Testing shoulder bump with bolt and action

[fattybinz]

I'm a new reloader that just recently learned the method of testing shoulder bump by taking the firing pin and extractor out of the bolt and then bumping case shoulders until the bolt drops on a loaded case without resistance. Then the ol' scotch tape trick to double check. Cortina's video on that was great. Worked great on my hunting 6.5 PRC Seekins element, then great on my Lone Peak Fuzion 6 Dasher. I'm feeling good about myself and feel like I'm starting to get it...but then I pick up a custom build with a Bighorn Origin in 223 rem. The bolt doesn't have an extractor (see below). So I just take out the firing pin assembly. I tried some virgin brass and bolt closes no problem. But then I put in some x1 fireformed brass that was shot out of this same rifle, and bolt also closes as freely as the virgin brass. Am I missing something? Shouldn't the fireformed brass be sized, and shouldn't the bolt be tough/impossible to close with this unsized fireformed brass? If it isn't, how am I supposed to do the old bolt/scotch-tape test if even unsized brass fits fine? Thought maybe the barrel breakin rounds I shot were too light to truly fireform the brass, but that seems really unlikely. I fireformed with Varget; velocities were upper 2700s, and TAC; velocities from 2700 to almost 3100.

 

[K22]

The method you described was used by many of us old reloaders before bump gauges were widely available. It can work but it can be tedious. It also assumes that all cases in a lot will be the same head space wise and expand and size the same which often is not the case.

Using a bump gauge with a caliper makes the process of monitoring case headspace much more efficient and easier because you can measure several cases quickly. You also obtain a precise measurement of the fired and size case condition.

I full size all my cases every time but set my die for zero bump until the cases are fully fire formed to the rifle chamber and need bumping which is often after several firing and sizing cycles. What you are observing is that the cases are not fully fire formed yet. Therefore, there is no need to bump the shoulder which will over work the cases. This why a bump gauge is so important, it takes the guess work out of the sizing process. You know precisely how much, if any that the cases expanded.

Because the F/L die also sizes the radial dimension of the case, often that is all that is needed until you pass several firings. It is also prudent to spot check the size case in the rifle chamber like you have been doing. When the bolt drops without any resistance at all, the case was probably oversized. There should be some very slight resistance to bolt closure, usually exhibited by the bolt dropping halfway then requiring some very slight pressure to close it. Again, this is why I prefer a bump gauge, it's more precise.

For consistency, you should start with virgin cases, dedicate them to a specific rifle and rotate their use so they receive the same number of firings and sizing's.

 

[Oso]

There are two things to keep in mind about cases:
1) “Spring Back” means that the brass case expands during the firing, but then as it cools its shrinks ever so slightly. This is the reason that your fired cases are able to be removed from rifle’s chamber.
2) New cases may take as many as 2-3 firing before they stabilize to match a rifle’s chamber. For this reason some shooters choose to only resize the case neck (re-establish neck tension to hold a bullet) after initial fire-forming. The goal is to leave the shoulder unmolested until case dimensions stabilize / match the chamber.

If you choose to FL Size these 1x fire-formed cases then a good process is to determine the baseline for the shoulder (case base to shoulder datum). Measure the shoulder before sizing and then remeasure after sizing. Don’t be surprised if the shoulder measurement has increased. This has occurred because the shoulder on the fired case is still short and as the FL Sizing Die squeezes the case body it pushes the brass forward into the empty space (ie void between actual shoulder and shoulder profile of FL Die.

 

[David Christian]

What he said. /\ /\ /\

Fire that brass again and retest sizing.

 

[fattybinz]

@Oso and @K22 thank you for the info! I just pulled out my headspace gauge and my x1 fired cases are all one to one and a half thousandths longer than the virgin brass. Seems crazy to me that it wouldn't fully fireform with one firing. So if I'm understanding correctly, I should FL size these x1 cases to basically return them to their current headspace (which means, as K22 said, they will get longer initially, and then bump back to that baseline), and then fire them again and repeat the back-to-baseline-bumping-back UNTIL they reach a firing where they no longer chamber freely. I'd then consider that to be true fireformed and can bump back .002" from there?

