neck trimming,tension,concentric,will it help?

bsb · #1 11-26-2007, 01:01 PM

Right now I shoot a 7mm sendero(350 shots thru it) and I get consistant
4"- 5" 5 shot groups at 670yrds
I also just picked up a 7mm 700P and it shoots the same as the sendero
(60 shots thru it)
Question is! if a guy does the neck trimming, tention thing and gets the bullet coming out of the cases straight, realistic what would the group size go down to?
right now I use the RCBS standard dies and I just reload! No case prep other than chamfer and bevel necks! I am thinking about going crazy on the redding dies, gauges etc
Thanks for your advice,comments, and those that have been there done that! who might would maybe save me a lot of time and money!

AJ Peacock · #2 11-26-2007, 01:27 PM

With factory chambers, neck trimming won't buy you too much if you have good brass. I typically only trim .001" or less off the high side of a lot of brass and call it good. Making the brass thinner means it will be working more each time you shoot and resize it (shorter brass life). If the brass is not consistent, then it will start to bend a little each time it is fired/cooled. I use the concentricity gauge on my fired rounds and toss the ones that are starting to bend (turn into a banana) by more than .001" (I mark them and use them as foulers etc.). The bending is from one side of the brass being thicker than the other side (so it stretches/rebounds differently). Turning the necks to consistent thickness, only fixes the necks. The body of the case usually mimics the inconsistency.

4-5" repeatable groups at nearly 700yds is pretty darn good, how much better do you want to be? Shrinking the groups by 1/2 would be a lot!

AJ

CatShooter · #3 11-26-2007, 01:41 PM

What AJ said.

Turning will get you nothing that is measurable with a factory chamber and factory barrel.

You would be better off (and save a lot of money and time) if you just buy a fair amount of extra brass, and mic the necks, and throw away the ones that are way out... more than a total of 0.002"

bsb · #4 11-26-2007, 02:26 PM

Thanks for the info! that does help a lot! the groups are pretty good and I thought if it would cut the group size in half I would do it, but it dont sound like it will do much with the factory chambers, and it makes sense what you guys said.

#5 11-28-2007, 07:59 AM

Quote:

Originally Posted by bsb

Thanks for the info! that does help a lot! the groups are pretty good and I thought if it would cut the group size in half I would do it, but it dont sound like it will do much with the factory chambers, and it makes sense what you guys said.

For me, it is basically a better use of my time to turn the brass case necks initially than to measure the neck thickness deviation/departure with a micrometer or dial-indicating spinner and still have cases that will have different neck tension from one loaded round to another. Once they are the same thickness and concentric (ie., fireformed), one could look elsewhere for additional accuracy "tweaks". And, until you do it, it will always be out there for you to try. Try five or so and see what happens. You may or may not benefit from it. But, you will only find out if you try a small sample.

Chawlston

Winchester 69 · #6 11-29-2007, 03:14 AM

Get a run-out gauge and see for yourself how good your loads are.

Nomad · #7 11-30-2007, 06:27 PM

Might want to think about true primer pockets and do a flashhole job
on the inside as well. With standard dies when setting the bullet reseat
at 90 or so degrees to true.
Sizing the brass to the chamber if possible on your dies will help a lot also
to help. Read a book or two on benchrest reloading..
All the above is good information on the other posts..