View Full Version : tight chamber test using a live cartridge.
the idea is to disassemble the rifle, drop a live round in the chamber, push it in with a finger, and then turn the muzzle up and see if the round falls out.
Is this "test" valid? Or just more internet BS?
For what it's worth, I did this to my cmmg upper.
The round would not fall out but one downward shake/jolt or bump to the back of the receiver would release the round. The chamber didn't seem tight at all.
I would think just based on the fact that most of the measurements in the AR chamber are down to a thousandth of an inch, that this test will in no way indicate if you have a tight chamber or not. My thought is that you will get the same results with both kinds of chambers regardless of the ammunition used. What those results will be I couldn't tell you, but my hypothesis is that simply due to surface tension it will take some sort of violent action to remove the round from the chamber, whether that chamber is .223 or 5.56.
I would think just based on the fact that most of the measurements in the AR chamber are down to a thousandth of an inch, that this test will in no way indicate if you have a tight chamber or not.
I don't see why not.
Unless the 5.56mm nato chamber allows for a round to wiggle in the chamber and not stay put, I can't see how a barrel (in my case) would be considered "tight".
I did the same to my wasr and the 7.62x39mm live round was literally wiggling in the chamber and would not stick at all. But when I put a spent casing in there, I had to mortar the rifle to get it out, just like I have to mortar my ar15 at the range when I get an FTE with steel cased ammo.
But I don't want to talk about my rifle and problems with steel case ammo. I would like to hear about other ar15 rifle owners and there findings after doing this so called "test" with ammo at home.
If you are in doubt, just have someone ream the chamber for you. That would be the best way to insure it's the proper spec and not guess doing what you plan to do. You can't duplicate the forces applied to the cartridge in a safe manner. Nobody would want you injured trying to "push" the cartridge in.
Be safe
Mark
The chamber spec may be to the nearest thousandth, but the reamers and gauges used to cut and inspect the chamber are precision ground to 0.00001 or better. With these tolerances, one has to consider even small temperature changes and inspection gauges and gauge blocks are never supposed to held by someone not wearing gloves. My guess is that ammo is made to a larger tolerance than the chamber. What I was taught as far metrology is that the instrument used for inspection must have a discrimination less than or equal to 1/10 of the total tolerance of the piece to be measured.
For example if the part I'm measuring has a tolerance of +/- 0.005, the total tolerance is 0.010. Therefore i need an instrument that measures at least 0.001 for my inspection to be valid.
Crow Hunter
11-19-10, 07:30
What I was taught as far metrology is that the instrument used for inspection must have a discrimination less than or equal to 1/10 of the total tolerance of the piece to be measured.
For example if the part I'm measuring has a tolerance of +/- 0.005, the total tolerance is 0.010. Therefore i need an instrument that measures at least 0.001 for my inspection to be valid.
You are correct sir!
ursus.peracto
11-19-10, 08:19
You are correct sir!
Absolutely correct. 10% rule of discrimination is the standard.
The chamber spec may be to the nearest thousandth, but the reamers and gauges used to cut and inspect the chamber are precision ground to 0.00001 or better. With these tolerances, one has to consider even small temperature changes and inspection gauges and gauge blocks are never supposed to held by someone not wearing gloves. My guess is that ammo is made to a larger tolerance than the chamber. What I was taught as far metrology is that the instrument used for inspection must have a discrimination less than or equal to 1/10 of the total tolerance of the piece to be measured.
For example if the part I'm measuring has a tolerance of +/- 0.005, the total tolerance is 0.010. Therefore i need an instrument that measures at least 0.001 for my inspection to be valid.
Meaning to us lay people that sticking a round in the chamber and trying to shake it loose is in no way an accurate gauge of one's chamber?
Meaning to us lay people that sticking a round in the chamber and trying to shake it loose is in no way an accurate gauge of one's chamber?
Correct.
OK but why would a chamber difference of a couple thousandths of an inch dictate extraction reliablity so long as the chamber dimensions are within tolerances?
