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Old January 20, 2013, 10:26 AM   #1
wever
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Headspace 7mm Rem mag

Does anyone KNOW the difference of how much a 7mm Rem Mag case increases in length between an unfired case and a once fired case? My Savage 111 increases .021 from unfired to once fired. I ordered/received a NO-GO gauge, removed the extractor and ejector from the bolt head, inserted the NO-GO gauge and the bolt does not close, so technically speaking, Savage could say that the headspace is ok.
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Old January 20, 2013, 10:50 AM   #2
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There is no single correct answer. Mag cases headspace on the belt. The SAAMI drawing gives the chamber a belt top end surface location of 0.220" to 0.227". In other words, 0.220" with a +0.007" tolerance. It gives the case belt a maximum of 0.220" with a -0.008" tolerance. Combine the two tolerances and you can have up to 0.015" difference in one gun and case brand combination to the next. And that's before you even measure shoulder height difference from one gun and case to the next and its tolerance (2.1162" -0.007" to the shoulder datum from the back end of the case head.

I am assuming in the above that by case length, you mean from the head to the shoulder datum line in the middle of the shoulder. If you mean the total length to the case mouth, that's another matter. Most of that length is increased and needs trimming due to squeeze of the sizing die returning the case to correct dimensions for general reloading (general as in to fit all chambers and not just to fit your specific chamber). You can minimize that and also shoulder datum position growth if you set the sizing die up to just bump the shoulder back a thousandth or two so the case then headspaces on the shoulder instead of on the belt thereafter.

So, what are your exact chamber dimensions and what are your exact brass dimensions before you shoot? What are you referring to as case length? If you mean the total length of the case and the amount you are having to trim off, then 0.021" is perfectly possible with the tolerances stacked against you. Also, you have a moderately high pressure round with capacity for a lot of powder. Start bumping shoulders back and stick to sub-maximum load levels and cases will grow a lot less, and brass will last a lot longer. So will your barrel. Save the full house loads for actual hunts. As that doesn't usually amount to more than a few sighters and game shots each season, they won't cut into bore life all that much in that quantity.
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Last edited by Unclenick; January 20, 2013 at 10:57 AM.
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Old January 20, 2013, 11:47 AM   #3
wever
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Your reply, I am assuming in the above that by case length, you mean from the head to the shoulder datum line in the middle of the shoulder.
You're dead on, I am using the Hornady Cartridge Headspace Gauge, measuring the shoulder datum.
Your question, what are your exact chamber dimensions and what are your exact brass dimensions before you shoot? Case pressure ring measurements correspond to the SAMMI drawing you included: R-P brass = unfired .505" fireformed .512"; W-W brass = unfired .507" to fireformed of .5125"; Hornady brass = unfired .508" to fireformed .512". So, my thinking is that the chamber dimensions are in accordance with the SAAMI drawing.

I did not want to prejudice any responses by including my over pressure signs in my original post, but I have tried NUMEROUS resized case lengths in .002" increments from fire formed -.002" to as much as .020" back. I have found that I cannot use even the minimum charge loads of H1000 and H4831 without pushed back or blown primers and/or ejector pin blown back and stuck into the bolt head.
I will include the bullets I've tried with those powders if you think that makes a difference.
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Old January 20, 2013, 12:28 PM   #4
243winxb
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Load data would help identify a problem. Light loads will let the primer back out. The head to datum shoulder set back from sizing, .020" seems excessive, when the bottom of the die is contacting the shell holder? Strange. Edit/add> From your other post-
Quote:
The difference between new brass and f/f brass in my Savage 7mm Rem mag is .022" using the Hornady headspace comparator.
Common, as factory is most times underside. To get a true reading of the head to datum measurment of a fired case, neck size only till bolt closes hard. Or back the FL die out .010" and size, see if sized case will chamber. If not move the die down more. Near maximum loads are needed to full expand the brass.

