Headspace vs Shoulder Bump

[cbratcliffe]

I have seen many threads on here about headspace vs shoulder bump even to the point where some members with the propensity of being cyber ruffians have resorted to personal attacks over the topic. I have a question concerning this topic but do not wish to be violently attacked over the subject. So please allow me to post my question, obtain courteous answers and be on my way unscaved.

Alright I understand the reason and need for proper headspace. I also understand why some benchresters are bumping shoulders only to a point to allow the bolt to fall down part ways with the firing pin removed. Of course one method negates the purpose of the other.

If one's seating depth sweet spot says that the bullet should be into the lands then that round is not only going to push the back of the case against the bolt face, it is also going to center the bullet in the throat/start of rifling. To me that is good and leads to accuracy. But what about rounds that the bullet seating sweet spot dictates that there be a bullet jump?

I have a 6mm BR that the gunsmith says is set up with a .002 headspace. Tests have shown that the cartridge that I am loading likes to be jumped .020. Thus, I cannot count on the bullet into the lands to center the cartridge in the chamber and keep the back of the case against the bolt face which I personally consider to be an accurate method. Soooo....

I am counting on bumping my shoulders to where the bolt will fall almost all the way down before meeting resistance (with the firing pin removed) in order to keep the head of my case against the face of the bolt and the shoulder keeping the cartridge centered in the chamber.

Am I just way wrong in thinking this way with my particular setup?

Thank you for your patience and all courteous replies welcome,

Charles

 

[CatShooter]

I have seen many threads on here about headspace vs shoulder bump even to the point where some members with the propensity of being cyber ruffians have resorted to personal attacks over the topic. I have a question concerning this topic but do not wish to be violently attacked over the subject. So please allow me to post my question, obtain courteous answers and be on my way unscaved.

Alright I understand the reason and need for proper headspace. I also understand why some benchresters are bumping shoulders only to a point to allow the bolt to fall down part ways with the firing pin removed. Of course one method negates the purpose of the other.

If one's seating depth sweet spot says that the bullet should be into the lands then that round is not only going to push the back of the case against the bolt face, it is also going to center the bullet in the throat/start of rifling. To me that is good and leads to accuracy. But what about rounds that the bullet seating sweet spot dictates that there be a bullet jump?

I have a 6mm BR that the gunsmith says is set up with a .002 headspace. Tests have shown that the cartridge that I am loading likes to be jumped .020. Thus, I cannot count on the bullet into the lands to center the cartridge in the chamber and keep the back of the case against the bolt face which I personally consider to be an accurate method. Soooo....

I am counting on bumping my shoulders to where the bolt will fall almost all the way down before meeting resistance (with the firing pin removed) in order to keep the head of my case against the face of the bolt and the shoulder keeping the cartridge centered in the chamber.

Am I just way wrong in thinking this way with my particular setup?

Thank you for your patience and all courteous replies welcome,

Charles

You are doing fine - relax and enjoy the ride.

 

[M-61]

unscaved? UNSCATHED

 

[dixieppc]

Charles, right or wrong, that is close to how I do my setup for all my cartridges whether they are jumping or not. I have a Harrell die for each one of my barrels. Each one of them is set to where I bump my shoulders to allow the bolt to 'just' make it 100 percent of the way down, touch bottom on its own (with firing pin removed of course). Learning how to properly load cartridges for both accuracy and safety is a hell of a lot more important than spelling, punctuation and proper grammar on a Shooting Forum.

Respectfully........
Dixieppc

 

[Tim Singleton]

I have seen many threads on here about headspace vs shoulder bump even to the point where some members with the propensity of being cyber ruffians have resorted to personal attacks over the topic. I have a question concerning this topic but do not wish to be violently attacked over the subject. So please allow me to post my question, obtain courteous answers and be on my way unscaved.

Alright I understand the reason and need for proper headspace. I also understand why some benchresters are bumping shoulders only to a point to allow the bolt to fall down part ways with the firing pin removed. Of course one method negates the purpose of the other.

If one's seating depth sweet spot says that the bullet should be into the lands then that round is not only going to push the back of the case against the bolt face, it is also going to center the bullet in the throat/start of rifling. To me that is good and leads to accuracy. But what about rounds that the bullet seating sweet spot dictates that there be a bullet jump?

