Shoulder Bump Range... What's Acceptable??

[Full Curl]

I recently prepped 100 300rum cases for loading. All Norma stamped and all fired 3 previous times in the same rifle (my rifle). I use a Redding Type-S Full Length Bushing Sizing Die. I did not size the cases at all when they were new for the 1st firing so this will be the 3rd time they have been FL sized with the same die. They have not been annealed yet. My goal when FL sizing is to bump the shoulder .002". After FL sizing 100 cases and measuring each one, my actual bump range was .005" to .001". I never changed anything on the die from case 1 to case 100. My average was right about .0025" but I'd say about 15% were .004" or greater and another 10% were .001". I typically do not measure every single case after FL sizing but did this time to see what the numbers were. I was a little surprised at the .005" to .001" range, I thought it would be a little more consistent. I have not fired any of the rounds yet, but plan on doing a little testing to see if the cases at the edges of bump range shoot similar to the ones at the average.

This leads me to a question for you more experienced loaders… what is an acceptable bump range or does one even exist for you guys? I'm sure every rifle is different, but will .003" to .005" variation have a very noticeable effect on accuracy? I can't even get a perfect .002" measurement for every case on freshly anneal cases regardless of caliber.

I load primarily for field use and not much match. And I'm assuming this has been the case previously for me when loading batches since I used the same die and process and my rifle still shot well. I know annealing would probably help some, but even after annealing is there any variation in shoulder bump range that can be expected and what would be considered acceptable for extended range field use?? Thanks.

 

[K.E.C. Darkside]

I believe you bump the shoulder to fit your chamber. If you can strip your bolt so there is no resistance. Open and close your bolt with a sized brass. When the bolt moves freely, you should be good. Most look for. 002 .

 

[cajun]

Did you measure the cases before bumping? If there was a variance to begin with then your shoulder bump will not be consistent.

 

[MagnumManiac]

Firstly, you are getting variance because the cases are varying in hardness at the neck and shoulder and, the cases grow longer as they are squeezed down and your brass is resisting the sizing at the shoulder. Annealing every firing is the only way to keep this measurement consistent. It took me some time to realise why this was happening to me too.
As to tolerance, .005" is way too much, personally I strive for under .002", but .001-.002" is all that's generally needed for good brass life. My comp guns generally run .001" bump, the closer you get the tolerance the better…neck tension is another aspect in this scenario too.

Cheers.

 

[ShtrRdy]

What kind of case lube are you using?

 

[Pdyson]

I don't bump my bolt action guns until I get 2 often even more firings as the brass is still moving to fill the chamber. I'll set for .001 to .002 on bolt guns and .002 to .003 on my semiautomatics and levers.

 

[milo-2]

What kind of case lube are you using?

This ^^^ along with how are lubing them? Usually inconsistent bumps are lube related if brass is from the same lot.

 

[MagnumManiac]

This ^^^ along with how are lubing them? Usually inconsistent bumps are lube related if brass is from the same lot.

This is not necessarily true, as brass comes from several sources, presses and can/does have differences even within the same lot.
Heck, I've even seen headstamps within the same bags and boxes with small lettering and larger lettering, meaning they were formed on different presses…

Cheers.

 

[Tiny Tim]

If you have not bumped shoulders back until now, how have you established that it needs it and where this position is?

KEC and Cajun make good points. During load development I usually get a couple cases that are difficult to close on after firing. I will strip the bolt and find the point it closes freely at and then go another .0015" - .002. I believe Alex Wheeler has a great video demonstration of this.

Alot of variables at this point. Isolate them one by one until you find that sweet spot.

 

[243winxb]

https://redding-reloading.com/online-catalog/35-competition-shellholder-sets
When the shell holder contacts the bottom of the fl die, slop in the press is removed.

The few RCBS & Redding S fl dies i have checked, will not push the shoulder back more then .005" This is not enough shoulder set back to cause problems. Ok for a hunting rifle.

Set back of .010" or more, case separation will happen. May take a few firings.

 

[memtb]

I've certainly do "not" have the experience or knowledge of many here ….but a thought and a question!

Are you using a "neck expander" when sizing? If yes, could resistance inside the neck as the expander is withdrawn due to improper/insufficient lube or neck thickness irregularities cause the change in shoulder measurements? Just a thought! memtb

 

[Tiny Tim]

Are you using a "neck expander" when sizing? If yes, could resistance inside the neck as the expander is withdrawn due to improper/insufficient lube or neck thickness irregularities cause the change in shoulder measurements? Just a thought! mememtb

Great thought. I guess that may have more or less effect depending upon how close to the neck/shoulder junction you measure. Depending upon cartridge and comparator used, you may be more affected by this on some cartridges.

 

[Longtine88]

^^^^^^magnum nailed it! He's spot on.

 

[C-130 Dude]

I recently prepped 100 300rum cases for loading. All Norma stamped and all fired 3 previous times in the same rifle (my rifle). I use a Redding Type-S Full Length Bushing Sizing Die. I did not size the cases at all when they were new for the 1st firing so this will be the 3rd time they have been FL sized with the same die. They have not been annealed yet. My goal when FL sizing is to bump the shoulder .002". After FL sizing 100 cases and measuring each one, my actual bump range was .005" to .001". I never changed anything on the die from case 1 to case 100. My average was right about .0025" but I'd say about 15% were .004" or greater and another 10% were .001". I typically do not measure every single case after FL sizing but did this time to see what the numbers were. I was a little surprised at the .005" to .001" range, I thought it would be a little more consistent. I have not fired any of the rounds yet, but plan on doing a little testing to see if the cases at the edges of bump range shoot similar to the ones at the average.

This leads me to a question for you more experienced loaders… what is an acceptable bump range or does one even exist for you guys? I'm sure every rifle is different, but will .003" to .005" variation have a very noticeable effect on accuracy? I can't even get a perfect .002" measurement for every case on freshly anneal cases regardless of caliber.

I load primarily for field use and not much match. And I'm assuming this has been the case previously for me when loading batches since I used the same die and process and my rifle still shot well. I know annealing would probably help some, but even after annealing is there any variation in shoulder bump range that can be expected and what would be considered acceptable for extended range field use?? Thanks.

You said most of your shooting is field use. But it sounds like your looking toward closer tolerances. Try for .001-.002 sholder bump. ALWAYS anneal before sizing. It will set your brass to a constant and repeatable state. This will also prolong your brass life by softening it so it will work the same way. And it will reduce neck splitting. Use and apply you case lube as directed. Watchout for excess lubing. I use wax for small case batchs and spray lube for large batchs. It works for me. Just do it the same way every time. I also use FL w/bushing die. Works well for me. For consistency, the trick is when you are running the press arm, take a 3 second pause at the bottom of the arm stroke. Then pull the arm up. This pause allows the brass to settle and reduce/eliminate brass spring back. You will find better sholder bump consistency. It allows me to achieve .001-.003 consistency every time. I will not use brass that has more than .003. Brass is expensive. After this, always check the case length and trim accordingly. I've been processing my brass like this for more years than I can count and it just plain works. Best of luck!