I shot some three shot 100 yard groups yesterday. The velocity of one load using Varget was everywhere showing variances up to 158 fps with the same charge. I shot some more groups using the same rifle with IMR 4350. These loads were ultra consistent. The maximum variance in six shots was 9 fps. The trouble?? Neither shot great but the Varget had the best group size (1.1") and the IMR 4350 was 2.00".

The rifle" Rem Model 7 in 300 SAUM
Bullet: Hornady SST 165 gr
Case: New Remington Brass
Primer: Rem 9 1/2 M

Could seating depth have anything to do with this? I used a comparator to measure a "loose" round I chambered to find the distance to the lands in this rifle. I then seated all bullets I've loaded .20 deeper than that as a place to start. Yet, one of the rounds I mentioned above was hard to chamber so I took it out for a look. It had some marks on the bullet. I thought it may have not been seated properly so I measured it again with the comparator...it was right on measuring 2.2285" with comparator.

Wide swings in velocity will kill group size but consistent velocity is not an accuracy guarantee. My bet is that you nailed the solution with seating depth. The Varget load is probably closer to the harmonic optimum than the IMR.

That said, changing the depth may switch optimal load to the other powder. In other words, the load with uniform velocity seated at optimum depth may not be the most accurate regardless. Its "sweet spot " may simply be not as sweet as the non-uniform velocity load at its respective optimal depth due to slightly different operating pressures.

Just a guess, as I don't have a saum,(a 300 WSM), but I'd say the varget is too fast a powder for a SAUM. That and why are you using a magnum primer? I almost never use a magnum in mine, except when following a book load. That better group with the varget would be awfull at longer ranges. Also shooting another couple groups would show worse groups.

Three shot groups are VERY weak indicators of long-term performance. Five shot groups are only a little stronger.

Your sample is so small, that you cannot say that a shift from 1.1" to 2" represents any real change in gun or shooter performance. If you repeat your test, you are almost equally likely to get the reverse result next time.

It takes the average of many five-shot groups to establish true performance.

Check the inside diameter of your fired cases at the neck.
Simply take the fired case, and try to slip a bullet into the neck; it should slide easily.
If you find it is tight on a few of the fired cases, you have your culprit.
I don't know why some cases from the same lot/manufacturer would vary, but the last time I saw velocity variations like you describe, that was the problem.
Garrett

N.,

I have not measured any of them yet however, I can tell you that the brass came from a new bag of fifty and they were in pitiful shape. The measurements were extremely varied. I bought another bag of .243 Win brass...they were super! Then, I bought a bag of 7mm Rem Mag (all REM brass) and they were a mess.

I'm having trouble with this rifle...I think in that I can't find any load or bullet that works with consistency.
I have tried H414, IMR 4350, Varget
with: Hornady SST 150 and 165 gr., Nosler Partition 180 gr., Nosler Accubond 180. Believe it or not, it has shot partitions as well as anything.

Another strange thing this rifle has done is that a good number of targets have one shot way out of the group and two holes that touch???

Denton,

That sounds like sound advice. As a matter of fact, I have already proved that to myself. I got a three shot group measuring .79 at 100 yards with 61.5 gr of H414 under a 180 gr. Nosler Partition. I thought that I'd found the load!Considering this is a factory Rem. Model 7 rifle with no mods. done, I'm thinking this is probably as good as it it gets. I loaded more of the same and got groups all the way up to 2". To make matters worse, the loads started to show signs of high pressure.