Different Brass Changes POI Drastically

[Jim Tarleton]

I loaded up some rounds for the range, and used two different brands of brass - Winchester and Lake City 54. All cases were full length resized, trimmed to identical lengths, loaded to within 1/10 grain of the same powder, and bullets seated to identical OAL's, and all had Winchester primers. Rifle has a tight chamber (on purpose), with slight force to close bolt on all rounds. Rifle had only 6 sighting rounds through the new barrel (three days previous). Only variant was brand of brass.

Winchester brass - 7/8" to 1 1/4" MOA right in bullseye, 2-5 shot groups

Lake City brass - 3" MOA 2" low, 2-5 shot groups.

I am somehwat puzzled by the drop in POI, not so much by the increased dispersion. The groups were shot in following order:
Winchester - 7/8 MOA centered in bullseye
LC 54 - 3 1/4 MOA centered two inches below bullseye
Winchester - 1 1/4 MOA centered in bullseye
LC 54 - 3 3/8 MOA centered two inches below bullseye

All fired in succession with target check between groups (probably 15 to 20 minutes).

All firing from rest at 100 yards, firing at a target with alternate white and black 1" rings (1" White bullseye). No signs of excessive pressure in any round, and I left the Chrono in the shop. I will repeat the performance tomorrow and Crono every shot.

Any ideas about what I consider an excessive drop in POI with LC 54 brass?

Jim

Information

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[mousegun]

Assuming .30-06, I Googled "Lake City Winchester .30-06 case capacity" and found several references that stated the Winchester cases have significantly more capacity than Lake City. One post stated that it took 1.9 grains more powder to achieve the same velocity. May not be the only cause of POI shift, but I'll bet it contributes.

[RicinYakima]

I agree with "mousegun". LC cases tend to have the least volume and thickest case necks, which is why I use them for cast bullet loads. Let us know if they are faster than the Win brass, noted for having the highest case volume. Ric

[Litt'le Lee]

LC=higher pressure-faster bullet-less time in barrel-will shoot lower

[joem]

My lyman reloading book recommends "for those that reload mil spec cases reduce the powder by two grains" from published data.

[Jim Tarleton]

Very good, gentlemen. Chronograph results today showed almost 200 fps higher velocity from the LC brass rounds. Due to the outstanding accuracy with the Winchester brass, I aim to stick with Winchester. I will work with the LC bass to find a more accurate load, since I have a lot of LC brass!

An added note - went to my local gun supply shop today and discovered that primers (of any size or brand) are nonexistent in this region. Is this true everywhere?

Semper Fi,
Jim

[Bruce McAskill]

Primers in general are in very short supply as people are grabbing them as soon as they show up. Panic buying as they are afraid what the President will do next. And the fact that the factories are going 24/7 with military contracts doesn't leave a lot of left over production for the civilian market right now.

[Allen]

The panic buying seems to have depleted the existing stock and what the dealers had already ordered but they (the dealers) can not get primers now.

[Jim Tarleton]

I can see my daily firing schemes going down the toilet. Has anyone tried the reloading of primers using match head components? Is it even legal?

Jim

[MEHavey]

To add a little verisimilitude to what otherwise might be considered a bold & unconvincing wives tale...
>
> At close ranges slower bullets will hit higher on target than
> a faster same mass bullet. This happens, because the
> slower bullet spends more time in the barrel, while the gun
> rotates about its mass center, thus leaving the muzzle
> at a higher departure angle.
>

This is at CLOSE ranges where flight ballistics are still otherwise not too dissimilar for the two different velocities.

Read http://www.desertsharpshooters.com/m...incredload.pdf