Bumping The Shoulder .002 Rifle Reloading

[WinterRanger]

Hi. New to the forum and been reloading a couple of years. I recently purchased a Bergara B14 in 6.5 CM and have been reloading my ammo. At first I chased the lands for a while and starting reading where that's no longer done and that all one really needs to do is bump the shoulder .002 and good, consistent performance (of course other things come into play like trying to match bullet weights, etc but that's a different thread). So I got some once fired brass and FLR it. Using an unfired piece of LC 6.5 CM brass as my zero I checked the length of the case from the rim to the shoulder with a headspace comparator tool. I used this measure to confirm my die was set right for FLR.

After shooting and then cleaning the brass I checked for expansion. Most cases only showed .003 of expansion. I was really surprised to see such little expansion over FLR. Is that number typical or is the rifle just built so well that its tolerances are exacting? Seems like bumping back .002 vs FLR, which is only .001 difference isn't work the extra time and measuring. Thoughts?

 

[Zero333]

It's all about how you set up the die.

Hence why we use headspace comparator to compare fired and sized brass. Everything else is not very relevant.

I have some FL dies that when they're set up to cam-over, they push the shoulder 0.006"... which is not ideal, and that much shoulder bump will result in headspace separation sooner than later.
0.002" shoulder bump is a sweet spot for brass concentricity and decent life span.

 

[jimmymac]

Chasing the lands and shoulder bump are two different topics. The former is for finding a good seating depth and the latter is for gun operation. Your shoulder bump setback is not going to affect your seating depth.

 

[dgeesaman]

It can take multiple firings to get brass shoulders to expand to the full length of the chamber. While you can play it (very) safe by bumping them back to their original length as-new brass, the point of bumping the shoulders back .002 is based on the brass being fully expanded such that the brass is .002 shorter than the chamber from base to brass shoulder.

Easiest way to get there quickly is to take tiny squares of scotch tape on one piece of unloaded brass and add one on the bottom of the brass and chamber it. If it chambers easily, add another, etc until you find the point where it's snug or hard to close the bolt. Now measure the base to shoulder using your comparator and take off .002 if it was just a snug fit or .004 or .005 if it was a hard close. This is the value you want your brass to be each time.

Now for the second phase: keep firing that brass and let the brass grow until it reaches that length. Now you can set your die to achieve this length after sizing. It's not really possible to set the die for correct shoulder bump until you have brass that's longer than the chamber.

 

[Zero333]

It can take multiple firings to get shoulders to expand to the full length of the chamber. While you can play it (very) safe by bumping them back to their original length as-new brass, the point of bumping the shoulders back .002 is based on the brass being fully expanded such that the brass is .002 shorter than the chamber from base to brass shoulder.

Easiest way to get there quickly is to take tiny squares of scotch tape on one piece of unloaded brass and add one on the bottom of the brass and chamber it. If it chambers easily, add another, etc until you find the point where it's snug or hard to close the bolt. Now measure the base to shoulder using your comparator and take off .002 if it was just a snug fit or .004 or .005 if it was a hard close. This is the value you want your brass to be each time.

Now for the second phase: keep firing that brass and let the brass grow until it reaches that length. Now you can set your die to achieve this length after sizing. It's not really possible until you have brass that's longer than the chamber.

I end up using a Go-Gauge to set up my FL die. If the Go-Gauge measure 1.6185" from base to datem.,. I size the brass to 1.6165"-1.6175" and call it a day. Anyway I look at it, the brass end up being bumped anywhere from 0.001" to 0.003".

However, before doing so, I measure the brass and chamber to verify it has a true Headspace of no more than 0.0035".

 

[Sandstorm]

Using an unfired piece of LC 6.5 CM brass as my zero

This is not formed to your chamber and therefore the numbers from unfired brass are useless
to find shoulder bump...
Id get some good manuals and do some reading to help with your reloading as well as some
comparitors and take good notes and keep records of everything. Stay Safe my friend above all.