 

[6MMsteve]

set to about .003 bump and have at it, easy to cycle bolt u don't have to worry with anything even .004 will get the job done if you go getting fancy and tight u will have issues and start cussin and throwing stuff...I do anyway leave some room and and smooth bolt throws

 

[Tangent]

This all explains some of the strange measurements I've had! I thought once fired would be enough but apparently not. I wondered why the shoulders weren't moving but still chambered fine, obviously still not completely formed to the chamber.

 

[dgeesaman]

Yeah it’s a weird place to be when the brass shoulder is still creeping forward. I’ve put 4,5,6 layers of tape on the base of the case to ‘find’ the shoulder when testing it in my chamber.

I also don’t strip the bolt when finding the shoulder because heavy bolt lift is pretty obvious. The stripped bolt is for when I’m trying to pin down where a seated bullet exactly touches the lands. That requires very fine feel.

 

[dellet]

But then I put in some x1 fireformed brass that was shot out of this same rifle, and bolt also closes as freely as the virgin brass. Am I missing something?

If the brass extracted easily, why would you expect it to go back in any differently?
If you size it without touch the shoulder and the shoulder moves forward, then you might have trouble closing the bolt. But brass that will not rechamber after firing, would be a sign of high pressure.

Shouldn't the fireformed brass be sized, and shouldn't the bolt be tough/impossible to close with this unsized fireformed brass? If it isn't, how am I supposed to do the old bolt/scotch-tape test if even unsized brass fits fine?

Keep adding tape, then when it starts to close with resistance, you will know roughly how far the brass needs to grow to fit your chamber.
A standard die is 7/8x14 threads per inch and will move up or down about .072” per rotation. So for every 1/16 of a turn about .009”. Screw your die down until it just touches the shoulder of a piece of fired brass and back the die off about 1/16 of a turn. After a couple firings/sizing your brass should be closing with resistance in the chamber.

Thought maybe the barrel breakin rounds I shot were too light to truly fireform the brass, but that seems really unlikely. I fireformed with Varget; velocities were upper 2700s, and TAC; velocities from 2700 to almost 3100.

It may not be the load being low pressure, as much as the virgin brass being well under minimum length, it’s not uncommon.

 

[dgeesaman]

Screw your die down until it just touches the shoulder of a piece of fired brass and back the die off about 1/16 of a turn.

I’ve never had fired brass that fits loosely in the sizing die. Even if it’s a bushing die and I’ve pulled the bushing, the body of the brass always has a few thou of interference on diameter.

So while I agree with this concept I don’t see how it will work on fired brass.

 

[William Vogel]

Everything is elastic. The brass does expand when fired but the chamber limits the expansion. The brass usually always relaxes back after firing which is the reason it extracts without effort as long as firing pressure is within spec and brass is good. It takes several firings to fit the brass to the chamber. Before resizing it’s important to fit a fired new brass and check bolt close before setting the die. Bumping the shoulder on 1x brass may set the shoulder back too far and work the brass. If you cut the chamber and set headspace with the gauge and know exactly where the datum line is at, then you know much better about the number. Bumping the shoulder on 1x brass will most likely still require resetting the die at 2x, 3x firing.

 

[perazziguy]

I have a 22-250 factory chamber in a Ruger M77 from the late 70's or early 80's and a 6br Savage PTA with CBI barrel. I have case gauges for both. The 6br, fired cases will drop into the gauge and will chamber easily back in the rifle. The 22-250, the fired case will NOT fully drop in the gauge. They stick out a lot. Before I started using the case gauges, I was loading 22-250 cases that were shot in one of three rifles(mine, dad's and brother's) and was not obtaining the proper amount of sizing. It was causing some grief with stiff bolt closing. All that was cured with the case gauge and proper die adjustment. Kind of like a "light bulb" moment. Any way, have fun, shoot often!

 

[dellet]

I’ve never had fired brass that fits loosely in the sizing die. Even if it’s a bushing die and I’ve pulled the bushing, the body of the brass always has a few thou of interference on diameter.

So while I agree with this concept I don’t see how it will work on fired brass.

I guess I should have been more detailed.
Start with the die a quarter turn off of touching the shell holder, size a piece of fired brass, then check the base to shoulder length. Adjust the die down slightly and check again . Do this until your die has just touched the shoulder.

Then based on tape thickness on the case you checked headspace, adjust your die up accordingly. Use small adjustments, as 1/16 of a turn will change base to shoulder length .008” -.009”.

If you have a method where you can set your die at touching the shoulder, on once fired brass, in a new chamber the first time, every time, I’d be interested in knowing it. I always have to basically use trial and error, even using competition shell holders.

