When sizing a fired case from your bolt action rifle used for benchrest shooting only. Mine is a Remington 700 308 caliber. My fired case measures 1.627, I can rechamber a fired case with no resistance on bolt lift or close. When I would size with the F/L sizer to 1.6285 the case would have a slight feel at the end of the close, giving me .0005 case space. So would you bump the shoulder back .002 from the fired case measurement of 1.627 as most instructions state. My way of thinking it would give me over .003 case space between closed bolt to case head. I dont neck size. What would You do ? Also I just ordered a Forster Go gage just to double check my RCBS Precision Mic's zero .
What would You do
- Thread starter cw308
- Start date
That is a good move in that I have found my RCBS Precision Mic in .308 Winchester to be off -0.002. When reading a known precision Go gauge of 1.630" my RCBS gauge reads 1.628" or actually pretty close to that. Over the years I ended up with two sets of RCBS Precision Mics in .223 Remington. To use a very technical measurement term one is dead on balls accurate and one is about -0.001. So while the gauges are very linear they are not exactly perfect in the numbers.
One of my favorite bench rifles is also a Remington 700 which I trued. My cases grow about 0.002" on firing when I start with a case of 1.630" the fired cases come out 1.632". This actually works out well because all of my other .308 Winchester chambers are larger than that Remington so when I size back to a nominal 1.630" I can shoot the stuff in any rifle. I generally use my brass 4 or 5 times and trash it so I do not worry about overworking the brass. I always resize to 1.630" (Nominal) and always trim to 2.005" as it works well for me.
When you check your RCBS Precision Mic please post what you find for numbers, I would be curious.
Ron
Go figure, for me it was Kew Gardens Queens before Uniondale. For my parents it was the American Dream. I was three years old in 1953 when we moved to Uniondale into a two bedroom Cape Cod type home. LI was an incredible place to grow up during those years. We had it all as kids.
We now return you to our regular gun forum .....
Ron
We now return you to our regular gun forum .....
Ron
Your over thinking the whole thing.
.0005 is 5/10,000 of an inch. Won't make a lick of difference even if you could measure it.
"...My fired case measures 1.627..." Where? A .308's trim-to is 2.005". There's no 1.627" or 1.6285"(that is not 2 thou different. It's 1.5 thou. Another dimension that won't make any difference to anything.) anywhere.
"...my cases are not getting longer..." They will. Be patient. You don't need to worry about case lengths until it goes over 2.015" anyway. Then, and only then, do you trim, chamfer and deburr. Where the shoulder of a fired case is makes no difference.
An RCBS Precision Micrometer Cartridge Headspace tool really does nothing but separate you from your money. Cartridges do not have headspace and "shoulder set back variation from initial set-up" means nothing.
.0005 is 5/10,000 of an inch. Won't make a lick of difference even if you could measure it.
"...My fired case measures 1.627..." Where? A .308's trim-to is 2.005". There's no 1.627" or 1.6285"(that is not 2 thou different. It's 1.5 thou. Another dimension that won't make any difference to anything.) anywhere.
"...my cases are not getting longer..." They will. Be patient. You don't need to worry about case lengths until it goes over 2.015" anyway. Then, and only then, do you trim, chamfer and deburr. Where the shoulder of a fired case is makes no difference.
An RCBS Precision Micrometer Cartridge Headspace tool really does nothing but separate you from your money. Cartridges do not have headspace and "shoulder set back variation from initial set-up" means nothing.
T.O'Heir
"...My fired case measures 1.627..." Where ? From the base of a 308 case to the datum, using the RCBS Precision Mic. I trim my cases every firing to 2.010, chamfered inside & out. My question is directed to case length from base to ogive to match chamber headspace.Now that I answered your questions. Could you answer mine. What would You do ?
"...My fired case measures 1.627..." Where ? From the base of a 308 case to the datum, using the RCBS Precision Mic. I trim my cases every firing to 2.010, chamfered inside & out. My question is directed to case length from base to ogive to match chamber headspace.Now that I answered your questions. Could you answer mine. What would You do ?
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I set up my Hornady comparator with my P.T.G. 1.630 headspace guage and zero it out, knowing that my rifle's headspace is 1.632 I adjust shoulder bump accordingly. Different brands of cases "bump" differently, I use under and oversize shellholders to get what I want. Main reason I do the checking is I don't want any cases too long for the M1a or overly short or long for the 700. My 700's chamber is a little short from the factory.
Case spring back will vary by more than .002. You need .002 of clearance, you need to measure 20 cases and see what the high and low mark are. They won't all measure the same. Them size 20, they won't all measure the same either. Variations in the amount of case lube and spring back will amount to at least .002. My resized cases vary by as much as .002-.003. Fired cases will vary that much as well. Find the low end of the fired case and the high end of the resized case. They need to be .002 apart.
As a general rule I try for 0.003" but due to differences in case hardness, the actual shoulder push back will vary. Cases change hardness and thus springback as they are fired and sized. Then some cases are thicker and so the resizing die has to be reset for them.
The only rifle I size cases to exact chamber headspace is my 35 Whelen. That case has a very slight shoulder and I had misfires which I attributed to insufficient firing pin energy on the primer. I believe that the case is actually pushed forward when the firing pin hits the primer, thus cushioning the firing pin blow. I also now use the most sensitive primers I have, which are Federal, for that cartridge.
Typically I've notice new commercial cases tend to be about 0.002" shorter than SAAMI headspace minimum. I suspect that's where the 0.002" number came from. Glen Zediker says it's enough to make semi-auto feeding reliable, so I've always used it that way.
