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Neck expander mandrel (Read 9559 times)

Red Cent Senior Forum Member Offline Posts: 316 Location: Benton, KY byway of WV, VA, NC Joined: Dec 25^th, 2016	Neck expander mandrel Nov 2^nd, 2017 at 5:06pm	Print Post
	The new rifle will have a groove diameter of .376 and I will start with a .377 bullet. I would like to achieve the old "slip fit" in seating the bullet. Taken at face value, that would mean I can push a lead bullet in the case with my fingers. In my research, I find that a couple of thousands of neck tension is good. How in the he..... heck do you measure .002" of neck tension? I plan not to resize anything other than "kissing" the mouth to keep the bullet in place.

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calledflyer Frequent Elocutionist Offline Posts: 3974 Joined: Mar 9^th, 2015	Re: Neck expander mandrel Reply #1 - Nov 2^nd, 2017 at 5:22pm	Print Post
	I've wonder how they measured that for about fifty years. I'm waiting for the answers with you.....................


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Cat_Whisperer Frequent Elocutionist Offline No 1, 9.3x74R Posts: 3987 Location: Mountains of Virginia Joined: Apr 17^th, 2004	Re: Neck expander mandrel Reply #2 - Nov 2^nd, 2017 at 6:02pm	Print Post
	Red Cent wrote on Nov 2^nd, 2017 at 5:06pm: ... In my research, I find that a couple of thousands of neck tension is good. How in the he..... heck do you measure .002" of neck tension? ... Easy. Measure the OD of the bullet and the ID of the case. A better term perhaps would be 0.002" interference fit. That is to say the bullet is 0.002" larger than the inside of the neck.

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craigd Frequent Elocutionist Offline Posts: 2058 Location: midwest Joined: Feb 22^nd, 2009	Re: Neck expander mandrel Reply #3 - Nov 2^nd, 2017 at 6:30pm	Print Post
	You could just assume .001" spring back from where ever the expander moves the brass. The slip fit that you want might be subjective, but no big deal to tweak it. Maybe, try unsized fired brass for your chamber, and see what happens.


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LRF Oldtimer Offline Posts: 714 Location: MN Joined: May 8^th, 2010	Re: Neck expander mandrel Reply #4 - Nov 2^nd, 2017 at 6:51pm	Print Post
	Go to (You need to *Login* or *Register* to view media files and links) and buy gage pins that range a few thousands on each side of the desired ID diameter you want which should be about .001 to .002" less then the bullet diameter. Using them measure the case ID. Then make a neck expander or sizer to achieve the correct fit. It takes a little work but very achievable. BTW all these tools can be bought.


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Red Cent Senior Forum Member Offline Posts: 316 Location: Benton, KY byway of WV, VA, NC Joined: Dec 25^th, 2016	Re: Neck expander mandrel Reply #5 - Nov 2^nd, 2017 at 7:58pm	Print Post
	I bought a .377 neck expander for the C Sharps and I bought a .379 neck expander to use in the Marlin. I shoot a .380 bullet in the Marlin. As I do not resize and do not plan to resize the C Sharps brass, I am aware of some .001 or so of expansion of the brass when fired and I am aware of some spring back. If one runs a certain size mandrel in the case, won't you get springback? I might be too picky but I want to understand the method so that I can realize a constant tension on the bullet. I do not want to get into turning case necks yet either.

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craigd Frequent Elocutionist Offline Posts: 2058 Location: midwest Joined: Feb 22^nd, 2009	Re: Neck expander mandrel Reply #6 - Nov 2^nd, 2017 at 9:07pm	Print Post
	When I mentioned spring back, I was thinking whatever size you can accurately measure your expander mandrel at, the opening will be .001" smaller. By no means is that rule, but it works for me in a general way. Yes, I think expanded brass springs back. That's why a neck turning mandrel is a tad bit smaller than the matching expander mandrel for the case prep enthusiasts. I think, if fired brass comes out of a chamber and needs to be expanded a little to get a bullet in, it probably won't chamber at that point. Or, at least there might be some pressure spike risk because there wouldn't seem to be much (any?) room for the brass to expand on firing. Only thoughts.


