Inconsistent Shoulder bump

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Jase PTRC
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Joined: Sat Nov 29, 2014 11:15 pm
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Inconsistent Shoulder bump

#1 Postby Jase PTRC » Thu Dec 08, 2016 10:33 am

After measuring some cases recently i have discovered that i have a variation in my cases base to shoulder measurement, I am reloading for .308 and all cases measure the same after firing 1.619" but after sizing im getting a variation of lengths from 1.6185 to 1.6165 (so varying .002 thou with most ending up at 1.618 and im not really sure why.
Im using a Redding body die, lubing with an Rcbs lube pad, looking for help to work out what im doing wrong.

mike H
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Location: JUNEE NSW

Re: Inconsistent Shoulder bump

#2 Postby mike H » Thu Dec 08, 2016 3:02 pm

Jase PTRC wrote:After measuring some cases recently i have discovered that i have a variation in my cases base to shoulder measurement, I am reloading for .308 and all cases measure the same after firing 1.619" but after sizing im getting a variation of lengths from 1.6185 to 1.6165 (so varying .002 thou with most ending up at 1.618 and im not really sure why.
Im using a Redding body die, lubing with an Rcbs lube pad, looking for help to work out what im doing wrong.

I don't think that you are doing anything wrong,do you find any variation in force required to size the cases? If you wanted to drive yourself silly,you could try adjusting the die to size the cases a bit less,measure them,then extra size the longer ones.After that measure the loaded rounds with a bullet comparator and give yourself something extra to worry about,if they are not all the same length.
I try to be exact when loading,but honestly,I think that there are tolerances,and sometimes you have to accept them.If you are really worried,measure the head space and C.O.L. after loading,and batch them up and shoot them in some sort of order.If this effort makes a difference to your scores,it will be worth it,if it doesn't,at least it would have kept your mind off politics.
Mike.

Peterla
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Location: Barossa Sth Australia

Re: Inconsistent Shoulder bump

#3 Postby Peterla » Thu Dec 08, 2016 3:04 pm

I found a cheap LEE press gave me the same issue
I then changed to a Big boss and made sure I set the press to cam over on the dies and that made a huge difference.
I had to use the competition shell holders to get the right bump with the cam but it worked a treat

I hope that helps

Jase PTRC
Posts: 221
Joined: Sat Nov 29, 2014 11:15 pm
Location: Adelaide SA "PTRC"

Re: Inconsistent Shoulder bump

#4 Postby Jase PTRC » Thu Dec 08, 2016 3:21 pm

Im using an RCBS Rockchucker, I have a theory that the die may be too short internally, so when i try to get my 1 thou bump im only just kissing the base of the die with the shell holder. Do i need to solidly cam the press over to get a consistent re size?

johnk
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Re: Inconsistent Shoulder bump

#5 Postby johnk » Thu Dec 08, 2016 3:32 pm

Even a Rockchucker has some compliance & not necessarily uniform from throw to throw. Try incrementing the die further, checking as you go.

RDavies
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Re: Inconsistent Shoulder bump

#6 Postby RDavies » Thu Dec 08, 2016 7:07 pm

I get the same think with my rock crusher, even though it is correctly set up, correct shell holders etc. you will likely find that annealing cases will help to get consistent shoulder bump.

Jase PTRC
Posts: 221
Joined: Sat Nov 29, 2014 11:15 pm
Location: Adelaide SA "PTRC"

Re: Inconsistent Shoulder bump

#7 Postby Jase PTRC » Fri Dec 09, 2016 6:09 am

Thats interesting Rod. So how much variation would be considered acceptable relating to bump. I had this idea in my head it was critical there was no variation especially as im.only trying to bump a thou.

cheech
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Re: Inconsistent Shoulder bump

#8 Postby cheech » Fri Dec 09, 2016 6:54 am

Finding difference's is frustrating so I quit measuring for this process.

I set up all dies so I actually get the right " feel" of brass as its chambered in my action . For this you must remove firing pin assembly , and primer popped out the brass , clean chamber .

Reason for this is measuring can give varied results every time it's repeated on the same case just because of the tools we use a given number is not adsolut especially when you are looking for 1 thou ,

As Pete said comp shell holders can make this easy , or winding the die , PMA tool have a nice gadget for this also

Good habit is size brass in big batches, I only prep brass once a batch is all fired the same , and check for feel before a full run .

RDavies
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Re: Inconsistent Shoulder bump

#9 Postby RDavies » Fri Dec 09, 2016 7:05 am

Jase PTRC wrote:Thats interesting Rod. So how much variation would be considered acceptable relating to bump. I had this idea in my head it was critical there was no variation especially as im.only trying to bump a thou.

Not really sure what acceptable is but I usually try for 2 thou bump. In cases which have not been annealed for a while, maybe 30% will move back .001" or .003" and one or two would go .000" and these are the ones which feel tighter than others to chamber.

