case volume v.s. velocity

[scaxeman]

I am new to the whole case volume debate, but I am having fits trying to correlate case volume differences to velocity changes. For starters, this is twice fired brass,.308) that has been measured, weighed, trimmed,,neck) sized within an inch of it's life. Loaded with 48.40gr,acculab 123) of varget, capped with weighed/measured/spun 155gr. HPBT, then fired across a CED Millenium chronograph. The following is the case volumes/velocities with no apparent correlation. Am I wasting my time trying to polish a gnat's hindquarters or is there some connection that I am missing?,my object is long range - F-class)

# water wt.,gr.) velocity,fps)
1. 57.78 2876
2. 57.64 2873
3. 57.75 2868
4. 57.84 2884
5. 57.76 2872
6. 57.82 2878
7. 57.66 2871
8. 57.70 2880
9. 57.46 2882
10. 57.58 2872


Thanks for any assistance/perspective!!

Darrell

 

[Cheechako]

Darrell

I think you are trying to polish that gnat's a$$ although I don't see how you get them to lay still.

I never look at case water weight as having any correlation to velocity or accuracy or any thing else for that matter. I think it's simply a way of making capacity comparisons between one brand or lot against another or for eliminating grossly different cases. You do not know where that extra weight is distributed for one thing. Also you can get some difference as a result of how you fill the case with water.

From your numbers I'd say you have some very darned good brass and a very darn good load. Some shooters would trade their only suspending gonad for those kind of numbers. I wouldn't psych myself into thinking there was something wrong with it or trying to make it better.

If you want to get really anal, take one of those cases, any one, weigh out 10 identical charges, go to the range and shoot the ten shots over the chronograph, reloading that one case for each shot. I'll bet you'll get an extreme spread about the same as the 16 fps you got using the 10 different cases.

Or, load all ten as you did before but this time weigh the loaded rounds. Then shoot them across the Chrono and record the results.

And one more thing, do any of these tests tomorrow or next week and you'll probably get different results. 10 shots do not make a basis for conclusions.

JMHO

Ray

 

[scaxeman]

Ray,

The brass isn't so special,Winchester bags o' 50),cheap!! :->). I have put a bit of time,read "a lot of time") into case prep. The thing that makes me play with it so is mainly the nice close tolerances on neck thickness,no neck turning necessary for me anyway, .0125" +/- .0005 to .00075 or thereabouts). The thing that is bugging me about this load iteration is that my SD,velocity) over a set of 10 test rounds is generally ~3fps, ES <10fps. It may sound silly, but at 1000 yds, my ballistics program says that an ES of 16fps will yield a dispersion of ~ 5",very close to the size of the "X" ring). With my relative inexperience at wind reading, I'll take any slight advantage I can wring from my equipment! A more pragmatic type would probably advise me to spend more time at the range studying conditions...... in progress!

Thanks,

Darrell

 

[Cheechako]

Darrell

I think just about every long range shooter is familiar with that old adage that xx fps velocity spread will mean xx inches of vertical at 1000 yards. The trouble is, it doesn't always work out that way in real life. Don't ask me why. I dunno. And neither does anyone else. The only way to confirm how a particular load will shoot at long range is to try it.

Not to scare you, but you do realize that a 10 round sample showing only 10 to 15 fps extreme spread is only valid for those 10 rounds. In an NBRSA 1000 yard match you could shoot as many as 150 rounds. The ES of all 150 has to be larger than the ES of 10 so your 5" of theoretical vertical is the minimum. If you believe the ballistic programs that is.

Ray

 

[scaxeman]

Ray,

Ah, tis quite true, I burned over 300 rounds last fall at Raton, NM, and If I had only the "theoretical" spread to worry about, I would have been a happy camper indeed! In the fullbore game, they have a nice civilized lunch break after the short line stuff,300, 500, & 600 yds). This allows plenty of time for the howling gales to build up for the long range shooting,900 & 1000). I don't shoot benchrest, I shoot F/TR, so I don't even have to compete directly with the F-open class folks. Shooting off a bipod introduces plenty of variability at 1000. I am continually impressed by those who do this with simply a sling!!

To answer your question though, I can pretty reliably hold together a 7 to 8" group at 1000 in minimal wind conditions. With the new, smaller targets being phased in, this will start to strain my ability to hold the 10, "x" ring, even if wind were completely taken out of the equation. As before, any little thing I can wring out of the rifle and ammo, means I can slack off all the more on the line!!

