7mm rsaum questions

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shooter mcreid
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7mm rsaum questions

#1 Postby shooter mcreid » Thu Mar 13, 2014 8:14 pm

Hey, I'm getting a 7mm rsaum built at the moment and have a few questions.
Firstly I will be necking 300 saum Norma brass down and was wondering what neck wall thicknesses are common before and after the operation? What thicknesses are people neck turning the formed brass down to? What size neck chamber have people got to match their specific wall thickness?
I already have the neck turning gear for 30 cal and was wondering if I could turn it before the necking down process, I guess I would have to make sure I go all the way down and a tinny bit into the shoulder. I have always had the best neck turning results when performing the operation first before any hardening processes.
Where is the best place to get a neck bushing die? I found that Forster don't make them, redding are out of stock and rarely make them, rcbs have a gold series with a 4 month turn around but I'm not sure how good these are?
I would really appreciate any constructive information,
Thanks
Josh

wilddog
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7 saum

#2 Postby wilddog » Thu Mar 13, 2014 11:34 pm

you have to turn down to suit your reamer you use ,give yourself about 3 thou clearance , all I use are lee collet does , you can ream out a 7-08 collet die with the same reamer ,I have 3 saum AI's and 2 normal saum's , after talking with Marty and Dave MC , I have tried to make most of my Chambers no turn ,saves you a lot of time pr.eping brass , finding the brass is the biggest problem.

DaveMc
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#3 Postby DaveMc » Fri Mar 14, 2014 6:57 am

Hi Josh,
I have a 0.316 neck chamber and turn to a 0.312 loaded round (would be happy with 3 thou clearance 0.313 loaded round as well).
As Mark said if I did it again I would go with a no turn neck and Lee collet dies. Marks rifles are as accurate at 1000 yards as any out there and it is a simple and effective formula. I am guessing a 0.318 to 0.320 neck for a no turn but would need someone to confirm that as I didn't measure the sized unturned Norma brass.

You can turn the brass before sizing when sizing down but not up (and you don't need to go as aggressively into the shoulder). There is some conjecture as to whether this creates slightly uneven wall thicknesses but from what I have seen it is generally acceptable - probably worth doing a couple and measuring carefully. (Or someone could loan you a 7mm mandrel??)

BATattack
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#4 Postby BATattack » Fri Mar 14, 2014 8:14 am

I'm running a 317 neck on my reamer and found that I have to turn my cases to 313 for 4 thou clearance. Any less than that and I wasnt able to put a bullet back into a fired case neck without slight resistance.

I had a 320 no turn chamber in my first barrel but my new ones seem to be more accurate. It may just be they are better barrels or it may be because of the tighter neck. . . . I don't know.

bruce moulds
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#5 Postby bruce moulds » Fri Mar 14, 2014 8:27 am

there was some talk earlier on that the thicker the brass, the quicker it work hardens.
not sure if this is true, but if it is, turning necks to 0.012 - 0.013 makes sense.
only problem then is if you drop one.
keep safe,
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880
http://youtu.be/YRaRCCZjdTM

shooter mcreid
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#6 Postby shooter mcreid » Fri Mar 14, 2014 10:03 am

thanks very much everyone

Rebel105
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#7 Postby Rebel105 » Sat Mar 15, 2014 11:26 am

Josh,
I've just done the same thing, all of of the above posts are spot on. I'm still learning from Adam.
i have a .318 chamber, tried no turn necks with 300 Norma brass, it didn't work for me as .002"wasn't enough neck clearance from a .316 loaded round.
I'm neck turning for .314 loaded round which gives me 1.5-2 thou neck tension. You need your reamer specs to work it all out.
have fun
Geoff

shooter mcreid
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Location: Ipswich

#8 Postby shooter mcreid » Sun Mar 16, 2014 7:15 am

Thanks Geoff, my smith doesn't have the reamer but was looking into borrowing one from some where. I was putting a lot of thought into getting them for my self, then I could choose exactly what I wanted. I would probably get them through him as he will exactly what to get. On a side note, is there one reamer that can do the job if you know exactly what you want or is a few required? I had a quick look and there seems to be roughing reamers, finishing reamers, free bore and more.
Thanks
Josh

shooter mcreid
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Location: Ipswich

#9 Postby shooter mcreid » Sun Mar 16, 2014 7:49 am

What problems arise when a total clearance of less than 3 thou is used? Everyone agrees that 4 is a good number but why?
Thanks
Josh

Rebel105
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#10 Postby Rebel105 » Sun Mar 16, 2014 7:08 pm

I'm still on the learning curve with BatAttack helping me heaps. I knew i had a problem as a fired case neck was still .316 & a projectile wouldn't fit in it easily. This meant the case neck wasn't expanding enough due carbon build up in the neck area, i was getting vertical,flyers & erratic speeds. The neck was grabbing the projectile. This my theory anyway. I have a Forster FL die with a ground .313 neck.
Testing today, all good after neck turning cases, now i think i can start tuning loads.
4 thou clearance is working for me now. These sizes suit my chamber, yours may be different depending on your reamer.
Geoff

BATattack
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#11 Postby BATattack » Sun Mar 16, 2014 8:41 pm

Basically the rule of thumb is that you should always be able to put a bullet back into a fired case without resistance. This shows that there is enough clearance to allow for the expansion of the neck upon firing and allow a clean release of the bullet.

If there isn't enough clearance it can create pressure spikes and all sorts of unusual accuracy problems.

May be in a bench rest environment and if you pay particular attention to the cleanliness of the neck area of your chamber and the inside and outside of your case necks you could get away with less clearance it could work.

For me 4 thou seemed to be the minimum clearance I could use. I wanted to run with 3 tho but it just wasn't enough after firing a few cases.

DaveMc
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#12 Postby DaveMc » Mon Mar 17, 2014 6:59 am

There is a fine line of distinction here. Under pressure the case (and neck) is fully expanded but then springs back after firing. there is a window where the bullet is not impinged at all during firing but also cannot be pushed back into a loaded case (in fact this is true at 1 thou clearance until carbon build up or brass movement)

The tighter the clearance the closer you have to monitor the carbon buildup and creeping brass into the base of the neck which will create issues.

The main point is there seems no harm to accuracy in running 4+ thou clearance. The issues are secondary - such as resizing brass a little more (so necks become stiffer quicker) and it is harder to maintain low runout - your dies need to be setup correctly to squeeze in further without bending the neck out of alignment.

Rebel105
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#13 Postby Rebel105 » Mon Mar 17, 2014 8:55 am

Dave,
I was getting 4 maybe 5 accurate shots then flyers from a clean barrel/chamber, this is what made me start to think something was wrong. Also, looking at Magnetospeed, speed readings, ES & SD were all over the place.
After talking to Adam, the penny dropped, and after neck turning the shot grouping has settled & has allowed me to fire over 15 rounds in group testing with good chronograph readings. I have to agree with Adam that 2 thou wasn't enough neck clearance. Another thing is the rifle is more settled and not jumping or maybe I'm starting to get the hang of it. I dunno?
Geoff

bruce moulds
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#14 Postby bruce moulds » Mon Mar 17, 2014 8:55 am

adam and dave,
it could be argued that that fine line is when a correctly annealed case will take a projectile after firing, but one that needs annealing won't.
keep safe,
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

bruce moulds
Posts: 2087
Joined: Sun Jun 19, 2005 4:07 pm

#15 Postby bruce moulds » Mon Mar 17, 2014 9:01 am

Geoff,
another thing that can cause the 4 - 5 shot thing then a change in poi
is that the barrel has yet to settle down.
some can take quite a few shots.
keep safe,
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM


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