High or Low datum when sizing
- Thread starter ffgats
- Start date
- Location
- Western Manitoba
Perhaps you are encountering varying springback in your re-sized cases?? If your sizer is not moving; if your measuring tools and abilities are the same? Idea, I think, is that you want the same chambering - slick, slight drag at lock-up, whatever - but all the same. You are apparently not getting the "sameness". So, if nothing flexing or moving, maybe try to just hold the brass at fully sized position for 30 seconds or so - seems to be a way to offset some amount of "spring back". Or, anneal the brass more often??? I am just guessing - do not recall ever experiencing what you are describing - my thoughts wandered off toward a crack in the press body, worn pins and so on, that could explain why the sizer die and the shell holder would not end up in exactly same relationship each time. If the mechanicals are known to be good, then would look to the brass for the issue, but maybe first about the capacity to measure - should want to check measure each one produced - should have been able to pick out the "long ones"?
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- Location
- Western Manitoba
Thinking about it some more - whatever you are doing is leaving some "too long" - so change - do a "longer" bump, "on average", so your longest one still goes easy?
Some guys do the sizing thing so well. Read up on the Houston Warehouse experiments - the guy Virgil - could prep his case necks to average .0007" clearance for his loaded rounds in his rifle chamber necks. Fired and reloaded his cartridges, WITHOUT RESIZING THEM. .025" 5 shot groups at 100 yards. I would have a lot of trouble to measure that group size, let alone the neck thickness. And those experiments done in 1980's. So getting to be 40 years ago...
FYI - experienced some hiccups some years ago - so, sounds boring, but every one of my re-sized brass gets chambered in my rifle before getting filled. And from my Dad, way back in the day, every loaded round carried - factory or hand load - when heading out on a hunt, has been chambered once already. Never want to discover an issue with a cartridge with game on hand!!!! I never did do the target shooting competition thing - so do not see it as "serious" if a round doesn't chamber, but others no doubt will see that differently.
Some guys do the sizing thing so well. Read up on the Houston Warehouse experiments - the guy Virgil - could prep his case necks to average .0007" clearance for his loaded rounds in his rifle chamber necks. Fired and reloaded his cartridges, WITHOUT RESIZING THEM. .025" 5 shot groups at 100 yards. I would have a lot of trouble to measure that group size, let alone the neck thickness. And those experiments done in 1980's. So getting to be 40 years ago...
FYI - experienced some hiccups some years ago - so, sounds boring, but every one of my re-sized brass gets chambered in my rifle before getting filled. And from my Dad, way back in the day, every loaded round carried - factory or hand load - when heading out on a hunt, has been chambered once already. Never want to discover an issue with a cartridge with game on hand!!!! I never did do the target shooting competition thing - so do not see it as "serious" if a round doesn't chamber, but others no doubt will see that differently.
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I'm sorry, but the devil is in the details, and your post is seriously lacking in the important details.
I'll take a bit of poetic justice here, and assume you are shooting a 308 Winchester. Next I assume that your dies are LEE and that when you screwed the die down to contact the shellholder, plus a 1/4 turn the shoulder was set back a bit too much. Because your brother in law borrowed your Redding Competition shell holder set you decided to just back off the die. The issue with just backing off the die is that it introduces a variable. Any case that requires a bit more pressure to size will be longer in the base to datum, which ideally should allow for app 0.002" to no more than 0.005" of clearance in the chamber. I'd suggest you call your BIL and get your set of competition shell holders back.
I apologise for even replying, just my WAG on your issue.
I'm no Tubbs, read his info on shoulder setback and Redding has a good write up on their Competition shell holder set.
https://www.youtube.com/watch?v=3hGvUzj7Zuk&ab_channel=TeamArea419
Hi ffgats,
I typically see 1 to 3 thou difference in base to datum (headspace) measure in fire-formed brass all of the same make and lot. But I am doing alot of ladder tests and seating depth tests, on hot days and cold days, so I am guessing the brass is behaving differently across a range of forces being applied to it.
I use the RCBS Precision Mic, or the Whidden Case Gauge (I have several depending on cartridge) to measure base to datum on the shoulder. These gauges have the zero set for SAAMI spec. The gauge reading lets you know if your chamber (as revealed by your fire-formed case) is one or two or three thou over or under SAAMI zero headspace. I shoot Sako and Tikka rifles in several calibers and interestingly they all measure fire-formed cases 0.000 to -0.003 on the gauges, with most being -0.001 to -0.002 indicating these Finnish chambers are slightly tight for headspace compared to the SAAMI spec.
I don't need to calculate an average because using these gauges I know I just need to not exceed 0.000, and usually default to resizing to -0.002....if I need to FL resize at all. I neck size most of the time and never seem to have a problem.
