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DIY Chamber Length Gauge

Jig Stick

Gunny Sergeant
Full Member
Minuteman
Aug 27, 2010
1,439
4
44
Pittsburgh PA
I need to measure my chamber length in order to properly trim some cases. I think I remember coming across a post where a guy made his own chamber length gauge out of two pieces of brass. Like he took one piece and cut slits in the neck, and fed another case or something down through the neck. And when he chambered the contraption it compacted to the length of the chamber. I cant find the post though. Any help?
 
Re: DIY Chamber Length Gauge

There are several videos on YouTube showing step by step on how to make your own chamber gauge and how to use it.

This is your second post about trimming your cases. Why are you so obsessed with case trimming? I'm just curious. It is the most "pain in the ass" step in the reloading process and most people don't do it until they have to because their brass will NO longer chamber in the rifle. You already said your's still chambers just fine.

You need to shoot them till they are all difficult to chamber, then measure your chamber length, then trim off just enough to get shooting again.
 
Re: DIY Chamber Length Gauge

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: John_H</div><div class="ubbcode-body">Start reading at post number 7 <span style="color: blue"><span style="font-weight: bold">Here</span></span>

John "Hoot" Hill</div></div>

Nice trick but not what this guy is trying to do. He wants to know how to make his own chamber gauge so he knows when to trim his brass.

If all else fails you can just buy one for cheap from Sinclair.
 
Re: DIY Chamber Length Gauge

I've never really been too concerned with trimming to the length of my own chambers, but I recently bought a trimmer and just started checking to make sure everything is under max.
I don't know a whole lot about reloading yet but I picked up an X-die for my 300 SAUM and figured if I was going to be specific...that's one to do it for.
Spent about a 2 hours I suppose prepping new Remington brass cause it was pretty shitty to say the least.

I re-sized it to get the necks at least round. Most were pretty dented and dinged.
Then ran the mouths over the VLD chamfer tool on my RCBS Prep Station.
Trimmed to 2.004 and re-sized again to take the small ridge off the mouth from the VLD chamfer tool.

I don't know exactly where my chamber length is...but as long as all my brass is 2.004 and stays in that range...I'll be happy...for now.

(that comment isn't so much as a looky-looky but more of a...please tell me if I'm doing it wrong
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)
 
Re: DIY Chamber Length Gauge

Where did you buy the X die? I'm looking for some.
 
Re: DIY Chamber Length Gauge

I had one in my cart at Sinclair's for quite awhile.

Then out of sheer curiosity I went and started looking at my parts bins and found a plastic molly made for sheet rock that was the same diameter as my .308 case mouth and actually had small gripper tabs on the sides that added tension in the case.

The head on it was just a little wide so I slid it in the case, lightly chucked it up in the drill and held a file against it while the drill was turning to get it to the right diameter.

I'm sure purchasing the Sinclair gauge is a much better route for consistency.
 
Re: DIY Chamber Length Gauge

Sorry for the confusion. I need to be a better reader. It turns out I was wondering the same about my new LAR-8 as well. I'm sure a fellow could fashion one like that Sinclair product from rummaging through his rod stock bins. Assuming you hoard hardware like I do.
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John "Hoot Hill
 
Re: DIY Chamber Length Gauge

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: badeyes</div><div class="ubbcode-body">I believe VarmintAl has what you are looking for on his reloading page. http://www.varmintal.com/arelo.htm#CaseHead. Scroll up to Case Trimming, Poor Man's Gage. </div></div>

I went to that page to see your reference and emerged an hour later,having read lots of excellent information besides the poor mans chamber gauge. He and I share a lot of similar opinions and ideas, but the sheer quantity of good ideas and accompanying data he churns out is quite humbling. Thanks for the link.

I use a similar technique to his for smoothing case mouths. Instead of spinning the steel wool in a cup though, I spin the case using a Lee lock stud from their case length kits while reaming and chamfering. Once deburred inside and out, I take a pad of 0000 steel wool in the palm of my hand and press the spinning case mouth against it until I feel the drag of the edge of the mouth on the pad drop suddenly. At that point, it is smooth.

Like him, I also Flitz my dies. and expander balls. I hate taking the decapping stem out to clean the imperial wax buildup out of a die and seeing brass built up on the expander ball like bullets load up the bore with copper. That just can't be good for accurate resizing the neck ID after case resizing.

Also, in my inexpensive Midway case neck prep kit. The one with the nylon bore brushes in a blue plastic holder, with an area in the front to put some powdered mica that comes with it in. It brushes the inside of the case necks leaving a fine coating of mica dust inside to reduce the expander ball friction and fight brass buildup during resizing, in concert with the case lube on the outside. I found that instead of mica, using .5 micron teflon powder instead, does an even better job. I usually give the decapped and resized brass a tumble afterward anyway and it cleans the residual teflon powder off from inside the neck, rather than having a little still in there when I seat the bullet.

A lot of my reloading friends find amusement at the lengths I go to with my cases, but I figure, even if it only contributes a miniscule performance enhancement from each step, these small steps do add up to enhance results and equally important, they serve to add consistency, albeit small amounts per step, to each rounds behavior.

Lot of other small OCP steps I do, but I don't want to put everyone to sleep, assuming I haven't already done so. If nothing else, these steps give me a small degree of confidence for each one I do and we all know the value of positive thinking on groups.

John "Hoot" Hill
 
Re: DIY Chamber Length Gauge

Saturday night, I modded a .308 case to replicate the "poor mans chamber length gauge" and measured mine several times. It is 2.03 inches. Sure was easy to make and use.

