Shoulder bump questions

[Cush]

Hi, I am new to reloading. Started reloading for my Rem 700 5r
I have loaded and shot three batches with differing results. Using Newberry's OCW method to find what powder load shoots best in my rifle.
1st batch did well with only minor pressure signs toward the higher end of the powder loads. FL sizing with 1.570 on the shoulder(that is what the Fed Prem 168 factory rounds were set to), neck bushing is .335
the 2nd batch, I loaded only 3 each of the highest end of the powder load from the 1st batch because I messed up the targets and wasn't sure about the outcome. I got some mildly tight bolt situations with a few of these.
The 3rd batch I changed to 1.575 on the shoulder and used 336 bushing for the neck.
I got way more pressure signs on this batch especially the last 4 or 5 pressure loads (The last one blew the primer out)
I decided for the next batch to go back to the 1.570 or maybe 1.572 for shoulder length since these seem to not bind when I loaded the FL empty casings in the chamber. The fire formed casings were measuring 1.578-1.582 Is that normal to have to bump that much?
What is the proper way to determine appropriate shoulder bump?
How does neck tension affect things? I will try not to be so long-winded next time.

 

[Brians356]

You may be long-winded (I wouldn't say), but I read your post carefully and cannot find any mention of which cartridge you are loading. (Sure, I can guess, but to what purpose?) You might also want to divulge load details (powder, charge weight, etc) just to provide useful context.

 

[zipollini]

This is what you want in your appropriate chambering.

http://www.whiddengunworks.com/product/case-gauge/

 

[BoydAllen]

Assuming that you have the proper tool to measure cases shoulder to head, and know how to use it, I would first suggest that you measure a new case or factory round and then a fired round, and then think about the usual recommendation to only bump back shoulders one to two thousandths. Next, I suggest that you research the terms incipient separation, and case head separation and their causes. It has been my experience that once fired brass from factory loads is not at its maximum head to shoulder dimension for the rifle that it was fired in, and that usually if ones FL die is set to reproduce that dimension, and the die is not too large in body diameter dimensions for that chamber, that sized cases will chamber just fine. I assume that we are talking about a .308, but this advice applies equally to any CF caliber when loading for a bolt action rifle. For semiautomatics one needs to bump more so that they will operate in a reliable and safe manner. If you cannot size cases so that your bolt close has the feel that you want at the proper die setting for bump, you need another die that has smaller dimensions in the area of the case body.

 

[fguffey]

The fire formed casings were measuring 1.578-1.582 Is that normal to have to bump that much?
What is the proper way to determine appropriate shoulder bump?
How does neck tension affect things? I will try not to be so long-winded next time.

Cush, I can not help you, I find it most difficult to bump the shoulder without case body support; because of that I find my shoulders do not move when fired and when sized. Neck tension effects; same thing, I do not have a tension gage that measure tension, I can measure interference fit and I can measure bullet hold in pounds; all I can do with neck tension is talk about it. Forgot, there is also crush fit.

F. Guffey

 

[Cush]

You may be long-winded (I wouldn't say), but I read your post carefully and cannot find any mention of which cartridge you are loading. (Sure, I can guess, but to what purpose?) You might also want to divulge load details (powder, charge weight, etc) just to provide useful context.

All bullets are Sierra 168
All primers were winchester large rifle for standard rifle loads
Pwdr is IMR 4895 for all test loads
Pwdr chgs for all three batches were the same- 42.3, 42.6, 42.9, 43.2, 43.5, 43.8, 44.1, 44.4, 44.7, 45, 45.4 (3 of each for testing purposes)
Cartridge is win 308 ADI (Aust Outback) for 1st batch neck bushing is .335, shoulder was 1.570 (same as factory loads)
Cartridge for 2nd batch which was only 3 sets of 3 from batch 1, 44.7, 45, 45.4 all other info the same as batch1
Cartridge for batch 3 was WIN Federal Premium Neck bushing is .336, shoulder is 1.575
The air temp was 30 degrees for 1st batch and 60 for 2nd and 3rd if that matters

 

[BoydAllen]

I am not familiar with the cartridge that you are reloading. Could you describe it in detail, also how are you measuring your shoulder to head dimension?

 

[fguffey]

my shoulders do not move when fired and when sized.

dmoran, what would happen to my case if the shoulder moved when fired? How could I tell if the shoulder on my cases moved when fired?

F. Guffey

 

[Cush]

Assuming that you have the proper tool to measure cases shoulder to head, and know how to use it, I would first suggest that you measure a new case or factory round and then a fired round, and then think about the usual recommendation to only bump back shoulders one to two thousandths. Next, I suggest that you research the terms incipient separation, and case head separation and their causes. It has been my experience that once fired brass from factory loads is not at its maximum head to shoulder dimension for the rifle that it was fired in, and that usually if ones FL die is set to reproduce that dimension, and the die is not too large in body diameter dimensions for that chamber, that sized cases will chamber just fine. I assume that we are talking about a .308, but this advice applies equally to any CF caliber when loading for a bolt action rifle. For semiautomatics one needs to bump more so that they will operate in a reliable and safe manner. If you cannot size cases so that your bolt close has the feel that you want at the proper die setting for bump, you need another die that has smaller dimensions in the area of the case body.

