Lyman headspace gauge

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Lyman headspace gauge

Postby offrink » Thu Jun 27, 2019 5:34 pm

So I have just started reloading for 450 BM and I’m having an issue with a Lyman headspace gauge. I’ve reloaded for 6 different calibers (3 rifle and 3 pistol) for years so I have some experience. I’ve checked factory loads and they fit just fine but my reloads, which are exact down to the thousandths, won’t fit in the headspace gauge. They chamber in my 450bm ar but I haven’t yet shot them. I have never had an issue with sizing of a round before so not sure what the issue is.
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Re: Lyman headspace gauge

Postby Hoot » Thu Jun 27, 2019 10:00 pm

Welcome n aboard offrink!

I don't own a Lyman chamber gauge but I do check my reloads against my chamber as its what ultimately decides what sizing is appropriate. SAAMI specs generally come in slightly smaller than the minimum a chamber will accept, to guarantee that the reloads will chamber in even the tightest of chambers. Sounds to me like your sizing die is not reducing your cases to the precise SAAMI specification set forth by that gauge but in your case, your chamber isn't overly tight, My original Bushmaster upper also had a generous chamber. About the only downside that came from that was that my brass got worked a little more each time it was sized and I seemed to produce empties that had experienced excessive case head growth that other members using the same recipe were not experiencing. Eventually, I got over worrying as much about what readings other members got when they measured their case head growth compared to mine. Never had an issue with cases failing in over 2k of reloads over an 8 year period. If the inability to check your finished loads using your gauge troubles you, send the sizing die to Hornady and tell them you're concerned that it isn't properly sizing your cases. They'll check it out and they're pretty generous about replacing dies that trouble their customers. If you opted for the less expensive Lee die set, I san't speak to how they receive customer's concerns.

How far into your Lyman gauge does your sized cases go before they seize up? Is is a fit problem only after a bullet has been seated? Are you screwing your sizing die down to where the shell holderbumps up against it at the top of the ram stroke to generate a small amount of "cam-over"? Lastly, you are lubing your cases prior to sizing right? If so, how much lift resistance do you feel as they're being sized? even with slippery Imperial Sizing Lube that I prefer over 1-shot, there is a distinct amount of resistance as the cases go up into the dies from the moment they entire it, until they bottom our, not just down where the wall almost reaches the web. Some things to ponder. Also, is you have a precision micrometer, not digital caliperwhat is the widest case diameter you see as the case passes through the micrometer? If after sizing, your cases are still .5015 or more at their widest point, then your sizing dies definitely has an issue. There is a trick I perform where I shorten the height of the shell holder, to encourage a slightly greater insertion into the sizing die, to squeeze that last little bit of resultant diameter down abouty .050 more. This is consistent with what is known as a small base rezsizing die when referring to a 5.56 caliber sizing die. It buys you a little more wiggle room when trying to fit a sized case into a chamber gause. While it is a bandaid to an overly generous sizing die, it is a cheap workaround if you want to use the chamber gauge for your "thunk" test, as opposed to using your rife's chamber.

Just throwing ideas out there to see what sticks and to coax more information from you. As I said, the ultimate test is whether your finished rounds "thunk" your rifle's chamber. If that's the case, your are not in any danger. you just own a chamber gauge you cant rely upon to get the warm fuzzies. Straight walled cartridges are in a league that's different than botteneck calibers.

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Re: Lyman headspace gauge

Postby offrink » Fri Jun 28, 2019 4:30 am

So I am using a hornady 3 die set. The round goes most of the way into the gauge. It typically stops at the taper at the base of the round. The problem seems to be that the neck crimp is .4795” to .480” on a 250 grain FTX measured using a medical micrometer by Stryker Medical. Hornady is at .478-.4785”. I reloaded with other bullets with a cannular, 200 grain FTX, and it crimps down to .4785” and is a little tight but fits in the gauge but needs a little poke with my finger to get it to drop out. It

I didn’t think to check about the sizing due not going down far enough. I’ll have to check on that.
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Re: Lyman headspace gauge

Postby offrink » Fri Jun 28, 2019 4:35 am

Also I have a few reloads from another reloaded with 250 grain FTX and the crimp is even wider at 0.481 but still shoots.
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Re: Lyman headspace gauge

Postby Al in Mi » Fri Jun 28, 2019 4:51 am

does a resized case fit in the gauge?
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Re: Lyman headspace gauge

Postby offrink » Fri Jun 28, 2019 8:44 am

Yes. Slides in and out easily.
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Re: Lyman headspace gauge

Postby Hoot » Fri Jun 28, 2019 9:23 am

I'm assuming that by crimp, you're referring to the crimp imparted by the taper crimp die and not the seating die!
The degree that the taper crimp reduces the diameter at the mouth is totally adjustable across the range of none to too much. I advise people to screw their taper crimp die down far enough to create a resultant mouth diameter of:

.476 on smooth sided .452 bullets,
.475 on smooth sided .451 bullets,
.474 on cannelured or driving band groove .452 bullets
.473 on cannelured or driving band groove .451 bullets

Those diameters will come back to you in spades where your velocity SD is concerned but its most important on lighter bullets that can't rely upon Newtons 1st law as much as heavier bullets.

