Resizing? Shoulder Bumping

[justinp61]

I'm new to rifle reloading and have a question. Reading some of the other posts on resizing I saw mention of shoulder bumping. I understand the principal of it, but how do you determine when it's needed or how much? Do you measure it with a comparator? I have full length resizing RCBS dies and am curious as to how I need to set it up.

Thanks

[keeki]

Do you mean shoulder bumping? When the cartridge is fired the brass will stretch and after several firings it will become too long to chamber in your gun. When this happens you have to bump the shoulder back or just full length size it.

[justinp61]

Sorry, yes shoulder bumping.

[keeki]

If your using full length dies your already bumping the shoulder back. However you can neck size only with full length dies by just backing the die out a little.

[justinp61]

If your using full length dies your already bumping the shoulder back. However you can neck size only with full length dies by just backing the die out a little.


That I understand, but do I need to adjust it to where it just bumps the shoulder?

Thanks

[keeki]

not until the brass has stretched to the point that it wont chamber

[keeki]

you want that cartridge to fit your chamber tight.

[82boy]

I am in the school that the shoulder should be bumped back with a properly adjusted FL die everytime the cartridge is loaded. There is several ways to measure the amount of bump that the shoulder is moved back. If you buy a good custom die you will usualy get a piece of brass, or something else with it, cut to the taper of the shoulder. You simply place this tool over your case, mesaure it then size the brass, put the tool back on, and measure it again, subtract the diference, and you get the amount of shoulder bump back. You would then either adjust your die, or place shims under it to get a desired bump back. I like to bump back about .0005 to .001. I like mine on the tight side of things, but some will do .002, and it works fine for them.

There is other tools as well, having a custome barrel made by a good smith they should give you a piece of barrel with the reamer used to chamber the barrel, reamer ran part way in to make a gauge, the gauge is used in the same fashion as the aformentioned gauge. L.E Wilson makes a "case gauge" that also works in a similar fashion. Sinclair and Hornady make similare tools that will attach to a caliper, and would measure the case dimentions.

Some still go by a less accurate method and they play trial and error with the case in the gun. On Remingtons (And other like style actions.) they remove the firing pin assembly, and size the case untill they can chamber it, and when they close the bolt feel just a small amount of resistance at the bottom of the stroke on closing. Unfortinaly this method doesn't work well on savage do to the inability of removing the firing pin assemble and having a bolt that would hold togeather. If you have an action that has been reworked (T&T) you can fell this when chambering the round and make adjustements.

It is a good thing to check the amount of bump back, as there are diferent tolerances in dies, and I have found that some dies do not push the shoulder back, or will push it back too far. These dies need to be modified to correctly bump the shoulder back. If anything you should use it to properly set up your dies, just setting the die to where it touches the shell holder, doesn't properly set the die. I have also seen dies that was cut made to short right out of the box, and thay would push the shoulder back way too far and at the point, where the round could not be extracted because it was dangursly too short. Over sizing bras will lead to short life, and some beileve that it will cause accuracy problems do to the case being cocked by the ejector. With that all said, properly adjusting and setting the dies to the rifle is a must.

[justinp61]

82boy, can I use my Hornady comparator to measure the shoulder? If I install the .27 or .30 cal bushing and measure before and after resizing will it be accurate enough?

BTW this for a 22-250.

[82boy]

82boy, can I use my Hornady comparator to measure the shoulder? If I install the .27 or .30 cal bushing and measure before and after resizing will it be accurate enough?
BTW this for a 22-250.


No, that is for measuring bullet seating depth measured from the ogive of the bullet, it will not show you shoulder set back. You need to measure from the shoulder of the case. Hornady makes a tool that is similar to the comparator, and it may use the same parts just with a diferent bushing, I don't know.
http://www.hornady.com/store/Lock-N-Load-Headspace-Kit-With-Body-1-Each/

[jsimonh]

+1 on what 82boy has said. I set my FL dies up to bump the shoulder just enough to allow proper functioning. I don't neck size only anymore because a properly setup FL die does all you need.

