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How to set how much to bump?

T

taseal

Gunny Sergeant
Minuteman
Apr 18, 2011
1,492
14
40
SE FL
#1
I've been reading on this, and it says that shoulders should be bumped .002 for optimum performance...

ok, that's great, but how the hell do I know how much I bumped my shoulder? how do I set it in my body die? is like one full turn after the bottom of die touches the shell holder .001 or something? I have no idea!

right now what I do is only neck size until the brass becomes hard to chamber (I've only used some lapua brass once or twice so haven't needed to do this except when I got a new barrel) and I pretty much put the body die in, twist it in all the way, and then untwist until I see very slight gap (enough for light to pass through) between shell holder and the die.

I have a feeling i might be doing this wrong, and not bumping shoulders correctly, which might give me either unaccurate loads, or false symptoms on overpressure signs
 
#3
Re: How to set how much to bump?

You can just use a caliper, measure from case head to neck-shoulder junction. This should give you a close enough reading, setting your die to that press is a one time process.
 
#4
Re: How to set how much to bump?

Or the Hornady comparator. With different inserts you can measure both shoulder and loaded length at ogive for multiple calibers. Just running the die down to shell holder and hoping for best is not right or safe. Need to measure fired case then size, measure again and adjust die until you get desired measurement.

On the amount to bump, might go less if it's a bolt gun. I use .001. For semi I use .003 but know others using .002 and some .004.

Glen Zediker's book "Handloading for Competition" has a good section on this topic and is pretty good all around book. I mention this particular book because it seems local stores like Sportsmans Warehouse and others have it on shelf.
 
#5
Re: How to set how much to bump?

You need the sinclair bump gauge. Then I suggest taking some fired brass and resizing one at a time and measuring. Figure an average for your fired brass as they won't all be identical, then subtract that .002.

Screw the die in till it makes contact with the shellholder. Resize a case and measure. If you need a little more use pliers and tighten the die just a smidge, basically as soon as you see movement stop. Resize again and measure. Lather, rinse, repeat till you get what you are after.

Rich
 
#6
Re: How to set how much to bump?

Decap the fired brass for a consistent reading, measure only brass that was fired in the weapon that you want to reload for, all the brass should have the same reading with the HS gauge, if not for what ever reason use the ones with the longest reading as your determining pieces for setting up your FL die, .001 bump is perfect for bolt actions, please note that your press may cam over in order to achieve the desired bump.
 
#7
Re: How to set how much to bump?

Using a O-ring under the die as described here, allows for very precise adjustments. I bump the shoulder back every time from .001-.0015.

http://riflemansjournal.blogspot.com/2009/08/reloading-headspace.html

Here's what I came up with for a shoulder bump gauge, Sinclair comparator body/insert along with a cheap Enco granite comparator stand. Works well.

015.jpg




 
#8
Re: How to set how much to bump?

German Salazar's write up is very good. A quick and dirty way to check until you buy the uberexpensive gauges is to use a resized and deprimed .40 S&W case (in .308). The .40 cal case mouth is very close to the datum line for measuring .308W. It really doesn't matter exactly as Salazar points out, since you are only measuring before and after sizing dimensions. Put the pistol case over the mouth of the fired case and measure the overall length, then set your sizing die to shorten that measurement after sizing to be.001 to .002 less. Since you are using a rough set up, repeat with 4 or 5 cases to make sure. Then chamber one of the sized cases...you'll be able to lower the bolt handle with just a "touch" of feel. If it is hard to lower, resize again with the die screwed in an additional 1/16 of a turn and recheck the chambering. You'll be very close to the proper dimension. JMHO
 
#9
Re: How to set how much to bump?

You need a tool that measured the datum line to the base. There are a few out there. RCBS makes their precision mic. I prefer to us the Hornady style system. Even better, Sinclair brought out their own shoulder bump system that is better than Hornady's.

This is what it looks like compared to the Hornady. http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1108079

Here's a blog how to set headspace. There are links in the blog to the Sinclair products.
http://blog.sinclairintl.com/2011/01/31/setting-up-your-full-length-sizing-die/

You need a digital caliper. You deprime (no sizing) a fired case from your rifle and put the case into the gauge and measure. You zero your calipers (0.00) on the measurement. You then full length resize the case. Put the case back into the gauge. You should see your shoulder bump measurement. Ideally, you should see a measurement of -0.001" to -0.003". If you see any more than that, you are bumping the shoulder too far back, you'll have to back your sizing die off a bit. If your F/L sizing die is not bumping the shoulder at all, you'll see no - movement. If there's no minus (-) movement or you see a plus (+) movement, you are not bumping the shoulder back enough and you have to turn your die in about 1/12th of a turn more. You do this until you get the correct readings. You;ll need about 10 fired cases fired in your rifle. The reason you deprime the case is so you don't get a false reading from primer protrusion, it can give false readings.

Most of the time, reloaders don't put enough shoulder bump into the F/L resizing. That could be why you are getting a few cases not chambering.

Here's a video on the Hornady gauge to show how it's used. I prefer the Sinclair system over the Hornady because Sinclair uses a steel gauge instead of an aluminum one that Hornady uses.

http://www.youtube.com/watch?v=P-UrMTyJ1_E

without using some kind of measurement showing you shoulder bump, you are just GUESSING at what the issue is. A digital caliper will show you the actual numbers! It will all make sense after that.

