Groups opened up

[rstbkt69]

i have been working up some loads using 5 different bullets and two primers. Shooting has been kept to 100 yards. The first portion of the development was on new Norma brass with no case prep at all. With the exception of a flyer in each group tested I had been able to get my groups to under 1/2 inch. Some close to 1/4 inch. Adding the flyers and all were less than 1 1/4 actually less tha .75 with the exception of one bullet. The flyers were probably me when behind the trigger or in the loading process.

Went out today with what was supposed to be my last testing at 100 yards and it was basically to verify my primer selection for each bullet and powder charge. This time it was with once fired brass. All the cases were well within the case length so no trimming was done. Basically I cleaned the primer pockets after tumbling and uniformed all the flash holes. Very little material was removed in that process because Norma evidently spends some time cleaning up the flash holes.

My groups opened up to almost twice what they were. Any thoughts. I would hate to have to start the process of seeking the best powder charge again. i didn't set the Chrony up this time because I thought I had everything nailed down.

[thomashoward]

Caliber?
If you have your powder charge try adjusting the seating depths from jam to jump .005 at at time. fire 5 at each seating depth.
Shoot a ladder then vary seating depths.I will be minute of dinner plate then all of a sudden it will be sub MOA

Its a 6mmXC. I have been seating the loads for each different bullet .003 off the lands. Correction .03 I was going to vary the seating depth on the 200 yard testing. I was hoping to have everything else nailed down at this point. I'm curious as to why once fired and flash hole cleaning changed everything so much.

.03 is a lot. there is a sweet spot about .009 again at .019 and around .027
you just have to find it for your rifle. Some like jam some like jump or degrees in between
also, try just neck sizing

[rstbkt69]

Its a 6mmXC. I have been seating the loads for each different bullet .003 off the lands. Correction .03 I was going to vary the seating depth on the 200 yard testing. I was hoping to have everything else nailed down at this point. I'm curious as to why once fired and flash hole cleaning changed everything so much.

[gau17]

How are you sizing the brass? Which dies are you using? Bushing? Neck tension?

[rstbkt69]

I use a forster full length sizing die and ultra micrometer seating die.

[gau17]

do you know how much neck tension you have?

[rstbkt69]

I have no idea how to determine that.

[rstbkt69]

Is that where you measure the sized case and then the loaded case and the delta is the case neck tension. I didn't realize that was what it was called I have the measurements at home but I cant remember. My chamber is a no turn neck also cut to .2748

[Thatguy80]

You have a coupe different things going on. Once the casing is fired you have now "fire-formed" the casings to your chamber as opposed to when they were brand new and to factory specs.

Usually when I buy new brass I will fire them once then build a load after that. When making precision ammo you leave no variables. You should know exact dimensions of your chamber, how far back to bump the should, how much it resizes the neck, etc... there is a lot of homework, but I feel its very rewarding and really bring the geek out of me when it comes to brass prep.

There is a lot of good info out there, keep digging and you will find it.

In a round about way to answer your question, you can measure a new case if you still have it and resize to factory specs or do a new recipe on your fire formed case.

I hope this helps.

[rstbkt69]

i knew the fireformed cases would change the poi but didn't think it would change that much. Man that was over 200 rounds. And they were pretty sweet groups. Just wish the heat and humidity would go away. It would be easier to get out to the range. I have plenty of new cases left. i was saving them to add as the ones I'm shooting wear out.

[rstbkt69]

Case tension.
Nosler Custom Competition 107 .0005 loaded size .268
Nosler Custom Competition 105 .001 loaded case .2685
Sierra Match King 107 .0015 loaded case .269
Hornady Match 105 .0015 loaded case .269
Berger 105 VLD .0015 loaded case .269

New case .2725
Fired case .273
sized case .2675

[30Cal]

How were the conditions today? Double a half minute group is not much.

[rstbkt69]

Didn't go today. winds were stronger than I wanted when I got home from work. I know I know. Just adjust for the wind. LOL I will after I see what the groups do. I remeasured the OAL again and made adjustments to the loads i have ready to go If they don't print too well I'll start over varying the powder charge. I'll just consider this my new data point., Double a 1/2 minute group isn't that much but I was consistently shooting under that if you take out the one flyer I had. Largest group I had on the loads before this last round was 1.15 including my induced error with the same load and seating depth. While my overall size may not have opened up much more than that my groups were .22 .30 and .35. just being too anal i guess. I mean this is the best I have ever shot. But i was stumped on why the difference. Conditions were almost the same just a tiny bit more of humidity

[huckberry668]

It seems everyone assume it's the 'load'. IT AIN"T THE LOAD.
The only new differences are fire formed brass and maybe primer. Those 2 things do not increase group size by 100% assuming shooter and equipment didn't change.

If it's not you, the shooter... which is probable since you mentioned your groups had fliers the opened the groups up to 125%. And I'm assuming you're using a sturdy tightened down front rest and a firm rear bag. I'd suggest checking your equipment settings. Action screws (I've seen too many of these), scope mount screws, scope rings/screws.

[rstbkt69]

I'm using a Caldwell Rock BR competition front shooting rest, With a kung fu grip. Cabellas sand bags resting the rear of the gun, my elbow and my trigger hand.

This is the rifle http://www.calguns.net/calgunforum/s...ight=bigbamboo

Vortex viper scope.

I know that I was inducing my own errors during my previous trips to the range. And I am not saying that i didn't this time either, but this time I never broke my cheek weld and paid more attention to my breathing. On the other days I would shoot and record the data then settling for another shot. One thing I did change up was on the previous trips I didn't pull the butt of the chasis into my shoulder as much to eliminate the way my heartbeat pulled my scope off the target. I couldn't maintain the same cheekweld shooting that way because the rifle would slide back off the rest a little. Would this change cause the problem? I timed my shots as close to between beats as I possibly could. if that is even possible