Bumped Shoulders too much

[parshal]

I've been messing around with this stuff a lot lately. Here's what I've gathered in no particular order.

There are micro die adjusters that make it very easy to move the height of a standard die in tiny increments. It won't work in a Forster press, though. Micro Die Adjusters - PMA Tool

I bought a couple sizing die blanks from Newlon Precision which I made into shoulder bump dies with my finish reamers. According to Newlon, the way to properly set up a sizing die is to have a little camover. Meaning, the ram should touch the bottom of the die and you should feel some resistance when you further move the handle and feel the "camover". This is the only easily repeatable method. However, this relies on your die to be set perfectly for your chamber. You may need to shorten the die by removing metal from the bottom using a lathe if you need to bump more or use the Redding competition shellholders to customize it. If you're getting too much sizing you'd need to deepen the die which really can't easily be done. You'd have to raise your die and have no camover and do it by feel.

When cutting the Newlon die for use with a .125" height shellholder you use the go-gauge used to cut the chamber. The base of the gauge should stick out .129" since most cases will spring back .002". When the die is set with the proper camover it should give you a .002" shoulder bump. Of course, you can shorten it to .128" or whatever you want to get the amount of bump you want.

My takeaway from making those dies and talking with Newlon is that you need to take a close look at your off-the-shelf die and make the modifications to have a repeatable setup. You can, of course, go by feel if your die requires no camover to bump the shoulders correctly but "feel" usually isn't as repeatable as camover.

 

[Mikecr]

No matter how deeply you try to make the cam-over notions work, the fact remains that each case has character of it's own. There never will be a 'set & forget' standard for bumping.
Same with bullet seating force and target CBTO, and priming.
You won't make good ammo with reloading FAITH.

 

[parshal]

You won't make good ammo with reloading FAITH.

Lots of measuring and re-measuring and double-checking.

 

[Mikecr]

Yes, and stressing a press with shell holder contact, over & over, will not change what the brass will do. The cases will just continue to spring back to where they have -until a logical adjustment to sizing is made.
I hate bumping, but I am really good at it for small to medium hunting cartridges, so far.
None of my dies contact shell holders with bumping. There is no reason that would be a proper setting for my brass, and loads, out of my chambers(they're all different). Most of my dies are also custom.
Can't imagine off the shelf dies having a better match of what my chambers produce.

All I can figure is factory die makers must be latching onto die bottom as a datum. They want you to take their die to that datum. Well, don't forget that factory dies likely do not match what your chamber/load produces in cases, and that bumping is a seriously precise action.

If making your own die. It's your choice, and I'm just suggesting you can make it work well either way.

 

[D.Camilleri]

I finally got a chance to go to the range this morning for a few practices shots. My first shots were with some of the RP cases that got accidentally bumped .010 too far back. Accuracy very good, velocity 2886 with 99 grains of RL33 and 300 gr Berger OTM, OAL 3.800 +-.002 This load turned out to be a little on the hot side, probably due to the shoulder being set back and reducing case capacity.

Next up were some new Bertram brass, OAL 3.800, 99 grains of RL33, 300 GR Berger OTM, ambient temp around 65 degrees F, Velocity 2815-2820 pressure seemed acceptable, no hard bolt lift, no noticeable ejector marks.

Last up Bertram Brass, 99 GRs RL33, 300 gr Nosler Accubond, 3.720 OAL, .020 off the lands, 2810 velocity, same vertical point of impact, about 1/2 inch right.

All of these loads shot sub .5 moa. So far the only draw back to the bumped shoulders is a rise in pressure. I might try dropping 1 grain of powder in these and try them again.

 

[Rhovee]

I just recently did the same thing. I am going to have to do some field testing to see what the difference in velocity is. I have about 40 rounds 3 thou bumped back. And 40 that are 6. Not really excited about it. Funny thing is every once in a while I get a case that won't bump back at all. These are all once fired brass out of a 28 nosler using 78.5 grains N570.