The only reason i don't like the RCBS precision mic is it comes in one caliber for $ 45.00. The Sinclair and Hornady systems can be adapted to many other calibers by just buying the proper insert and it is less expensive. I do prefer to read digital numbers on the caliper.
 
#10
Re: How to set how much to bump?

The shoulder of a once fired case has already shrunk back about 1 thou from chamber length. Therefore, for a bolt rifle, we only need to duplicate the sized shoulder to match the fired length. For an autoloader it may be better to set it back another thou or two. IMHO.

Only way a sizer die can be set that close is with a case 'headspace' gage; Hornady, Innovative Technologies, Sinclair, RCBS tools all do the same thing and they all work quite well.
 
#13
Re: How to set how much to bump?

A neck sizing die does NOT bump the shoulder. It only sizes the neck, it doesn't touch the case body. Just remember, after about 3 neck sizing and firings, you should full length resize the cases. A full length sizer bumps the shoulder and sizes the case body.
 
#14
Re: How to set how much to bump?

after reading this whole thread, I pretty much need to get the hornady sleeves. I already have the ogive comparators, so I I guess I'll get the headspace ones.
 
#15
Re: How to set how much to bump?

Damn, that Sinclair comparator seems really nice, but they're out of stock... who knows how long that'll take. and they don't have a damn notification system there either. gotta check all the time
 
#16
Re: How to set how much to bump?

Not that I'm recommending it but if you want a neck die that bumps the shoulder too, Forster has one. I haven't tried it myself so can't give you any more than that.

Today I full length resize every time using Forster FL die. Just for kicks I'm going to try two step process with Lee Collet and then Redding body die. I'm getting good results now w/ Forster FL but would like to work necks less and I keep hearing about great runout numbers with the collet dies. Either way will continue to size body and bump shoulder every loading.

If you stick with Hornady might consider adding the anvil base too. Provides larger surface for the "other" end and seems to provide more consistant measurements.
 
#17
Re: How to set how much to bump?

I just neck and body size separately. it's how I started and how I was taught, so I do it that way... maybe down the road i'll get a FS one. but for now my application works.
 
#18
Re: How to set how much to bump?

So what's a fellow to do if after doing <span style="text-decoration: underline">all</span> the above with the Sinclair gauge, there remains a .003" shoulder bump regardless how far the die is backed out?
Details; Forster FL Die, once-fired Hornady .308 brass, FN A2 chamber, .007" bump at 'cam-over'
 
#19
Re: How to set how much to bump?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: taseal</div><div class="ubbcode-body">Damn, that Sinclair comparator seems really nice, but they're out of stock... who knows how long that'll take. and they don't have a damn notification system there either. gotta check all the time </div></div>

Try gunstop.com

 
#20
Re: How to set how much to bump?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Pete H.</div><div class="ubbcode-body">So what's a fellow to do if after doing <span style="text-decoration: underline">all</span> the above with the Sinclair gauge, there remains a .003" shoulder bump regardless how far the die is backed out?
Details; Forster FL Die, once-fired Hornady .308 brass, FN A2 chamber, .007" bump at 'cam-over' </div></div>

Out of spec chamber, bad die or maybe fire forming with light load and it didn't actually "form"? If cases are 1x fired might try reloading again without bumping shoulder at all (need neck sized) and then see what you have after second firing. If you go that route I would load up one test round first and check to see that it chambers ok and there are no issues with bolt closing.
 
#21
Re: How to set how much to bump?

Crewchef,
I appreciate your well thought out suggestions. Here is the solution to the problem courtesy of 427Cobra : The newly-purchased Sinclair bump gauge insert/body was giving ridiculously incorrect readings as verified side-by-side with his Hornady gauge. Thanks again for thinking through my problem.
Pete
 
#23
Re: How to set how much to bump?

So I got that sinclair bump gauge...

well I measured a once fired brass, then zero'd the caliper.

then I body sized one of them accordingo the die's instructions (redding body die) and when I measure it, I'm not getting .002 difference like i'm supposed to. both are the same exact size. they're at .000 body sized and once fired.

Some more fired ones are .001-.002 and brand new virgin brass (all lapua)-.002 to .003

is this right? I tried to adjust the body die by screwing it in some more to try to get -.002 on the sized brass, but I didn't wanna mess any of the brass up until I came here and asked...

but as of now it just sets it to .000 for once fired brass

the way I set it is put the press all the way up and then screw the body die until it makes contact and then tighten the die.
 
#25
Re: How to set how much to bump?

I use Mo Gauges in 223 and 308. As mentioned as a downside about the RCBS product, you need a Mo Gauge for your caliber. That said, mine have been invaluable to my reloading. Mo's a real good guy too, I don't mind giving him the business at all.
 
#26
Re: How to set how much to bump?

Use comparator gauge. Full-length sizing die to bump back shoulder, not just neck resizer.

However, you may want to fire a few rounds with brass before bumping back, to make sure it is fully expanded and reflects your actual chamber size.
 
#28
Re: How to set how much to bump?

I wanted to add that a single firing might not get you the full headspace of the chamber on your brass. I go overkill and fire the brass three times with neck sizing only. That brass has fully expanded and will show you close to headspace. Or, if the bolt lift is a bit heavy, you know you are there. If the bolt lift is too heavy, your brass is probably too long, making your brass a bad indicator.

If you size to make this max length brass .001" shorter, you are in pretty good shape. If you experience a hard bolt lift and you think pressure are OK, you might want to back off another .001".
 
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