I have a 6mm BR that the gunsmith says is set up with a .002 headspace. Tests have shown that the cartridge that I am loading likes to be jumped .020. Thus, I cannot count on the bullet into the lands to center the cartridge in the chamber and keep the back of the case against the bolt face which I personally consider to be an accurate method. Soooo....

I am counting on bumping my shoulders to where the bolt will fall almost all the way down before meeting resistance (with the firing pin removed) in order to keep the head of my case against the face of the bolt and the shoulder keeping the cartridge centered in the chamber.

Am I just way wrong in thinking this way with my particular setup?

Thank you for your patience and all courteous replies welcome,

Charles

Very good method nothing I see to change. Roll on.

One observation. When a lot of guys use the term jumping. In a lot of cases maybe most. If the bullet is .020 back from a full jam it is probably still engaging the lead. If one were to smoke a bullet at .020 then look at it with a 10x loop he would probably see marks from slight engagement.
Just an opinion your mileage may vary

 

[Keith Glasscock]

I agree- you are on the right track. It should shoot well for you.

On the question of bullets aligning the case, it must be remembered that the freebore section of the throat is only slightly larger (.0005 - .0008") that the bore diameter. Even when jumping the bullet a reasonable amount, the freebore is going to align the bullet within .0004"

The only time this doesn't work is when the bullet bearing surface does not protrude far enough from the case mouth. No bearing surface into the freebore means not support there. In that case, I've found that rifles get really touchy about case sizing, runout, etc.

Hope this helps,
Keith

 

[Warren Dean]

unscaved? UNSCATHED

Dude... was that really necessary??? :-X

 

[CatShooter]

unscaved? UNSCATHED

Dude... was that really necessary??? :-X

They do it to me all the time... keeps me on my toes!

 

[CatShooter]

On the question of bullets aligning the case, it must be remembered that the freebore section of the throat is only slightly larger (.0005 - .0008") that the bore diameter. Even when jumping the bullet a reasonable amount, the freebore is going to align the bullet within .0004"

The only time this doesn't work is when the bullet bearing surface does not protrude far enough from the case mouth. No bearing surface into the freebore means not support there. In that case, I've found that rifles get really touchy about case sizing, runout, etc.

Hope this helps,
Keith

The diameter of the freebore section can be +0.0005", but it can be +0.002" or 0.004" larger than bullet diameter, and still be within acceptable SAAMI limits - custom rifles are an exception and can even have negative clearance.

 

[BenchShooter]

unscaved? UNSCATHED

Dude... was that really necessary??? :-X

It's the same story wherever you go. They can't add anything intellectually positive to the discussion at hand so they just look for spelling mistakes when they're not stirring up trouble.

I had one a while back that carried its venom into private mail to me on this site. It told some out right lies about what another member had said. When I called it on its lies, all it could do was respond with pointing out a word that I had misspelled.

Dana

 

[Laurie]

The alternative to the stripped bolt test is a case-gauge and callipers. L E Wilson supplies a neat little collar which sits on the case shoulder with its custom dies, and more mass market Hornady has its L-N-L comparator and gauges kits (often referred to by those who've been around a while as 'Stoney-Point' which developed the kit before being bought out by Hornady).

Since most people already have a comparator body to hold bullet gauges for batching and setting the COAL, it's a simple addition to get the approriate case gauge. Deprime a selection of fired cases and measure them; set the die to bump the shoulder a couple of thou'. It's so quick and easy, I recheck the die setting every time I size cases.

When full-length sizing, the resulting shoulder setting is not necessarily either a straightforward or consistent issue. The shoulder position is affected by the choice of case-lube, the amount applied and where, speed of press operation, the press design and condition, brass hardness in the shoulder area. I was first alerted to this many years back by an article in the old Precision Shooting magazine on headspace issues and resulting variations in loading match ammo for the match-prepped M1A service rifle whose design is such that it is very sensitive to headspace issues. Using LC (I think) match brass, the author discovered very substantial shoulder position variations across batches of cases. While it is much less of an issue today for those of us using prepped Lapua cases for instance, I for one simply wouldn't rely on a single case or two tested in the rifle.