When setting my full length resizing dies, I use the fireformed length of the longest cases (usually -0.001) as my real zero for the particular rifle, and size 1 to 2 thou smaller. But since I use the RCBS and Whidden gauges I know where the actual limit is, so I have never had and an issue of hard to chamber, (except for when I forgot to trim some brass for length, which was not a headspace issue).
With the Hornady headspace gauges (or other brands) and calipers, since its a relative measure and not referenced to the actual SAAMI spec measure, I can understand your issue with the variance in fire-formed cases. I guess you will have to take the shortest measure and consider that to be your chamber's interim zero. Maybe size the longer cases down to the shortest fireformed length. If there are any difficult bolt closures or openings, then you know you need to reduce that shortest length by 1 or 2 thou.
On my FL rezing dies I use a fine tipped sharpie marker to make tick marks in 1mm increments on the die's locking ring, and mark an index line on the side of the die. This method allows me to approach the desired bump and not overshoot, and once marked I have my settings.
Hope this helps.
Edit: Whidden makes some CIP spec gauges as well, e.g. for 6.5x47L. I don't know if RCBS makes CIP gauges.
I typically see 1 to 3 thou difference in base to datum (headspace) measure in fire-formed brass all of the same make and lot. But I am doing alot of ladder tests and seating depth tests, on hot days and cold days, so I am guessing the brass is behaving differently across a range of forces being applied to it.
I use the RCBS Precision Mic, or the Whidden Case Gauge (I have several depending on cartridge) to measure base to datum on the shoulder. These gauges have the zero set for SAAMI spec. The gauge reading lets you know if your chamber (as revealed by your fire-formed case) is one or two or three thou over or under SAAMI zero headspace. I shoot Sako and Tikka rifles in several calibers and interestingly they all measure fire-formed cases 0.000 to -0.003 on the gauges, with most being -0.001 to -0.002 indicating these Finnish chambers are slightly tight for headspace compared to the SAAMI spec.
I don't need to calculate an average because using these gauges I know I just need to not exceed 0.000, and usually default to resizing to -0.002....if I need to FL resize at all. I neck size most of the time and never seem to have a problem.
When setting my full length resizing dies, I use the fireformed length of the longest cases (usually -0.001) as my real zero for the particular rifle, and size 1 to 2 thou smaller. But since I use the RCBS and Whidden gauges I know where the actual limit is, so I have never had and an issue of hard to chamber, (except for when I forgot to trim some brass for length, which was not a headspace issue).
With the Hornady headspace gauges (or other brands) and calipers, since its a relative measure and not referenced to the actual SAAMI spec measure, I can understand your issue with the variance in fire-formed cases. I guess you will have to take the shortest measure and consider that to be your chamber's interim zero. Maybe size the longer cases down to the shortest fireformed length. If there are any difficult bolt closures or openings, then you know you need to reduce that shortest length by 1 or 2 thou.
On my FL rezing dies I use a fine tipped sharpie marker to make tick marks in 1mm increments on the die's locking ring, and mark an index line on the side of the die. This method allows me to approach the desired bump and not overshoot, and once marked I have my settings.
Hope this helps.
Edit: Whidden makes some CIP spec gauges as well, e.g. for 6.5x47L. I don't know if RCBS makes CIP gauges.
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Btw I’m using Forster FL sizing die honing done by Forster and my 20 yr old Dillon 550, Hornady Headspace gauge and Sinclair Shoulder Bump gauge. My guess it could be the gauges and most likely the 550 shell plate by design, although my ammo/ load is printing right now at less than .5 moa ( N150 43grs 175 SMK, N140 44Grs 155 ELD 308 Win) Looking for excuse to buy a single stage press just for resizing lol, I guess it’s the beauty of reloading where you try to pursue perfection, although it’s almost impossible given all the variables. My fired cases measures 1.658” - 1.656” datum to base snd 1.575”-1.572” shoulder to base . Like mentioned on my original post I took the average readings and go from there, or I can try using the highest number. Thanks
Out of curiosity, which bushing are you using in your Hornady comparator? 0.400" or 0.375"?
Not that it'll make much difference, just different numbers.
If there's any slop in your press, that might be a source of problems with sizing too. Bottleneck rifle cases are more critical of the press and die relationship than straight-wall cases.
The advice you've gotten so far is pretty good, in my experience freshly annealed brass will size 0.002-0.003" shorter to the shoulder datum than brass that has been hardened by working it through several firing/loading cycles without annealing it.
If the amount of bump in your die setup is less than 0.002-0.003" (bolt-action rifle), some cases will chamber hard as a result of the shoulder springing back more than others.
I'd suggest doing as Biologist said above, put witness marks on the die locking ring and the die thread with a fine tipped marker, then turn the die down a little bit at a time. It won't take much rotation to give you the reduction you're looking for.
