Bumping back shoulders.

[boomer135]

I have been loading for my 300WM for awhile now. neck sizing w/redding comp neck bushing and seating dies.

Brass still chambers fine (not excessively tight). I haven't needed to trim the brass the last few firings. Primer pockets are beginning to loosen but still gauge properly with the Ballistic tools swage gauge.

Neck sizing only I am on my 6th loading with federal brass. When do you feel the need (if at all) to bump your shoulders back?

Rifle (Remington 700 sendero) is used for precision shooting only, not hunting.

[ducky_0811]

I will do a shoulder bump once I feel the bolt getting stiff to close. That'll vary from rifle to rifle, for my 6.5 swede it's usually after 3 or 4 firings. Some guys will anneal at the same time, up to you, but at some point that bolt is going to get awfully hard to close.

[LynnJr]

As posted only when the bolt just starts to stiffen up.
If your shooting of of a front and rear rest and your bolt opens and closes with too much effort you will end up rocking the gun in the bags and sand will build up in the center of the bag/bags.
Benchrest shooters use tracking rails to prevent that from happening but bumping the shoulders for smoother bolt operation works very well.

[Fjold]

For match ammo, I adjust my full length sizing die so that I feel resistance just as I turn the bolt down to lock.

For hunting ammo, I screw the full length sizer down 0.002" from the match ammo setting.

[bsumoba]

I like to have no resistance on the bolt close and I FL resize all my brass and bump the shoulders 0.0015-0.002" every time. Seems to work well for me.

Another reason for me to FL resize is I know that every round will chamber with no issues. Also, I found that a round that takes minor effort to close the bolt on will usually result in a harder to open bolt after firing.

[boomer135]

Just wondering the norm as I haven't gotten to the point of the bolt becoming too tight yet.

[micro911]

As long as the bolt closes snug, it is okay. For magnum cartridge cases, I use a scraper to check inside of the case to see a sign of stretch ahead of the web area. I usually discard cartridge cases after 5 - 6 firings. It is cheap enough and I don't want to deal with case stretch or other issues.

[rsrocket1]

I used to use the Hornady case gauge to check the headspace on all my .308's



Now, most of the time, I simply chamber the empty cases after neck sizing to see if there is any resistance. Only then do I take the snug fitting cases and bump the shoulders back a few mils. This way, the cases last a long time.

[boomer135]

That is the tool I have been using, and the same technique as you mentioned. Still haven't needed to bump the shoulder yet.

I used to use the Hornady case gauge to check the headspace on all my .308's



Now, most of the time, I simply chamber the empty cases after neck sizing to see if there is any resistance. Only then do I take the snug fitting cases and bump the shoulders back a few mils. This way, the cases last a long time.

[Fjold]

The bad thing about the belted magnum cases is that they headspace on the belt. So, a cartridge comparator may not work because the rifle chambers can be different.

The best way to do it is to adjust your full length sizing dies to your individual chamber length.

[boomer135]

The bad thing about the belted magnum cases is that they headspace on the belt. So, a cartridge comparator may not work because the rifle chambers can be different.

The best way to do it is to adjust your full length sizing dies to your individual chamber length.

You are correct for factory and new brass. Although when reloading belted mags keep I keep a small amount of chamber clearance at the shoulder.

[slamfire1]

This article is very helpful in understanding the use of gages.


Extending Cartridge Case Life

http://www.realguns.com/Commentary/comar46.htm

I really don't want to crush fit cases in the chamber. I have been competing for decades now in NRA highpower competition and in my experience, particularly in the rapid fire sequences, you want ammunition that will chamber without any resistance and extract without any resistance.

The tolerances for chambers and ammunition were set up under the assumption that the case was fired once. If you notice in this diagram



there is clearance between the case and chamber before firing and awards. That is what is desired for maximum function reliability. You don't want a crush fit case because after firing, it will be sticking to the chamber walls. You want a little start clearance for a little ending clearance. How much clearance is available after firing depends on a lot of factors, primarily clearance at start, pressure of cartridge, and work hardness of the brass.

I full length size everything. I set the shoulder back no more that 0.003" because setting it back more increases case sidewall stretch. You don't want the case carrying load because the case will stretch, and it will stretch to the point you develop case head separations. These cases had the shoulders set too far after resizing, they were fired dry in dry chambers. Due to two factors: the case mouth is the thinnest part of the case and expands first, and due to the adhesion between case and chamber, the front of the chamber was fixed into position on initial combustion. But, as pressures rose internal pressures were high enough to stretch the case sidewalls to push the case head to the bolt face. If the initial clearance between base and bolt face is more than 0.006" or so, after combustion the side walls will be severely stretched and in most instances, break. As you can see in these cases, these have all experienced severe side wall stretching.

6.5 Creedmoor cases





300 WSM Cases