 

[CatShooter]

The alternative to the stripped bolt test is a case-gauge and callipers. L E Wilson supplies a neat little collar which sits on the case shoulder with its custom dies, and more mass market Hornady has its L-N-L comparator and gauges kits (often referred to by those who've been around a while as 'Stoney-Point' which developed the kit before being bought out by Hornady).

Since most people already have a comparator body to hold bullet gauges for batching and setting the COAL, it's a simple addition to get the approriate case gauge. Deprime a selection of fired cases and measure them; set the die to bump the shoulder a couple of thou'. It's so quick and easy, I recheck the die setting every time I size cases.

When full-length sizing, the resulting shoulder setting is not necessarily either a straightforward or consistent issue. The shoulder position is affected by the choice of case-lube, the amount applied and where, speed of press operation, the press design and condition, brass hardness in the shoulder area. I was first alerted to this many years back by an article in the old Precision Shooting magazine on headspace issues and resulting variations in loading match ammo for the match-prepped M1A service rifle whose design is such that it is very sensitive to headspace issues. Using LC (I think) match brass, the author discovered very substantial shoulder position variations across batches of cases. While it is much less of an issue today for those of us using prepped Lapua cases for instance, I for one simply wouldn't rely on a single case or two tested in the rifle.

^^^ THAT!

Read it twice!!

 

[bsekf]

I agree with Charles, I am trying to get information here. Not be graded for a college essay.

On to my question.

Quote: I am counting on bumping my shoulders to where the bolt will fall almost all the way down before meeting resistance (with the firing pin removed) in order to keep the head of my case against the face of the bolt and the shoulder keeping the cartridge centered in the chamber.

Does the firing pin project from the bolt when it is cocked and you use it to measure headspace? I can understand removing the spring loaded button in the bolt face that aids in ejection, but the firing pin? Please explain.

Bill

 

[dixieppc]

You are very correct that there will be variations and you are very correct in the cause of some of those variations. And I do get variations all the time. When I was pointing out my shoulder bumping process I didn't mention every little thing that I do during that process to curtail most of those variations, just the fact that I do bump and these were the tools that I bump with and this is how far I bump.

To detail it a little further please allow me to go through it again. Some might take issue with the way that I do it and that is alright. I do believe I've seen many many different methods of the way people shoulder bump on this site and mine is just one small way out of all of those. Out of the many things that I do for case preparation, here are three things that I do to my brass that could affect having consistency from case to case during shoulder bumping.

1. All of my brass is cleaned and annealed after every usage so only cleaned, annealed brass is being bumped. That brass is also from the same lot and have the same amount of firings on them from day one.

2. All the brass is being shot in tight necked chambers so it all has been turned and turned to the same depth into the shoulders.

3. While I do not internal volume sort my brass I do sort to weight.

Gauging Shoulder Bump:
Every Harrell bump/FL die I have ever purchased came with a shoulder bump gauge collar to use with your calipers. I gauge every single case I bump. If the shoulder is still a bit long I hit it again until it gets where I want it. If it goes too far, I mark it and set it aside for a fouler.

I choose how far to bump by how far down I want my bolt to free fall. I remove the firing pin. I do the test with no grease on the lugs or any other place that the bolt is touching the action, ie. a dry bolt and dry action. The piece of brass that I am using to establish my bump amount is also wiped completely clean and from the lot that will be used for this gun. I initially use one piece of brass to set the pump up. My first hit is with the neck sizing bushing in the die. All subsequent hits are done without the neck sizing button in the die during the test. I keep hitting it, adjusting the die, gauging it and chambering it until I get to the point where the bolt free falls to where I want. Then I use the gauge collar that came with that die to get the caliper reading that I will use to bump each case for use in that action/barrel combo. I then reconfirm with a couple of other pieces of brass, from the same lot again, as to where the shoulder will end up with one hit (with neck sizing bushing back in).

When running brass through the Harrell, I do not use any lubricant on the upper part of the brass, only the base area and that is just a very, very light film of Imperial. I use Redding titanium nitride bushings so I do not feel the need to have grease or lubricants in that area which could affect the shoulder bump. Remember, this brass has been thoroughly cleaned and annealed at this point.