[jwpark]

Like 82Boys said, on a bolt gun, you should set back the shoulders .001 to .002 or so.

If you're reloading .308 Win or .223 Rem, you can get the RCBS precision mic. It measures the free bore in your chamber and accurately measures the case length from the shoulders (datum line).

You can use the case length tool to also measure any cartridge in the same family. For example, you can measure the case length for a .243 win, .260 rem, 7mm-08 rem with the .308 win tool.

It's the most accurate thing I've found to measure case length.

[keeki]

I also bump my shoulders back evrytime I load them on most of my loads, but he said needed. It doesnt need to be bumped until the case wont chamber, thats why they make neck dies. the Lee collet die is one of the best neck only dies out there and the brass will last longer.

[GaCop]

I also bump my shoulders back evrytime I load them on most of my loads, but he said needed. I doesnt need to be bumped until the case wont chamber, thats why they make neck dies. the Lee collet die is one of the best neck only dies out there and the brass will last longer.


+1 for the Lee collet die.

[keeki]

If a FL die is "properly" set up it will fully resize the case back to saami specs not just bump the shoulder back. If you do however just want to bump the shoulder back then you can set a Fl die up to do this. Some die makers sell a shoulder bumping die that will bump just the shoulder when it is set up "properly"
My advise is to read the instructions that you receive with your dies, they will tell you how to set those dies up so they do what they were designed to do. After youve been doing it for a while then you can start manipulating shellholders and shimming and such. there is hundreds of little tricks that youll learn in the process thatll help you make accurate ammo.

[jwpark]

If you're reloading for bolt action rifles and want accuracy, invest in a good die set like a Redding Type S Match bushing die set, containing a full length die and seating die.

[bigedp51]

justinp61

With a "normal" rifle and average full length resizing dies you can "shim" the reloading dies for minimum resizing for "YOUR" chamber, but please note it's a "plus and minus" reloading world we live in. I set my full length dies to touch the shell holder as per the instructions and go over center with the slight "bump".

I then use headspacing shims under the lock ring of the die to control the shoulder hight of the die and how far it pushes the shoulder back.

For partial full length resizing I use "bigger" washers under the lock ring and "NOT" push the shoulder back.

http://i122.photobucket.com/albums/o254/bigedp51/IMGP7086.jpg

For full length resizing and only pushing the shoulder back .001 to .002 I use the headspace shims below.

http://i122.photobucket.com/albums/o254/bigedp51/IMGP4385.jpg

http://i122.photobucket.com/albums/o254/bigedp51/7-17-201054719PM.jpg

A alternate method is to use the custom length shell holders below to control cartridge headspace and the amount the shoulder can be pushed back.

http://i122.photobucket.com/albums/o254/bigedp51/7-17-201054345PM.jpg

A "non-normal" reloading condition is reloading for surplus military rifles with "long and fat" military chambers where full length resizing can cause case head separations from over working the cartridge at the base of the case.

Below is an example of firing a commercial .303 British cartridge case in a longer and fatter military chamber and stretching in the web area.

http://i122.photobucket.com/albums/o254/bigedp51/headspacestretch-1.gif

The quality of your brass and "who" makes the cartridge cases also makes a big difference in how you resize your cases.

Below from reloader Magazine.
NOTE: With proper firefoming techniques and not over resizing your cases (pushing the shoulders back too far) the cases below would have last longer and not had case head separations.

http://i122.photobucket.com/albums/o254/bigedp51/308fail.jpg

http://i122.photobucket.com/albums/o254/bigedp51/308fail-2.jpg

[justinp61]

Thanks for the info guys, I have a lot to learn.

[Waskawood]

I use the Hornady comparator with the insert that fits the shoulder for the caliber that you are measuring. Measure a once or twice fired case from the rifle you are relaoding for to determine a reference point for your chamber. After I have the measurement for my particular chamber I can adjust my die to give me the bump I want. I say once or twice fired because a twice fired case will closer to you chamber than a once fired round.