Quick question: Can bumping the shoulder too much case FTExtracts?

[TheGerman]

Had 2 FTExtracts in a row on a carbine AR.

Cleaned the shit out of the chamber after the first one thinking something got gummed up in there causing the case to get stuck and the extractor to rip off part of the rim. Shot it again last night, round fired, case stuck, 2nd case fed right into the rear of it. Exact same thing as before.

Went home and looked the rifle over. Extractor is fine, chamber got cleaned again and checked for machine marks/burrs, checked the buffer...nothing.

I put one of the rounds from the batch into the chamber on the upper and it had a little trouble going in the last little bit and didn't fall free. Tried this with a MK262 round and it fell out without much of a shake.

Measured the shoulder on some of the rounds I had made and they came in at 1.454, which is short. Not sure why. When I measured some Black Hills and MK262, the shoulder measured 1.4575 on both; .003 difference from my loaded rounds which I still don't know WHY they were 1.454 unless when I set up the die I started at 1.457 and had a moment and then decided to bump them down .003.

Anyways, would this be enough to cause this type of malfunction? When I slide the correctly sized 1.457 case in it drops free whereas the 1.454 has trouble.

 

[arnie19]

Whenever I had stuck cases it was always at the back end near the web area . I would coat some cases you have sized with a felt pen and then put them in the chamber and let the bolt fly closed and then either eject them or pull on the charging handle while some one else pushes with a cleaning rod on the case from the muzzle and once its out look and see where its hitting .You may be the rare case that needs a small base die .

 

[PittsDriver]

Bumping the shoulder indicates you are not full length sizing. Ok for a bolt but not for a gas gun.

 

[TheGerman]

Bumping the shoulder indicates you are not full length sizing. Ok for a bolt but not for a gas gun.

Unless I totally missed something, can't you Fl size AND bump the shoulder?

I'm using a FL sizer.

 

[mtrmn]

Just my opinion:

On the hard chambering, if you are crimping you may be crimping a little too hard and slightly collapsing the shoulder. This will cause hard chambering AND will set your shoulders back at the same time. This of course causes headspace to be excessive. Excessive headspace will cause false overpressure signs and possibly ripping rims off brass. Try a few rounds without crimp and see if the problem goes away. I recommend a Lee Factory Crimp die or a taper crimp die if you can find one. These are much more forgiving and insure a good crimp without collapsing shoulders. Seems the majority of folks swear there's no need for crimping, but I'm a stubborn old fool and insist on crimping any round that will be used in a semiauto due to the violent feed cycle. It helps ease my mind.

If you didn't crimp, then maybe this load is a bit hot or your gun may be "overgassed." Heavier buffer may be the fix. I found that most of my "carbine ARs" work much better with a Wolff extra power buffer spring and H2 buffer, which is heavier than the normal carbine buffer. Heavier reciprocating mass will slightly delay the unlock timing and allow chamber pressures a little more time to drop before the bolt unlocks. If the bolt unlocks too soon, the case will still be "welded" to the chamber walls while the extractor is trying to pull the case out of the chamber. That bolt is coming back with or without the empty case, so if it fails to comply the extractor will simply unsnap off the rim or rip a chunk out of the rim. If you used a cleaning rod to knock the case out of the barrel, how much effort did it require? If it was relatively effortless, then overgassing is likely the culprit. If the case was really stuck in the chamber due to out of spec dimensions-before or after firing-it should require considerable effort to remove.

ETA: The hard chambering could possibly cause the bolt to not fully lock into the locking lugs, which would allow the bolt to open too soon as well. I'm not too sure that the hammer would release if the bolt was only halfway locked though.

 

[PittsDriver]

Unless I totally missed something, can't you Fl size AND bump the shoulder?

I'm using a FL sizer.

mtrmn, great wisdom.

Thinking out loud, how do the dimensions at the base of your cases compare with the Black Hills? I'm just wondering if you have a slight buldge that isn't noticeable. Is this a new die or an old tried and true die?

 

[TheGerman]

mtrmn, great wisdom.

Thinking out loud, how do the dimensions at the base of your cases compare with the Black Hills? I'm just wondering if you have a slight buldge that isn't noticeable. Is this a new die or an old tried and true die?

Do you mean the diameter of the case near the rim?

The die I am using is a Dillon die I've loaded thousands of rounds with.

I am almost thinking that I bumped the case much too far back and then when the round fires the case unevenly fireforms somehow.