Thanks,

Darrell

 

[Clarence]

Scax Sir:
I personally don't see anything wrong with your numbers at the 1k line as I know of F class shooters with none better than you describe, however there is ONE possability to reduce the ES and SD's and that is with the Russian Primer KVB-7 you can buy them from Bob Jones as he has about 20,000 left, you can reach Bob @ bjonessights@yahoo.com.
My loads with Lapua cases with a spread of .7gr,allowed)inside flashhole champhered,just a bit)and 44gr of the Russian BW-68 powder will produce two 10 shot strings of 12 fps and 5 to 6 SD

That load will hold waterline at 1K within 3" out of the sling and Iron Sights, now if I could just HOLD the Wind, Raton was blowing hard last week.
Clarence

 

[scaxeman]

Clarence,

Well perhaps I am making mountains of mole-hills, etc. Recently though, the matches I have been attending have not had enough F-TR folks to make a separate class. This leaves us lumped in with the F-Open class folks. Tis a bummer to drop one point at 1K and end up third! Granted, their 6.5/284 setups are wonders to behold. Even with it blowing a gale, they aren't using all of the "X".... well, perhaps not a gale, but still, impressive indeed! Speaking of gales, is there ever a time at Raton that the wind isn't howling?

Getting back on topic, I keep hearing about these Russian primers. How do they compare to 210M, or BR2 for heat? I have had good results from the federal primers and very poor with the CCI stuff. This seems to be backwards from most who have tried the two. ,from what I have heard, the Federal primers are supposed to be "hotter", and the CCI "cooler")

Thanks,

Darrell

 

[scaxeman]

Just so I don't get flamed, those 7-8" 1K yd. groups are pretty much 0 wind,Douglas Ridge seems to be well sheltered). Aside from the matches I shoot there, wind re-asserts its evil influence.....

Darrell

 

[scaxeman]

so how would one determine whether or not they were at a node?

 

[Clarence]

My opinion as to the Russian's brisence is that they are equal to the Winchester marked,for mag or std loading) they are about .0003larger also.
I pulled targets for John Brewer,F class) at raton one year shooting a 6BR, of the fifteen record shots,read windy)all in the X, 11 of those were in 2.5" and in the spotter and hitting the Spindle four times.
Your cases MUST be the NEW Winchester as that much powder will not fit in the Lapua cases, AND I now wonder if you have the Old slow lot of Varget? another question is that of TIR with the Win cases have you seen the Bananna? I now think that some advantage is given the Lapua cases as one may reduce the powder charge to something like 45.8 to reach 2960 or so with the 155smk's, what is the speed of your heavy varget load?

Clarence

 

[scaxeman]

Clarence,

Brisance.... hmmm, I like that!

As regards F-open class shooters, we were using golf tees as spotters at 300 for the fullbore game last year, and it was tough keeping centers in the targets due to the number of exploded spotters making hash of the rest of the "X" ring. I would say that the best of the lot were using on average 1" of the 3" "X" ring.

"New" Winchester? The lot# is 1WA21, but I have had them for several years. The lot # of the Varget I'm running is "T0401" and after 3 firings, 48.40 grains of Varget reaches less than halfway up the shoulder. As a caveat, I should mention that I am filling my cases with a 4" drop tube. The fact that I can cram so much powder,without compression) is one reason I keep using the Winchester brass. I know that I could not fit as much in a Federal case, LC brass would be a joke. I probably couldn't get within 2-3 grains of my desired load with either of those cases. I have a bunch of Nosler's custom brass coming, and it will be interesting indeed if I can fit my entire charge in them.

A buddy of mine is running ~46 grains of Varget pushing a 155 at ~2950, the difference is he is running a 30" barrel, my rifle has but a 25" barrel. The first couple of firings with the Win. brass,fireforming, etc.) the velocities for 48.60 grains of Varget was ~2925. At this point, I kept reading that my load was absurdly hot, so I reduced it by a couple of tenths with no accuracy reduction. I'd reduce it more, but I am cutting it fine for velocity at 1000 as it is.

Darrell

 

[scaxeman]

Lynn,

Thanks for the input, I will probably end up bumping that load back up the 2 tenths I dropped it down simply because the speed at 1K is starting to make me nervous,calculated at 1223fps). I have noticed no pressure effects as yet, no cratered primers, certainly no popped primers, no difficulty extracting fired cases, and the primers still require a reasonable amount of pressure to seat. This may not be a problem much longer anyway, I have a rifle coming with a 28" barrel on it that should allow me to reduce the load greatly and still maintain velocity. That and work up a 175/180gr. load and retire the 155 to short line stuff. The palma folks may be restricted to 155's, but with F/TR, I am merely restricted to .308. I should probably stop shooting myself in the foot and run a more appropriate weight bullet at long range.

Thanks again,

Darrell

 

[AlNyhus]

Darrell: If you're concerned about reducing the vertical, you may want to speak with Randy Robinett at BIB Bullets about the flat based Palma bullets he's been making. -Al

 

[Clarence]

Al Sir:
I am courious about the BIB FB what do ya know as I am getting tired of the gyrations of the smk's

Clarence