Changing Powder Lots

[Swifty]

Hey guys, just wanted you opinions on this. I recently had to change powder lots for my .220 and of course some changes were needed. I had my powder thrower set so it threw about 39.2 grains of the old lot of Reloader-15. I would then trickle up to 40.0 grains which is the charge I have been shooting. When I bought my new lot of powder, I was doing some comparing and found that with the thrower set the same, it would throw 40.0 grains of the new lot of powder instead of 39.2, I just ignored this and loaded up my rounds with 40.0 grains of powder and they shot terrible! So I decided that being I had always trickled in another .8 of a grain after throwing with the old lot, that I would do the same with the new lot. So I loaded up some rounds with 40.8 grains and they shot a bughole group like my other loads did! The only thing that concerns me is that I was already at or over max load with the 40.0 grains and now I added even more! Did I do the right thing or should I have loaded them with .8 of a grain less instead (39.2)???

 

[BJS6]

Swifty,

Powder is made to me measured by weight not volume so it isn't entirely unusual to find that the same measure setting could drop a different weight charge of a new lot of powder. The temperature of the powder can also effect the dropped weight, the powder kernels expand (like most materials) when heated and as such take up more room in the measuring cylinder of the dropper. That results in the same measure setting dropping less weight of powder, if it is cold it will drop more weight for the same setting.

What you should have done is to load at the same charge as before, or maybe lower and work up again, and compare the chronograph readings of the old lot versus the new lot and adjust the new charge to duplicate the old loads velocity.

In theory if you did the above you have matched the old load to suit any variation in powder burn rate of the new lot. In terms of accuracy it may be necessary to fine tune a little either side of the load that matches the velocity assuming you really want to get the last bit of accuracy that load has to offer.

I'd guess that what you have done is ended up with a good load by sheer coincidence. I did that once, messed up on a measure setting without knowing it and wondered why the load all of a sudden started shooting better, checked the velocity and it was down, checked the dropped weight and it was down as well, I wasn't weighing them. Lucked onto a good load that I had missed earlier.

Bryce

 

[Clifdweller77]

Tread Lightly

From 6mmbr.com this is their recommendation and I would follow it.

WARNING: Lot variances with powders can be extreme. Whenever you buy new powder, even the same brand, start 10% low. NEVER assume pressures will be safe if you change lots or ANY component.

Sam

 

[Larry Elliott]

From 6mmbr.com this is their recommendation and I would follow it.

WARNING: Lot variances with powders can be extreme. Whenever you buy new powder, even the same brand, start 10% low. NEVER assume pressures will be safe if you change lots or ANY component.

Sam

I think that this applies especially if the lot of powder you were using is several years old.

A charge that exceeds a manual maximum may not be too hot in your rifle, but it's always good to play it safe when you change powder lots. The manual may have had a faster than usual lot of the powder in question and you may have a slower than usual lot, or vice versa. Better to start off a little low and work up rather than break something expensive - like you. New eyeballs and the like are in short supply, and expensive to replace.