The importance of case sizing (case OAL)

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TargetNorth

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Hi all

So, my savage 11 6mmBR (thanks shilen and mystic precision and ATRS) used to be a shooter. My first couple groups out of her were clover leafs. As I'm on the 5th resizing of brass though, I noticed it's been getting worse. The groups opened up to around an MOA. Yes, that's right, one whole MOA. Don't worry, at least they're 5 shot groups.

I also noticed that it's been getting rather difficult to chamber rounds. How much force does one need to get that stupid bullet into the gun anyway? **Reefs on bolt handle**

Anyway, I've been pondering these and other mysteries of the dark shooting arts, when suddenly it occurred to me that I haven't checked case OAL (or Over All Length for you newcomers). Sure enough, I was 15 thousanths over. Well, that doesn't sound like too much right? Let's trim it up and see what it looks like.

Trim trim trim trim trim trim trim TRIM TRIM TRIM TRIM trim trim trim....

Ok, so 15 thou. Is a lot. Like really a LOT. Like I ca see the difference between cases that are trimmed or not trimmed from mostly across the table.

I trimmed all my unloaded brass, and shot it comparing it to the brass that was yet-to-be-trimmed and ... Rather hard to chamber.

The effects were substantial.

Some groups from today (typical over the 100 rounds or so I put down the pipe). All groups of 5.

Trimmed @100m .40", one jagged hole
Untrimmed @100, .9"

Trimmed @ 300, 1.39"
Untrimmed @ 300, 2.49"

Trimmed @500, 1.365" (yes better then 300!)
Untrimmed @ 500, 3.5"

Wowzerz. There is the rifle I know and love again.

I don't know what horrible pressures I was exerting on the poor rifle with long brass; now I've got the rest of the brass to trim.

Hopefully you all can learn from my error.

Happy shooting,

Barry
 
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I should add the setup:

Savage 11
6mm Norma bench rest
Shilen select match barrel, 26" stainless, 1-9 twist
Choate tactical stock
Timney trigger
Sightron SIII 8-32x MOA/moa
Lapua brass, cci br primers
31.2gr varget, 70gr Sierra matchking bthp
~3200fps (6moa drop between 200m-500m)
 
Make sure you FL or neck size before trimming.

My 6BR grew really slowly too. Took til 7th loading before I trimmed.
 
Nice to see you back Barry. Good shooting. If I push my 30-06 very hard I trim every 3rd firing or so. Various headstamps, but fired in their own batches.
 
I always took the minimalist approach to reloading and always thought it was fine even if things were tight as long as the groups were there. Now change to a wildcat style caliber. 6mm crusader. Fire formed the first rounds, shot groups looking for loads, everything was small, tiny groups. Second load, all good, all of a student, pressure, unable to shoot my average loads and all over the place. Trimmed, helped a little, the sharper shoulder helped it grow slow, but still issues. Ready to give up. Started looking and pressure causes and all sorts of stuff. Took all my brass, full length sized and bumped shoulder back, trimmed to all equal lengths. Then, oh the blessed then. Neck turned. Couldn't drop a bullet into a fired casing. Turned, and turned. This was for 250 pieces of brass and with all the work it took me 3 days or probably 12-14 hours of work.

Results.....no pressure, groups back to tiny holes and first round hits at almost 1300 yards. Just when you think you've learned it and got it down, you,ear something new. Something else in the tool box. Glad you got it all figured. Sometimes the hunt for the problem is painful and frustrating.
 
To maintain the great shooting, consider:

Annealing necks - every 2 to 3 firing

Outside neck turn every 1 or 2 firing... the key is watching the base of the neck and touching into the shoulder a smidge. Gets rid of donuts before they become a real problem

Trim as needed - usually 2 to 3 firings depending on pressures

Body die - set up to bump shoulder enough for easy chambering but a hint of resistance just before the bolt handle goes to full lock. Consistent lock up is very important to maintaining consistency in barrel harmonics.

With proper maintenance, you can pretty much keep firing the same case a few dozen times with great accuracy.

Larger cases will stretch much quicker but that is due to other concerns.

Enjoy...

Jerry

PS, after 3 to 400rds, retune your load as your bore is now broken in.
 
@Emerson - good to be back. I hope to come visit sometime when Eli is out also. If you come out to southern Alberta I now have numerous 1km + shooting spots that are easily accessible and safe to shoot at. Truly the land of milk and honey here.

@c4pyro - neck turning eh? What kind of wizardry is this?

@6mt - yes, I'd love to post Picts. Unfortunately my wife is on holidays and took my computer so I'm on an iPad and have no idea how to post pictures with this. On the other hand, It was because she went on holidays I had a full day to shoot... Hmmm...

@mystic precision - annealing eh? Sounds expensive.... **reaches for credit card**
 
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