BULLET RUN OUT

[Webster]

Has anyone measured bullet run out (straightness) as reloaded and after chambering and extraction? Does closing the bolt and pushing the shoulder back cause misalignment?

 

[22BRGUY]

Sounds like the ejector spring might be too strong forcing the bullet to rub hard on the side of the chamber during extraction and pushing it out of alignment.

 

[BoydAllen]

Why would closing the bolt push the shoulder back? I have done what you asked about with a tight neck (.262) 6PPC, that had the bullet seated to engage the rifling. I intentionally pushed the bullet out of alignment, measured it, chambered the round, removed it, and remeasured it. It had been straightened to about .0015 runout, on the bullet. With a brass and chamber combination that is looser, I do not know what would happen. If you have a concentricity gauge, why not do the experiment?

 

[Webster]

I don't have a shoulder gauge. Why would closing the bolt push the shoulder back? See p. 120 in Tony Boyer's book. Take the firing pin and spring out of the bolt so you can feel resistance to closing the bolt. Any resistance to closing the bolt is caused by force required to push the shoulder back a few thou. If the bolt falls closed with very little resistance you have pushed the shoulder back too much. If you have not sized the case enough it will take increased force to close the bolt. You need to increase the amount the shoulder is pushed back in 1 thous increments to get the correct feel. Ideally the bolt will almost fall half way closed with slight increased pressure to close it. I was thinking that if the shoulder is being pushed (bent) it may affect the alignment of the bullet.

 

[BoydAllen]

I always gauge shoulder bump each time I set up to load, and every time I start to work with different batch of brass. I have not seen anything on targets that leads me to think that this is an issue, as long as all of the cases in a group have the same feel. As a matter of fact, years back, I won an individual match at 200 with a bolt that was way too tight, because I had not learned that I needed to reset my FL die as my brass work hardened over a weekend.

 

[Webster]

Thanks for the info. We cannot get answers if we don't ask questions.

 

[Shynloco]

I don't have a shoulder gauge. Why would closing the bolt push the shoulder back? See p. 120 in Tony Boyer's book. Take the firing pin and spring out of the bolt so you can feel resistance to closing the bolt. Any resistance to closing the bolt is caused by force required to push the shoulder back a few thou. If the bolt falls closed with very little resistance you have pushed the shoulder back too much. If you have not sized the case enough it will take increased force to close the bolt. You need to increase the amount the shoulder is pushed back in 1 thous increments to get the correct feel. Ideally the bolt will almost fall half way closed with slight increased pressure to close it. I was thinking that if the shoulder is being pushed (bent) it may affect the alignment of the bullet.

I use an RCBS Precision Mic to measure each casing as I have determined the exact "sweet spot" or shoulder position of least resistance for the bolt to close via the method you described of removing the firing pin, spring and extractor spring to get that least resistance point. I maintain a record of what the reference point or marking on the Precision Mic and bump the shoulder on brass to that position each time to eliminate any guess work. Now I recheck what that sweet spot is for each batch or make of brass and adjust accordingly to whatever marking the Mic shows. I admit sometimes I may be off by .001 on some brass, but it's darn close and seem to work for me. Bottom line, might be a good idea to buy a Precision mic to assist you in your efforts to maintain or to determine the degree needed to bump shoulders.

Alex

 

[tenring]

Don't like the RCBS Precision Mic as well as the Redding Instant Indicator. With the dial, I can see half a thou difference in shoulder bump.