Changing from Full Length to Shoulder Bump sizing

How will changing to shoulder bump affect my groups

  • Same

    Votes: 11 73.3%
  • Worse

    Votes: 2 13.3%
  • Better

    Votes: 2 13.3%

  • Total voters
    15

IDHUNTER

Lil-Rokslider
Joined
Jun 16, 2014
Messages
220
I have been full length sizing my brass and have a good load worked up but I'd like to start just bumping the should back. Should I expect the same, worse, or better groups with the same load?
 
Really no way to answer. How much were you bumping your shoulder and how much are you planning on bumping it, in relationship to your chamber?
 
Were you not bumping the shoulder back at all before? Post is sort of confusing. Using the same die I assume, but before you had it set to not bump at all and now it has grown to your chamber so now you'll bump the standard 2-3 thou?
 
I have been full length sizing my brass and have a good load worked up but I'd like to start just bumping the should back. Should I expect the same, worse, or better groups with the same load?
As I understand, you were previously setting up to full length size, as recommended by manufacturers, by turning the die in to touch the shell holder plus about 1/4 turn. Now you intend to "bump" the shoulder some amount compared to a fired case.

In the interest of reliable chambering in the field, I suggest bumping the shoulder about 0.003" compared to a fully fire formed case. Keep in mind that it may take 3 firings to fully fire form a case to the chamber.

In any case, I expect your groups will be the same.
 
As I understand, you were previously setting up to full length size, as recommended by manufacturers, by turning the die in to touch the shell holder plus about 1/4 turn. Now you intend to "bump" the shoulder some amount compared to a fired case.

In the interest of reliable chambering in the field, I suggest bumping the shoulder about 0.003" compared to a fully fire formed case. Keep in mind that it may take 3 firings to fully fire form a case to the chamber.

In any case, I expect your groups will be the same.
Yes, this exactly. Thank you.
 
What you are describing is still full length sizing. If you are sizing the neck, shoulder, and body of the case in one die, you are full length sizing. All you are asking is if you will see an accuracy benefit by adjusting the die so it isn't bumping the shoulder back as far. I've never messed with the super precision shooting, never competed. Maybe in that arena it can matter. In my realm, your shoulder bump or cartridge headspace is not really a factor in accuracy. If it has an effect, I have not been able to measure it.

One of the things to keep in mind is that you can have some slop in your reloading press, die threads, and the biggest factor is the brass springback. You really have to be on your game to be bumping shoulders .001". I don't own high dollar reloading dies, so maybe that's a factor, but I was never able to keep consistent headspace on a non-annealed case under .004". Less than that and springback became such an issue that headspace could vary plus or minus .002" case to case. Once you get to that .004 or .005" you are working the brass enough it takes a good set. With annealed brass I am able to get that down to the .002" to .003" range.

I bring up annealing not because it is for headspace, but because it can have an effect on accuracy. Consistent neck tension, the actual resistance to bullet pull, not the diameter measurement, is a very critical component to getting great accuracy. I've even gone so far as to have tried neck sizing only. Accuracy was unaffected. The only thing that changed is that chambering got really hard quickly. I'm sizing my brass with less shoulder bump, not because it is more accurate, but because it maximizes case life. Bumping a shoulder back .006", not annealing, and that case might be done in 5 shots. If you only bump .0025" and anneal every loading (some do every 2-3), then case life can skyrocket. I mean really go forever. If you shoot really hot loads your primer pockets may loosen over time. I've gotten 30 loadings on some 308 brass before. At a certain point you loose them, or they get dinged or something, but they don't develop neck cracks or case head separations if you do this.

I loaded as you did for quite a while, and in my opinion you may or may not gain anything. Without annealing you will still likely start seeing neck splits when they get to around 5 shots. This can depend on your sizer too. A big reason bottleneck cases are so prone to this is because a regular full length sizing with expander ball really works the crap out of the brass. It first sizes the OD of your neck down way more than needed so it can accommodate any case with any neck thickness. It then yanks that expander ball back through the neck to give it the right ID.
 
I have been full length sizing my brass and have a good load worked up but I'd like to start just bumping the should back. Should I expect the same, worse, or better groups with the same load?
My needs are pretty basic in terms of precision - just looking for minute of animal. I shoulder bump my bottlenecks (and anneal) to help preserve the brass, especially my .338 WM.

Edit: Crossed with Nova in the mail. Pretty much the same goal for me.
 
......
One of the things to keep in mind is that you can have some slop in your reloading press, die threads, and the biggest factor is the brass springback. You really have to be on your game to be bumping shoulders .001". I don't own high dollar reloading dies, so maybe that's a factor, but I was never able to keep consistent headspace on a non-annealed case under .004". Less than that and springback became such an issue that headspace could vary plus or minus .002" case to case. Once you get to that .004 or .005" you are working the brass enough it takes a good set. With annealed brass I am able to get that down to the .002" to .003" range.

I bring up annealing not because it is for headspace, but because it can have an effect on accuracy. Consistent neck tension, the actual resistance to bullet pull, not the diameter measurement, is a very critical component to getting great accuracy. I've even gone so far as to have tried neck sizing only. Accuracy was unaffected. The only thing that changed is that chambering got really hard quickly. I'm sizing my brass with less shoulder bump, not because it is more accurate, but because it maximizes case life. Bumping a shoulder back .006", not annealing, and that case might be done in 5 shots. If you only bump .0025" and anneal every loading (some do every 2-3), then case life can skyrocket. I mean really go forever. If you shoot really hot loads your primer pockets may loosen over time. I've gotten 30 loadings on some 308 brass before. At a certain point you loose them, or they get dinged or something, but they don't develop neck cracks or case head separations if you do this.
........
Sometimes the press wins, and sometimes the case wins. If the sizing die is setup without firm contact between the shell holder and the die (cam over), variations in the slop in the press, brass hardness, case lube, etc. can cause the cartridge case to datum (bump) to vary considerably.

My attempt to do just that with range pick up cases led to a reloaded 223 Rem cartridge that did not chamber fully in my AR-15. (The offending case was a PMP that was much heavier than the others.)

My solution is first to reload cases in batches with only the same headstamp and weigh them to ensure I am not using cases with much less case volume. Secondly, I obtained Redding Competition Shell Holders to allow firm contact (cam over) between the shell holder and the die. Redding Competition Shell Holders come in a set of 5 that are 0.002" to 0.010"deeper than the 0.125" standard shell holders.
 
I neck size only using a Lee collet neck sizing die. Brass goes with each specific rifle in cases of multiple rifles in the same chambering.

FL resize only when the bolt is stiff to close.




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