+/- 0.002" on base to shoulder!?

Status
Not open for further replies.
W

westernrover

Member
Joined
May 4, 2018
Messages
1,613
I'm using a RCBS Summit press and a Redding Body Size Die to size Starline Grendel brass with a couple of firings. To measure, I'm using a Brown & Sharpe dial caliper with a Sinclair #30A insert that has the correct shoulder angle and measures off the shoulder. My base-to-shoulder is varying by as much as 4 thou.

I can see the fired brass doesn't all come out of the chamber with the same dimensions. If I take a half-dozen that come out at say 1.135" (for comparison) and I set the sizing die so that it bumps the first one to 1.133", the rest come out 1.131", 1.133", 1.132", 1.135", 1.135".

When Gavin at UR measured the Base to Shoulder on an RCBS Summit, he got 0.0006708" SD. I'm getting an SD more like 0.0015"

The Summit is a cam-over press, and I am camming over. The only adjustment on the Redding Body Die is the lock ring.

Redding provides the following instructions:

To set a Full Length/Body Die up to Cam-Over:

1) Install the appropriate Shellholder into the Ram of your Press.
2) Raise the Ram so that it is in its uppermost position.
3) Screw the Full Length Resizing Die/Body Die down into the press until it firmly contacts the Shellholder.
4) Back the Ram away from the Die.
5) Screw the Die down FURTHER into your press an additional 1/8th to ¼ turn.

Note that you will feel the Ram/Shellholder contact the resizing Die before the stroke is completed. Completing the Ram Stroke will feel as though you are snapping the latch on a toolbox.


I have it set up like this. For step 5, the additional amount I screw it down determines how far I bump the shoulder. Brand-new Starline brass measures about 8 thou shorter than the brass that comes out of my chamber -- understandable since it has to fit a lot of chambers. I only want to bump mine a couple thou from chamber-expanded, but my results seem wildly inconsistent.
 
AJC1 said:
I recommend not only annealing but a hold time while sizing. Leave the case fully inserted into the die for 5 seconds. If that helps next consider removing the expander and using mandrels. It's a game of steady improvement and progress.
Click to expand...
have you found leaving cases in longer sizes the case more? I never though of that.
 
Back the body die off the shell hold .005" Size. If brass chambers, load and fire. Do this till you get a crush fit when closing the bolt. The brass has now fully expanded to the chamber. Now measure head to datum.

Works best in a bolt action that can size the brass. If careful, works for AR15s.

What cartridge, rifle?
 
westernrover said:
To measure, I'm using a Brown & Sharpe dial caliper…I'm getting an SD more like 0.0015"
Click to expand...

Not really the correct tool for .000X” measurements.

Instead of using something that follows the angle of the shoulder, I would use a datum or just a hole that contacts the shoulder at a given point vs a much larger surface area.

Lots of variables to consider, brass, lube, expander, type of die…a bit of grit on the shell holder might shove a case another .001” into a die, another one just like it anywhere on the shoulder or something that contacts the shoulder would add another.

Might segregate a group of brass that is perfect and an equal number that are “all over the place” between 1.131-1.135” and shoot two (more would be even better) groups, measuring them to the see the difference. Could be more helpful.
 
How confident are you in that dial caliper? In doing any fine measuremnets, I have 2 calipers that I started to suspect - and I was right, one dial and one electronic, both have some issues that will provide readings that are off if not careful. A newer Hornaday dial caliper I'm a bit more confident in, but have also - bought some cheap pin gauges, just to make sure I'm getting readings that are consistent and accurate. My older dial caliper works fine, but a bit too much thumb will give a reading that is off, and doing the same overthumb will cuase it to lose zero - and all bets are off. The cheap digital one I have - about every 4th time it is turned on or off, it loses zero and will be 1.5 thousands off. Turn it off and on again and it is spot on again.

Another thought - and someone with more experence than me might know about this, but I've always wondered if the inside of the neck is not lubed consistent case to case, and a dryer one, would pull harder and cause the headspace to vary as it might pull up and deform the shoulder just a hair. Never validated that theory, but food for thought.
 
