Do old powder cause big extreme spreads? Tried the old IMR7828 in the can for my 7 Mag and 160 Accubonds and ES is awful and jumping back and forth between 20 to 100 fps. Checked the color of the powder and it looks normal. All my brass is prepped properly and annealed.

Tack Driver, I have burned a good bit of powder in 7 rem mags. There are others that will give more velocity, but if a low ES with a 160 out of a 7 mag is what you are looking for, 3 good ones to experiment with are H4831sc, Retumbo, and Vihtivouri N-165. All are capable choices for match grade ammo. Most often the lowest ES will be found just short of a maximum pressure load with a fairly full case. Atleast in the 7 mags I have fooled with.

Smokey, I'll switch to RL-25 or Retumbo for better case fill and see how it does. Thanks

Might look at RL-26 as well, have seen some good things from that powder.

7828 would work fine in the 7 mag. A high ES can be caused by many factors. The top item is a consistent powder charge accurate to .1 grains or less. Other factors would be out of the accuracy node, low pressure load on a magnum round, different brands of brass/head stamps, different neck tensions, internal barrel conditions (clean vs fouled). There's all kinds of factors. It's hard to nail down your exact casue without knowing more info on your loads, rifle condition and such.

Agree with Chad...one other thing, primers.

Yep. Last three rifles I have worked up loads for all had best results with the same primers. One really it was pretty much a wash between Federal and Sellier &Bellott but the other two gave best ES with the S&B.
Also the S&B seem to have a "tougher "cup

It could be a low pressure issue, I was running 2930 fps with 64.5 grains which is half a grain over max. I was expecting it to be over 3000 fps with max charge. It should tighten up its ES if I approach 3000 to 3100 fps. Using CCI 250 primers as well. I have seen the 7 Mag shoot accurate at close to max or at max charges.

I don't know that powder. But I'm pretty familiar with 7 Rem Mag and .300 Win Mag, each with Retumbo or H-1000. Each seem to always do well with a full case of 100% or more fill, with the two powders mentioned.

Case fill helps as well, I just loaded rounds for my ladder tests, RL-25 and Retumbo. Hope to see good results this weekend.

You will get more consistent burn when pressure is high enough to promote the burn. You may be on the edge of sufficient pressure.

64.5 grains with a 160 grain bullet shows to be a max load, if not over max load by some data. But, as powders get older, the burn rate decays, slowing down the burn, and requiring more powder to compensate for this. So, with your exact set up, I'm not sure what would cause 100 fps. There's nothing wrong with 7828 powder in a 7 mag. It's a good magnum powder. This combo itself should not be causing a high ES. But work on the load some by changing the powder charges slightly, and see what results you get. Also, the chrono you are using is a big factor. The cheap $100 chronos are just that, cheap. They are very light sensitive. So, depending on your equipment, results could vary.

+1 on Chad's comment about chronographs. IMO, stats provided by them are probably not all that reliable.