Shoulder Bump

[hotrodlouie]

I was reading the tech article on shoulder bump, it was stated for a AR15 .003” to .005” bump was recommended for reliability. I have never had problems with reloads so for, I did some checking on cases. I'll start with new Lapua brass as a base line, every case mic exactly the same. Checked three different new factory loaded brands and found them -.005' to + .005” different from the Lapua new.
Next checked fired cases and annealed cases including Lapua some still running -.005” most running +.005” over new Lapua cases dimensions. Using a Redding full length sizing die every time, instructions say this die should bump the case. What should I be concerned with are what should I do with all these mixed sizes.

 

[Glenn Powell]

Measure a case that has been fired in your rifle, size it, and then measure it again. That will tell you how much bump your getting. Measuring factory loaded rounds will tell you absolutely nothing. Measuring new unfired brass will tell you absolutely nothing. What you are measuring with shoulder bump is "your" chambers shoulder with the fired unsized case, and the dies chamber shoulder with a sized case. Hope it helps, I am not nearly as articulate as most on this sight, hopefully someone will correct me if I have steered you in the wrong direction. And from what I have read you need to push that shoulder back a bit for AR's, otherwise they might not cycle.

 

[300 RUM]

I have several AR's (Armalite) in both .223 and .308 some stock and some for competition. About two months ago I was on here looking for a reason why I was having cycling problems in my .223. I was freaked out, but come to find out I had mixed my comp brass with my so called battle brass. My comp brass is not bumped as far back as I single load them but to get them to cycle I have to bump the shoulder back .004 on avg. This was actually on my 3 gun AR so I was trying to shoot like all hell. My Gissele trigger lets me shoot extremely fast and when ammo don't load itself it doesn't shoot.

 

[FroggyOne2]

When you get your die set.. you will only need about .003 bump on the shoulder.. bumping more than that can lead you to problems due to too much headspace on the brass.. Watch a guy shooting rapid fire.. case head seperated and blew the magazine right out of the mag well!!!! Come to find out.. he was bumping his shoulders too far back.. If your seperating your brass, you can use less of a bump on your 600 yard brass, since it is slowfire only.. but your rapid fire brass should be headspaced for function.. .002 to .003 is all you need.. no less to no more is needed.. just a thought

 

[hotrodlouie]

Mic the fired cases and re sized, now I have a .005" case dimension shorter for max bump which is recommended. I still have cases which mic short after re-sizing, they range .005" to .010 shorter then the correct bump size I need. Is these cases OK to shoot, I still have new ammo that mic .005" to .010" shorter that bump size needed??. What is the Pros/Cons with these short cases.

 

[ElJay]

How are these shoulder measurements made? What is being measured?

 

[Glenn Powell]

Good question Eljay. Louie, is the die hitting the shell holder? If so back it out, I work the die down till I get the bump I desire. As to safe, probably not, too much head space, I would think.

 

[FroggyOne2]

With my 223., the Lapua brass new had a headspace of .005. But I was seating the bullet into the lands, so the headspace of the case didn't much matter as worrying about the case getting slammed around in the chamber from the firing pin. I feel that .005 is about the limit for headspace. But the nice thing is that after it is fired the first time. You will be able to set the headspace correctly for future firing of the case.

As for checking and measuring your headspace on the case and the shoulder bump. You will need a dial calilper and the Hornady adaptors that fit on the blade of the caliper in order to measure them. They were called Stoney Point before Hornady bought the rites to the tool. These gages are a must have in order to get the case shoulder set back properly.. there are other gages that do the same thing. Any of them will do the job.

 

[woolenmammoth]

buying one of those shoulder gauges for your calipers is a purchase that should happen before a sizing die or scale IMO. I struggled with reloading for a while until I got one of those and then I saw the light. I cant imagine how you can effectively set any die in a press unless you are able to measure how far the case shoulder is actually moving. Yes, this is obvious to all of us who know but it isnt stated nearly enough with emphasis for those that dont, IMO. If you have a scale and a press and dies and a rifle and plan to reload, you NEED to acquire a shoulder gauge of some sort if you want to have any effective control of how much your case is being sized. Using calipers to measure from the case head to the mouth of the case tells you nothing about what the shoulder is doing.

 

[racesnake]

Wilson and Dillon make an easy-to-use, drop-in, case gauge that's simple and effective.

 

[GSPV]

http://forum.accurateshooter.com/index.php?topic=3797313.msg36128893#msg36128893

Good tool. Good man to work with.

 

[bricktop]

I think the easiest way to get you desired 'bump' is with the Redding competition shellholders. That way your shellholder will contact the die every time and will be most consistent. Having unscrew the die a bit to get your bump I think will be prone to errors, but it is possible if you are careful. I found that my Redding bushing FL dies would size 0.002" under a fired case with the 0.008" shellholder (just an example with my 260, your results I'm sure will vary). Quick fit tests with sized brass in the chamber confirm a snug fit but still easy to close the bolt. Simply using brass that was neck sized left the bolt a bit hard to close after two+ firings.

 

[hotrodlouie]

I borrowed a gauge and found it had a small bur giving me all these crazy sizes when I started to check, will get my own. What would be best bump size 3-5 is recommended, go to min .003",.005" seems a lot ?? Thanks for all the help guys, if any other recommendations I'm all ears, going to start over again .

 

[FroggyOne2]

Gas Gun..003 Bolt Gun..001