Velocity Deviation: causes? cures? (H4350 in a 30-06)

brotherjack

brotherjack

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So, after a quick run to the range today with my new (to me) toy (a semi-custom Interarms Mauser in 30-06), I have some questions. I used what I thought should have been as close to a "sure thing" load as anything (previously worked up in this rifle; lest anyone think I started here):

CCI 250/magnum primers
H4350 (58 grains)
Nosler 168 grain Ballistic Tips
Winchester brass

Accuracy at 100 meters was fairly decent (not great, but decent), but the velocity deviation was massive; over 100FPS difference between the high and low over 6 rounds. I realize I'm probably a little spoiled by using Varget in a 308 Winchester (those velocity deviations are typically around 2 or 3 FPS), but 100FPS+ seems totally out to lunch to me. Also, the fliers in the group were the ones that were on the ends of the velocity spread -- so I'm fairly certain that this rifle will shoot much better if I can fix that velocity spread.

So -- anyone have any suggestions on what might be causing that kind of deviation (and how to fix it)? Powder was my first thought, but H4350 is supposed to be pretty good stuff, isn't it??? If not 4350, then what??? Are the magnum primers a bit much maybe (they were not my first choice, but it's what the previous owner was using, so all the pre-tested load data I have for this rifles is using CCI 250's, and I had a bunch of 250's laying around, so I used them)? The firing pin strikes look good to me (consistent depth and shape)... what else would cause that kind of thing?

Any/all suggestions are welcome.
 
I would not use any load that showed 100 fps difference from high to low. Is your brass all the same lot number? Variations in neck tension can create differences in velocity. With 165/168's I personally like IMR 4350 better in the '06, but also have had great results with RL 19, Vihtavuori N160, H414, W760. The magnum primer should not be an issue. Regards, Eagleye.
 
30-06 + accuracy

I have a model70 featherweight. The load I like is imr 4350-57gr and an accurate 165gr bullet, primer is NOT a magnum. Use brass from the same lot.
The rifle barrel has to be fouled before you start measuring velocity [5 to 6] rounds fired. Without doing this you are fouling your barrel from clean and some lub will still be there from last cleaning, so velocity will rise until the barrel is fouled. Neck tension as stated is important and should should be consistant through all the brass, it doesn't have to be all that tight but firm for hunting loads.
Enjoy Bill
 
Of all the things mentioned, there are only 2 that come to mind:

1. Mag primers -- I will try this again with non-mag primers.

2. Neck tension -- the bullets in question were pulled from from some 308 rounds that had been loaded for a year or two. It doesn't seem too unreasonable to guess that might have caused enough variance to alter neck tensions a bit (though, not much, I wouldn't think). The brass on the jackets was dull and tarnished, so that's not too far fetched, I wouldn't think. I will try this again with fresh bullets.

If anyone else has any more thoughts/feedback, keep em coming.

Thanks,
 
Gee! This seems to be a tough one. Good quality components and a 99 ft/sec range in velocities. I get a spread of between 20 and 30 ft/sec with similar components in my 06 with 165 g Hornady spire points. H4350 has been a very good powder for me as have IMR 4350 and H414. Many years ago I tested the difference between magnum and non-magnum (Federal) primers in -20 deg f without finding all that much difference in spread or average velocity (bit of a surprise that). In fact I didn't find big differences in velocity or variation with changes of neck tension either, except when using moly. But the need for a bit more neck tension with moly was easily anticipated. Maybe it is a matter of a number of the variables suggested here going together to throw things off. As a thought, do you weigh your powder charges? I have also seen spreads this large with reduced loads using cast boolits. Part of the problem was related to how hot the primer was and another part was amount of powder. The hotter primer reduced variation.
 
Follow up:

OK, some more data to throw out there. Digging through my shooting notes that day, I (re)discovered that I took some chrony notes on the last few rounds that came with the rifle when my buddy sold it to me (an almost identical load: 57.5 grains of H4350, CCI250's, Winchester brass, except a 180 grain Hornady Interlock instead of a Nosler BT) -- and the velocity deviation over 6 rounds was only 35FPS (and that, only becuase the 1st round from a cold barrel was off from the rest by 25 FPS; overall deviation would have only been 10FPS over the 5 after the fouling shot). I did a whole pile of shooting yesterday, and had forgot that I took chrony notes on those rounds.

So, that makes me feel a lot more like maybe the bullets themselves were the problem -- and since they were both pulled (the collet might have caused slight deformation), and well tarnished around the bases from having sat loaded in 308 cases for about 2 years before I pulled them --- I'm kind of thinking that herein is probably my problem. I'll load up some more with fresh/new/clean bullets and take them back to the range and see what that gets me.

Also, to clear up a few things: the brass is already fireformed/partial-sized, mounts/screws are tight, barrel has been cleaned, etc.

Thanks for the suggestions guys, and if anyone thinks of anything else, by all means, beak up about it!
 
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