 

[Coyotefurharvester]

The go gage is actually short in your rifles chamber. Possibly a couple thou. Not what I would use to setup(adjust) my FL die.

 

[jepp2]

Thoughts?

For each of my rifles I keep a record of:
1. case head to datum length where bolt contact occurs
2. case head to datum length I size my brass to
3. I always measure the case head to datum on new brass to know more about it

After the first firing, brass will almost always be much shorter than it would be after you fire it 2-3 more times. However, I can help make it longer. By setting my die high enough so I don't set the shoulder back any (no contact) the case head to datum length will increase as the die squeezes the case body inward.

When you check for bolt contact, your bolt should be stripped to improve sensitivity.

I encountered new brass where the case head to datum was 0.010" shorter than the bolt contact measurement in my rifle (Fiocchi 204 Ruger factory loads). As mentioned, do NOT use factory brass as the basis for setting your full length sizing die.

I size my brass to be 0.001" short of bolt contact. But a few things allow me to do this. First my application and choice of sizing lube supports this. Second my method for measuring the case head to datum is the most accurate method I have found (Whidden case gauge). And lastly, I anneal each case on an AMP annealer using the Aztec setting for my lot of brass.

Most folks size back 0.002" for a bolt rifle and 0.003" on a semi auto (+/- a thousandth or so). But these should be taken from a reference of fully formed brass from your rifle.

Hopefully my process description will be of some benefit to you.

 

[markm87]

I'm a cave man. I simply fire brass until it's tight, then spin the die down until it chambers using 3-5 pieces as a sample.

To each his own, but measuring every thing with every instrument an tool you can buy isn't appealing to me. (I don't shoot competition... just recreational long range)

 

[dellet]

Something you can do, just to see how things work.
You have once fired brass form your rifle and another that you bought.

Back your sizing die off 1/2 turn, size and measure the base to shoulder length. Most likely it will have become longer. Squeezing the sides in size doe this. Most likely the brass fired in your rifle will chamber, unless it was a near max load and the base needs sizing. The brass you bought could go either way depending on chamber size of the chamber fired in.

If either brass does not chamber, work the die down and 1/8 turn at a time and keep checking until it does. This will help you start to develop a feel for bolt closure and interference.

It will probably surprise you that the not fully sized brass, that has lengthened, still fits the chamber. This is one way to cut down the firings needed to have the brass grow to full chamber length.

 

[Charlie-NY]

Assuming that the new, once-fired case can be easily rechambered, I'd run the case into the FL die with the die backed out enough to NOT move the shoulder back at all. Fire again and repeat. At some point (2-3-4) the case will need the shoulders set back. Using a .002" setback seems to be the norm but if you measure all the cases that you've just resized you will notice that the amount of setback will vary. I lube and resize as consistently as I can, but the shoulders don't all setback the same. Annealing helps but things do vary a bit.

 

[Eagle Six]

Using an unfired piece of LC 6.5 CM brass as my zero I checked the length of the case from the rim to the shoulder

Out of curiosity, where did you obtain Lake City virgin brass?

 

[Coyotefurharvester]

An EASY verification method( no comparator needed) is using a partially seated spent primer. I check a couple NEW cases, a couple once fired. All you do is seat a spent primer 0.010 proud and chamber/close action, extract and measure again. Now you have the bolt face to cartridge base gap(headspace). Most of my ammo is field use( need to be able to load and unload, repeatedly) so I set for 0.001-0.002, my AR's 0.003+( these all must drop fit an ammo checker) so no surprise in the winter.

 

[G Liles]

At first I chased the lands for a while and starting reading where that's no longer done

I don’t mean to derail your thread but how can you stay in the most accurate node with out chasing the lands?

 

[JackWagon]

Don't get all wrapped up in just .002 bump.

Get wrapped up in what YOUR rifle wants. You may need .003 or .004

 

[Pete Wass]

There are good Youtubes on how to resize brass. Watch some of them.

