Book COL sucks!

4

45C

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I've been following the Hornady book COL,for my 7mm magnum, at 3290 COL.

I was consistently getting 2 MOA groups or bigger.

So I stuck a bullet in the case and slowly chambered it,turns out ,it was 3485 to the lands.

So I loaded some up at 3455 COL and shot a couple of 5 round groups.

4 shots measured .396 MOA with 1 flier which opened it up to a touch over moa.
So maybe I dont have to smash this Xbolt,across a tree? Lol.

Just have to figure out the flier.
 
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I am glad that you found such an improvement! A bit curious though - do you measure "run out" on your loads? I know that excess distance to lands sometimes makes for poorer accuracy, but many rifles (Weatherby) were made that way on purpose. I have one or more here with really stupid long difference between what I can put into the magazine, versus how far it truly is to the lands - has me wondering about solutions, other than single loading - not so easy on Mausers...
 
The "Book" COAL is for THEIR rifle. It is assumed that you will measure your own rifle and seat appropriately.

If you shoot the gun a lot, the throat will advance with wear. My 308s need about 5 thou longer each summer.
 
I've had good success with my 6.5 using the manufacturer's COL, maybe theres room for improvement.


But this 7mm was driving me crazy.

I guess it's time to step it up and by some gauges
 
45C said:
I've had good success with my 6.5 using the manufacturer's COL, maybe theres room for improvement.


But this 7mm was driving me crazy.

I guess it's time to step it up and by some gauges
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I did just that for my 7mm rem mag, i now load to 10 thou off cbto
 
I think the rifle and ammo is trying to tell you something.

Now try 20 thou shorter and longer.

I usually start testing at 20 thou off, and most ammo is best for me around 20 to 30 thou off.

You don't need fancy tools to find a good OAL.

The OAL for your rifle is determined by your mag length and the chamber throat in YOUR rifle. Each rifle is different. And the throat erodes as you shoot it, so each year you might find you have to seat your bullets longer.

Go back to the bench and load a round. Now turn the seater a quarter rev deeper, and seat the bullet some more. Does this chamber ok? Probably not.

Load another round and seat the bullet another quarter rev deeper and try that. Keep doing this until a round chambers without rifling marks. Each quarter rev seats the bullet about 12 thou deeper.

Then load one more round, seated another quarter rev deeper and measure it. That is the max OAL for that exact bullet.

Make a note of that OAL in your log book. It is about 20 thou off the rifling. Now take all the "long" rounds and seat them to the new setting.

I do this with live ammo if I have a rifle I trust. I live on a farm and have a "safe' wall to aim at while chambering live ammo. You might prefer to do this with a case with no powder in it.
 
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Ganderite, 1/4 turn of the seater stem = .012 ? What pitch is the thread? Is this more or less standard.
My dies are mostly Lee, I’ve been trying to figure this out, but it is hurting my head.
 
Leatherstocking said:
Ganderite, 1/4 turn of the seater stem = .012 ? What pitch is the thread? Is this more or less standard.
My dies are mostly Lee, I’ve been trying to figure this out, but it is hurting my head.
Click to expand...

It is a number I have running around in my head for the last 50 years. When I make an initial OAL measurement I use that factor to suggest how much to turn the stem for the next try. It seems to work.
 
Ganderite,that's exactly what I ended up doing.
I found the lands and just kept moving in until there were no rifling Mark's.

It measured about 30 thous less than the mock up cartridge I made.
 
Thanks Ganderite.
Come to think of it I’ll test your theory. Measure CBTO, turn down 1/4 turn, re-measure.
I recall Barnes is recommending.020 increments for finding best jump.
Burger recommending.025.
3 shot groups, one should be noticeably better.
Then fine tuning.
 
Book COLs will usually fit in short box magazines, feed through your grampa's '94 thutty-thutty, and always seem to be the length to the cannular on bullets so equipped.

Beyond that they aren't good for much.

While some handloaders agonize over whether they should weigh their powder or primers on a lab scale or not; most of them would be better served with a list of rifles that have a magnum length mag boxes on standard length cartridges, or those with easily removed spacers.
 
One thing to love about certain rifle designs. A decent magazine inside length.
No worse combination than a short magazine and a long throat, IMHO. Dave.
 
Eagleye said:
One thing to love about certain rifle designs. A decent magazine inside length.
No worse combination than a short magazine and a long throat, IMHO. Dave.
Click to expand...

Yep, and buying said combo smacks of poor planning. ;) Some remedial work can be done with Wyatt boxes; but its so much easier to plan ahead if you want something to shoot.
 
The mag has more room than needed.
As you can see from my picture, the longer round did much better.
If not for that flyer,the other 4 rounds measured under .4 MOA.
I think I need to see if that flier was me, or the ammo.

The barrel was getting hot as well.
It's a Browning Xbolt SS,with a pencil barrel, and I was running out of daylight.
 
I did the same with factory Federal 6.5x55 ammo 140 Partitions.Shooting a Win 70 FWT got 1 1/2 groups so I bumped the bullets out with a kinetic hammer and set them just shy of the rifling under 1/2" groups at 100 yards and still room in the magazine. Did up the 100 rds I had as I needed brass at the time as well.
 
Most seating dies use a 20 threads per inch pitch on the seating stem thread. Some micrometer dies are a bit finer thread pitch. Anything with a 20 pitch thread one turn is 0.050”, 1/2 turn is 0.025”, 1/4 turn 0.00125”. There is always abit of slop in the thread, so depending if the dies have a lock ring on the seating stem(redding rcbs) the tension on the threads can make a couple thou difference.
 
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