Shoulder bump

[powderbrake]

I stopped measuring the setback once I started using the Wheeler method to find the correct headspace for a free falling bolt knob.

Take a measurement on the sized case and keep it for reference..... remembering to ALWAYS use the EXACT SAME shoulder measuring device to measure with. A different device will give a different reading.

 

[INTJ]

Upon being struck by the firing pin, the chambered round moves forward, until something stops it. A looser fitting case is not sitting in the bottom of the chamber when it fires.

True, but does it fully center up the case in the chamber? I would think it might help a little but wouldn't the brass need to be expanded before extract alignment happened?

 

[BDman]

I began bumping less and less for better brass life and it took me quite a few rounds to figure out why my known accuracy loads were going downhill. I first thought Carbon ring, dirty barrel, scope, mount and checked everything. Then, sitting down at the reloading bench, it dawned on me that reducing my bump had been the only change I'd made. I went back to bumping .002-.003 and all was good again. JME...

Edit: I discussed this with a BR shooter friend and now believe that with a looser, no turn chamber, a FL and "over" bumped piece of brass, can better self center. A tight fit will not align as consistently in these chambers. With a super minimum NT chamber that tight fit might work better. I use min standard, no turn chambers so I can't verify that.

 

[INTJ]

I began bumping less and less for better brass life and it took me quite a few rounds to figure out why my known accuracy loads were going downhill. I first thought Carbon ring, dirty barrel, scope, mount and checked everything. Then, sitting down at the reloading bench, it dawned on me that reducing my bump had been the only change I'd made. I went back to bumping .002-.003 and all was good again. JME...

Edit: I discussed this with a BR shooter friend and now believe that with a looser, no turn chamber, a FL and "over" bumped piece of brass, can better self center. A tight fit will not align as consistently in these chambers. With a super minimum NT chamber that tight fit might work better. I use min standard, no turn chambers so I can't verify that.

We find that it's even more important with tight chambers in BR and we are turning for more clearance than we used to.

 

[mikecr]

The tighter your fitting, the tighter your reloading better be. Fortunately, your best die is your chamber, and a tighter chamber produces better brass. The path is self perpetuating.
Now if you can't reload well, perhaps due to poor practices or planning, then a tighter fit will hurt you.
Then you'll be in the sloppy chambers are better mob, because they are -for you.
Again, a self perpetuating path.

The better reloaders here can make good ammo on either path. That I'm sure of.

 

[Uncle Ed]

The Cartridge should fit the chamber like a rat turd in a violin case.

Click on the image to enlarge

Below German Salazar is answering a question about partial full length sizing vs full length resizing and case clearance in the chamber. (The rat turd in the violin case)

The Rifleman's Journal
https://web.archive.org/web/2015031...om/2010/06/reloading-partial-neck-sizing.html

Now the last scenario, a full-length sized case in which the neck is also fully sized. There is clearance at the neck and in the body of the case, the closest fit anywhere is the bullet in the throat. If the neck to bullet concentricity is good (although it needn't be perfect), then the bullet will find good alignment in the throat and the case body and neck will have minimal influence. Let's not forget that the base of the case is supported by the bolt face or the extractor to a certain degree as well; this is yet another influence on alignment. As you can see, there are several points from base to bullet that can have an effect. My procedure is to minimize the influence of those that I can control, namely the case body and neck, and let the alignment be dictated by the fit of the bullet in the throat and to some extent by the bolt's support of the base. Barring a seriously out of square case head, I don't think the bolt can have a negative effect on alignment, only a slightly positive effect from minimizing "case droop" in the chamber. Given that a resized case will usually have a maximum of 0.001" diametrical clearance at the web, this isn't much of a factor anyway.

In conclusion, I believe that allowing the bullet to find a relatively stress-free alignment in the throat by full length sizing (including the neck) and turning necks to enhance concentricity gives the bullet the best probability of a well-aligned start into the rifling. Additionally, I place a high value on easy bolt operation and true full length sizing helps that quite a bit. I favor easy bolt operation as a prone shooter because I keep the rifle in my shoulder for the entire string and struggling with the bolt not only can shift the buttplate (always with adverse consequences) but it is also a distraction from my attention to mirage and wind flags which ideally occupies all of the non-aiming time.

Germán

 

[INTJ]

The tighter your fitting, the tighter your reloading better be. Fortunately, your best die is your chamber, and a tighter chamber produces better brass. The path is self perpetuating.
Now if you can't reload well, perhaps due to poor practices or planning, then a tighter fit will hurt you.
Then you'll be in the sloppy chambers are better mob, because they are -for you.
Again, a self perpetuating path.

The better reloaders here can make good ammo on either path. That I'm sure of.

Interestingly, the best shooting barrel I have has an oversize chamber. I made a couple of rookie mistakes when chambering it last year. The issue is it's about .002" larger in the back, which makes sizing the brass a pain. I am just going to cut an inch off and rechamber. It will still be almost 28" long.

 

[mikecr]

I believe that allowing the bullet to find a relatively stress-free alignment in the throat by full length sizing (including the neck) and turning necks to enhance concentricity gives the bullet the best probability of a well-aligned start into the rifling.Germán

Yes, stress free is good in that there are no chambered pressure points.
You know what the difference is between stress free in a sloppy chamber -vs- stress free in a tight chamber?
A good reloader can achieve the latter.

 

[Uncle Ed]

The difference between a factory chamber and a tight chamber is how much "wiggle room" the cartridge has.
Meaning the tight chamber is less forgiving and has less room in the violin case for the rat turd.

Bottom line, the people here with custom rifles with tight chambers will need custom made dies to give the rat turd some wiggle room in their chamber.

 

[INTJ]

I measure bee case after sizing. On my CoAx, 70% are spot on. 20% are .0005" long and 10% are .001" long. I simply size the long cases again. Sometimes I have to add more line. When I am done they all measure the same. Give it's doubtful that even with my Mitituyo digital calibers I really am measuring that perfectly--even though I do get consistent results--may cases are likely without .0005".

Since I bump .0025" to .003", I never feel the shoulder on bolt closing. I usually have single digit ES. While that doesn't always show on the target, single digit ES does validate my loading consistency.