While I was at it and given that my rifle is relatively new, I polished the case, coated the neck and shoulder area with Dykem and noted where it marked up when chambered to get an idea of how close my RCBS .308 die came to the chamber dimensions. I was not happy to see that it headspaced not in the middle of the shoulder between the neck transition and case transition, but right on the step where the shoulder transitions to the case and more on the case side than the shoulder side of that step. That would lead me to assume the shoulder is totally unsupported when the case is in battery, until it begins to expand. Is that normal for AR 7.62 variants?

Not that I can do anything about it as the resizing die was already hard enough against the shell holder so as to make the Rock Chucker lightly <span style="font-style: italic">cam over</span> at the top of the ram stroke.

Am I concerned too much about a platform not designed to represent a match chamber in the first place?

Hoot
 
Re: DIY Chamber Length Gauge

I might be wrong and somebody correct me. That's one of the reasons you need to neck size once fired brass that you shot out of your rifle. Once you fired the cartridge out of your rifle the brass is now formed to your chamber.
 
Re: DIY Chamber Length Gauge

That's what I do with my bolt action rifles, but I've never tried it with my autoloaders.

Hoot
 
Re: DIY Chamber Length Gauge

I missed that it was an AR. It's possible to send your spent brass to a die maker to make custom dies. I think ch does this. http://www.ch4d.com/
 
Re: DIY Chamber Length Gauge

Yeppers, that's always an option. I'd imagine that for esoteric calibers where the brass alone costs a king's ransom, you'd earn it back over time in not overworking them. Some day, I'll find my wallet and splurge on a set for one of mine.

I may have that part about not being able to screw the resizing die down far enough, backwards. Perhaps if I screw it down less, it won't knock the shoulder back so far and the shoulder will catch the chamber more toward the center and less toward the case. I spent this evening modifying a Lee .45-70 FCD for use on a 450 Bushmaster, for a friend and am calling it a day. I'll try screwing the resizing die down less tomorrow evening and see what I can accomplish. It's just an off-the-shelf RCBS. I can always get a Forster. My experience with them has been one of a more precisely controlled manufacturing process. Everyone has their favorite brand. Hornady dies used to be nice, but lately, they seem caught up in the race to the bottom price. Both they and RCBS have treated me good when I had an issue with one of their dies. Even though they're usually associated with being the "cheap date", I've had good luck with Lee colleting, neck only, sizing dies. Go figure...

Hoot
 
Re: DIY Chamber Length Gauge

John, I was glad to hear that you had success with the Poor Man's Chamber Length Gauge. As for your other problem, use a Hornady Headspace gauge and measure your case before firing, after firing and after reloading with the die backed out at least one quarter of an inch. This will probably not push the shoulder back yet. Turn the die in toward the shell plate a tiny amount at a time and measure with the gauge again. Keep doing that until you notice a shoulder bump. Keep adjusting the die until you get your desired bump. The bump for a semi should be around 0.005 inches. Alton P.S.: Copied from another thread: Re: How to set how much to bump? [Re: taseal]
former naval person
Chief Warrant Officer

Registered: 05/08/03
Posts: 3336
Loc: Mississippi
German Salazar's write up is very good. A quick and dirty way to check until you buy the uberexpensive gauges is to use a resized and deprimed .40 S&W case (in .308). The .40 cal case mouth is very close to the datum line for measuring .308W. It really doesn't matter exactly as Salazar points out, since you are only measuring before and after sizing dimensions. Put the pistol case over the mouth of the fired case and measure the overall length, then set your sizing die to shorten that measurement after sizing to be.001 to .002 less. Since you are using a rough set up, repeat with 4 or 5 cases to make sure. Then chamber one of the sized cases...you'll be able to lower the bolt handle with just a "touch" of feel. If it is hard to lower, resize again with the die screwed in an additional 1/16 of a turn and recheck the chambering. You'll be very close to the proper dimension. JMHO

 
Re: DIY Chamber Length Gauge

Having worked for a while in the Metrology department of a defense contractor, I'm appalled at such an imprecise method even being suggested. As someone who has worked on countless firearms for the past 35 years, I of course, Love It! I have cobbled up some unusual substitutes in my time as well, so I won't <span style="font-style: italic">cast the first stone</span>.
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Actually, I already got past that point since I last spoke. I took some LC brass, shot from the rifle in question and adjusted the sizing die quickly down until it resized the entire length of the neck and then slowed down and advanced the die about 30 degrees of rotation at a time until The entire shoulder was showing marking in the Dykem that it was fully supported in the chamber. It was still stiff going into lock, so I advanced past that point in 10 degree rotations until it <span style="font-style: italic">felt right</span> going into lock and the Dykem still showed the shoulder being supported for the most part. At that point, not having moved the lock ring yet from where the die body contacts the shell holder, I saw that I was shy by about 60 degrees of rotation. I moved the lock ring to that new location.

In terms of how short I was compared to right at the shell holder, I can't say as I did not record the gap with a feeler gauge yet. That 60 degrees of rotation isn't much in terms of length though. In theory, it would be .012 inches for a 7/8-14 threaded die body, but that doesn't take into account tolerance stacking or thread slop.

Keep in mind, we're talking an autoloader, not a bolt action. The amount of buffer spring power was more than capable of driving the long-sized cases into battery before I shortened them enough to be able to ease the bolt closed and have them go in without sensing too much resistance, so the platform is tolerant of too-long size jobs. Being relatively new, the action still has a lot of inherent resistance going into battery with nothing in it, but I felt confident I was feeling it lightly engaging the shoulder at the last setting.

I will do the relative to one another measurements using the .40 S&W case and see what it indicates. I have a box of Federal Power Shok .308 hunting rounds squirreled away somewhere and will use them as a reference, even though they are not based upon the 7.62x51 NATO LC brass I'm using for reloading. Should prove enlightening.

Hoot