If a steel cased cartridge doesn't "spring back" the way brass does, then wouldn't there be no difference between a "tight" chamber and a "correct" chamber in terms of extraction? Consider in both chambers, that the casing would be formed into the shape of the chamber and not able toretract like brass, therefore having no difference in extraction because the surface tension of the spent steel casing against the chamber walls would theoretically be the same.
If the chamber was in spec according the correct design, not some wider tolerance used to save money, there wouldn't be any reliability issues. The point is that a casing, brass or steel, is not made to a tight enough tolerance to use for gauging a chamber.
OK but why would a chamber difference of a couple thousandths of an inch dictate extraction reliablity so long as the chamber dimensions are within tolerances?
If a steel cased cartridge doesn't "spring back" the way brass does, then wouldn't there be no difference between a "tight" chamber and a "correct" chamber in terms of extraction? Consider in both chambers, that the casing would be formed into the shape of the chamber and not able toretract like brass, therefore having no difference in extraction because the surface tension of the spent steel casing against the chamber walls would theoretically be the same.
Blankwaffe
11-20-10, 22:22
I reference this test frequently,so Im probably the dumb redneck responsible for it being mentioned here the most.
Here is a snip from one of my posts:
"you can try a little test I used a few years ago with my tight chambered Armalites in selecting ammo.
Remove the upper from the lower.Remove the BCG,and clean the chamber and make sure its dry.Then point the muzzle at the ground.Take one of the unfired cartridges from the same lot your having issues with and drop it in the chamber.Apply a bit of pressure on the case head with your thumb or finger to fully seat the cartridge.Once that is done tip the muzzle upwards.If the round drops out of the chamber,repeat using several of the rounds.If the cartridge sticks,knock it out with a cleaning rod and check the ogive of the bullet for rifling and/or leade marks.
Thats a pretty quick little redneck test to see if the chamber is short and the ammo is suspect.
If the chamber is short you will either have to stay with .223 Rem ammo.In some cases even .223 Rem can cause issues,classic example would be Wolf as that ammo is loaded long and has a ogive on the bullet that is further foward than most(per Wolf and my personal experience) which will effectively jam the bullet in the short leade and pop primers."
Im pretty sure this is not a documented test or a valid industry standard type test used by professionals.It is basically something to use in the field if there is a pressure/popped primers type issue that does come about with a questionable rifle or ammo.
This little redneck test is to see if the chamber has a short "leade" or if the ammo is out of spec causing the bullet ogive to be forced into the rifling causing pressure issues such as blown primers.In my experience the problem is 99% of the time a short leade .223 Rem chamber that is to blame.
It has nothing to do with the chamber width,how the chamber actually headspaces or how tight or loose a properly sized cartridge case fits in the chamber.
Whether or not its a valid test or not,all I can say is Ive used to select ammo per batch for a tight chambered AR that would blow primers all day long with different brands/loads.That said everyone of my AR's have proper spec'd chambers from known quality sources...so they can pass the little redneck test with any 5.56 NATO,Wolf and heavy OTM's etc..
If you want a better verification method then buy one of Ned's chamber gauges...it will tell you real fast if the leade is cut to 5.56 NATO spec..Then have it reamed to spec. using Ned's 5.56 reamer.
HTH
VelveteenMole
11-21-10, 00:52
If you have a milspec style barrel wouldn't reaming an out of spec chamber remove the chrome lining? I always see people say to just ream the chamber, but what about this? Couldn't it cause flaking to propagate from the edges of the reamed spots in the chrome or result in uneven fouling or accelerated leade erosion?
If you have a milspec style barrel wouldn't reaming an out of spec chamber remove the chrome lining?
Whats your other option with a chamber that is too tight?
I reference this test frequently,so Im probably the dumb redneck responsible for it being mentioned here the most.
Here is a snip from one of my posts:
I had no idea this test was supposed to figure out the leade.
I thought it was to determine the tolerances of the chamber wall from base to shoulder.
so when some say you might have a tight chamber, they're really talking about the freebore/leade and not the chamber wall from base to shoulder?
VelveteenMole
11-21-10, 02:25
Whats your other option with a chamber that is too tight?
New barrel?
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