Bump gage

[Longshot4]

I read the threads... and still I don't quite understand how you can bump the shoulders of a case back .002 and not full length resize the case. I am missing some thing. I shoot a 700 V.S. 222 I purchased a Redding Type S FL die. The bushing is just what I expected prefect fit.
The problem is when I put a fired round up into the die the body contacts the case first so I am not able to bump the shoulders .002 until the case is FL sized. of course it's a FL die. What did I miss?

 

[F. Guffey]

I read the threads..

Longshot4, You read the threads, I read the threads, problem. Those that write the responses to the threads do not read the threads. I find it impossible to bump a shoulder with out the die contacting the case body and neck.

I adjust the die off the shell holder with a feeler gage, I adjust the gap between the bottom of the die and top of the shell holder to prevent the die from returning the case to minimum length. I am the only reloader that determines the length of the chamber from the datum/shoulder to the bolt face first for the sole purpose of cutting down on case travel.

Bump sounds like an accident, there is nothing about what I do that is an accident. I have instructions that go back before memory. One set of instructions list die adjustment for a bump press and for a non bump press. Handy for me only, because I have presses that bump and I have presses that do not bump. I could say I bump a case with a bump press but still I find it impossible to bump a shoulder without sizing everything.

F. Guffey

 

[mehavey]

1. Get a case headspace gauge (Hornady gauge set or RCBS Precsion Mic)
2. Take about a half dozen fired cases (making sure these cases will still chamber)
3. Use the headspace gauge to measure the headspace dimension on these cases and take an average. Barring other complications, this is (approx) your chamber headspace
4. Adjust your sizing die to produce cases ~ 0.002" less than that average case headspace dimension




NOTE: This is for Bolt guns, and 'can' apply to gas guns if done very carefully and with a few extra steps before measuring the cases. (My recommendation, however, is to FL-resize gas guns)

 

[F. Guffey]

Mehavey, if a case had head space.

Adjust your sizing die to produce cases ~ 0.002" less than that average case headspace dimension

I make one measurement, average is too wordy.

F. Guffey

 

[mehavey]

Here we go again.

1. Cases have a headspace dimension.
2. Chambers have headspace dimensions

Make #1 (above) 0.002" less than #2.

 

[T. O'Heir]

Sounds like you're overthinking the whole thing. Just set the die(and all the dies) up so the bottom of the die is just kissed by the shell holder with the ram all the way up and you'll be fine.
Two thou is so small it won't make any difference anyway. Regular computer printer 50 lb. paper is 3.8 thou thick.

 

[mehavey]

Setting the die to any relation to the shell-holder will not produce a repeatable headspace dimension -- especially not one having any relation to your rifle's actual headspace.

If the brass has no springback, the headspace produced will be likley absolute SAAMI minimum -- which may be (god forbid) 10 thousandths (plus) less than your actual chamber (which still passes a Field gauge).

If it does have springback, you could be multiple thousandths over SAAMI minimum -- but still have no idea where you are in relation to the actual chamber dimension.

Moreover, all presses "spring" themselves -- depending on the press design AND the lube used -- i.e., more uncertainty on what you've really left the case dimension to be.

Therefore: Measure the chamber (~fired cases) and measure the sized case. Only then will you know where you are.

 

[Bart B.]

Longshot4, you well understand how you can bump the shoulders of a case back .002 and not full length resize the case. Good thinking on your part. But you can control how much a fired case shoulder gets set (bumped?) back by the position your die's set in the press.

Read post #35 in:

http://thefiringline.com/forums/showthread.php?t=544432&page=2

That's how to measure a fired case headspace then measure it after its full length resized. Cheap and precise enough for folks on this planet.

Mehavey knows what he's talking about.

Read post #11 in

http://thefiringline.com/forums/showthread.php?t=553534

. . .to see how you can adjust your sizing die in precise amounts.

You can also use a set of Redding competition shell holders that have .002" incremental increases in height. Using the right one that stops against the bottom of the die controls the case headspace spread to a smaller range that having a gap between a standard shellholder and the die's bottom.

http://www.redding-reloading.com/online-catalog/35-competition-shellholder-sets

 

[Colorado Redneck]

Bump the shoulder is slang

When you FL resize a bottle neck case, the instructions from RCBS say to raise the shell holder on the press to the top, screw the FL die in till it touches the shell holder, then lower the shell holder and screw the die in another 1/8 to 1/4 of a turn. This results in cam over when you stroke the press the full range of motion. The resulting case dimensions may or may not (and probably won't) be very close to the chamber dimensions on your rifle. If the resized cases are shorter when comparing "head space" then the brass will get worked more possibly resulting in case head separation.

Individual rifle chambers can and will be just a bit different in size. To closely approximate the same dimensions as your rifle's chamber, the method suggested above, using a "headspace gauge" to determine what dimension the fired case is, and then setting your FL die to size cases 0.002" shorter will yield longer case life, and the cartridges you produce will sit in the chamber a bit better and supposedly produce better accuracy.

