I have noticed on my lapua .308 brass that some of the brass comes out of my chamber with .0005 runout and some with .001. What would cause the variation in runout? The brass has been fired 7 times with annealing done after 3rd firing. The chamber is a custom. Perhaps I am under annealing? Thanks in advance.
Runout after firing.
- Thread starter goatliver
- Start date
Re: Runout after firing.
Are you taking into account powder fouling in the chamber / throat? Changes in humidity can cause some powders to foul differently than in dry conditions. Concentrate on the runout BEFORE firing. After it's fired is all history. Note it in your notebooks and keep going.
The right front tire of my truck leaks down over a period of 3 or 4 months and I have to air it up. I check the tire pressure every couple of weeks and make adjustments. I note it in the maintenance log and keep going.
Not ALL custom chambers run 100% true. Especially when checked to .0005"
Are you taking into account powder fouling in the chamber / throat? Changes in humidity can cause some powders to foul differently than in dry conditions. Concentrate on the runout BEFORE firing. After it's fired is all history. Note it in your notebooks and keep going.
The right front tire of my truck leaks down over a period of 3 or 4 months and I have to air it up. I check the tire pressure every couple of weeks and make adjustments. I note it in the maintenance log and keep going.
Not ALL custom chambers run 100% true. Especially when checked to .0005"
Re: Runout after firing.
I agree,that small amount is not going to be a problem.But the difference you are seeing could be the way you cycle the bolt.The ejector could be slapping the mouth of the case against the edge of the barrel/chamber,bending the neck or case mouth. Pete
I agree,that small amount is not going to be a problem.But the difference you are seeing could be the way you cycle the bolt.The ejector could be slapping the mouth of the case against the edge of the barrel/chamber,bending the neck or case mouth. Pete
Re: Runout after firing.
Vic's got a point there...
I expect to see .001 or less run-out of the loaded round before firing. Proven it to myself more than once that the less run-out the better the groups can be. If it gets over .001, something usually needs attention.
Neck concentricity and tension are probably the largest contributors to loaded run-out. If your neck wall thickness varies and you are over sizing the neck, it can really make it worse.
I can tell when my necks are getting hard and need annealing because the bullet starts to feel different when being seated. Some of my customs have almost no run-out after firing, others might get close to a thou.
Vic's got a point there...
I expect to see .001 or less run-out of the loaded round before firing. Proven it to myself more than once that the less run-out the better the groups can be. If it gets over .001, something usually needs attention.
Neck concentricity and tension are probably the largest contributors to loaded run-out. If your neck wall thickness varies and you are over sizing the neck, it can really make it worse.
I can tell when my necks are getting hard and need annealing because the bullet starts to feel different when being seated. Some of my customs have almost no run-out after firing, others might get close to a thou.
Re: Runout after firing.
Thanks guys, you all have valid points. I never really thought about it, but it does make sense when you cycle the bolt it can change the concentricity of the casing. My nesika bolt has a very aggressive ejector, which could be a contribution. I couldn't agree more with having low run out prior to firing, that's a different issue for myself!
I have tried every bloody method, techniques and suggestion........ it's the sizing process that has given me grief. I am currently using redding's type s bushing die. Brass is Lapua .308, neck turned. Fired brass diameter is .341, loaded round measures .3365..... with a .335 bushing. My press is a Forster Coax. I think maybe I should size the brass in two passes, first with a .338 bushing then followed by a .335 bushing. I wonder if it will make a difference sizing in smaller increments. Sorry for the RANT, maybe one of you guys has had the same issue?
Thanks guys, you all have valid points. I never really thought about it, but it does make sense when you cycle the bolt it can change the concentricity of the casing. My nesika bolt has a very aggressive ejector, which could be a contribution. I couldn't agree more with having low run out prior to firing, that's a different issue for myself!
Re: Runout after firing.
I started using a lee collet die to take down the difference from my fired neck OD and then finish the final neck sizing with a redding bushing neck die. That seemed to help some. My fired neck OD measures .339-.340" My loaded rounds measure .336". I probably don't need the extra step in neck sizing but it made a little improvement to my loaded runout. Also, for me, using my redding comp seating die, any load compression will tweak the loaded round runout as well. Non compressed loads I get much better runout results.
I started using a lee collet die to take down the difference from my fired neck OD and then finish the final neck sizing with a redding bushing neck die. That seemed to help some. My fired neck OD measures .339-.340" My loaded rounds measure .336". I probably don't need the extra step in neck sizing but it made a little improvement to my loaded runout. Also, for me, using my redding comp seating die, any load compression will tweak the loaded round runout as well. Non compressed loads I get much better runout results.
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