Measuring Bump

S

SGJennings

New member
OK guys, I need some more help.

I'm having trouble getting my bump consistent. I think part of the problem is that I'm just not measuring very well. I'm using my Mitutoyo calipers and a barrel gizzy. I'm trying for 1 thou bump. The issue is that I can wiggle things around and get anything from zero to .002. I'm just not that good and I'm getting frustrated with this.

Is there some way to set up a fixture or something? Keep in mind that I'm shooting a Grendel necked up to 30.

Best regards,

Greg J.
 
Not to be a smart ass, but the best tool is the action and bolt with the firing pin removed. It's a feel thing.
 
I'm good with using the stripped bolt as part of getting the die set up.

What I need, however, is something to measure cases as I'm loading. Something that measures accurately. I want to know that the bump is 1 thou on each case. Just some kind of thing that I can put it in pretty quickly, see a needle go to zero and rock on.

I'm looking for something both quicker and more consistent than using calipers and barrel gizzy.
 
That you want such a device is good enough for me but I can tell you straight up that you don't need it. The "bump" criteria is that your cases feed without excessive force on the bolt handle. Said force is purely a distraction and has nothing to do with accuracy....but it does affect group size. Now, put a bump measuring device in the equation.....What do you do if you have some cases that measure .001 and others that measure .000? Two choices...shoot them as is or adjust your die and run them back through. If you shoot them as is you may find uneven bolt force. If you run them through again you'll find that some measure .002 and others .001 !! When you shoot the latter you likely won't detect bolt closing differences and all will be well - except that you will know there's a difference and that's a mental distraction if you are so inclined.

All that said, you will be better off bumping just enough to allow the bolt to close easily and skip the measurement deal. If, during a match, your cases become springy and you find the bolt difficult just turn the die in a skosh and continue. That's what you're gonna end up doing anyways which is why I'm attempting to discourage you from cooking up the measuring device.
 
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OK, I've tried to cut to the chase. I guess I'm going to have to provide the gory details.

I get zero bump if I don't lean on the press handle a bit. Then they get tight and I have to fight the bolt. That rocks the rifle around in the bags, slows me down and generally distracts me.

If I lean on it too much, I get .003 bump and the bolt handle just plain flops down.

If I lean on it the right amount, I get the right amount of bump. I want something to check the bump so that I can train myself to lean on the handle a consistent amount and get a consistent amount of bump. I don't care if some measure 1 thou and some 2 thou, BTW. I just don't want to fight it and I don't want to get .003.

I can't crank the die in any more. It's already on the shell holder. When things are right, when there is a case in the die, there is the barest amount of daylight between the shell holder and the base of the die. I mean like half the thickness of a piece of paper. Something like that. You can't see it unless you put a flashlight behind the shell holder/die base.

Ideas?
 
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I have one of these http://www.sinclairintl.com/.aspx/pid=37479/Product/Sinclair-Concentricity-Gage . With a 30 deg shoulder angle and the indicator tip on the shoulder, wouldn't bump be twice what was shown? That's hard to see on a .001 indicator. If I had an indicator that was really 1/10 of a thou, I'd just shut up and color.

I also have one of these dealies. http://www.sinclairintl.com/.aspx/pid=38161/Product/Sinclair-Digital-Case-Neck-Micrometer .

I don't guess anyone has combined these two to get an easy to use measuring tool.
 
What press are you using? Does the ram go past TDC? If it does not, that may be part of your problem.
Using the rifle to evaluate a die's setting presumes that the base of the die is small enough to size the base an adequate amount when the shoulder is bumped by an acceptable amount. This may not be the case, and if it is not, and you do not actually measure bump, you will end up with more case length growth donuts forming sooner (With short bullets and long necks, this may not matter.), and if the bump is on the long side, and the number of firings and FL sizings great, an incipient separation. Shooters will reply to this that they have done it by feel for years, and if their die is correct for their chamber, there will probably not be any problems, but if it is not, there can be. Friends ran into this with custom barreled 6 BRs. Sending fired cases to Harrell's solved their problems.
 
Boyd Allen said:
What press are you using? Does the ram go past TDC? If it does not, that may be part of your problem.
Using the rifle to evaluate a die's setting presumes that the base of the die is small enough to size the base an adequate amount when the shoulder is bumped by an acceptable amount. This may not be the case, and if it is not, and you do not actually measure bump, you will end up with more case length growth donuts forming sooner (With short bullets and long necks, this may not matter.), and if the bump is on the long side, and the number of firings and FL sizings great, an incipient separation. Shooters will reply to this that they have done it by feel for years, and if their die is correct for their chamber, there will probably not be any problems, but if it is not, there can be. Friends ran into this with custom barreled 6 BRs. Sending fired cases to Harrell's solved their problems.
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Ah, I was hoping the conversation would go here so I could cure some of my ignorance.

Here is my press. Don't laugh too much. http://leeprecision.com/reloader-press.html .

I guess I'm ignorant about TDC on the ram. I'm familiar with TDC on a Chevy Rat engine, but not this press.

When I was pondering about this today, I got to wondering if the bend of the arm between the two linkages might not be impacting my bench or the washers that I used when mounting it to the bench.

Now, keep in mind that I'm not 100% confident of my measuring ability with calipers. There is 'wobble'. With that said, with bump *backed off* from .001, the bolt stops at the top. With .003, it falls with no resistence. With bump that measures around .001, I usually get a something nicely in the middle. That's what I want to get consistently.

