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Determining Seating Depths for VLD's

 
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  #1  
Old 05-28-2012, 10:44 PM
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Determining Seating Depths for VLD's

Ok so I just finished up trying to find some seating depth numbers for Berger 175 VLD's in my palma rifle. I started by attempting to use my Stoney Point gauge, but ended up dropping the gauge and damaging the case mouth to the point of "unusableness" (probably not a word). That was the only fired case I happened to have on hand that was drilled and tapped for the gauge. %#$@! Thought to myself what now, so I pulled out the unopened Frankfort Arsenal Overall Length Gauge. Now I know this gives the C.O.A.L. using the tip and I usually use the Ogive, but I think I can do the figuring. Here's my numbers; first two before Stoney Point went to the floor.
1. 2.300 (Ogive)
2. 2.219 (Ogive)
Dropped Stoney Point , son of a $%#@.
Frankfort Arsenal
1. 2.808
2. 2.765
3. 2.798
4. 2.811
5. 2.819
6. 2.808
7. 2.805
8. 2.806
9. 2.805
10. 2.798
11. 2.805
So After I started to get the feel for things and how the system was suppose to be used I think I started to get some consistancy, (Some). Now I'm just curious as to what some out there would do with the numbers, take an average now somewhere between the 2.805 and 2.808 and just pick a spot to start ? Those VLD's are a ^%$*!

C.D.
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Old 05-29-2012, 08:00 AM
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Re: Determining Seating Depths for VLD's

I'd seat bullets out to where they set back about 5 thousandths when the round's chambered. Trying to use ammo with bullets seated off the lands some amount ends up with a greater jump-to-rifling distance due to case headspace spread. That .308 round gets driven hard against the chamber shoulder centering it in the chamber. That contact point's distance from the case head typically varies a couple thousandths or so.

Use light neck tension to hold those bullets, especially if they're single loaded. A light neck tension has a smaller range of release force needed and that contributes to lower muzzle velocity spreads. Coupled with the bullet lightly pressed into the rifling typically ends up with best accuracy. The US Palma Team typically uses ammo so loaded. As the throat wears from use, you'll have to seat bullets out a bit further every couple hundred rounds or so, but that doesn't effect accuracy.
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Old 05-29-2012, 09:15 AM
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Re: Determining Seating Depths for VLD's

Take an average, it is just a reference point to work from. Then if you havent tried Erics method I would highly recomend it. I just used it and was amazed to find a great sweet spot clear out close to -.100" off the lands. Moving in either direction from this showed the groups to open up and the results were repeatable. It went from 1 moa to .4's. and back out. This was with VLD's and not what the normal frame of mind is for these bullets.

Getting the Best Precision and Accuracy from Berger VLD bullets in Your Rifle

Jeff
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Old 05-29-2012, 06:49 PM
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Re: Determining Seating Depths for VLD's

IMO, unusableness is just as handy as unusefulness!
I hate the Stoneypoint approach completely, and the plastic Frankfort probably won't get it.
You could use an R-P tool, as discussed here by Woods:
Reloader's Nest Forum - OAL

I also recommend Berger's testing method, with any bullet, any cartridge.
Don't guess or assume where best will be.
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Old 05-29-2012, 07:37 PM
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Re: Determining Seating Depths for VLD's

+1 to Broz' comments.

Using Eric's guide, I recently found a more accurate node at greater than .100

I too was surprised that this great a jump was preferred by the rifle projectile combination.
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Old 05-29-2012, 07:48 PM
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Re: Determining Seating Depths for VLD's

Quote:
Originally Posted by Broz View Post
Take an average, it is just a reference point to work from. Then if you havent tried Erics method I would highly recomend it. I just used it and was amazed to find a great sweet spot clear out close to -.100" off the lands. Moving in either direction from this showed the groups to open up and the results were repeatable. It went from 1 moa to .4's. and back out. This was with VLD's and not what the normal frame of mind is for these bullets.

Getting the Best Precision and Accuracy from Berger VLD bullets in Your Rifle

Jeff
I've got some Berger's on their way and want to make sure I've got this right before I start testing. If I understand things correctly, you work to find the rifle's favored jump with a moderate load of powder as the first step. Then, using that favored jump you would then go through whatever ladder or OCW test you prefer. Is that correct?
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Old 05-29-2012, 08:19 PM
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Posts: 2,114
Re: Determining Seating Depths for VLD's

Quote:
Originally Posted by blackdog View Post
If I understand things correctly, you work to find the rifle's favored jump with a moderate load of powder as the first step. Then, using that favored jump you would then go through whatever ladder or OCW test you prefer. Is that correct?
I'd skip any moderate load testing unless you plan on shooting only moderate loads. Save some barrel life and use close to maximum loads.

I'd also skip OCW and Ladder Tests. Unless you shoot at least 5 shots with each load, the data you get won't be very accurate. I think you would do better by trying 3 or 4 loads near max and shoot 10 to 15 with each. The results you get will have a higher probability of being the "best" in that load range.

Or start out with the same load that hundreds (thousands?) used in competition when the .308 was "the" round for best accuracy through 600 yards with shoulder fired rifles. 168's, 175's, 180's and 190's shot the most accurate with 45, 44, 43 and 42 grains of IMR4064 in that order of bullet weights. This assumes your barrel's groove diameter is a few ten thousandths smaller than the bullet diameter you'll use. They typically shot sub 1/2 MOA through 600 yards and all but the 168 shot under 3/4 MOA through 1000 in good barrels properly fit to a decent built rifle.
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