When the light finally came on for me (after Bart and Guffy poked the information into my feeble mind for umpteen times) I bought a Hornady Headspace kit and began the process by first comparing new unsized brass, my fired brass and then trying various fired cases in my rifle. When I found a fired case that required some force to close the bolt, that was too long, and I started sizing those cases by "bumping the shoulder back" in a trial and error process. That process was accomplished by adjusting the die into the press just touching the die to the shell holder at the top of the stroke and then sizing a case that was too long to easily close the bolt on. If it didn't work any better after sizing, I screwed the sizing die in just a wee bit further, sized and tried in the rifle again. When I found the correct setting for the die (which was where the bolt finally closed easily), I recorded the "headspace gauge" measurement and then set the die lock nut.

So, as you can see (if you stayed with me on this ) "bumping the shoulder back" is slang for "setting the FL die to the correct dimension for your rifle's chamber." It is still full length sizing.

 

[Bart B.]

^^^^^^
Good post!!

In the reloading industry, full length sizing means all outside fired case dimensions from the case pressure ring to mouth have been reduced except for case length which gets longer. They don't have to be reduced as much as the die can do not back to the original dimensions of the case when new nor SAAMI minimum case specs.

Even though Redding and RCBS full length bushing dies leave the necks back 1/32nd inch unsized, they are full length sizing dies. Both companies claim that unsized part of the neck helps center the case neck in the chamber neck.

 

[Longshot4]

I know I spend more time on this sight than I do actually reloading. I remember going through this bump system before but as I wait for powders, bullets, Walleye fishing, Duck Hunting and Deer Hunting... I fall behind kind of like now where was I. Thanks again for your time and PASHENTS. Bart you are a most valuable asset to this forum. As are the rest of you.
I have noticed it dose get easier the more I hear and see the examples. I'm sure others out there appreciate your help also.
To all of you have a Merry Christmas

 

[Colorado Redneck]

Thanks Bart! It took you guys a while to get me going down the right path on this, but it has worked really well now that I understand. Thanks to you for the education on resizing (and other topics as well!).

 

[F. Guffey]

[QU1. Get a case headspace gauge (Hornady gauge set or RCBS Precsion Mic)OTE][/QUOTE]

I have comparators, I make comparators, you suggest I get a head space gage. Problem I make head space gages. My head space gages look nothing like my comparators, I can measure my head space gages with my comparators and because I am not hard headed I can make head space gages that go from minimum chamber length to infinity. I also make head space gages from gagers, I turn go-gages into chamber length gages that goes from go-gage length to infinity, or a more practicle field reject langth. Another problem, finding anyone on the Internet that understands what I am talking about.

F. Guffey

 

[mehavey]

Any comparator that has any chance of providing anything near SAAMI case headspace dimensions has a specific hole diameter for each case family, and that hole contacts the case sholder at ("very" approximately) mid-point. EXAMPLE: 308 Win uses a 0.400" dia hole.

The Hornady 'Headspace Gauge' is a set of just such various hole sizes in short (1") alluminum cylinders that fit snugly onto your calipers. As you note, any machinist can make exactly the same comparator inserts.



postscript: I can understand what you write, FG
(But sometimes I do have to practice my TS Elliot beforehand)

 

[Bart B.]

Guffey, I too, understand what you're talking about. But too often, you leave out the details (or they're masked by riff-raff) of how something done so everyone can understand. For example: how do you change a .30-06 NO-GO or FIELD gauge to one with a GO headspace dimension?

I do not understand how you can turn go-gages into chamber length gages that goes to infinity. Infinity's longer than any headspace gauge.

 

[Unclenick]

Longshot,

The terminology seems to be in flux. "Bumping" and "setting the shoulder back" with an FL die seem now to be used interchangeably by many, the YouTube video makers in particular.

As I understood it, the original bump concept was to move the shoulder back only. This was done for custom rifles by taking a die blank and using the same reamer that cut the rifle's chamber to cut the shoulder bump die. IIRC, a separate neck-sizing-only die was then used to size the neck. I've never done this, personally, but do recall the die blanks being advertised in Precision Shooting.

Forster makes its bushing bump sizing dies to do the above. Some users say they need no case lube, since the sides of the die are not being sized, though I would not do that, for the die's sake. I don't know how Forster is choosing their die ID to prevent pressure on the shoulder from swelling the sides of the case beyond fit. Perhaps there is enough springback after a short bump to prevent that becoming an issue.

The problem with the bump system, as described above, is that there is little to no chamber clearance once a case fattens enough to be snug in the chamber. As Bart has discussed before, you want at least half a thousandth narrowing of the case. This is because most cases don't have perfectly uniform wall thickness, so they expand more on the thin side when they are in the chamber. This results in what Merrill Martin and the late Roger Johnston called a "banana" shaped case. It will not be on center if you put it back in the chamber that way. Re-narrowing it at least a little is the only way to ensure it has the opportunity to self-center when the firing pin shoves the case shoulder into the chamber shoulder.

So, it seems to me, using the FL die to set the shoulder back a thousandth (or two for magazine feed) remains a better accuracy option than bumping.


Bart,

I think Mr. Guffey is using the grinding tools he mentioned earlier (I infer that he has a pretty complete machine shop) to customize gauges. I think he meant that has an infinite choice of sizes between any two limits that he could grind a guage to by doing that.