Case weight/volume

[GTS Dean]

Hi folks - new member here and first post. I've read several pages to get a feel for the forum and am ready to ask a question:

I've been working with .270 Win and 7mm Rem Mag quite a bit over the past couple of months. I started simple with mixed brand brass, then segregated brass, then got more methodical as I zeroed in on more and more accurate case length/OAL/powder charges/bullet weights. I seem to have hit a wall on accuracy now. I'm able to get 3-shot groups around 3/4" at 100 yards with both rifles, but always seem to have two holes touching and one flyer. I don't have a chronograph, but I assume that my biggest hurdle is case volume and pressure variation. I tried weighing cases, then filling them with water through a titration burette. The problem is that the surface tension meniscus on the cases isn't very constant and there's sometimes a drop of water hanging off the burette. Count that, don't count that? Geez..... a 0.1 ml difference doesn't seem accurate enough to explain the variation I'm seeing.

I've thought that maybe weighing the cases, then filling them with a consistent density medium like sand, striking off level and weighing the case + sand might be the best way.

BTW - I'm not shooting match bullets - just a variety of FBSP hunting bullets by Hornady and Nozler.

Thanks in advance for helpful comments,
Dean

 

[Shoney]

I am a firm believer in better optics for working up loads. I use a high quality 24X scope. Groups are usually much tighter.

I also use a titrating burette for case volumes; and yes, the meniscus is a trick. I start with new cases. The cases must be sized and prepped in the same identical manner.

I use distilled water, but quickly found out that a few drops of Dawn dish washing soap per 2 liters of water works best. It may also help you with the drop hanging on the burette. Mine doesn’t do that.

 

[TimRB]

Your biggest hurdle is statistics. You can't come close to evaluating the accuracy of a load with only three shots. Two shots touching, and the third that doesn't must be a flyer? I don't think so.

Tim

 

[Niles Coyote]

Something else to consider as well. If you continue to see two grouping, I have found that playing with your seating depth can bring those outside shots in.

 

[ants]

GTS Dean, Niles Coyote. Welcome to the forum! It's a very nice little corner of the World Wide Web. Nice to have you join us, friends.

I used to fill the burette with alcohol, but a guy showed me the Dawn trick mentioned by Shoney and I use that now.

I use a scope with Adjustable Objective to get the parallax right. Parallax error was a much bigger source of error than I previously realized. Of course, I'm my own biggest source of error!

I agree with Tim on the round count. Two rounds touching and the other round away? Maybe the two touching are the flyers. Eh?

Do your mass and volumetric study AFTER sizing and trimming the cases to same length (I use +/- .0025" as my standard for length, you make up your own and be consistent).

Very well made flat-base bullets can be accurate, and are certainly cheaper as you learn your craft. Eventually you will explore match grade boat tail. But if you are developing hunting loads, definitely use the bullets you will hunt with.

 

[Kernel]

Don't sweat the meniscus, it's trivial. Case volume is a huge factor, but only to 3 sig figs -- plus or minus a 10th of a grain. This is where a digital scale becomes a God send. Sort based on case volume. Cull case that are too high and too low. Work with a lot that's +/- a couple of 10ths.

Weight them right up to the neck both with water and and the powder your going to use. Water tells you the case's true capacity in grains. Knowing powder capacity allows you to calculate load density based on bullet geometry and how deep it's seated into the case.

IMO it's 99% about load density, powder capacity, burn rates, finding a bullet your rifle likes, crimp pressure, seating depth, COAL, and the distance off the lands. Play-testing loads with a Powley Computer can be a big help in understanding how those realasionships intertwine.

Check this link out: http://kwk.us/powley.html. The site ain't laid out that great, but it's all there, an online Powley Computer, basically a free Load-From-Disk program. Tons of info, read the notes, follow the hot links, and go from there.

 

[MCMXI]

If you've fired the same brand of cases a few times in the same chamber, neck sized only after each firing then trimmed to the correct length, wouldn't sorting by weight be accurate enough? If you're measuring the volume using a liquid, what criteria do you use to sort the cases ... 0.1cc, 0.01cc, 0.001cc etc.

 

[GTS Dean]

Thanks for all the thoughful replies, folks. I will start working with 5-shot groups in the near future.

Shoney, I'll give Dawn a try.

I fully agree with Niles about doing the volumetric studies after the sizing and trimming operations, but what do I use to keep from leaking fluid out of the primer flash hole - tape?

1858 - I assume one would sort based on the precision of the available measuring equipment. And, the limit of one's obsession with chasing zero.

BTW - The 7 Mag Sako has a Shilen barrel, trigger work and a 7.5x Leupold. The .270 is a vintage Pre-'64 Super Grade stocker with a BalVar 2.5-8x.

Re: Optics -
Would you guys suggest buying one quality scope for range use and moving it to the other rifle after a few trips to the range develping one caliber? What I've been doing is taking both and alternating between shot groups to let the barrels cool. It makes more efficient use of my range time.

 

[rcmodel]

I would hardly consider a 3/4" three shot group with one hole not touching to be a "flyer"!

Especially in a .270 or 7mm Mag!

Both cartridges are what might be considered "over-bore" slightly, and one hole groups will be pretty hard to come by with either one.

I'm not shooting match bullets - just a variety of FBSP hunting bullets by Hornady and Nozler.

That right there might be your problem!

Simply amazing you are getting the results you are getting with those bullets.

I'd forget the case-volume quagmire, and buy a box of decent HP match, or plastic-tip varmint or hunting style bullets.

rc

 

[GTS Dean]

Both cartridges are what might be considered "over-bore" slightly, and one hole groups will be pretty hard to come by with either one.

Idunno - they seem to be coming regular enough for me to consider it a consistent problem - even with average optics.

I'd forget the case-volume quagmire, and buy a box of decent HP match, or plastic-tip varmint or hunting style bullets.

rc

That's not what I hunt hogs, white tail or mule deer with.

Thanks anyway!

 

[rcmodel]

Well, Excuuuuuse me!

I thought you were trying to get them to shoot better groups.

You didn't mention what you were going to do with them if you did.

rc

 

[1858rem]

but always seem to have two holes touching and one flyer. I don't have a chronograph, but I assume that my biggest hurdle is case volume and pressure variation

....couldya reload using the same case every time? it sure would give the bbl lots of time to cool between shots lol.....mebbe thats what i oughta do till i resolve my own problem with shots rising.....for three shots i easy keep 3/4....2 shots keep less than half inch often one oblong hole...but #4&5 are killin me opening things from 1 1/8" to 2 3/8"!!!


oh yah, but i got a .308 lol

 

[GTS Dean]

I ordered a bullet comparator from Sinclair the other day, along with a 4.5-12 Leupold on Cabela's closeout.

I'm a car forum junkie, but I've been surfing various handloading and optics forums over the past week. There's an amazing amount of great tips and information out there just by taking the time to use the Search button. I can't imagine how long it would have taken to assimilate this much knowledge 20 years ago. (Probably 20 years)