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JLouis Frequent Elocutionist Offline Posts: 10625 Joined: Apr 8^th, 2009	Re: Neck expander mandrel Reply #7 - Nov 2^nd, 2017 at 9:40pm	Print Post
	The spring back of the brass can vary so it can be dependant on the brass you currently have on hand and if changed its something that could also change. This also goes for the bullet being used it too can also change based on the casting temp. or a change in alloy hardness in regards to the diameter of which will also change. The in mould bullet shrinkage for the 38 is also more than one might think and in regards to the measuring CW had that process correct but trying to consistently hold and maintain a .002 bullet fit can be a real long term or short term challenge based on the above. JLouis

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beltfed Frequent Elocutionist Offline Posts: 1826 Location: Central Wi Joined: Dec 20^th, 2007	Re: Neck expander mandrel Reply #8 - Nov 2^nd, 2017 at 9:49pm	Print Post
	And don't forget hardness changes in the brass. Annealing "occasionally" will be desireable for you to help control the neck tension at whatever fit you desire beltfed/arnie


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uscra112 Frequent Elocutionist Offline Posts: 4079 Location: Switzerland of Ohio Joined: May 7^th, 2007	Re: Neck expander mandrel Reply #9 - Nov 2^nd, 2017 at 11:07pm	Print Post
	You will wind up making your own mandrels. I must have half a dozen for the plain old .38 Special alone. So many variables! Some years ago I bought a few lengths of 9/16-18 allthread. That's the thread at the top of the Lyman M dies. Make what I need from that. (You need to *Login* or *Register* to view media files and links)

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coljimmy Senior Forum Member Offline Posts: 283 Joined: Nov 10^th, 2012	Re: Neck expander mandrel Reply #10 - Nov 3^rd, 2017 at 11:04am	Print Post
	If you need 0.001, 0.0015 &tc feeler gauge, get some shim stock. I heard this tidbit last night while drinking beer. James


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marlinguy Frequent Elocutionist Offline Ballards may be weaker, but they sure are neater! Posts: 18057 Location: Oregon Joined: Feb 2^nd, 2009	Re: Neck expander mandrel Reply #11 - Nov 3^rd, 2017 at 11:40am	Print Post
	One thing to complicate the neck tension you're trying for is the need to bell case mouth to seat the bullets. Once you've belled the mouth and seated the bullet, you'll need to remove the bell without adding tension. I test fit my cartridges in the chamber as I gradually remove the bell. Once they chamber I stop, and then do all the cartridges at that setting.

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Schuetzenmiester Frequent Elocutionist Offline Posts: 6707 Location: Cool Wet Side of WA Joined: Apr 27^th, 2008	Re: Neck expander mandrel Reply #12 - Nov 3^rd, 2017 at 12:34pm	Print Post
	I never bothered to remove the bell, but it was not much of a bell just enough to not shave lead. That requires very uniform case length.

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calledflyer Frequent Elocutionist Offline Posts: 3974 Joined: Mar 9^th, 2015	Re: Neck expander mandrel Reply #13 - Nov 3^rd, 2017 at 12:40pm	Print Post
	With cast bullets I try for just having a snug interference fit. But, in my jacketed loads, I've tried numerous variations of neck tension, usually making little difference, if any. Bullet positioning in the throat seems much more critical to me than tension. Assuming all cases in a batch are the same. It does, however, point out one of the good things about breach seating- no variability in neck tension. That one, even I can figure out.


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Cat_Whisperer Frequent Elocutionist Offline No 1, 9.3x74R Posts: 3987 Location: Mountains of Virginia Joined: Apr 17^th, 2004	Re: Neck expander mandrel Reply #14 - Nov 3^rd, 2017 at 12:49pm	Print Post
	Schuetzenmiester wrote on Nov 3^rd, 2017 at 12:34pm: I never bothered to remove the bell, but it was not much of a bell just enough to not shave lead. That requires very uniform case length. agree. Unless you build a shoulder on the tool for belling that stops the case; that way the case gets belled the same amount regardless of length.

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