Pete

 

[Clancy]

Don’t set the shoulder back at all until the brass has had a couple of full house loads through it. Then, decap a few cases and set your die to bump .002 or .003 for easy cycling.

I'm a cave man. I simply fire brass until it's tight, then spin the die down until it chambers using 3-5 pieces as a sample.

To each his own, but measuring every thing with every instrument an tool you can buy isn't appealing to me. (I don't shoot competition... just recreational long range)

With respect, this is alarming. At least use a spent 9mm case as a comparator- that’s free.

I’ve seen a case separate and rupture just above the .200 line (not in my own rifle) and the damage was fairly significant. With a Sako extractor, it can even be harmful to the shooter.

 

[6Creed73]

I don’t mean to derail your thread but how can you stay in the most accurate node with out chasing the lands?

I know guys who either seat to mag length and never even measure for the lands. Or guys who measure to find jam and then seat some length off the lands, say 0.020, and never think about it again...they only measure to find jam to stay away from it. After that they simply use a barrel tuner to stay in their node.

I still keep track of where I am in relation to the lands, but I don't use barrel tuners.

 

[gunsandgunsmithing]

The E-Z Chek'r lands tool works great for determining shoulder bump IN YOUR CHAMBER. I'll post a link to the thread here and instruction sheet. You just need a fired case that will chamber easily, just drop in fully and then size the case to the bump you want. Super easy and precise.

What accent? Lol!

Link to discussion

Finding the lands...Tool!

This is a tool I've used for years for different things, from finding the lands, checking shoulder bump, chambering barrels and even cutting cone depth with an attachment I have inside that contacts a "datum" or reference point from an old bbl that transfers to the new one when cut. Super simple...

forum.accurateshooter.com

Instruction sheet below

 

[Straightshooter1]

Hi. New to the forum and been reloading a couple of years. I recently purchased a Bergara B14 in 6.5 CM and have been reloading my ammo. At first I chased the lands for a while and starting reading where that's no longer done and that all one really needs to do is bump the shoulder .002 and good, consistent performance (of course other things come into play like trying to match bullet weights, etc but that's a different thread). So I got some once fired brass and FLR it. Using an unfired piece of LC 6.5 CM brass as my zero I checked the length of the case from the rim to the shoulder with a headspace comparator tool. I used this measure to confirm my die was set right for FLR.

After shooting and then cleaning the brass I checked for expansion. Most cases only showed .003 of expansion. I was really surprised to see such little expansion over FLR. Is that number typical or is the rifle just built so well that its tolerances are exacting? Seems like bumping back .002 vs FLR, which is only .001 difference isn't work the extra time and measuring. Thoughts?

I'll reiterate some important things that have already been said:

The first thing one needs to do with new brass (even once fired brass) is to fire form them to your gun's chamber. Once fire formed, which typically take at least 2 firings, then where ever the shoulder is then, is what you want to bump back your .002 or whatever you choose for ease of chambering. If shoulder are bumped too much, it will shorten the life of the case resulting in case-head separation. Once you've does this process, your cases will have the movement for what you set for for bumping.

Virgin brass is not something to use to gauge where you're shoulders should be bumped to. They are manufactured so that they'll fit within the range of SAAMI spec where there a wide range in which various chambers are produced.

I like to bump my case shoulder back by ~ .0015, which provide enough room to allow for spring back after sizing still give me ease of chambering each round. This means less brass flow in the case body that helps with the longevity of my cases. The only other issue regarding case longevity I have for my non-custom barrels is the amount of expansion of the body at the just above the case web, where a lot of factory chambers can have a lot of play.

And BTW: I agree in no need to be chasing the lands unless you're loading your cartridges to touch or jam. Once I find a seating depth that works (usually starts from .010 to .020 from the lands) - , I'll leave it there until it doesn't work. . . which in one instance was for over 2,000 rounds (in my .308) as the throat eroded substantially. Then I had to make a small seating depth adjustment, without regard to distance to the lands, and it all came back.