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Old January 23, 2006, 12:54 PM   #1
zoyd
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Join Date: January 18, 2006
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COL question

I’ve only been reloading rifle cartridges for a couple of months but I’m starting to see some interesting relationships between case overall length and brass type. I’ve been testing several different powder and primer brands. Primer brands F210M and CCIBR2 have been loaded with Powders IMR4064, Varget and Reloader 15. Brass types are Lake City Match and M118LR, Winchester and FC brass.
My rifle is a REM 700 VSS .308 24” barrel with 1:12 twist.

My most accurate loads have been with Lake City Match brass and Lake City LR M118 brass.
These Loads are Varget 45gr F210M primer Lake City Match brass and 168gr Nosler CTBT seated 2.827“. The Velocity measured, 2690fps with a .244” five shot Group.

The Next most accurate was 42.5gr IMR4064, CCIBR2 primers, Lake City M118LR Brass and 175gr Sierra MK seated to 2.827”. Group size was .335” and Velocity 2630fps.

I just started testing the Reloader 15 this weekend. No firm data yet.

What I’ve noticed is that the commercial cases, Winchester in particular requires a deeper seating depth to get the better groups. Basically the depth is somewhere around SAMI standard. Still testing.
I noticed a huge difference in group size when I tried the 2.827” seat depth with the Winchester brass. My groups ballooned to 1.4 inches until I started seating the bullets deeper.

I’ve read that there is a relationship between seating depth the jump to Lands and groves. But my data says there is a stronger relationship between case design and seating depth. I would assume that the relationship is case volume or density and seating depth.

Does anyone have any more data on this.

One other question; I’ve been testing during outside temperatures of 45 to 55 degrees Fahrenheit and have been unable to achieve the max velocities(above 2700fps) from loads posted on any reloading table . Why is that?
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Old January 28, 2006, 11:08 AM   #2
Swede
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You have some good info, and bring up some good questions zoyd.

I use a competition die for my Swede target rifle, the main reason is because I received the die with the rifle. Swede's have a long throat and it makes a difference how far out the bullet is seated and the length is different in each of my rifles.

I've always thought this has to do with bullet jump to the rifling but I am not sure why it makes a difference. Hopefully someone with more knowledge than I can help.
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Old January 29, 2006, 12:12 AM   #3
rwilson452
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Cartridge over all length

I’ve read that there is a relationship between seating depth the jump to Lands and groves. But my data says there is a stronger relationship between case design and seating depth. I would assume that the relationship is case volume or density and seating depth.

The short answer is Yes, all of the above have an effect as does the jump to the lands. I would suggest you stick with one type of case. LC match is good stuff. Down load the powder by 2 grains then work up in .2 grain increments until you find the "sweet spot" then start with the COAL. then do it over. when you get it as good as it's going to be. you can change something else. powder, case or whatever. the trick is to only change one thing at a time. you will find that the best load with LC brass wil not be the best for winchester or ever other case type. Are you trimming your cases?
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Old January 29, 2006, 10:25 PM   #4
scottys1
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I can't help much on the seating depth issue, but here is my experience with my .308.

The rifle is a Winchester model 70 heavy varmint with a 26" barrel that I bought used. I have a supply of Federal match ammo (168gr) that shoots very well and runs right at 2700fps in this rifle. I tried loading 168gr Sierra MK's at a similar velocity in an attempt to duplicate the accuracy. 45.0gr of Varget in R-P cases and Winchester WLR primers runs 2750fps and shoots a tad better. My testing has been mostly warm (80-90 degree) weather. Overall length is 2.845". This is as long as comfortably fits the magazine. My rifle was either chambered with generous freebore or the throat has eroded from previous use. I haven't tried to chase the lands and probably won't as long as it shoots well with magazine length rounds.
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Old January 31, 2006, 12:28 AM   #5
cdoc42
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Location: Pennsylvania
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I've lately wondered about the relationship between bullet seating depth and accuracy. I've always started seating my rounds 0.015" from the rifling with 5 round each of max book load, and one grain down each for two more sets of 5. If I didn't get less than 1" groups I changed to 0.01" and 0.02" and start all over again. I have not yet experienced a pressure problem even though I'm not starting at the traditional 10% below max. I suspect it is because the bullets are seated much further out than the manuals provide in their data. I have a .270, for example, that easily shoots less than 1" groups with 57 grains of H414, while the latest Hogdon book lists max at 53.5 gr. The bullet is a Hornady 130gr SST and the cannelure looks like it is WAY above the mouth of the case.

My wondering is: is seating depth close to rifling the accuracy factor or is it more simply just a pressure factor based on seating depth? For example, if I seat that 130gr bullet 0.2" (what I can find in factory rounds) and reduce the powder charge to book max or less, will I get the same velocity (and pressure) and accuracy as when I have the bullet seated with much more powder and a shallow seating depth?
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Old January 31, 2006, 01:36 AM   #6
rnovi
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Join Date: July 10, 2005
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I can't comment much on the .308 - it's a great cartridge with accuracy potential beyond the range of most of us mere morals. However (thankfully?) your problem isn't limited to just .308's...

It's something I am dealing with right now with my Rem 673 .350RM Bolt gun. It's a true short-action (and considered to be the "original" short mag dating back near 30 years now). The 350 is limited to a 2.800" max COL. I can tell you unequivocably that 2.900 COL's will NOT fit into the mag well at all. 2.800 is it - the max.

This round was designed to handle a 200gr pointed bullet over around 55-62 grains of powder (4895 or so). 200 gr bullets normally seat right at the cannelure.

This short 2.800" COL poses several problems, not the least of which are cannelures and 250 grain bullets. Both the 250 Speer and 250 Hornady bullets have cannelures that ultimately get burried deep within the case just to be able to stick to that 2.800" max COL.

So, in addressing one of your questions: Don't worry much about the cannelure and where it should be seated. If you are getting great accuracy at the speed/power you want, who cares where the cannelure is!

As to the question of whether or not COL affects accuracy, it absolutely does! A couple hundreths of an inch can make a measurable impact on a group. Some people argue that they want the "jump" that the bullet makes from the case to the rifling to be as short or non-existant as possible. Dan Newberry makes quite a commentary on this and I highly recommend that you take a look at his webpage on that:

http://home.earthlink.net/~dannewber...addevelopment/


I'm not going to bother to try to parapharse his work. there is a lot of good writing in there and it's well worth the read. Long story short, Dan suggests that one find a stable powder weight/bullet combo and then by varying the bullet seating depth one can further affect accuracy.

Anyways, welcome to the wider wonderful world of reloading!
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