Accuracy loss in fired brass - 30 Nosler ?

[Broz]

Ok, this is a new one on me. But out of the bag, new, unsized, unfired, Nosler brass is shooting noticeably better groups that once fired after I size it.

The head space is actually a wee bit tight on a few of the new and they still shoot tighter.

I tried dropping a bushing size to no avail. Seating pressure feels the same and is smooth with both new and fired / sized.

I did notice a slight increase in pressure with the once fired so dropped a gain of powder and no change.

I am using Redding S type bushing dies.

Shoulders on my sized brass are being pushed back .002" from zero head space.

Could it be the rifle likes the brass to fit with zero head space? Haven't tried that. But the new unfired brass is at zero or +.001" I would say.

Confused on this one. Just when I thought I was about done, it all went to crap.

Thanks for any help.

Jeff

 

[CatShooter]

Ok, this is a new one on me. But out of the bag, new, unsized, unfired, Nosler brass is shooting noticeably better groups that once fired after I size it.

The head space is actually a wee bit tight on a few of the new and they still shoot tighter.

I tried dropping a bushing size to no avail. Seating pressure feels the same and is smooth with both new and fired / sized.

I did notice a slight increase in pressure with the once fired so dropped a gain of powder and no change.

I am using Redding S type bushing dies.

Shoulders on my sized brass are being pushed back .002" from zero head space.

Could it be the rifle likes the brass to fit with zero head space? Haven't tried that. But the new unfired brass is at zero or +.001" I would say.

Confused on this one. Just when I thought I was about done, it all went to crap.

Thanks for any help.

Jeff

Why are you pushing the shoulders back 0.002" if the cases fit the chamber?

You don't need to move the shoulders unless the bolt is too hard to close.

Let the case fill out the chamber to fit perfectly.

 

[cape cove]

Is this a new rifle. Have you used other brass before or is it only with the Nosler brass that this happens. Have you checked your run out on the resized cases. Reason I mention the run out is because I had the same thing happen to me with one of my rifles and run out induced in the sizing was causing my problem.

 

[Broz]

Is this a new rifle. Have you used other brass before or is it only with the Nosler brass that this happens. Have you checked your run out on the resized cases.

New rifle, new 30 Nosler brass. I believe this is all that is available for brass right now.

TIR in my sized brass is averaging .0005" with a few going .001"

Thanks

 

[Broz]

Why are you pushing the shoulders back 0.002" if the cases fit the chamber?

You don't need to move the shoulders unless the bolt is too hard to close.

Let the case fill out the chamber to fit perfectly.

I measure, and also going by feel with firing pin assembly removed. I am only bumping the shoulder back .002" from a true zero head space. Anything longer than zero results in drag during bolt closure. This is a tried and true method I have used with all my precision rifles. But the new brass is at zero HS or +.001. So I just sized some for zero HS and will shoot them.

Thanks
Jeff

 

[cape cove]

It's a little weird to see a pressure increase in resized fire formed cases. In my experience it has generally been the opposite. What ever is happening the answer may lie here. I would do alot of measuring between the virgin brass and the fired/sized ones.Just a suggestion.

 

[Broz]

It's a little weird to see a pressure increase in resized fire formed cases. In my experience it has generally been the opposite. What ever is happening the answer may lie here. I would do alot of measuring between the virgin brass and the fired/sized ones.Just a suggestion.

I have often seen a slight increase in pressure / velocity with fully formed cases. I did expect it. But not this much. I am dropping back on charge weights to see if accuracy returns. Bore was cleaned also. Rifle shoots well cleaned with new brass too. I will chrono later to see where we are at.

I have tested volume H2O weights from fire formed to new and found FF brass has .6 gr more volume. That is normal I believe. I measured the shoulder set back many times on many cases. Measured above web and at shoulder. All looks good. The only differences I can detect is head space and .001 of neck tension.

Thanks for all suggestions. I will report back as I strive to figure it out.

Jeff

 

[rcoody]

I have often seen a slight increase in pressure / velocity with fully formed cases. I did expect it. But not this much. I am dropping back on charge weights to see if accuracy returns. Bore was cleaned also. Rifle shoots well cleaned with new brass too. I will chrono later to see where we are at.

I have tested volume H2O weights from fire formed to new and found FF brass has .6 gr more volume. That is normal I believe. I measured the shoulder set back many times on many cases. Measured above web and at shoulder. All looks good. The only differences I can detect is head space and .001 of neck tension.

Thanks for all suggestions. I will report back as I strive to figure it out.

Jeff

Every time I have ever done load development with new brass once the brass was fireformed I had to start all over

now what I do is load them up with a medium charge and cheap Amax bullets and shoot them before I even start load development.

everything from neck tension to volume changes after firing it a few times

 

[cape cove]

Every time I have ever done load development with new brass once the brass was fireformed I had to start all over

now what I do is load them up with a medium charge and cheap Amax bullets and shoot them before I even start load development.

everything from neck tension to volume changes after firing it a few times

Does your pressure generally go up or down with your fire formed cases.

 

[rcoody]

Does your pressure generally go up or down with your fire formed cases.

Like.i said.i don't do any load.development before the.brass is.fired.the.first.time.

 

[Broz]

Every time I have ever done load development with new brass once the brass was fireformed I had to start all over

now what I do is load them up with a medium charge and cheap Amax bullets and shoot them before I even start load development.

everything from neck tension to volume changes after firing it a few times

I believe this is a great plan. I use to but got sloppy trying to save time and components. I will report results in a separate post.

Thanks

 

[Broz]

Ok, made some progress. In two steps I did 3 things.

1: Reduced charge weight by 2 grains to remove slight ejector marks that showed up after fire forming cases.

2: Set head space / shoulder bump to zero

3: Remember I had dropped .001 in neck tension to see if it helped. It did not so went back to the original bushing. The chain of events pretty much prove this was an irrelevant change.

I just shot those 3. first two tore a hole and went .2 moa. Shot 3 opened group to just under .5 moa. This is a pattern both Dan and I have seen with this gun. Could be the carbon barrel?? But shot 3 opens group. Shots 1 and 2 from a cold rifle are usually center aim point.

So, either head space or charge weight. I am betting charge weight with increased visible pressure after fire forming. I have seen this pressure increase many times. I always expect it. But it is not usually this large. It has always been my opinion that brass that is not fully fire formed to chamber works like an accumulator in a hydraulic circuit. It cushions the pressure spike while it expands. Result is lower chamber pressure. I will chronograph to see where we are velocity wise now.

Jeff

 

[rcoody]

I believe this is a great plan. I use to but got sloppy trying to save time and components. I will report results in a separate post.

Thanks

I have done it to myself on several rifles. Take.brand new lapua brass and run an expandrel mandrel through it. Put.together.5 groups of 5 different loads and go shoot them. OCW or.ladder it doesn't matter. Pick what i thought would be a good starting load. Even gone so far as doing seating depth testing with the new brass because you want to keep them grouped by times fired.

Well no doubt i was scratching.my head in wonder why did those loads just go to $&*@.

Don't do that any more.

Brand new lapua brass can throw some.beautiful groups but they won't last

 

[Broz]

Velocity testing shows 3075 average for the reduced load of 82 grains. While 84 gr in new brass produced 3100. Both have good ES and SD. Knowing what I do about VV N-570, 2 grains should be well more than 25 fps. especially in this case size. So, it is my opinion that the increase in pressure in the fire formed brass screwed the pooch. From now on I will do all my load work up in fully fire formed brass.

Thanks for all the input.

Jeff