Missing what I thought was a basic concept on shoulder bump..

[TheGidds]

So I have thought that I take a fired case from my Ruger Precision 308, full length size and push back the shoulder .002”. Using a comparator with Sinclair 20degree shoulder gauge. I seem to have set up correctly. I will also add that I cleaned the case and annealed it, prior to sizing,

I was under the assumption that with the .002 reduction in shoulder, by bolt should drop free on that case (with ejector removed). It seems that I actually have to back the shoulder back .005 or .006 to accomplish free dropping bolt.

Lapua brass, FYI. Bolt only has extractor.

I tried deburring mouth also.

 

[rijndael]

I usually bump mine back .003 because I want less bolt close resistance. .002 is a ballpark, not absolute. But you probably don’t want to do .006, it’s overworking the brass and will likely reduce the life.

 

[Benchrest Braxton]

So I have thought that I take a fired case from my Ruger Precision 308, full length size and push back the shoulder .002”. Using a comparator with Sinclair 20degree shoulder gauge. I seem to have set up correctly. I will also add that I cleaned the case and annealed it, prior to sizing,

I was under the assumption that with the .002 reduction in shoulder, by bolt should drop free on that case (with ejector removed). It seems that I actually have to back the shoulder back .005 or .006 to accomplish free dropping bolt.

Lapua brass, FYI. Bolt only has extractor.

I tried deburring mouth also.

sounds like your die doesn't match your chamber that well. It's probably the 0.200" line that is causing your resistance on bolt close, because 2-3 thou should be plenty of shoulder bump to get free fall.

 

[boltfluter]

sounds like your die doesn't match your chamber that well. It's probably the 0.200" line that is causing your resistance on bolt close, because 2-3 thou should be plenty of shoulder bump to get free fall.

This is exactly right.
Paul

 

[M-61]

I tried deburring mouth also.

That’s for bullet seating
Maybe you meant trimming
And 6 thousandths bump is wrong for many reasons
Looking for easy bolt closure don’t load a cartridge at all , lol
Before you arbitrarily start with shoulder bumping, you have to understand what you’re doing.
At some point whatever the headspace was set at, won’t matter at all.

 

[AlNyhus]

Quick question...did you remove the primer before checking the fired case with the comparator? Leaving primers in will skew the measurement from .001-.003.

 

[JEFFPPC]

A fat .200 line could also contribute plus give you clickers. You need a tenth mic to check that properly.

 

[Coyotefurharvester]

Why are you setting the shoulder back, do fired cases not chamber/hard to extract? Is the chamber clean?

 

[mgunderson]

Get the marker out and figure out where the case with the shoulder pushed back 0.002 in is hitting the chamber.

I am not a fan of the bolt drop method. It doesn't help solve the problem in this situation.

 

[LHSmith]

Why are you setting the shoulder back, do fired cases not chamber/hard to extract? Is the chamber clean?

^^^ Exactly. If you are starting with new brass - they usually start out several thou short of ideal H/S for most chambers. Many times it takes more than one firing to fully form the brass to your chamber. Take a sized fired case and add layers of scotch tape to the case head (over the headstamp) and by adding layers until you get to where the bolt handle won't fall. Record this number.

 

[J_idaho]

Some new chambers are so rough you can not chamber a round. If it is send it back and make them fix it.

 

[K22]

In the old days before bump gauges, reloaders used the rifle chamber as a gauge to set the F/L die for optimum sizing since the F/L die mfg.'s instructions often resulted in oversizing. The process involved incrementally sizing until the case fit the chamber.

With the firing pin assembly removed, the idea was to size to the point where the bolt offered some slight resistance (an approximate 1/2 to 3/4 bolt drop) with the casing chambering and extracting without difficulty. But not a "free bolt drop" because the amount of "free drop" was too difficult to assess and often resulted in over sizing.

With the development of bump gauges, a better and more precise way was offered to set the F/L die. Lots of good advice in prior posts so I won't repeat but you should not have to bump the shoulder back that amount to obtain optimum sizing.

 

[Dimner]

So I have thought that I take a fired case from my Ruger Precision 308, full length size and push back the shoulder .002”. Using a comparator with Sinclair 20degree shoulder gauge. I seem to have set up correctly. I will also add that I cleaned the case and annealed it, prior to sizing,

I was under the assumption that with the .002 reduction in shoulder, by bolt should drop free on that case (with ejector removed). It seems that I actually have to back the shoulder back .005 or .006 to accomplish free dropping bolt.

Lapua brass, FYI. Bolt only has extractor.

I tried deburring mouth also.

I have had this problem many times and it always ends up as other say, my die is not setting back at the same datum as my chamber wants. In addition, my comparator is also not at the same datum as my die. So now you have 3 different places on your brass that is being referenced. Die, comparator, chamber.

One more thing to make sure is to fully clean, brush, whatever you need to do to get all the gunk/carbon before you do this process.

So what I do, is I just use the die to bump very slowly, until that piece of brass chambers easily. I note that reading with my comparator. and leave my die locked to that setting.

Edit: What I guess I'm saying is, numbers/readings/measurements do not matter until you have gotten to the point where the sized brass chambers the way you want it to.

 

[Chuckhunter]

Agree with those who have stated that your issue maybe at the base of your brass, not the shoulder bump.

 

[Pete Wass]

A small base die will cure your ills. Brass stops springing back all the way after it has been worked a few times so the small base die pushes it back enough to make things "right" again.

The proper way to find the proper case fit is with a stripped bolt. There are plenty of Youtubes to watch on this issue.

 

[Pete Wass]

A small base die will cure your ills. Brass stops springing back all the way after it has been worked a few times so the small base die pushes it back enough to make things "right" again.

The proper way to find the proper case fit is with a stripped bolt. There are plenty of Youtubes to watch on this issue.

Another way is to open the ass of your chamber up, then the die you have will or should work for you.

 

[Richard Jones]

You could also try a 45 ACP die, used as a body/ring die. Maybe you have one? Lots of info on this, search for " 45 ACP body" etc. Good post on this by Boyd Allen.

 

[rijndael]

I preferred my 45 die over a ring die.

I would also not ignore a sizing issue at the body / shoulder junction. I've had insufficient sizing there mimic a base sizing issue, from stiff closing perspective.

 

[K22]

One other note, the Sinclair bump gauge indexes on the shoulder whereas the Hornady and Whidden gauges index on a datum line off the shoulder.

I wonder if this kind of bump gauge could be causing some problems with setting the F/L die for optimum sizing?

 

[TheGidds]

Quick question...did you remove the primer before checking the fired case with the comparator? Leaving primers in will skew the measurement from .001-.003.

Yes, primer removed prior to anything….