Actually, once I have established where that distance is with the Harrell collar gauge that allows the bolt to freefall to where I want it to, that distance is never ever going to change for that barrell/action combo as long as I don't remove and reseat the barrel and even then, probably will not change if I stay close to the same torque. I've never noticed the gauged bump distance to change after removing and reinstalling a barrel with my switch barrel setups. All I have to do is keep tweaking my die to keep giving me that gauged distance and that tweaking is seldom after initial setup probably more due to annealing.

Now the question might arise as to how many cases that I bump are ending up exactly where I want them compared to how many need further action. Honestly, I've never kept track of that but I do know that of the ones that do not bump to where I want them to on first hit are usually running a tad long and need to be hit one more time to get them exact. I would say that out of a hundred cases done, which is usually the size of my lots, 5 or so will bump too far on first hit and maybe 2-3 will end up too far on a second hit for a total of less than 10 per hundred. So, I'm ending up with around 90% of my lot bumped to exactly where I want them to be.

This whole process can be made invalid if I misspelled any words in the writeup.

Best Regards.......

 

[fguffey]

I have a 6mm BR that the gunsmith says is set up with a .002 headspace. Tests have shown that the cartridge that I am loading likes to be jumped .020. Thus, I cannot count on the bullet into the lands to center the cartridge in the chamber and keep the back of the case against the bolt face which I personally consider to be an accurate method. Soooo....

cbratcliffe, your gunsmith says it is set up with .002" head space. I would ask him the length of the chamber form the datum to the bolt face. The .002" of the difference in length between the chamber and case when the chamber is measured from the datum to the bolt face and the case from the datum to the case head. SAAMI says in their glossary of terms many are confuse, they confuse clearance and head space. The case does not have head space. When centering the bullet, it is impossible for a reloader to understand the difference between full length sizing and off setting the length of the chamber with the length of the case. If your gunsmith had written down the information on your chamber it would only be a matter of you adjusting the die correctly to size cases that fit your chamber.

What did he mean to say? No clue, he could have said you have a go-gage length chamber, when sizing cases for your chamber size your cases .002" shorter than a go-gage length chamber as opposed to minimum length. Minimum length cases for the 30/06 measure .005" shorter than a go-gage length chamber. Now we have every reloader on all reloading forums claiming they bump the shoulder .002".

How difficult is it to bump the shoulder? I can not do it, I can not bump a shoulder of a case. I must have case body support, my sizing dies contact the case body before it contacts the shoulder. Meaning my case body is sized before the shoulder is sized (or moved back).

I have dies I use for forming cases, my favorite forming die is the 308 W, next favorite is the 243 W. I use the two forming dies to come as close to bumping as a reloader can get. Eventually the two forming dies support the case body simply because the forming die forms the shoulder with pressure, pressure causes the case body to expand. By the time the case body expands .012" the case body is making contact with the forming die. So, no matter how I word it, I can not bump the shoulder without bumping the case body and case neck. I know, there are reloaders that purchased bump dies.

I do have bump presses, I also have presses that do not bump.

F. Guffey

 

[dixieppc]

I agree with Charles, I am trying to get information here. Not be graded for a college essay.

On to my question.

Quote: I am counting on bumping my shoulders to where the bolt will fall almost all the way down before meeting resistance (with the firing pin removed) in order to keep the head of my case against the face of the bolt and the shoulder keeping the cartridge centered in the chamber.

Does the firing pin project from the bolt when it is cocked and you use it to measure headspace? I can understand removing the spring loaded button in the bolt face that aids in ejection, but the firing pin? Please explain.

Bill

Bill, first I always forget to mention the ejectors when discussing this because I never use them. There are no ejectors in my bolts so they do not come into play in this. The reason for removing the firing pin is not because the pin would be protruding into the back of the case which of course it's not when cocked. The reason for removing the firing pin is the fact that the cocking process offers resistance to the movement of the bolt handle up and down. That resistance would give a false impression of where the bolt handle would freefall before meeting resistance determined by how far the case shoulder had been bumped.

Damn, I hope I said that right! Someone correct me if I didn't.

Respectfully......

