308 Winchester Federal case variance

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IMR4320

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So I've been reloading all kinds of cartridges but my jewel is precission rounds for my varminter in 308, for the most part with pretty good results but as usual, mostly consistent grouping with the occasional fly off. The ammo I load for this rifle is 168 gr. Hornady BTHP(1:12 twist), IMR 4064 and Federal 210 primers, for consistency I only use Federal cases, neck sized only so all of my cases are perfectly formed to my chamber. Now, I have noticed something new, I have never actually bought any factory match ammo, from day one I spent the time to develop a load and shoot it. For the first time I bought Federal match 168 BTHP with Sierra match king bullets and to compare them I've weighted every single round, they all ran within 2 grains, then I weighted my reloads and they ran within 5.3 grains. It is not the bullets as I check them, it is not the primers, and the powder gets individually weighted to the very last 0.1 grain so I have checked my primed up cases only and they also ran 5-6 grain apart. That would be because of different batches which I understand but what happens to my load when the internal capacity varies this much, I run a compressed load already because that is the load the rifle likes the most and it is still a hair under the IMR catalog given maximum. Could it be this variance in internal volume that could cause the sometimes fly off ?
Thanks for any imput
 
The brass can stretch with use and if you trimmed them they get lighter because you trimmed the case. The case weight between them can be differen't

The charge and length of the round makes the biggest difference I find. I load 308 on a progressive press and it does really well even though I'm not checking every round its just close enough it seats good enough for me. I found it worked really well.
 
I weight sort Lapua brass into 1 gr batches, after I FL resize and trim to length. 5 gr difference may not be noticable at 100 yards but it will show up at longer ranges.
 
Federal brass isn't junk, but it's not nearly as desirable as Winchester, Norma, Lapua, etc.

A 5-grain weight variation could well be (and probably is) from normal variations in weight from case to case.

You could shoot this ammo out to 600 yards and you would probably not be able to tell *any* group size opening up because of this. It is completely fit for this purpose. If you were to shoot it at 1000 yards, it would probably group a _bit_ bigger, to the extent of being detectable (if really good brass would give you ammo that shot into 1 MOA at 1000 yards, this "crap" (not really!) brass might shoot into 1.5 MOA at 1000 yards).

With so-called "crap" brass, a good bullet that isn't particularly fussy about the distance to the lands (exhibit A, Sierra 168 HPBT) seated to magazine length, and a thrown (not individually weighed) charge of an appropriate amount of a suitable powder (e.g. IMR 4064), you will have ammo that will shoot very well at 100 yards, and at 300 yards, and at 600 yards. If you carefully re-read the first sentence of this paragraph, you will see that this is exactly the 'formula' used to make Federal 168 match ammo (and most other very good factory match ammo too).
 
For myself, Nosler are the one my results are the best, the concentrity of the case is almost perfect all the time and the primer pocket while not being the tightest, are very uniform from case to case... JP.
 
I buy new Lapua brass (1000) and sort it in pails of 0.3 gr increments.

Or, I get 1000 once fired cases all from the same lot of ammo, and sort it in 0.5 gr increments. The ammo then gets loaded into 50 round plastic boxes. You only have to sort by weight once, so it is a good investment of your time.

5 gr spread is normal for non match brass.
 
"...1:12 twist..." Too slow for the .308. Wouldn't worry too much though. Unless it's a high end match grade barrel.
Federal brass is known to be softer than other brands. That really only means it won't last as long as other brands. Primer pockets enlarge faster.
"...they ran within 5.3 grains..." Consistency is far more important than the actual weight difference. Except to the bench rest guys case weight don't matter a whole lot. Those guys are looking for one hole groupd that are smaller than the bullet diameter(no idea how that happens, but it does). Hunting or regular match grade ammo(match bullets are not made for hunting anything but varmints) doesn't need that much fussiness. I wouldn't worry about the case weight at all.
 
Used to shoot Lapua cases but got big improvement in my results with the Nosler cases, they are just the best in my book... JP.
 
I read on an m14 reloading article - it was posted here but can't recall the guys name - that he could not discern any
difference between regular federal and federal match brass, save for the stamp. I personally use Lapua for my target
gun, and Lake City for my m14.
 
If you want info on shooting bug hole groups go to http://www.accurateshooter.com/

Your case internal capacity will control chamber pressure, if the internal capacity varies so will the chamber pressure and your accuracy.

Below using Quickload near the center of the photo you will see "Maximum case capacity in grains of water (H2O)". The same charge of powder in a case with more internal volume will be lower than a case with less internal volume. The more the case weight varies the more variation in chamber pressure and velocities you will have. (ES & SD) The default volume of a .223 case in Quickload is 28.8 and you must check your internal volume and enter it to get the correct pressures and velocities.



Below, Lapua is the best brass with the most uniformity and the least amount of case weight variance at 1.2 grains in 100 cases, and Winchester cases have the worst uniformity and vary 6.5 grains.



"NOW" the arguing point, case weight vs case capacity, as a general thumb rule the more the case weighs the internal volume "should" be "less". The competitive shooter at Accurateshooter.com argue over this all the time and the only sure way is to fill each case with water and check them. This is a pain in the back side so they just buy Lapua brass and call it quits.



Example of the arguing point below and volume vs weight meaning it depends "where" the brass is located. The Federal case below weighs more than the military Lake City case does and the Lake City case is thicker in the base BUT weighs less and has more internal volume.



The photo above was not taken due to internal capacity, it was used to show "WHY" Federal primer pockets stretched on the first firing in a AR15 and were worthless for reloading.
 
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