.308
more detailed charge info is in a post above
Redding FL Type S die with bushing
Redding Comp Bullet seater
trim length is 2.005
Bump Gage and dig calipers
Factory's measure 1.571 shoulder, .337 neck on loaded factory
Fire formed shoulders aver. 1.578
So, if I bump .002 from 1.578, that leave me with 1.576 which is very tight to load in the chamber, ie fairly hard to close the bolt
Just for clarity: I check the cartridge for fit after FL Sizing to make sure they are not too tight
So case head separation can be caused by excessive Head space...this is a term that can be confusing as some folks are referring to OAL length and some shoulder length. Some folks say too tight a neck shoulder causes high pressure and some say it does not, but all seem to agree that too much shoulder space can cause problems
So since the first batch was sized at factory size of 1.570 or 1.571, and did fine, I guess the 3rd batch which I made 1.575 might be the culprit?
And yes, my 1.575 shulders grew to as much as 1.582. Is it too much to bump from 1.582 down to 1.571?
so if the body is sizing too big, why then does reducing the shoulder length make bolt close comfortably? Dose the shoulder itself get resized in diameter as well as length with a Full Sizing die?

 

[Cush]

I am not familiar with the cartridge that you are reloading. Could you describe it in detail, also how are you measuring your shoulder to head dimension?

.308
Win cartridge (from once fired factory ammo from Outback )
Comparitor bump gage body and calipers

 

[fguffey]

Factory's measure 1.571 shoulder, .337 neck on loaded factory
Fire formed shoulders aver. 1.578

Measure before and again after. I am the fan of measuring the length of the case from the datum to the case head before firing and again after firing, then there is after sizing. There is .007" difference between the two lengths. For anything 308 W that is too much. When compared to go-gage length and no go-gage length you are getting close to field reject length.

Again, I have a 30/06 M1917 with a chamber that is .016" longer from the shoulder to the bolt face than a minimum length/full length sized case; this does not bother me, I adjust the full length sizing die off of the shell holder .014" and size 280 Remington cases for the long chamber. When finished I have the magic .002" clearance between the shoulder of the case and chamber shoulder. Then there is that thing that locks everyone up. When I pull the trigger the shoulder on my case does not move.

Then there is the 'if it did' I could say my case stretched.

F. Guffey

 

[BoydAllen]

Returning the case to the head to shoulder measurement is NOT the goal at all. You should be using a fired case as your reference and you may have enough clearance if you set your die to duplicate that measurement. Is the shoulder angle of your chamber and fired cases the same as .308? If not, it will confuse the process considerably when comparing unfired to fired. In any case, forget using new brass as a reference for bumping. Don't do that. What sort of die are you using?

 

[Dusty Stevens]

There is headspace. Then theres the case with no headspace. Theres do nots and then theres no do nots.

 

[Brians356]

Is the shoulder angle of your chamber and fired cases the same as .308?

Boyd, the chamber is standard 308 Winchester. The OP uses "cartridge" rather than "case", the latter is just reloaded ADI 308 Win ammunition. OP wrote "Cartridge is win 308" i.e. 308 Win.

 

[Brians356]

All bullets are Sierra 168
All primers were winchester large rifle for standard rifle loads
Pwdr is IMR 4895 for all test loads
Pwdr chgs for all three batches were the same- 42.3, 42.6, 42.9, 43.2, 43.5, 43.8, 44.1, 44.4, 44.7, 45, 45.4 (3 of each for testing purposes)

Note: Hodgdon publishes MAX 44.0 grains compressed IMR 4895 for 308 Win 168-gr bullet.

YMMV but your final four doses are progressively bulging the envelope. Just sayin'.

 

[Spike A]

I gotta agree with Brian, I would just try dropping down in powder charge and do a few test

 

[Cush]

Measure before and again after. I am the fan of measuring the length of the case from the datum to the case head before firing and again after firing, then there is after sizing. There is .007" difference between the two lengths. For anything 308 W that is too much. When compared to go-gage length and no go-gage length you are getting close to field reject length.

Again, I have a 30/06 M1917 with a chamber that is .016" longer from the shoulder to the bolt face than a minimum length/full length sized case; this does not bother me, I adjust the full length sizing die off of the shell holder .014" and size 280 Remington cases for the long chamber. When finished I have the magic .002" clearance between the shoulder of the case and chamber shoulder. Then there is that thing that locks everyone up. When I pull the trigger the shoulder on my case does not move.