No matter what else, I want to be able to measure bump consistently. I don't want to be able to put the calipers on and make the measurement vary by .001 by how I hold my jaw, etc.

While I'm here, I want to thank you guys for all the help. When someone asks for honest help, you fog it in there with it. Best dang group of folks on the planet.

Greg J.
 
Measure bump

RLHBUSL said:
Here is what I use to check exactly how much I am bumping the shoulder after I have stripped down the bolt and set up my die by feel: http://www.redding-reloading.com/un...ant-indicator-headspace-and-bullet-comparator. It works great - but you will need an extra loading press when using it to set up a sizing die.

Ryan
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I second what Ryan says. The Redding Instant Indicator is fast, accurate and easy to measure each case by bump. I go thru 20 cases at a time, then separate them by bump. The closest to .001 get set back first, then I lower the die a "scoch" to bring it down about a thou and so on. With the 30 degree shoulders, I use the 6mmBR tool with my 30BR for bump. Wish they made it in a Dasher.
 
"The Single Hardest Mechanical Thing We do"

On page 99 of his book, "Extreme Rifle Accuracy" Mike Ratigan states,

"Proper full length resizing is the single hardest mechanical thing we do."

And I most certainly agree. During the past few years of teaching benchrest in my tunnel, I have found this to be the most problematic area of all with most shooters. Very few completely understand it and do it right.

In order to do the job properly, you must have a good match between your chamber and sizing die. You must also have a good accurate dial caliper, one that is calibrated so that one revolution represents .100 not .200. You must be able to read accurately to within .0005. This operation is so important it is best to have an expert go through it carefully with you. :)

Gene Beggs
 
To be honest, I was stealing a engine building term. What I meant was if you lower your press handle till it stops, has the ram come back down ( a few thousandths ) from its highest position?

Not to long ago, I was discussing setting up FL dies and issues related to getting a consistent bump with a friend. He told me that after having some difficulty setting a die for consistent bump, on his Lee Classic Cast Iron press, that does not allow the ram to pass its highest position at full stroke, He switched the die to a RCBS Rockchucker that does, and his problem went away. A little friendly advice, you might want to look around on Ebay, and find yourself a good clean Rockchucker. The press that you have might be suitable for seating bullets, or priming, or expanding cases, but respectfully, I think that it is part of your problem.
 
I'm probably a little late to this dance but I was thinking exactly what Gene and Boyd said. Supposing your dies and chamber match and all is well there, your press could be the problem. I see this all the time with the three presses I own. They all vary in their ability to maintain consistent sizing (and seating for that matter too) because of their designs. My smallest press, the RCBS partner, can vary .003" just by how hard I push on the handle. My thickest press, an old RCBS JR2, doesn't vary a bit no matter how hard I pull the handle. So, as I see it, either get a different press or you can use the Redding comp shellholders to get bottom out on the die and then just push hard every time you use the press you are currently using.

Also, I use the Stoney Point headspace gauges rather than the Redding die indicator simply because it's easier to use, cheaper, and you don't need a seperate press for it. With a little practice, you can get very accurate readings with the Stoney POint (now Hornady). I can have somebody hand me cases blindly and can segregate them into correct piles with 100% accuracy with this tool.

Just my 2. Hope it helps!
 
Good deal, Boyd. I appreciate the input. I'll head down to "the lab" in a few minutes and check it out. I'm not opposed to getting a better press if it is more consistent. With that said, how will I know that it is more consistent?
 
My vote is for the Hornady/ Stoney Point caliper attachment, over a barrel stub, for checking bump. I have a stub, cut with my reamer, and I have uses for it, but for checking bump on my PPC, I use the little brass gauge that came with my Harrell, FL die. It lands entirely on the shoulder, and does not come close enough to the neck to have any problems. Once, when I was setting up a die for a friend's .262 neck ppc, I found that the unsized part of the neck (bushing die) was a smidge larger in diameter than my chambers, which threw my bump setting off, by an significant amount. I have acquired a second 6PPC, and would rather not have that problem with it. The Harrell gauge is universal.
 
Boyd Allen said:
My vote is for the Hornady/ Stoney Point caliper attachment, over a barrel stub, for checking bump. I have a stub, cut with my reamer, and I have uses for it, but for checking bump on my PPC, I use the little brass gauge that came with my Harrell, FL die. It lands entirely on the shoulder, and does not come close enough to the neck to have any problems. Once, when I was setting up a die for a friend's .262 neck ppc, I found that the unsized part of the neck (bushing die) was a smidge larger in diameter than my chambers, which threw my bump setting off, by an significant amount. I have acquired a second 6PPC, and would rather not have that problem with it. The Harrell gauge is universal.
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If you would cut the barrel stub w/ your reamer and the drill the stub to .002 or .003 over the neck diameter, you would a tool (fixture) that would be a truly usable measuring device. Just make sure you have at least 90% of the shoulder in the "gizzy" and then drill it out. That way you are measuring and indicating off the shoulder. Also, be sure you face off the opposite end to square and flat..

As an aside, the "bolt drop" method O)NLY works if you have a size die that is correct. You could easily have a size die that does not size the web enough and be pushing the shoulders WAY too far. ALWAYS measure the shoulder bump!!!!!!!!!!!!!
 
Boyd, on my RockChuckers the ram will not go past TDC without grinding material away from the bottom linkage. On a Redding Boss, you simply remove a roll pin and you get a generous amount of travel past TDC.
 
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