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Neck Clearance

 
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  #15  
Old 12-16-2002, 06:53 PM
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Join Date: Dec 2002
Location: Northwest MN
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Re: Neck Clearance

Thank you, DB--that is some very, very helpful info. In my case [pun probably intended!], it will be particularly helpful, because the dimensions are so unusual to begin with, and I'm cutting tolerances fairly tight. Anybody ever work with cases that sport an "abnormally" long neck? Example: My case is 6mm PPC modified; it will be about 1.503" from head to case mouth, 1.0745" from head to beginning of shoulder, and 1.1564" from head to bottom of shoulder, leaving a neck of .3486", if I leave it that way. As it stands now, the neck on a normal case would be .272" LONG--6PPC style. I like the thought of that long-neck, though.... Could go for one right now, actually <glances at the fridge> [img]images/icons/grin.gif[/img]

Dave
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  #16  
Old 12-26-2002, 07:51 PM
MAX MAX is offline
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Re: Neck Clearance

Other than McPherson's hemispherical shoulder(SMC2 is the case name or company name), his position was that the 45* shoulder was the next most efficient shape for ignition efficiency. I don't recall what support he put forth in the article for that. As I recall it had to do with the shoulder angle focusing the primer shock pattern at a point below the bullet base.

He has patented the hemispherical shape BTW, and it may be just as well for he reports difficulty in forming cases.
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  #17  
Old 12-26-2002, 10:52 PM
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Join Date: Mar 2002
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Re: Neck Clearance

Cybra,

Since when does a "Mouse-gun" shoot 95 grain bullets? Where do you find them that big? [img]images/icons/confused.gif[/img] I've a true "Custom Mouse gun" Before I had it built, I measured a few hundred of my loaded rounds, then had the neck of my new barrel cut with .0015 *Per Side* clearance for over 75% of those I measured. A few with only .001 clearance still remain, I culled the rest.

The new rifle is .013 under SAMMI, but I didn't want to have to get into neck turning. It might be nice to turn to get the necks the same thickness all around, but I don't think you need a chamber so tight that it forces you to turn necks. Just have it cut tight enough to fit the loads you make.
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  #18  
Old 12-27-2002, 05:54 PM
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Join Date: Dec 2002
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Posts: 76
Re: Neck Clearance

Max, thank you very much for putting that in! I have read such in various places. I should find out if I can get in touch with McPherson--at the very least, a letter might really help to enlighten me. Of course, I have heard pros and cons, as with all things, but I'm one of those guys that loves to deviate just a pinch. Ken, over at K&M seemed to think that McPherson's case designs would be out soon, Norma make I think he mentioned. But, the case capacity is more than I'd need, and I suspect to shorten THOSE cases, it'd be...well, it'd be a b*tch, and I'm tied of encountering those!!

Tim! Ah, that was funny, huh? I stated the item as a "mouse gun" for the humor of those that post here consistantly--most of these gentlemen, as the Forum's name implies, shoot some rather big stuff. I do, too!--so when I got the nerve to post a topic about a friggin` 6PPC, I was sure I'd get some "what the..%$#& is this??!" [img]images/icons/grin.gif[/img] <chuckles> Yah, a 95gr. VLD in a mousegun...uranium's get'n cheap these days; check out Saddamsstash.com to buy yours today! [img]images/icons/tongue.gif[/img]

Ok, seriously, now...<still chuckling>. Well, I don't mind turning the necks, really. Actually, given my current environment, I don't have anything fun to do, so... And, maximum case life was something I wanted to pursue, although to be honest with you, at least 95% of the .220 Lapua brass I have microed thus far has held wall thickness in the neck region to easily under a thou. I bought 1100 pieces at once, and am d*mned glad I did. I am planning on running half a thou per side, but I'm a picky cleaner, so I should do all right. Really, brass swelling at the neck/shoulder junction may be my biggest concern, but I have a three mandrel set that I use for sizing. The last one micros out at .24325", approx., and I let the brass "spring" back and grab the bullet. Works great, and I'm getting virtually zero runout {I seat bullet-to-lands, so I'm thinking blow-by shouldn't be an issue.} I have read in various places that if the brass's yield strength isn't pushed too far {a lot of folks think this is somewhere in the neighborhood of 55-60000 psi, depending on the brass, some higher, so lower, obviously}, the spring will stay present for a long time. I'm excited to test it, really!! [img]images/icons/cool.gif[/img]

Hope everyone had a good holiday; may the bullets whistle freely in the New Year.

Dave
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