 

[Coyotefurharvester]

I find the spent primer method is easier/more accurate for actually measuring bolt/headspace clearance, especially with new brass or brass that a first firing doesn't result in fully formed brass. Your hunting rifle is fine 0.002-0.004 clearance (bolt just drops free). A quick second shot and dusty/dirty conditions won't affect functionality of the rifle. When I have new brass I want to know the actual bolt/cartridge face clearance. An often discussed event here are fail to fire, occasionally it is related to too much clearance with new brass. Totally different loading methods are needed to form brass in one firing, which would be important with short for chamber brass. Know you new brass clearance to avoid issues at the range.

 

[K22]

@Oso and @K22 thank you for the info! I just pulled out my headspace gauge and my x1 fired cases are all one to one and a half thousandths longer than the virgin brass. Seems crazy to me that it wouldn't fully fireform with one firing. So if I'm understanding correctly, I should FL size these x1 cases to basically return them to their current headspace (which means, as K22 said, they will get longer initially, and then bump back to that baseline), and then fire them again and repeat the back-to-baseline-bumping-back UNTIL they reach a firing where they no longer chamber freely. I'd then consider that to be true fireformed and can bump back .002" from there?

You don't want to wait until it's difficult to chamber before bumping. It increases the stress on the bolt lugs and if you are at a match or in the field, you don't want to find out that you have a case that is difficult to chamber or worse, won't chamber.

The idea is to monitor the fired (primer removed) case head space. I usually check 3 for the group I am about to size. It only takes a few minutes or less. This way, the measurements will show you when you need to bump the shoulder to avoid functionality problems.

Each time I size a group of cases; I record, on the cartridge box, the fired and sized case head space of the 3 or 4 samples I measured on the cartridge box. This way I always know what's going on with my cases since the last firing and sizing. No guess work. Measurements do not lie if taken properly.

What you striving to achieve is optimum sizing and case fit in the rifle chamber. The bump gauge measurements make it easy to achieve goal.

 

[K22]

One of the issues I didn't mention because I didn't want to overwhelm you was that I use Skips Shims which fit under the lock ring of the F/L die. I can easily change the amount of sizing by changing the shim size.

This makes die adjustments quick, easy, and efficient. Once my cases show an increase in head space after fully fired formed, I simply insert a thinner shim to increase the sizing about .001 to .002" to return the case the fully fire formed dimension. This way, I am always keeping the case at optimum sized condition. My target is zero to .001" under full form head space.

 

[SKWERLZ]

Just went through this recently
New barrel and brass
Kinda helps because I know I set headspace go gauge + 1 thou which is + .003 for my new brass.

On first firing brass was same length as go gauge and I set my die to just kiss the shoulder.
In next firing I’ll set die closer to the -.002 I normally run.

 

[Webster]

I have a 22-250 factory chamber in a Ruger M77 from the late 70's or early 80's and a 6br Savage PTA with CBI barrel. I have case gauges for both. The 6br, fired cases will drop into the gauge and will chamber easily back in the rifle. The 22-250, the fired case will NOT fully drop in the gauge. They stick out a lot. Before I started using the case gauges, I was loading 22-250 cases that were shot in one of three rifles(mine, dad's and brother's) and was not obtaining the proper amount of sizing. It was causing some grief with stiff bolt closing. All that was cured with the case gauge and proper die adjustment. Kind of like a "light bulb" moment. Any way, have fun, shoot often!

All chambers and gauges are not the same. Don't worry about it. A 22-250 will not drop in the gauge but chambers easily. Sounds like a gauge that doesn't relate to your chamber size. No problem. You only have problems when you start measuring everything.

 

[perazziguy]

All chambers and gauges are not the same. Don't worry about it. A 22-250 will not drop in the gauge but chambers easily. Sounds like a gauge that doesn't relate to your chamber size. No problem. You only have problems when you start measuring everything.

Bingo! Life got easier when I learned to properly adjust the sizing die to allow easy chambering. Over the winter, I polished and processed a bunch of 22-250 cases, now time to load and shoot!

 

[mgunderson]

Started buying a go gage for the rifle calibers that I reload. These questions are much easier to answer with a few measurements. Many on the forum have suggested using a go gage to help set up the sizing die as well. The knowledge on here is awesome.