Last edited by 243winxb; January 20, 2013 at 12:56 PM.
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Old January 20, 2013, 01:39 PM   #5
wever
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Just a sample of load data: 160 gr Barnes TSX seated .050" from lands, H4831 52 gr (min. charge according to Barnes manual). R-P case resized .004" back from fire formed, WLRM primer. Results = ejector pin mark on case head along with significant "smiley face" (and horrible accuracy).
150 gr Swift Scirocco seated .030" from lands, H1000 68.4 gr (min. charge according to Swift manual), W-W case resized .002" back from fire formed, WLRM primer. Results = ejector mark on case head and stiff bolt.
243winxb, I'm hesitant to load any higher to fully expand the case as you recommend, along with the results above I've also had overpressure blowing the ejector pin into the bolt head with another min recipe.

So the question still remains, is .021" head to shoulder datum excessive causing my overpressure problems?
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Old January 20, 2013, 03:15 PM   #6
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Per the SAAMI drawing:

The belt on the case is between 0.212 and 0.220"
The belt in the chamber is between 0.220 and 0.227"
That would mean the the firing pin would push the cartridge forward between 0.000 and 0.015" for the cartridge to be stopped by the belt.

The shoulder of the case is between 2.1092 and 2.1162"
The shoulder on the chamber is between 2.1253 and 2.1353"
That means the firing pin would push the case forward between 0.0091" and 0.0261"

The shoulder should then grow between minus 0.0059 and plus 0.0261"
So with a random distribution of case and chamber dimension tolerances, the shoulder should grow 82% of the time.



But the brass and chamber distribution is not random within tolerances.
All my 7mmRM brass is between 0.213 and 0.0215" to the belt.
The chambers from factories are mostly 0.221" to the belt.
That means that the case moves forward between .006" and .008".
The factory chambers are ~~2.127 and the brass is ~~2.111.
The shoulder grows ~~.008 to .010" most of the time.
Then the case stretches .006" back to the breech face.

To get around this, when I ream a 7mmRM chamber for myself, I set the chamber belt space at 0.215".
My cases don't have to stretch.
Attached Images
File Type: jpg SAAMI dwg 7mmRM.JPG (213.5 KB, 10 views)
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Old January 20, 2013, 03:17 PM   #7
243winxb
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Quote:
So the question still remains, is .021" head to shoulder datum excessive causing my overpressure problems?
I would guess no. The difference from new factory brass to fire formed can be that much, head to datum. Wait and see what Unclenick & others have to say on the subject.
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Old January 20, 2013, 03:55 PM   #8
wever
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Thanks gentlemen, Clark, your quote "The shoulder should then grow between minus 0.0059 and plus 0.0261". So, if I understand correctly, .021 shoulder "growth" could be somewhat expected?
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Old January 20, 2013, 05:31 PM   #9
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Given the combinations possible from the SAAMI drawing, yes, that's not out of line (what I tried to say in my earlier post). However, all the pressure signs, especially sticky bolt lift, are unusual with minimum loads. Also confusing that you have a low pressure sign, like protruding primers. They usually happen because primers normally back out under their own pressure when they are fired, but are reseated when the case stretches to push the head back against the breech face. A protruding primer indicates too little pressure to set the head back again. But an ejector or extractor (depending on the design) mark on the case head says the head did go all the way back, even though such marks by themselves are not reliable pressure signs; some brass is just softer these days. Do you have both a mark and a protruding primer at the same time? That would make for a good mystery.

Do you have the bullet comparator inserts for your Hornady adapter head and their LNL Overall Length Gauge? I'm wondering how far off the lands you are seating? A bullet touching the lands can increase pressure.

Some photos might be useful.
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Old January 20, 2013, 06:05 PM   #10
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Quote:
wever
Thanks gentlemen, Clark, your quote "The shoulder should then grow between minus 0.0059 and plus 0.0261". So, if I understand correctly, .021 shoulder "growth" could be somewhat expected?
No, I expect the brass to be pushed .008 to .010" forward, the shoulder to push out, and then the case to stretch .006, so the shoulder will look like it got .014" longer on the first firing... but .021" is possible on the first firing, and ... on the second if the shoulder was pushed back too far in full length re sizing.
The brass takes a one time bad hit, but if the shoulder is only pushed back .001" when sized, the brass can still last a long time.
This has little to do with pressure, other than if the loads are too wimpy, the case will not stretch and the fired case will have the primer sticking out .006"
Some of the pressure signs you describe are ambiguous.
Quote:
ejector pin mark on case head along with significant "smiley face" (and horrible accuracy)
blowing the ejector pin into the bolt head with another min recipe.
ejector mark on case head and stiff bolt.
But stiff bolt lift is not good.

