Another Brass Question

J

Jayhawker

New member
I've got 200 rounds of new 6mm BR Lapua brass and although it appears they are all of a uniform length that probably won't last long after the shooting starts. How much "grace" from a given length do folks give before trimming it back? Or do you trim any that are longer than they should be every time you reload?

Pete
 
Pete,

if you'll REALLY pay attention to the concept of buying and properly using fitted FL dies you can save yourself a lot of hassle. I've got 6BR (and 22BR and PPC and .308 and WSM and 6X47L) cases that have been fired 30-40-50 times and never trimmed. FULL LENGTH SIZED for a drop-bolt fit every time........

I'm not saying not to check 'em, but with proper sizing technique you can set up so's your brass never grows. The growth is a sizing thing not a pressure thing.

All of that said, I run only about .005 clearance on the casemouths but this is because I CAN and DO have ways to set it, monitor it and stay on top of it. For me if cases DO grow at all it's a sign I need to revisit my die setup. I also monitor the carbon ring and since I don't get one I have no fear of crimping onto a bullet.

If you don't have this ability then my advice is to trim back around .020, give yourself .003 radial clearance and not worry about it. The cases will bust at the web before you run out of length. My first try at a 6X47L is cut with a 6BR reamer and consequently has 30 thou of deadspace at the end of the chamber and it shoots 600yd competitively.

al
 
Al,
Good to see your input on this. As I do not have a 6 BR, I dont really know about the case growth aspect of the round. However I have been shooting a Cooper 22 in 220 Swift for about 6 years now. It seems the round has always been dissed due to the fact of case growth, and short case life. This however has not been my experience with this particular round. I now have 19 loadings on some Norma brass that I just shaved 2 thou to get it back to where the length was after the initial forming to the chamber. I full length size every time, as Neck sizing never really produced the results I wanted. The brass when new was 2.195 in length, after the initial forming it grew to 2.197, and after 18 times it only grew to 2.199. I dont figure thats too bad for a round that people say is notorious for case growth, and short case life. I have also had the same experience with RP, and Win brass also.


DR
 
DR,

I'd be interested in what your handload is for your Cooper.

Thanks, Tom
 
I apologize to jayhawker, as I didnt mean to hijack his thread.

Tom,
The results I am getting may surprise you, going to post some accurate, and hodgdon load info and go from there.

2700 50 HDY V-MAX 42.8 3,793 45.0 4,035 62,500 2.680
2700 55 NOS B-TIP 41.3 3,602 43.5 3,832 57,000 2.680
55 GR. HDY SP Hodgdon Varget .224" 2.680" 34.0 3516 47,000 CUP 36.0 3645 51,900 CUP

I have actually found 3 accuracy nodes with my swift, The first is a 55 gr sierra BlitzKing with a load of 32 grains varget, CCI BR2. The velocity average for this load for 20 shots 3445 fps, E.S 58, S.D 19. Below is a target shot with this load in a 10 mph wind,


DSCN2100.jpg
[/IMG]

The second accuracy node Is a 55 grain Blitzking, 38 grains AA 2700, BR2, Average velocity for 25 shots 3645, E.S 140, S.D 48.1. Below is a target for this load shot in a variable 10 to 15 mph wind.


DSCN2099.jpg


The third one is a 52 grain sierra match, 41.5 grs AA 2700, BR2 Velocity average for 20 shots was 3885, E.S 122, S.D 40.5. I cant find the target for this load as I dont intend on shooting it anymore as I have already burnt up a barrell by shooting a load pushing a 52 gr at 4075 and not being maxed on the powder charge.

The reason for the fliers is my bench technique, and the fact that at 100 yards I dont use wind flags, as at 20X I cannot see them and do not shoot free recoil.


DR
 
Pete ...

Jayhawker said:
How much "grace" from a given length do folks give before trimming it back? Or do you trim any that are longer than they should be every time you reload? Pete
Click to expand...

Here's another way to look at this subject from a SAFETY standpoint. I believe it still answers your question.

Chamber Length Safety Zone

Q: How many thousandths shy of actual chamber length does one establish as a safety zone, before assigning a "trim-from" length, once measurements have established a rifle's true chamber length ???

Mike Bryant

A: I use .010" for each increment. For instance, if the chamber length is 1.570" from the base to the end of the neck on the chamber, then the maximum case length would be 1.560" with a trim length of 1.550". Don't let the cases get over 1.560" and you'll be in good shape.

Jackie Schmidt

A; I use a .010" window. 6mmPPC chambers have been shortened to 1.510". Since shooters fire cases to expand them, the cases come out close to 1.500". I trim them back to 1.490." :)
 
DR,

I submit that the reason your groups look like that are because.......

it's a Cooper :)

No offense but you can shoot better than that, even w/no flags.

al
 
alinwa said:
DR,

I submit that the reason your groups look like that are because.......

it's a Cooper :)

No offense but you can shoot better than that, even w/no flags.

al
Click to expand...

No offense taken Al, in fact it gave me a real good laugh. Thanks for that :) you must remember my shot out 77V huh LOL :cool:

DR
 
I always have my gunsmith include maximum chamber length when rebarreling or rechambering any barrel, and ensure NEW cases are trimmed no further then .010" less than maximum chamber length after first firing.

With 6mm BR Lapua cases, I traditionally notice a slight (less than .003") growth in length at first firing, thus will trim back to .010" less than maximum chamber length.

After first trim, in my experience I see no appreciable growth using 6mm BR Lapua cases.

I do occasionally trim cases to square case mouth thereafter, and trim all to shortest measured case length.

With proper resizing method, and removal of die resizing balls, case growth is minimized.

Die resizing balls I consider to be "Tools of the Devil"!

Older Cob
 
Once you know the "actual chamber length" you'll know how long you can let your cases get before you "need" to trim. A few examples:
.221 Fireball: Max case trim length is 1.400. Actual chamber length is 1.427.
2 different 6BR chambers: ("actual chamber length") 1.580 and 1.584. Max trim length is 1.560.
In my case I shoulder bump maybe .001 to .002 "max" and neck size. Throw in a body size if the case starts getting snug in the chamber. Brass won't grow and has been resized maybe 20 times with no problems. Get close on the chamber measurements and you'll have figures to work from. Full length resize if you choose to but know the "actual" chamber length and go from there..
 
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