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

[TheGidds]

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.

I agree with the above. Most of my documentation for the Forster dies states that a bump of .001 to .002 is typically obtained (FL&NS). Firing pin and ejector removed from bolt. I am not using virgin brass. Once fired. Brass wet tumbled and it’s beautiful. All bump measurements after cleaning are within .0005. I have also watched numerous videos and viewed may posts describing the similar method, but most are on custom chambers, mine is factory.

The clean, unsized, deprimed brass I mention above takes a slight effort to chamber.

I think I am going to get the marker out as described in earlier response and see what is hitting. I think I’ll load a small batch at a .002 bump and see if more firings change the profile to match chamber.

 

[TheGidds]

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.

I guarantee I have watched every video you are probably referring to. I also tried the Cortina mandrel die (that sizes base also) and it sized the lower 1/4” to 1/2“ at the base of the case, depending on the case/web.

 

[alphapygmy]

I had a similar problem recently and it was a die not quite sizing the shoulder/body junction quite enough. I switched to a little tighter die and all is good.

Using both a Whidden case gauge and a Hornady tool the bump was .0015-.002 but some wouldn't chamber still. Switched to a die I know is a little tighter but with the same amount of shoulder bump and all the brass chambered easily after that.

 

[LHSmith]

Does the bolt fall freely on an empty chamber? If not check your bolt body for rub marks. An overly long front action screw or scope front base screw could cause the bolt to close with resistance.

 

[TheGidds]

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

I hate to ask but the .200” line…..is that from the bottom of the case up the body, or somewhere else (shoulder, neck, etc.).

 

[TheGidds]

^^^ 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.

Once fired, not new.

 

[TheGidds]

Does the bolt fall freely on an empty chamber? If not check your bolt body for rub marks. An overly long front action screw or scope front base screw could cause the bolt to close with resistance.

Bolt falls freely on empty chamber. Bolt falls freely when I got to the oversizing point (sacrificial case) of .005 / .006 distance.

 

[LHSmith]

Once fired, not new.

Again, it may take several firings to fully form.

 

[archerforkids]

Mr. BoydAllen had me chuck a piece of sacrificial brass in a drill. I then took a piece of Emory cloth while turning the brass and lightly removed enough brass to reduce the diameter at the base of the brass. I did it in about three steps exercising caution and not being greedy. Sure enough problem resolved. Ordered a small base die from Wilson. No more problems.
Thanks again Mr. BoydAllen.

 

[Coyotefurharvester]

Take a clean unsized piece of fired brass that chambers and seat a spent primer about 0.010 proud( longer than the case measures). Use the bolt to chamber the empty case. Measure again, you have your case head clearance( shoulder clearance). Do a couple cases. As long as the case is short of chamber length you will get good numbers. You can then measure with the comparator and have an actual measurement.

 

[JEFFPPC]

I hate to ask but the .200” line…..is that from the bottom of the case up the body, or somewhere else (shoulder, neck, etc.).

Your correct. From the bottom up. Don't be afraid to ask good questions.. Use the Search function. It contains a wealth of information.

 

[Crumster]

Why would you ever want the bolt to drop free? When you get to that point you have lost reference. You can't know for sure there hasn't been an anomaly, and you have set the should back to the danger point!

 

[Coyotefurharvester]

Factory new brass is often 0.006-0.008 or more short. Just need to avoid returning to the much shorter length, repeatedly. The other end, galling lugs from repeatedly chambering long for chamber brass.

 

[TheGidds]

Factory new brass is often 0.006-0.008 or more short. Just need to avoid returning to the much shorter length, repeatedly. The other end, galling lugs from repeatedly chambering long for chamber brass.

That’s the exact measurement (0.0065) that I got on the Factory round I sampled.

 

[Coyotefurharvester]

Try the partiality seated spent primer method I described above with a new piece of brass and fired brass, information about YOUR rifle is the best information. Especially chamber/die fitment information. Clean chamber is paramount to good measurement and proper die setting.

 

[Bugs]

I know it's not possible with a factory rifle but having a shoulder bump gauge made with the same reamer that was used to cut your chamber solves a lot of these kinds of problems.

 

[M-61]

I hate to ask but the .200” line…..is that from the bottom of the case up the body

Yes.

 

[M-61]

and you have set the should back to the danger point!

Yup.
At a .006 bump you are there. (Danger point)

 

[JFrank]

The one thing that I find very helpful and telling is measuring and recording the brass before and after ignition at all locations. And just drawing out a case on paper to compare the numbers and judge just exactly how well the die fits the chamber. Problems are not always a shoulder bump issue.

Case shoulder junction
.200 line
Base to shoulder data
Overall length

 

[JFrank]

Once fired, not new.

Rare imo that you would have a headspace issue with once fired brass. Look elsewhere