Also this from Erik Cortina on setting up your sizing die.
htt
ps://youtu.be/htvk1UYOXm8
I experimented with his method, it worked quite well for me, provided that the brass was equally soft from piece to piece. He makes mention of that late in the video, along the lines of "do EVERYTHING the same every time".
Whenever I start loading for a new rifle, I make a point of finding out the longest head-to-shoulder datum measurement that will chamber in the rifle. Once I know what it is, I write it down and the note goes into the box with that particular die.
My 6.5 CM, for example, will accept anything up to 1.564" from head to shoulder datum. At that measurement, it's tight to close. So, I set my die to produce nothing longer than 1.562", most are 1.561". That number varies slightly depending on how hard the brass is.
I check the final shoulder position on 3 or 4 pieces of brass out of 25 at random as I'm sizing them, QC to be sure nothing has changed.
Like somebody else said earlier, every hunting load gets chambered and ejected before it goes in my pocket to hunt with. I really don't want to discover that the first (or even worse, the second) round won't chamber.
My target loads don't need that degree of testing. I haven't had any (yet) that won't chamber, though some have been snug.
Not that it'll make much difference, just different numbers.
If there's any slop in your press, that might be a source of problems with sizing too. Bottleneck rifle cases are more critical of the press and die relationship than straight-wall cases.
The advice you've gotten so far is pretty good, in my experience freshly annealed brass will size 0.002-0.003" shorter to the shoulder datum than brass that has been hardened by working it through several firing/loading cycles without annealing it.
If the amount of bump in your die setup is less than 0.002-0.003" (bolt-action rifle), some cases will chamber hard as a result of the shoulder springing back more than others.
I'd suggest doing as Biologist said above, put witness marks on the die locking ring and the die thread with a fine tipped marker, then turn the die down a little bit at a time. It won't take much rotation to give you the reduction you're looking for.
Also this from Erik Cortina on setting up your sizing die.
htt
ps://youtu.be/htvk1UYOXm8
I experimented with his method, it worked quite well for me, provided that the brass was equally soft from piece to piece. He makes mention of that late in the video, along the lines of "do EVERYTHING the same every time".
Whenever I start loading for a new rifle, I make a point of finding out the longest head-to-shoulder datum measurement that will chamber in the rifle. Once I know what it is, I write it down and the note goes into the box with that particular die.
My 6.5 CM, for example, will accept anything up to 1.564" from head to shoulder datum. At that measurement, it's tight to close. So, I set my die to produce nothing longer than 1.562", most are 1.561". That number varies slightly depending on how hard the brass is.
I check the final shoulder position on 3 or 4 pieces of brass out of 25 at random as I'm sizing them, QC to be sure nothing has changed.
Like somebody else said earlier, every hunting load gets chambered and ejected before it goes in my pocket to hunt with. I really don't want to discover that the first (or even worse, the second) round won't chamber.
My target loads don't need that degree of testing. I haven't had any (yet) that won't chamber, though some have been snug.
From the Hornady instructions...
Most handloaders prefer to carefully “zero”
the caliper’s indicator on the longest (fire-formed) case. This allows them to gauge the headspace variations from this fire-formed (maximum) case dimension.
Many experienced handloaders prefer to set the case’s
shoulder back .001" to .002" from the fire-formed case
dimension to achieve a close fit with the chamber. This
reduces case stretching to a minimum, reduces work-
hardening, extends case life, and improves accuracy.
Remember: Different lots of fire-formed brass may measure
differently due to alloy and temper variations in the brass.
Also, work-hardening, which results re-sizing and firing, will
have an effect. The type and amount of lubrication applied
to the cases can have an effect on the re-sized dimensions. A variation in your lube technique can and will be detected by the gauge. Always adjust re-sizing dies in small increments to achieve the desired results.
I think a single stage for sizing would be a good idea, not that a Dillon 550 isn't a good press, it is, I have 2. I bought a single stage adapter for my 550, lets me use standard shell holders. The 550 does not bottom against the shell plate, you lose a bit of precision to gain production. My buddy loads exclusively on his Dillons, and his groups are always good. A bit of variation may not be a problem for accuracy. what you don't want is ammo so tight that you wipe the lube off the lugs as you chamber a round. You can gall the lugs fairly quickly. I had some tight ammo in my 8x57 and within 10 rounds I could feel the problem, I quit shooting and reworked the ammo. To much clearance and incipient head separation is guaranteed, been there as well.
Single stage Adaptor?, never heard of it, ... I leaning towards a Rock Chucker, but don’t want to buy the kit, just the press and Redding Comp Shell holder, my 233 Bolt Rifle can also benefit from the press. Thanks again for all your feedback gents
