How much variation is there between powder lots?

For sure you need to load down a few rounds, and watch for pressure signs with each as they work back up to your preferred load.

I have seen huge variance between Varget lots. But nothing to speak of in 4350.
Don't assume this for yours though.

 

In wearing out several 30 caliber barrels with IMR powders of 4895, 4064 and 4350 plus some Varget, I've not seen any difference between lots. I'm sure there's a small difference in peak pressure and muzzle velocity, but accuracy up to 1000 yards never changed. I used the same charge weights as with previous lots and never noticed any difference. Same sight settings worked too.

Sierra Bullets doesn't work up loads when they change powder lots or test barrels for a given cartridge. They just meter the same charge weight used before and get excellent accuracy; probably better than anyone else shooting their bullets.

 

It has been known to have very wide variances. for a specific example, there was a very bad lot of RL 22 for about 5-7 yrs ago that got recalled even. I had to drop 4 grains in a 6.5-6 AI to get back down to my previous velocity and MV. My failure to check lots was due to running out of powder the night before leaving for a match and had to go get another lot. Cost me the match and blew three trigger sears in two days.

Just keep in mind, that if you are working loads on the upper end of the pressure curve, then you really need to verify each and every lot. Otherwise your risk serious pressure issues and damage to the gun.

If you are working that upper curve, even changing primers can put you into the dangerous zone.

Also, you can bet that any reloading manual printed today stops showing data well before that upper zone and most lot to lot or primer variances will not put you into that danger area, but do not bet on it.

Here is a picture of a bolt face that was burned. They did not rework loads while switching from WSR to Rem 7 1/2 primers.




BH