Just now seeing this post. To the OP:
You’re camming over, which is good,
You’re running a body die, so there shouldn’t be any neck expander issues going on
The die is a Redding, so we know it’s a quality die

Is the brass the same headstamp/lot, and have you annealed it? If not does it all have the same number of firings on it?

I’ve found non-annealed brass can vary several thousandths on sizing between cases after 1-2 firings even. Always anneal before sizing if you can, it does help with consistency, and brass life.
 
westernrovser said:
I can see the fired brass doesn't all come out of the chamber with the same dimensions. If I take a half-dozen that come out at say 1.135" (for comparison) and I set the sizing die so that it bumps the first one to 1.133", the rest come out 1.131", 1.133", 1.132", 1.135", 1.135".
Click to expand...

At some level, you are going to see the affects of the variance of brass compositions and work hardening of brass, and the variance of lube film thickness in the sizing die. Might even be a variance to the press spring back. It all varies. I recommend sizing to an average 0.003" shoulder set back, that way, it all chambers without resistance, including the ones where the shoulder is only set back 0.001".

Nature varies quite a bit. This is very frustrating. I was surprised to find how many things are blended because nature will not produce mustard seeds that all taste the same, nor tomatoes either. All your brand name sauces, juices, canned foods, confectioneries are blended. Even single malt scotch is mixed to an average flavor. You can pay more for single barrel bourbons, never tried one, but I bet the flavor is different. Unless, behind the scenes they are re casking the bourbons as the whiskey ages, one trick which Master Distillers do to nudge the whiskey to an average before mixing.
 
I get a .001 spread with quality cases, all fired the same number of times, occasionally a difference of 1, annealing every time, and careful sizing.

It only gets worse from there.
 
westernrover said:
I'm using a RCBS Summit press and a Redding Body Size Die to size Starline Grendel brass with a couple of firings......
Redding provides the following instructions: To set a Full Length/Body Die up to Cam-Over:
1) Install the appropriate Shellholder into the Ram of your Press.
2) Raise the Ram so that it is in its uppermost position.
3) Screw the Full Length Resizing Die/Body Die down into the press until it firmly contacts the Shellholder.
4) Back the Ram away from the Die.
5) Screw the Die down FURTHER into your press an additional 1/8th to ¼ turn.........
For step 5, the additional amount I screw it down determines how far I bump the shoulder. Brand-new Starline brass measures about 8 thou shorter than the brass that comes out of my chamber -- understandable since it has to fit a lot of chambers. I only want to bump mine a couple thou from chamber-expanded, but my results seem wildly inconsistent.
Click to expand...
The fact that your turning the die down a bit reduces the case head to datum length indicates that you have not reached cam over while actually sizing the cases that come out too long. Test this by using a feeler gauge to measure the gap between the bottom of the die and the top of the shellholder.

From my reading and from my own limited experience, it is clear to me that Redding sizing dies tend to be a few thousandths of an inch shorter than sizing dies from other manufacturers. Redding also sells "Competition Shellholders" in a 5-piece set that result in sized cases being 0.002 to 0.010 inches longer from case head to datum than cases sized while using a standard shellholder with a deck height of 0.125 inches.

Others have suggested possible causes of the variation in sized cases and suggested ways to minimize it. The bottom line is that if the variation is still too large, select the appropriate Redding Competition Shellholder and adjust it for firm contact with the bottom of the die at the top of the sizing stroke.
 
A lot of great information given already. I will add just a bit more. If you really want things to be consistent, follow the suggestions given and also make sure all cases are from the same manufacturer, same lot, fired the same amount of times. And you can also get a micrometer to check the case thickness and separate them that way too.
 
Like said earlier, Annealing will give you the most consistent sizing. Annealed brass will be all in the same state of hardness. Varying degree of hardness impacts how the brass respond to the sizing. All being in the same state will ensure that the brass will be a very close match.

As far as measuring the shoulder position it's best to use a tool that contacts the shoulder at the datum point. This eliminates any malformed shoulder from giving you a false reading. The Sheridian gauges are very good. As a poor mans way you can use most anything that will contact the shoulder some where near the middle. I have used hand gun brass for this since there are many different sizes to chose from. The RCBS Precision Mic will give you good results too.
 
