• This Forum is for adults 18 years of age or over. By continuing to use this Forum you are confirming that you are 18 or older. No content shall be viewed by any person under 18 in California.

What is bumping shoulders and how do you do it?

DRGreysun said:
FWIW, I'm sure most of you are using custom FL dies cut with your chamber reamers. I also wonder how many shooter who ask questions here use non-custom FL dies and factory cut chambers.
I'm not a BR shooter, however I do read this forum and glean every little bit of info I can from it. What I know and many of you know this too. The difference between a factory cut chamber and a custom cut chamber and die is like night and day. I'm not new to reloading and I learn new stuff everyday. What I have learned is that brass is most likely made to min. SAAMI spec. and most factory chambers are cut to max. SAAMI spec. Even then they can vary a great deal from one manufacture to another. As well as one chamber to another within the same manufacture. Plane and simple all things are not created equal. Brass that 'lasts forever' in a custom cut chamber can turn to junk with one hot load in a factory cut chamber. Neck size, spit necks etc. will be the last to cause a problem. The head will stretch first and show up as loose primer pockets. Another thing with non-custom FL dies and bumping shoulders, there is no such thing as bumping the shoulder back .001-.002". I reload 30.06 for a post 64 Mod. 70 and have found that when my bolt gets stiff on closing and I want to 'bump the shoulder back' .001-.002" I am actually moving the shoulder .010 to .012". Not to mention working the sides back to near SAAMI spec. It's like squish, squirt and crunch which is really hard on the brass and doesn't take much to work harden it from web to neck. I know this is a BR forum and for BR discussion but I thought I would throw this out for those, like myself that visit here looking for the straight skinny from the 'experts' in accuracy shooting. Thanx for your time!

D R
Click to expand...
FL dies are not cut with chamber reamers. Because brass springs back, in order to reduce the diameter of the case body, and in the case of one piece dies, the neck the die must be smaller than the chamber, which requires a FL die reamer. There are two exceptions one that was unique, where the part that was reamed with a FL die was forced into a sleeve that reduced the ID of the interior of the die, and others where dies are made by CNC boring rather than reaming. However they are manufactured, to work, the insides of FL and body dies must be smaller in diameter than the chambers that they are designed to work with.
 
Last edited:
Thats kinda what I do on some rifles but I called it partial full length sizing. I dont measure nothing just back the die off till the case will chamber kinda hard and run em. Doug
 
Dgd6mm said:
Most of us have the tools to set up shoulder bump. Excessive shoulder bump will eventually lead to headcase separation. If you set a die up per most manufacturing specifications you'll be over bumping and not even know it without proper measuring tools. It's no big deal as you put it until one comes apart in your chamber.
Click to expand...
The poster that I replied to joined yesterday morning.. His last sentence context was about bumping the shoulder back too much. HE said a little bit of being a smart aleck ( so what's the big deal).
Not in the form of a question.
I have to admit, I did not read this whole thread. Now I'm on a mission.
 
If you have shot and reloaded for many years you continue to pick up on things. I now have 2 reamers for each of my PPC and 30BR. The chambering reamer also reams my seating die. My sizing die reamer is speced .003 smaller at the web and .002 at the OD of the shoulder. Before doing this early in my career if I had a hard chambering round I would crank the dies down until the bolt felt a little resistance. I had a case head separation because my problem wasn't too long headspace, it was a too fat case. I keep a case for each chamber set at the correct headspace or you can use your headspace gauge. I made a gizzy to be able to check the headspace during a match.
1667777667566.png
Write your headspace down and you have it there to check when you are at the range. Pop your primer out before checking as the crater will give you a bad reading.
 
butchlambert said:
If you have shot and reloaded for many years you continue to pick up on things. I now have 2 reamers for each of my PPC and 30BR. The chambering reamer also reams my seating die. My sizing die reamer is speced .003 smaller at the web and .002 at the OD of the shoulder. Before doing this early in my career if I had a hard chambering round I would crank the dies down until the bolt felt a little resistance. I had a case head separation because my problem wasn't too long headspace, it was a too fat case. I keep a case for each chamber set at the correct headspace or you can use your headspace gauge. I made a gizzy to be able to check the headspace during a match.
View attachment 1382597Yep
Write your headspace down and you have it there to check when you are at the range. Pop your primer out before checking as the crater will give you a bad reading.
Click to expand...
yep been doing this for years. That works perfectly on both sides.:cool: I have gizzy's for all my rifles.
 
If a die is a little too big for the chamber, by the time you get the bolt feel that you want, you will have bumped the shoulder too far. This is why I measure cases before and after sizing, for OD of the shoulder, at the .200 line, and for bump. Once I know that the die reduces the OD of the body of the case before it is set to bump, I can conclude that any change in stripped bolt feel is because of shoulder to head fit in the chamber. I also keep track of the dimension and which tool I used to measure it, either a gizzy or the Stoney Point (now Hornady) tool. Once fired cases rarely need bumping. My advice is to set a FL or body die to reproduce the head to shoulder measurement of the fired case, and then test the case in the rifle. Most times the bolt fell will be OK.
 
You must log in or register to reply here.

Upgrades & Donations

This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.


Click Upgrade Membership Button ABOVE to get Gold or Silver Status.

You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.


To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.

Classified Ads

Forum statistics

Threads
165,790
Messages
2,203,509
Members
79,128
Latest member
Dgel

Share This Page

Back
Top