Forster die "bump"? How much bump?

[308BAR]

Off hand does anyone know how much or measured how much these dies bump the shoulder back? They only state "optimal" head space which is 0.001-0.002 but what is the actual?

Anyone with a precision mic could measure one on a 223rem and 308win?

Cheers and thanks in advance.

 

[Pr589]

308,

Would the bump not depend on how you have your die set-up? Not trying to state what might be obvious but it seems to me that just as with any full length sizing die, the amount of bump will depend on how far in you have the die screwed, relative to the TDC of your ram.

 

[308BAR]

308,

Would the bump not depend on how you have your die set-up? Not trying to state what might be obvious but it seems to me that just as with any full length sizing die, the amount of bump will depend on how far in you have the die screwed, relative to the TDC of your ram.

Yes you're right but I need something measurable (a figure). If the shell holder is kissing the die, what is the "bump" 1 thou, 2, 3, 8 ???? I don't have a set of precision mic and like to know how much the shoulders are set back so I could adjust the "bump" accordingly.

 

[roberti11]

You cannot do this without measuring , SAAMI spec for .308 can be 10 thou between go and nogo, if ur chamber is cut to 1.635 (SAAMI headspace min =1.630, max 1.634) and ur bump die is cut to 1.631 when u resize snug to the shell holder u will bump the shoulder 3-4 thou. The tool at the link below is excellent and can be used on nearly any case to assess headspace changes relative to a fired case
The whole point of that die is to bump the shoulder 1-2 thou for easy chamber in but minimal change to the rest of the case

http://www.larrywillis.com

see also .......

http://riflemansjournal.########.ca/2009/08/reloading-headspace.html

 

[yodave]

thickness of your shell holder versus mine is going to flaw the results of any measurement I take..........so with that said adjust your die the way you would any other die, drop the die a quarter turn and at a time until your brass chambers easily in your chamber........

I was told by someone at forster that the die will bump the shoulder back 2 thou under minimum case dimension, I took that to mean under minimum saami spec and have always set my dies accordingly, if the case is snug to chamber then drop the die a quarter turn and try again.

The bump die is designed to only move the shoulder and not size the body of the case, but I know that you already knew that.........

 

[bigedp51]

Below is a Hornady cartridge case headspace gauge that is calibrated to read true headspace. The case measurement shown below is the cases fired length.

Below is the same case after sizing with .003 shoulder bump.

Colt Field headspace gauge for the AR15, 1.4736

Headspace gauge in the Hornady gauge, and you can't do that with the Larry Willis gauge.

 

[308BAR]

Below is a Hornady cartridge case headspace gauge that is calibrated to read true headspace. The case measurement shown below is the cases fired length.

Below is the same case after sizing with .003 shoulder bump.

Colt Field headspace gauge for the AR15, 1.4736

Headspace gauge in the Hornady gauge, and you can't do that with the Larry Willis gauge.

Thank you for this info. Do you have your shell holder kissing your bump die or did you set the die up just to bump 3 thou?

 

[TrxR]

I have always wondered how do you calibrate to read true headspace on the hornady setup?

 

[big boar]

I have the RCBS precision case mic for just that reason. When I set my dies (Forster) I've use the mic to measure how much to "bump".

 

[Innovative]

How to measuring chamber clearance more accurately.

Whenever you resize a case, it is far better to start by knowing the "exact" size of YOUR particular chamber. There is very little benefit to comparing your handloads to a gauge, even though it "might" resemble your chamber. The Digital Headspace Gauge calibrates to the size of YOUR particular chamber. Then, you can measure one of your handloads, and it displays the exact shoulder clearance that YOUR handloads have in YOUR particular chamber.

A full length die adjusted "accurately" is always your best bet. Other resizing dies are rarely (if ever) needed. The Digital Headspace Gauge also measures the bullet jump to the rifling. It shows everything you need to know about how things actually fit inside your chamber.

 

[blauber]

thickness of your shell holder versus mine is going to flaw the results of any measurement I take..........so with that said adjust your die the way you would any other die, drop the die a quarter turn and at a time until your brass chambers easily in your chamber........

I was told by someone at forster that the die will bump the shoulder back 2 thou under minimum case dimension, I took that to mean under minimum saami spec and have always set my dies accordingly, if the case is snug to chamber then drop the die a quarter turn and try again.

The bump die is designed to only move the shoulder and not size the body of the case, but I know that you already knew that.........

^^^Not true. The bump die will push or "bump" the shoulder back and size the entire body of the case. Moving a die a quarter turn could move your shoulder out of SAAMI spec as well - meaning a 1/32 of a turn could be all you need to get the .001-.002" bump.

I use the Hornday headspace gauge - when a fired round becomes difficult to close the bold on, I take a headspace measurement. Then I will adjust a die tiny amounts at a time and re-measure until the shoulder has moved back .002". Redding makes a shellholder kit that has 5 shellholders machined in .002" increments (total range is 0.010") to assist with your sanity when trying to get a die set just right for a headspace correction.

 

[bigedp51]

We live in a plus and minus world of manufacturing tolerances, each .223/5.56 die below will bump the shoulder back a different amount when contacting the shell holder the same amount. Not pictured below is a Lee full length die that will push the shoulder back .005 more than any of the dies pictured.

On top of this you have all the different brands of brass, new brass, old brass and variations in annealing and spring back rates.

Get the Hornady gauge and a good set of vernier calipers, then measure the cases fired length and then bump the shoulder back approximately .001 to.002 for a bolt action and .003 to .004 for a semiauto.

If you do a little research you will find that long range competitive shooters full length resize their cases for the best overall accuracy.

Also a digital vernier caliper or Larry Willis's Innovative digital gauge is VERY easy to read and use, especially when you have chronology gifted eyesight. (and braille gauges are so hard to find) Yes the "GOLDEN" years are wonderful, BUT they are more challenging.

The "medicine" below helps with aging. (a Christmas gift from my son and 8.50% ABV)

http://www.beeradvocate.com/beer/profile/180/1385/