I will anneal the cases and see how that affects it. They are all Starline brass and fired the same number of times. They haven't been annealed because I'd only fired them twice. I might determine the need to anneal every time. I hadn't that conviction.

I'm measuring with a Brown & Sharpe dial caliper with a Sinclair #30A shoulder comparator (that Sinclair specifies as the correct shoulder angle for Grendel). The Brown & Sharpe is a quality Swiss-made dial caliper that reads in 0.0005" increments. It should be in the same class as Mitutoyo or Starrett. Even so, I realize it's not a micrometer. A variation of 4 thou can be measured by lesser calipers.

Cartridge is Grendel. Chamber is in a bolt-action.

I'm doubtful that holding the press handle down longer will change the dwell time at full-stroke which I believe occurs during cam-over rather than when the handle is all the way down. It is a body-only die. The cam-over is obvious on the press because the handle snaps down the last portion of its stroke. If I were to screw the die any farther down, I would be bumping the shoulder 5, 7, 10 thou. I don't want them that far undersized to the chamber.

My brass might not be fully expanded. Grendel is a low-pressure cartridge. I'm probably right around 46,000 psi (according to QL). MAP is 52K and I probably can't achieve that with the powder and bullets I have (already compressing a ball powder) and getting different power or bullets at this time is not practical. Even if they're not fully expanded, the die should allow me to reduce the base-to-shoulder length to something less than how they come out of the chamber, and I would hope to do it consistently.
 
Also consistent lube with lube in the case neck. Trying to lube every case the same makes my shouldet sizing dimensions closer.
 
12Bravo20 said:
A lot of great information given already. I will add just a bit more. If you really want things to be consistent, follow the suggestions given and also make sure all cases are from the same manufacturer, same lot, fired the same amount of times. And you can also get a micrometer to check the case thickness and separate them that way too.
Click to expand...
Excellent advice here.
I would like to add that lacking the micrometer (with the ball for inside the case), you could separate your cases according to weight after sizing, cleaning and trimming. Cull cases that are +/- 1.0gr and you will find much better consistency in case wall thicknesses.
When I am checking shoulder setback (like the OP apparently is concerned with) a 0.001" to 0.003" variation is acceptable for me. With the RCBS Precision Mic I mentioned earlier, you can also measure the length from the base of the case to the ogive of the bullet to allow you to set the jump/jamb dimension at the leadeinto the rifling. When doing this I seat all my bullets about 0.010" long. Then I use my RCBS Competition Bullet Seating Die and the RCBD Precision Mic to seat each bullet so that each base-to-ogive dimension is exactly the dimension I want it to be. In the case of my .270 Win. high power silhouette rifle, that jump distance is 0.011" with the Berger 140 grain bullets. With the 6.5x55 SM and 108 gr. Lapua Scenar, it is a jamb dimension of 0.004". These give ME the best accuracy I have been able to glean from these two rifles. YMMV and probably will. I do not do this for every rifle I have. A boby can only chase the rabbit as far down the hole as he deems necessary or enjoyable. Only you can decide how far down the rabbit hole you want to go. :scrutiny:

It's just a hobby. But a fascinating one that allows you to explore the extent of you abilities, intelligence and your patience. Welcome to one of the most interesting and fun obsessions you can imagine to do alone and fully clothed.... ;) :neener:
 
I just try to keep my tire pressure in all tires within 2 lbs using a Chinese air pressure gauge.o_O

Edit: I should have entered

2.000 psi for all 5 tires.(full size) using a Rhino USA’s Heavy Duty Tire Pressure Gauge
 
Last edited:
Status
Not open for further replies.

Similar threads

DKSDonnie
  • Locked
Shoulder Bumping
2 3
Replies
69
Views
7K
quest4perfection
Q
BBarn
  • Locked
Press Frame Clearance at Top of Stroke
Replies
3
Views
216
PWC
PWC
W
  • Locked
redding body die adustment
Replies
5
Views
2K
mallc
M
J
  • Locked
LnL Question
Replies
7
Views
672
PsychoKnight
P
MCMXI
  • Locked
Redding Competition Shellholder sets - you may be in for a shock!! (No you won't!!)
Replies
14
Views
5K
MCMXI
MCMXI
Back
Top