Here is a pic of a 7mmRM case head I fired that the primer fell out. This had .017" of extractor groove growth and the primer fell out.
This is very bad. Don't do that.
If you see any extractor groove growth anywhere around the case with dial calipers, the powder charge is too high.
This is not in any book, just what I do.. but I like to see extractor groove measurements before and after firing. If you are certain that there is growth, the charge needs to be reduced by at least 4% for a useful load.
CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.
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Old January 20, 2013, 06:26 PM   #11
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Good advice. It didn't occur to me to ask if his protruding primers were actually loose primers. If so, there's no conflict between that sign and the sticky bolt lift sign.
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Old January 20, 2013, 10:18 PM   #12
243winxb
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Brass flows back into the ejector hole. Normal load right. Working up to Hot load on left, with expanded primer pocket. Primer fell out. Caused by high pressure. The primer pocket may open with 1 loading that is very hot. Or it may take several reloads at maximum to slowly expand the web area of the primer pockets. Common to Rem, Sako, Savage ejectors. If the primer flows back into the firing pin hole, around the pin, pressure may be to high or the hole is oversize.

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Old January 20, 2013, 10:25 PM   #13
243winxb
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If you push the should back .021" each sizing, the stretching will cause a case seperation. If you know all this, sorry. I dont like the hard bolt lift, very bad sign for a starting load. Has me confused.
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Old January 21, 2013, 09:24 AM   #14
William T. Watts
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No mention of factory ammunition being fired thru the rifle first, why?? Are you using Barnes OAL of 3.240, if your not your asking for trouble because of the all copper construction? William

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Old January 21, 2013, 11:44 AM   #15
243winxb
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Shoot some factory ammunition, as said above. Great idea. One i forget at times.
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Old January 21, 2013, 03:52 PM   #16
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I wanna chime in here, Wever, I had the same phenomenum in my 7mm rem mag, but what I did was quit trying to shoot those Swift Sirropcco's. I' can't comment on the Barnes but here's what I found in my testing, If a bullet needs that much jump, then there will be potential pressure problems, I also had Hard Bolt Lift with the H4831 while testing 150 grain Swift Sirrocco's, but I tried every powder I could find to make that bullet work in my rifle, and when it came down to it, the rifle wasn't haveing it.
Fortunetly there is friendlier bullet's with every bit the ilk of the Swift bullet like Accubond's and they don't need a gigantic jump as the Swift's do.
And Post # 12 .243winxb, the cratered primer pics look like a problem my 111 has, and I wonder if the firing pin hole is too large.
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Old January 21, 2013, 06:12 PM   #17
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243winxb, your right hand case head in the picture shows brass extruding back into the ejector hole. That's caused by excessive pressure. It is not a normal safe load. Cartridge brass starts extruding at about 65,000 CUP; about the same as 80,000 PSI.
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Old January 21, 2013, 08:29 PM   #18
243winxb
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Bart
Quote:
243winxb, your right hand case head in the picture shows brass extruding back into the ejector hole.
This can be seen on factory loaded/fired ammo. Soft batch of brass would make the difference.
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Old January 21, 2013, 08:43 PM   #19
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I'm surprised that no one (that I can see) has mentioned resizing to fit the shoulder -- even in
a (bottleneck) Mag/belted case. That is how I control case stretch after 1st firing.
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Old January 21, 2013, 08:57 PM   #20
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My .02

I've loaded the 7mm Remington for 40 years and never had a case, primer, or pressure problem until the case was discarded after about 5-7 maximum loads. Per Ken Waters, as soon as I saw primer flattening, or more than .005 increase in head measurement, I would back down .5 grain. The primer pocket "prolapse" was the usual culprit. I was taught to full size the case when new; then, place a nickel between the shell holder and the die. The belted cases head space on the belt, so any additional working of the brass accelerated insipient head separation.
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Old January 24, 2013, 08:54 PM   #21
wever
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Thanks Gentlemen!!!