The standard practice of setting a shoulder back 0.002" from as-fired value is premised on the as-fired value reflecting your actual headspace. Usually, though, and unless you are shooting a pretty hot load, the brass has already sprung back about 0.001". That's why neck-sized-only brass works, and often pretty well. But eventually it stretches to fill the case. So if you don't have a way to measure your headspace, try neck-sizing-only, measuring after each firing and always chambering it with the headstamp orientation the same until it just starts to get snug. Check your records and see what the last unsnug measurement was. Go for sizing 0.002" below that number if you want to feed from a magazine, and 0.001" below that number for single-loading for benchrest.
A lot of BR shooters have switched to that -0.001" number it seems. Just relying on neck sizing doesn't set new records the way it once did. It seems the slight unevenness in brass wall thickness expands it to fit slightly off-center, and in some guns that shows up when you are shooting below 1/2 moa.
YMMV, so experiment to see what your gun actually likes.
The standard practice of setting a shoulder back 0.002" from as-fired value is premised on the as-fired value reflecting your actual headspace. Usually, though, and unless you are shooting a pretty hot load, the brass has already sprung back about 0.001". That's why neck-sized-only brass works, and often pretty well. But eventually it stretches to fill the case. So if you don't have a way to measure your headspace, try neck-sizing-only, measuring after each firing and always chambering it with the headstamp orientation the same until it just starts to get snug. Check your records and see what the last unsnug measurement was. Go for sizing 0.002" below that number if you want to feed from a magazine, and 0.001" below that number for single-loading for benchrest.
A lot of BR shooters have switched to that -0.001" number it seems. Just relying on neck sizing doesn't set new records the way it once did. It seems the slight unevenness in brass wall thickness expands it to fit slightly off-center, and in some guns that shows up when you are shooting below 1/2 moa.
YMMV, so experiment to see what your gun actually likes.
I have found that using the Redding Competition shell holders, and having the tooling to make "short" shell holders, lets me seat the ram and shell holder solidly up against the bottom of the die. This has greatly reduced the variation in shoulder bump in a given batch of cases if they are all the same headstamp and fired the same number of times. Sometimes though, I get some cases that the shoulder just won't bump enough or just springs back. Then I anneal the whole batch and try again, usually works.
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Unclenick
My fired value of a fired case isn't giving me the chamber measurement in length.The case is getting wider by .001 not longer. Fired case is .003 shorter then the SAAMI Spec. 1.630
I can size to 1.6285 that gives me a .0015 case space. Is it better to have the case fit better length wise or width ? I only shoot benchrest, load one round at a time. My rounds are accurate, Always looking to improve.
My fired value of a fired case isn't giving me the chamber measurement in length.The case is getting wider by .001 not longer. Fired case is .003 shorter then the SAAMI Spec. 1.630
I can size to 1.6285 that gives me a .0015 case space. Is it better to have the case fit better length wise or width ? I only shoot benchrest, load one round at a time. My rounds are accurate, Always looking to improve.
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1100 TAC
I also use the Redding Competition Shellholders, with the RCBS standard F/L die & the Redding Competition seating die. My runout is .001 and better. The cases are Federal & ADI, both are on the thick side, working well for me.There are different viewers as far as neck sizing, until they chamber tight. I like the idea of full sizing to minimum case space, from base to bolt face at the minimum. My chamber seems to make the case wider instead of longer. When I size it lengthens the case to where I want it using the #10 shellholder.
When Forster customizes your die, I don't neck turn my brass. What happens when you change to a thinner or thicker brass.l ordered a Forster Go gage to check how accurate the RCBS Precision Mic. is .Today was my range day, using 168 gr Sierra a .009 jump grouped good also A-Max 168 liked a .015 jump. I could talk all day on reloading. Until tomorrow, Be Well , Chris
I also use the Redding Competition Shellholders, with the RCBS standard F/L die & the Redding Competition seating die. My runout is .001 and better. The cases are Federal & ADI, both are on the thick side, working well for me.There are different viewers as far as neck sizing, until they chamber tight. I like the idea of full sizing to minimum case space, from base to bolt face at the minimum. My chamber seems to make the case wider instead of longer. When I size it lengthens the case to where I want it using the #10 shellholder.
When Forster customizes your die, I don't neck turn my brass. What happens when you change to a thinner or thicker brass.l ordered a Forster Go gage to check how accurate the RCBS Precision Mic. is .Today was my range day, using 168 gr Sierra a .009 jump grouped good also A-Max 168 liked a .015 jump. I could talk all day on reloading. Until tomorrow, Be Well , Chris
I try different things and end up using the method that gives the most accuracy.
Some of my rifles don't seem to care as much as others. Some are fine with a FL sized case that would work in any semi auto as well, while others prefer a neck sized round with a little "crush" closing the bolt with OAL's beyond factory spec.
Only way I have found out is from trying everything, at least once.
jmorris
When you say crush, are we talking jamming your bullet ? If so I tried jams & jumps, found a jump also a jam that shot just as good. Will stick with the jump, don't want any pressure problems. I also try different recipes, makes reloading a challenge. How are you setting up your sizing die , and how do you measure the case ?
When you say crush, are we talking jamming your bullet ? If so I tried jams & jumps, found a jump also a jam that shot just as good. Will stick with the jump, don't want any pressure problems. I also try different recipes, makes reloading a challenge. How are you setting up your sizing die , and how do you measure the case ?