The sizing die only affects the case size down so far. Most folks who end up with cases that are too big, have it happen down by the web, beyond where the die can help. IE the area where Case Head Growth is measured. As I already related in my previous post, generous chambers like the one I had allow too much case head growth with normal loads, much like that which occurs with loads that are too hot. Once again, I'll assume that you are experiencing chamber gauge bind when resizing first fired factory cases, not reloads that you may have pushed too far, the second or more times around. Cases slowly grow at the head as a normal function of the number of times they've been reloaded. Usually that growth is slow but it can be accelerated by repeated hot loads. I've had excessive CHG occur in as little as 1 reload where I loaded rounds way too hot and I've had it take 5 or more before CHG has become too great to allow them to fit in my chamber. The tighter the chamber as in my current Bartz rig, the less tolerant it is of CHG leading to a gross diameter in excess of .5015. My old Bushmaster brand upper tolerated gross CHG up to as much as .502. Doesn't sound like much difference but in terms of chamber tolerance, .002 is a lot.

As i said, you're in luck that your chamber is more forgiving than your chamber gauge. It will tolerate more CHG due to its looseness than the chamber gauge and that buys you some time before your resized rounds wont fit in your chamber. By taking a shell holder and reducing its height to increase the sizing distance down the case (small base), you can add to that time. If you can ultimately get 5 reloads from your brass, count yourself as having broken even. As a habit, in my AR based 450b, I don't reload my cases more than 5 times anyway. That would require annealing and I'm just too lazy to do that. Besides, in generous chambers, the case length shrinks more rapidly than in tight chambers. That too is incremental. I don't reload cases that have shrunk below 1.680 in length as measure after resizing. It adversely impacts the consistency of the taper crimp which relies upon the length of the case in determining the resultant mouth diameter and consistency is what reloading is all about.

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Re: Lyman headspace gauge

Postby offrink » Fri Jun 28, 2019 12:12 pm

Well I guess I’m just dumb! I have always done just a crimp from the seating die and never had an issue with any reloads! Even hot ones. For some reason t thought the taper crimp die that came with the die kit was a second resizing /depriming die. The die box never shows that step or what the proper name of the die is, just the general hornady paperwork. I will be addressing this in the next couple of days to see if I can get it to work properly! Any other tips?
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Re: Lyman headspace gauge

Postby Hoot » Fri Jun 28, 2019 12:31 pm

offrink wrote:Well I guess I’m just dumb! I have always done just a crimp from the seating die and never had an issue with any reloads! Even hot ones. For some reason t thought the taper crimp die that came with the die kit was a second resizing /depriming die. The die box never shows that step or what the proper name of the die is, just the general hornady paperwork. I will be addressing this in the next couple of days to see if I can get it to work properly! Any other tips?


A little bird told me to bring that up because the die instructions have left a lot to be desired since they were first introduced and based upon the resultant diameters you were reporting. There's a lot of discussion about the die settings but its quite old and consequently buried way back in the forum. Nothing you can do wrong that hasn't already been done back when the caliber really took off in 2010. It was a growing process we all shared. Glad I could be here to give a little back for all the advice I got.

Yes, like you I've mostly relied upon the seating die to impart the crimp with the exception of a few more precise calibers that require fine tuning. Then again, the 450b isn't like any bottleneck caliber I had encountered beforehand. The assumption is totally understandable.

No one here will cajole you over newbie questions, so when in doubt, ask away.

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Re: Lyman headspace gauge

Postby offrink » Fri Jun 28, 2019 1:06 pm

Even if they did I would still ask! Someone ALWAYS helps out us dumb ones! Actually I’m very glad to have found this forum because of the wealth of information that has been learned by very few and shared openly. This is still a growing caliber and for me the toughest to reload for so far. Previously it was my first tapered rifle round.

So once I get the round seated to the proper depth and crimped with the seating die, do I just go back and run the taper crimp? Can the handle over, tighten down the crimp til it touches the round, cam the handle back and tighten down a half turn at a time until I get the crimp I want. Sound right?
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