Your responses were very, very educational! Instead of a headspace problem with my Savage, what I have/had is a mixed bag of apples and oranges and you guys sorted them out.
1)The shoulder datum increase of .021" from new unfired to fire formed , my original concern, is not a problem at all, but led me on a witch hunt for more perceived problems; The shoulder should then grow between minus 0.0059 and plus 0.0261"
2)My "Pushed back primer" results; This has little to do with pressure, other than if the loads are too wimpy, the case will not stretch and the fired case will have the primer sticking out .006", and [I]Good advice. It didn't occur to me to ask if his protruding primers were actually loose primers. If so, there's no conflict between that sign and the sticky bolt lift sign./I]
3) "Stiff Bolt" ; I also had Hard Bolt Lift with the H4831 while testing 150 grain Swift Sirrocco's. An anomaly perhaps?!
4)" Smiley Face" and/or ejector pin hole mark on case head; some brass is just softer these days

My plan of attack: ensure to resize only .001-.002" from fire formed, different bullet/powder combination and Per Ken Waters, as soon as I saw primer flattening, or more than .005 increase in head measurement, I would back down .5 grain.
I assure you I appreciate all of the info and responses, I should have asked a long time ago here, I might have trusted my Savage in Wyoming last elk season, THANKS AGAIN!

Last edited by wever; January 24, 2013 at 09:00 PM.
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Old January 25, 2013, 03:55 PM   #22
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Wever, just a thought: do you measure each of your cartridge OAL after seating or do you seat one, and having determined that is 0.05" from the lands, just continue to seat the rest and not measure?

Barnes may have improved, I don't know because I don't reload Barnes, but when I did years ago in my .270 Win, I found significant variation in the final measurement and I thought it is explained by a changing bullet ogive position even in the same box of a given lot number. I chalked it up to a possible idiosyncrasy seen with pure copper bullets. That also explained to me why Barnes, at that time, suggested you should not seat the bullet any closer than 0.05," but again, this was just me brainstorming.

Thus if you didn't measure each one, maybe some were seated right out to the lands and this increased your pressure. The same may be true of the Swift Sirrocco bullets since you are starting there at 0.03".

I routinely measure every seated round. Even if the bullet is not the problem, differences in neck thickness can change the seated depth. If your dummy round is made with an unfired case, and you reload a round into a case fired multiple times that has been routinely trimmed and chamfered with a variation in enthusiasm from time to time, the internal diameter of the neck can be thicker and your seated round will be longer.

Just a thought.
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Old January 26, 2013, 07:55 AM   #23
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The mechanical knowledge and detail analysis you folks post is remarkable. Yet I wanted to respond because years ago I loaded for the 7mm Rem Mag and did not have such issues with difficult extraction. Seems I recall that even though the 7mm Rem Mag has a belted case it still headspaces off the shoulder, not the belt. Using once fired cases I always neck sized after fire forming which should eliminate any headspace issue for that particular case in that particular rifle. That said, if I continued to experience pressure issues with well established loads I would be concerned about mechanical issues with the action, locking lugs engagement, etc. regarding setback and/or undersize bore, heavily fouled barrel, etc. If the loads are good something is wrong with the gun and it needs inspection by a competent gunsmith. Clearly from the primer craters and more this gun has experienced high pressures and those may induce some of the mechanical issues with the action that may not have existed before the excessive pressure rounds had been fired in the gun.

My two cents,

TB
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Old January 26, 2013, 01:54 PM   #24
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243winxb, I agree that a soft batch of brass would make the difference. But bass that soft is typically too soft for cartridge brass intended for commercial rounds that'll be reloaded. I'm surprised the factory let that stuff out the door.

Other causes with factory ammo case heads extruding back into bolt face cutouts are too tight a bore, extremely hot powder temperatures and just a plain bad lot of ammo.
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