Shoulder bumping

[spudgun]

I learn something everyday, but last Wed I learned about shoulder bumping.

I am posting my experience to maybe help someone else that may be having this issue.

So, here I go....

Been reloading since the 70's and never had the issue that I have had over the past 2 months.

Shooting 6.5 CM and 6mm CM. Noticed that about 2 months ago my sized cases were becoming very difficult to close the bolt on both rifles.

Started measuring the cases and comparing them to virgin brass and noticed that the base of the brass was about .003 - .004" larger in diameter than virgin brass. My thought was I needed a small base die to size the complete case in stead of my FL die that I have been using for 6 years now.

Talked to a couple guys I shoot long range with and showed them my virgin brass and my sized brass and explained what was happening. Right off the get go they both looked at the cases and said bump your should back about .001-.002". I have read about bumping the shoulders but never understood how to do it. My dies are set to touch the case holder and then go 1/2 turn further to get the caming of the press.

They told me to just sand some of the shell holder off the top so it will push the case further into the die. Well that got me to thinking, that ain't going to be hard at all.

When I got home I noticed that I had 2, #3 RCBS case holders sitting on the bench. Took a caliper and did some measuring. Sure enough one was .004" thicker than the other.

Somewhere about 2 months ago I must have switched to the larger holder and that's when my issues started.

At 75 years old you can still learn something new in this hobby.

BTY, I have ground the larger holder down and now both work perfect.

Hope this helps someone who may be having a hard to close bolt.

 

[jepp2]

My dies are set to touch the case holder and then go 1/2 turn further to get the caming of the press.

Depending on your dies (and as you discovered) the shellholder, this could result in excessive setback of the shoulder. Redding and Whidden are two that are this could occur with. This is the recommendation that some of the die makers include but they really don't care about brass life. They are more interested in not getting complaints about guns that will not close on brass sized in their dies.

I started loading in the 60's and am close to your age. I learn more from this forum than any other forum I have spent time on.

 

[mikecr]

You should determine headspace (bumped to clearance) and always measure to confirm 1-2thou of it.
It's safer, and you can get more life out of your brass, with less trimming.

I like Alex Wheeler's method to find zero HS: https://www.wheeleraccuracy.com/videos
Watch the video on 'Sizing Brass'

 

[jelenko]

^^ This.
The resizing die should be set to bump the shoulder the specific amount that you decide.

If I screwed in my sizing dies 1/2 turn more than touch, the shoulders would be set back a LOT below SAAMI zero.

 

[Coyotefurharvester]

^^^^especially with Redding. I don't mix shell holder/die brands.

 

[K22]

I'm your age and have been loading for 50+ years which only means I've made just about every mistake and I'm still learning. 

Personally, I've never been a fan of modifying shell holders. As long the shell holder is of the same mfg. as the die, it should work as designed. Also, I'm not a fan of using a small base die to correct sizing problems in bolt rifles if the rifle chamber has been reamed properly.

In my opinion, the best way to access the appropriate amount of full-length sizing is to use a bump gage and caliper. It takes the guess work of the process. This is a minimal investment. And while it takes a little practice to refine your technique to obtain consistent results, it's not difficult to master.

The other, old proven method is the trial-and-error method of slowly adjusting the die and checking the sized case in the rifle chamber. This is tedious but it can work and was the method used in the "old" days before there were bump gauges. The problem with this method is that as cases age and hardened after repeated sizing, some sizing die adjustment may be needed. That's why the bump gauge method is easier to use to monitor case conditions. I check a few every sizing cycle with the bump gauge.

Even though I use the bump gauge method, I still occasionally check the size case in the rifle chamber just as a double check on the adequacy on my sizing.

The one condition you want to avoid is oversizing that can lead to excessive case stretching after repeated re-sizing's that can result in a case separation. In my opinion, when you modify a shell holder from the mfg. specs you are entering an area of unknown sizing especially if you are not measuring the actual set back.

 

[Kracken McGraw]

The Redding Competition shell holders have been a good investment to get your bump set up easily.

 

[mikecr]

With sufficient rim clearance in a shell holder, you can use feeler gauges to adjust bump.
For each barrel in service I keep a reloading box with all dies, gizzys, and a shell holder (often from Redding comps) that puts shoulder bump very close. From there I can adjust 1/2thou with lube amount on the shoulder.
My correct shoulder measure is logged, and I always check it with every single case I size.
Just like I check CBTO, and primer crush with every single loaded cartridge.

 

[wildcatter]

I have been reloading over 50 years, and as others, am still learning, even as I have been an avid Wildcatter,,, (as my screen name states), and making brass as so many chambers I've owned can't be purchased, and many require much more than just fireforming-trimming-turning and so on.

First misconception I have seen here is micing the shell holder???? Doing so would requier to many variables to get you at .001", as this would mean locating the mean,

position the contact point of the holder to the top of the ram,,,

Then one needs to know where the location from the seat of case sets on the holder itself,,,

Then we need to know the distance from that to the surface that contacts the die,,,

I've witnessed to many use their calipers to measure just from the surface above the ram to the top of the shell holder.

Next I use several presses, from a very sturdy RCBS Rockchucker, to Harrels range press, to full machined massive aluminum with steel inserts for die and ram surfaces. All will have a 1 to 2 thousands difference if not cammed into the die and the shelholder where all surfaces are as tight as possible against each other.

I have modified shell holders for this in the past by placing three spots of weld on the face of the shell holder then it is chucked and squared in a lathe just like we were truing an action face or cutting a barrel. Then turned to whatever it takes to force it to the die it is being used with and bumps my case to .XXX" I prefer .002" to .0025". But doing this I can use this now "MARRIED SET" die and shell holder in any press and get the same results every single time.

In the past I have set my dies to closely fit my fired case with up to .005" to .009" then make shims out of brass or aluminum shim stock with a hole to slightly fit larger than the case, then use the thickness I need to bottom that out with cam pressure between the "MARRIED DIE SHELL HOLDER" combo to that cartridge for one specific chamber.

But I don't stop their, I measure my fired brass circumference at the shoulder just bellow where it starts it's taper to the base of the neck, as well as just above the solid base or web. I will keep all three of these measurements inside of .001" to .003" to decide on the bump for any case to a specific chamber. I have seen some dies that I had to sell and acquire others. But Redding have been very good for matching up and holding all three surfaces within that tolerance.

For all my competition rifles and chambers I build with die that custom made to give me a .002" bump everywhere on that case from that chamber the gunsmith cut, but still rely on shell holder to die solid contact to resize my prized match brass!

If you allow an air gap between die and shell holder, you will introduce variable tolerances, even though they may be to little to matter on some rifles depending on their use and precision, but on precision rifles for absolute accuracy, as well as brass life, I strive for "0" tolerances as much as I can on everything I shoot today, even my 30/06 and 6mm AI hunting rifle's.

 

[GetReal]

Playing with this now, 6 ARC. (Resizing 6.5 Grendel to 6 ARC, actually.)

I have the SAAMI drawings of both the factory loaded round and chamber maximums.

For bolt guns I try to bump the shoulder 2 thou. For this semi, I'm bumping 3.5 thou below the chamber maximum length, to make sure it will chamber, and not get me an OOB fun & mexcitement.