the pistol, obviously the load is too week to run my gun, however the same recipie runs the same make and model in other guns. Rocky thanks for the explanation, I bought the can of powder and have been going through it pretty quick, so unless it sat on the shelf it shouldnt be verry old. Ive got a 4 lbd keg comming in this week, Ill try the same load and compare it to the can Ive been using. Thanks for the responses.

[cgrivois]

would primers play that much of a role in the velocity of a pistol bullet. If a different brand primer can change velocity by over 100fps in a pistol than that could be my problem. Im running CCI and I know a friend of mine running the same load throught the same gun was running federal primers.

[Rocky Raab]

It's possible, perhaps. Changing primers can result in more velocity, or less velocity, or no change at all. Your buddy's gun may be the same type, but it is NOT the same gun. Consecutive serial number guns can have very different likes, or different results with the same load.

[leadman]

Borrow some of your buddies Federals and answer your question.

As an example of what primers can do in a rifle let me tell you of my 7mm Rem mag. Encore rifle.
I worked up a load out of a book with the old IMR 7828, Nosler BT 150gr, CCI200 primer. No pressure signs, velocity was about 3,275fps in my 28" barrel, 1 1/2" group at 200 yards.
For some unknown reason I switched primers in a batch to Winchester LR magnum. Velocity reduced to 3,100 fps, accuracy decreased to about 4" at 200 yards. But the primers were flattened, and the cases expanded about .003" more than the previous loads with the CCI primers.
I finally reliazed what I did, switched back to CCI, all is good.

[Rocky Raab]

Leadman, in a different thread, I made the statement that changing primers can result in LESS velocity but MORE pressure. Somebody took rather pointed exception to that in an off-channel communication.

Thank you for providing a concrete example that apparently demonstrates my claim.