 

[fguffey]

Does the firing pin project from the bolt when it is cocked and you use it to measure headspace? I can understand removing the spring loaded button in the bolt face that aids in ejection, but the firing pin? Please explain.

The firing pin does not protrude from the bolt face when the rifle is cocked. I measure the length of the chamber three different ways, not one of 'the ways' requires removing anything. I can measure the length of the chamber inside the chamber or from the outside of the chamber.

F. Guffey

 

[Laurie]

dixieppc, so, as I read it, that's a bolt-fall check on top of using a collar type case gauge, on top of annealing for every firing. I take my hat off to you Sir! Unfortunately, even if my patience stretched to that level, my waking time probably wouldn't with the around 5,000 rifle rounds I load annually, each of which I try to treat as a precision production.

However, the OP didn't mention 'headspace gauges' (case gauge is a term I'd prefer) and as I read it is asking for advice on setting up his dies using the rifle chamber and bolt as a gauge. I'm not in any way disagreeing with the methodology, but my impression was that this is the sole method being used. It also implies (but it may not be the case in fact) that it was a one-off job, while I would certainly want to do continuous checks case by case.

At the end of the day, is it really necessary to do things to this level? After all - and I'm not being sarcastic or 'funny' about this in any respect, once one takes things to a certain level, one has to start applying some really scientific or precision engineering techniques to the business. For instance, when you measure things by how far the bolt falls under its own weight, are you sure the bolt-lug and lug recess are identically clean and have exactly the same amount of oil film (or whatever) on them each time? Does ambient temperature affect this process both through its effect on the case dimensions, also those of the bolt and receiver steel? ..........and so on, and so forth?

In true rocket science, and the design and fabrication of say thermonuclear weapons, key components and parameters are calculated and designed in to micron and miligram levels of precision. Fortunately, I really don't think that even the best of precision firearms and ammunition either need that or show any benefit from it. If we ever get to that level, I'd pack things in!

Again, please don't take this as a criticism - we all do what we hope works for us and sometimes it seems to pay off and sometimes not. One lesson I've learned over the years is that it's a ratchet process - once somebody produces some kit or a new procedure appears and we give it a try, we hardly ever back off later and reduce the workload. (What if all that batching and bullet trimming and pointing gave me that good score in the last match? I daren't not do for this important upcoming match just in case!)

Now, I don't know to what level of precision the OP wishes to size his or her brass, but I'm simply pointing out that the bolt fall method is one option whereas there are others and for most precision shooters and handloaders who if they don't already have a Hornady or Sinclair comparator body for bullet comparison / COAL setting, they should do, and for a few dollars more a case gauge bushing ('B' for the OP's 6mm BR) is quite good enough, by my standards at any rate. He or she can and no doubt will decide what's best for him or her.

 

[barefooter56]

cbratcilffe,
If you are worried about your shoulder bump affecting your seating depth off the lands. Suggest first you find out what the actual seating depth sweet spot is and just neck size the brass as you are doing this using the same cases each time. Cartridge cases do not expand at the same rate so this may/will get you a couple or more cases that begin to chamber with some resistance. Measure these and keep them out to set up your shoulder bump like has been discussed. (dixieppc and the gentleman that suggested taking the firing pin and ejector out of the bolt to get a better"feel" of whats happening as you close the bolt as far as resistance have great suggestions). Measure these cases from base to datum line of shoulder with either the Hornady (Stoneypoint) or Sinclair bump gauge inserts ( either bump gauge will work with the Sinclair and Hornady body that attaches to the caliper jaws. Just use the dummy round, (a fired neck sized cartridge that still chambers or chambers with slight resistance is best) you made to the lands to figure what the cartridge OAL base to ojive needs to be for your sweet spot and set your seater up for that ( EXAMPLE OAL TO LANDS = 2.00.Your sweet spot is at .020 off the lands so the OAL sweet spot is 1.980 cartridge base to ojive so seat the bullets in the sized cartridges to 1.980) Even though you are bumping the shoulder back your cartridge base to ojive measurement for your sweet spot will be the same for the sized cartridge cases. Hope this helps!
Take care,

 

[M-61]

unscaved? UNSCATHED

Dude... was that really necessary??? :-X

No harm meant at all....just was good use of a seldom used word and it caught my eye. Not to offend.