Barry Davies
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Re: Inconsistent Shoulder bump

#10 Postby Barry Davies » Fri Dec 09, 2016 7:47 am

Why " bump " the shoulder at all?
Talking .308.
If your head space is set at say 1.630" then all fired cases won't come out at 1.630". There will be a variation of maybe a thou either side.
I set my body die to give an average of 1.630" ( my rifles are 1.630" ) in other words some shoulders are bumped a thou some are not touched.
Someone tell me what does it matter if some cases when chambered have a thou crush ( which you won't feel ) and some have a thou clearance?
Does it make a significant ( or any ) difference to grouping capabilities? I doubt it.
You will always get some variation because there are variations in every sizing such as -- more or less sizing lubricant, case hardness, slop in the press pivot pins etc. but as long as you are within a thou or so of rifle head space what does it matter?
Jase PTRC, Your measurements 0f 1.618 etc are not correct for a 308. 1.630/1.634 are Min/ Max so there seems to be something not correct with your gauge, I would fix that first.

Jase PTRC
Posts: 221
Joined: Sat Nov 29, 2014 11:15 pm
Location: Adelaide SA "PTRC"

Re: Inconsistent Shoulder bump

#11 Postby Jase PTRC » Fri Dec 09, 2016 8:04 am

Barry Davies wrote:Why " bump " the shoulder at all?
Talking .308.
If your head space is set at say 1.630" then all fired cases won't come out at 1.630". There will be a variation of maybe a thou either side.
I set my body die to give an average of 1.630" ( my rifles are 1.630" ) in other words some shoulders are bumped a thou some are not touched.
Someone tell me what does it matter if some cases when chambered have a thou crush ( which you won't feel ) and some have a thou clearance?
Does it make a significant ( or any ) difference to grouping capabilities? I doubt it.
You will always get some variation because there are variations in every sizing such as -- more or less sizing lubricant, case hardness, slop in the press pivot pins etc. but as long as you are within a thou or so of rifle head space what does it matter?
Jase PTRC, Your measurements 0f 1.618 etc are not correct for a 308. 1.630/1.634 are Min/ Max so there seems to be something not correct with your gauge, I would fix that first.


Im using a Hornady head space bushing insert D .400 which is the one they list on their website. I have measured the insert and it measured exactly .400
I understand what you are saying about chamber specs but im only interested in the difference between a sized case and one not sized and trying to reduce the amount of variation of sized cases.

Barry Davies
Posts: 1383
Joined: Tue Aug 24, 2010 12:11 pm

Re: Inconsistent Shoulder bump

#12 Postby Barry Davies » Fri Dec 09, 2016 8:21 am

I'm not familiar with the Hornady gauge you mention but I guess that the D.400 relates to the reference diameter along the shoulder to neck taper. The .400 being the basis for a 308 head space measurement ( 1.630 ) But you are getting 1.618 so there is something wrong with your gauge . I realize it is a comparative measurement but it is not correct.
Like I said what does a thou or so variation in headspace matter unless it can be proven that such a variation gives a significant variation in group size.
I really think you are worrying about a measurement that has no bearing on ultimate performance providing your sizing is within +/- a thou of your rifle.

Jase PTRC
Posts: 221
Joined: Sat Nov 29, 2014 11:15 pm
Location: Adelaide SA "PTRC"

Re: Inconsistent Shoulder bump

#13 Postby Jase PTRC » Fri Dec 09, 2016 8:38 am

1 thou might not matter at all Barry but im not experienced enough to know if it is important or not, but removing variables seems like a good idea and that's what i'm trying to do.

Jase PTRC
Posts: 221
Joined: Sat Nov 29, 2014 11:15 pm
Location: Adelaide SA "PTRC"

Re: Inconsistent Shoulder bump

#14 Postby Jase PTRC » Fri Dec 09, 2016 8:39 am

Barry Davies wrote:I'm not familiar with the Hornady gauge you mention but I guess that the D.400 relates to the reference diameter along the shoulder to neck taper. The .400 being the basis for a 308 head space measurement ( 1.630 ) But you are getting 1.618 so there is something wrong with your gauge . I realize it is a comparative measurement but it is not correct.
Like I said what does a thou or so variation in headspace matter unless it can be proven that such a variation gives a significant variation in group size.
I really think you are worrying about a measurement that has no bearing on ultimate performance providing your sizing is within +/- a thou of your rifle.


I will also look into the gauge issue, thanks for you input mate.

mike H
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Joined: Mon May 08, 2006 5:34 pm
Location: JUNEE NSW

Re: Inconsistent Shoulder bump

#15 Postby mike H » Fri Dec 09, 2016 9:24 am

Barry,
I have a Hornady gauge,the same as the one mentioned,mine gives identical measurements to those of Jase.My son,Chris has a gauge Adam Davies made for him,whenI measured my fired cases with it,they measured 1.630".I think the gauge body has a slight bevel on the entrance,causing the odd measurement.


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