Then there is the 'if it did' I could say my case stretched.

F. Guffey

I am getting more and more confused. There are far too many terms thrown out that are called by different names or named but never explained.
"Datum" line? What is it? I looked it up and it appears to be an imaginary line somewhere on the length of the shoulder of the casing. If it is in fact the point at which the casing bears against the "shoulder" portion of the chamber itself then OK, but how does one measure that distance since every chamber is different.. I tried to find a gauge that might do that but als, the places that sell gauges of every sort see never to explain what the thing actually does. And then there is head space.... the distance from the base of the casing to the point at which the shoulder touches the chamber? Or the distance from the Base of the "cartridge to where the bullet touches the lands?
Sorry for the frustration, its just hard to get clarity.

 

[fguffey]

"Datum" line? What is it?

Datum line? There is no datum line. It is a bad habit that got started long ago in loading manuals and the early Internet. There was a drawing of a bottle neck case with a line through the shoulder with an arrow pointing to it with the words identifying it as a datum line.


Reloaders had no concept of mechanical drawings. Had the publisher of the drawing furnished a view of the drawing from the front reloaders could have possible figured the datum was a circle, not a line. All of my life I have referred to the datum as a round hole circle. The most common datum round hole is .375” then comes the .400”.


Because my cases do not have head space I do not struggle with finding the correct datum unless I want my measurements to match SAAMI specifications. What that means is I do not insist on matching datums if I am using a comparator. Problem with that and the Internet, reloaders believe everything has head space and ever gage is a head space gage.


Again, my cases do not have head space; I check my cases with a case length gage. Another concept that is impossible for a reloader to grasp. Is head space gage. They believe a reloader needs three. One is the go-gage, next is the no go-gage and finally the field reject length gage. One gage can do all three measurements and everything in between and beyond. I am convinced it can be done; reloadrs have convinced me they can not do it.

F. Guffey

 

[ireload2]

1. The datum line is required by ASME Y14.5. It is the national standard for geometric dimensioning and tolerancing.
2. Many reloaders/handloaders are engineers, designers, drafters, tool makers and machinists. They are fluent in design drawings. If you will bother to read the notes on a SAAMI standard cartridge and chamber drawings the datum is explained. If you have problems understanding the SAAMI drawing it is fully defined in ASME Y14.5.
3. Go, No Go and Field Gauges are used by are armorer's and gunsmith's gauges. They are not required for handloading. Most handloaders never touch a headspace gauge so you are wrong.

You will notice that there is a line on the shoulder that is dimensioned .330 B (for B see the notes). This is a .330 diameter circle that would correspond to a sharp cornered hole in a locator such as a comparator. The basic term means it has no tolerance - it is theoretically perfect dead on .3300. This provides a standard way for everyone to measure the chamber and the case or loaded cartridge the exact same way. Use this standard and ammo made anywhere will fit a rifle chambered to this standard anywhere.

 

[IrishJim]

I feel for you Cush, maybe I can be of help. You appear to have the tools needed, and an understanding of what they are for. Maybe just a basic suggestion of how to proceed will be of help to you. Start with your neck bushing size, and it will depend on your brass neck thickness and the amount of tension you wish to put on the bullet. You have a .308 bullet, plus a case neck of perhaps .015 thickness, so the formula is bullet size plus twice the neck thickness. .308 + .015 + .015 = .338 If I wanted to put two-thousandths .002 of neck tension on the bullet which is a reasonable starting amount, I would choose a neck bushing of .335 which will allow .001 of brass springback plus .002 of neck tension, leaving an outside neck diameter once the bullet is seated right about .336. If your brass is thinner, or you wish more/less neck tension, then take that into account when calculating the bushing size you will use.

For shoulder size, you now have some fired brass that you have measured as long as 1.582 at your shoulder datum-point and when chambered is giving you a stiff bolt close/open. That is a good case to work with. Back-off your sizing die, and feed-in this case. In very tiny increments, turn down your die by a thirty-second of a turn, very tiny amount, and re-measure that shoulder. When you get it to bump down by .001 which will be 1.581, take it back to your rifle and re-chamber it feeling for any bolt stiffness. If still stiff, go back to the press and turn down another thirty-second to 1.580 and repeat re-chambering. Continue until the bolt closes freely or with just a tiny amount of friction, at that point you know right where your shoulder (headspace) is as measured with your tools and dies. You would then turn the die down a further .002 and lock the die in place. That setting should give you smooth trouble free chambering of your rounds, and minimum case stretch.

At this point, you should measure your overall case length, and trim the neck if necessary. Your basic brass prep is completed, and you move to experimenting with powder and bullet seating depth!!! At some time in the future you may wish to go back to your neck tension settings and look into neck turning to establish exact neck thickness and further control your neck tension settings. Have fun!!!! Sorry to be so long winded.