 

[TheGerman]

Just my opinion:

On the hard chambering, if you are crimping you may be crimping a little too hard and slightly collapsing the shoulder. This will cause hard chambering AND will set your shoulders back at the same time. This of course causes headspace to be excessive. Excessive headspace will cause false overpressure signs and possibly ripping rims off brass. Try a few rounds without crimp and see if the problem goes away. I recommend a Lee Factory Crimp die or a taper crimp die if you can find one. These are much more forgiving and insure a good crimp without collapsing shoulders. Seems the majority of folks swear there's no need for crimping, but I'm a stubborn old fool and insist on crimping any round that will be used in a semiauto due to the violent feed cycle. It helps ease my mind.

If you didn't crimp, then maybe this load is a bit hot or your gun may be "overgassed." Heavier buffer may be the fix. I found that most of my "carbine ARs" work much better with a Wolff extra power buffer spring and H2 buffer, which is heavier than the normal carbine buffer. Heavier reciprocating mass will slightly delay the unlock timing and allow chamber pressures a little more time to drop before the bolt unlocks. If the bolt unlocks too soon, the case will still be "welded" to the chamber walls while the extractor is trying to pull the case out of the chamber. That bolt is coming back with or without the empty case, so if it fails to comply the extractor will simply unsnap off the rim or rip a chunk out of the rim. If you used a cleaning rod to knock the case out of the barrel, how much effort did it require? If it was relatively effortless, then overgassing is likely the culprit. If the case was really stuck in the chamber due to out of spec dimensions-before or after firing-it should require considerable effort to remove.

ETA: The hard chambering could possibly cause the bolt to not fully lock into the locking lugs, which would allow the bolt to open too soon as well. I'm not too sure that the hammer would release if the bolt was only halfway locked though.

I doubt its a buffer issue at this point, but am keeping that on the list to work my way down to.

The first FTextract came out easily, the one last night actually required me to put the cleaning rod down the barrel and tap with a hammer.

I'll check the crimp as well, I use the Dillon crimp.

I'm leaning more towards its something I did because I've had zero FtExtracts in all the .223 loading I've done in years, and I re-set up my toolhead a while ago and now I'm having these issues. This is leading me to think its something with how something is set up.

 

[mtrmn]

The link below is for a good case gauge for finished ammo. They are made with actual chamber reamers so that the gauge is just like a normal chamber with tapered walls etc. I don't know about ALL the other brands of gauges, but all the ones I've seen are simply drilled to a certain depth to check headspace--therefore the sidewalls in the gauge are straight rather than tapered. The JP's will check ALL dimensions including the tapered portion of the case. This will catch the cases with collapsed shoulders etc. If you ARE over-crimping some rounds due to variable case length/thickness and the shoulders are collapsing, you can usually visually detect a slight bulge just below the shoulder if you hold it up to the light and look at the side profile of the case. Obviously you can measure the diameter of a factory case just below the shoulder and compare it to one of your problem loads.

Also I am not familiar with the Dillon crimp die---is it a taper crimp die?

I fought this crap a long time back in my early days of reloading (like 30 yrs ago) and I was using the seating die to crimp. I learned to always crimp in a separate operation, and crimped each round by "feel" because all brass is not the same length or thickness. Back in the day there were no taper crimp dies or Lee factory crimp dies to be found and I had to make do with what I had. (I was also quite poor) Nowdays I have the FCD in station 4 of my Dillon and every finished round goes through the JP gauge before it goes into the ammo can.

MATCH CASE GAUGE | Brownells P ENTERPRISES

 

[bigedp51]

TheGerman

You biggest clue is as you stated is part of your rim was ripped off and the cartridge failed to eject. This means the case was still gripping the chamber walls as the bolt was moving to the rear. This means your gas port pressure was higher than normal so I'm going to make two wild ass guesses.

1. The amount of bullet crimp increased, causing a rise in chamber pressure and higher port pressure.

2. Your dispensing more powder than normal causing higher chamber pressure and higher port pressure.

I also use a Hornady Cartridge Case Headspace gauge and retired my Wilson case gauges due to chronologically gifted eyesight, and being tired of braille guesswork reading Wilson gauges. (old eye bifocal humor) I also have a Colt type field gauge (1.4736) that I use to zero my vernier calipers so they read actual headspace readings. New factory Federal and Lake City 5.56 ammunition are .005 shorter than my fired cases. And if my full length resizing dies are setup as per the instructions with the press reaching cam over the cases can be .007 to .009 shorter than fired cases. Bottom line, these "short cases fired without problem and then I bought the Hornady case gauge and the headspace to get better shoulder bump readings and not over resize my cases.

Me thinks your way over gassed caused by high chamber pressure. Are you seeing ejector marks and case swipes on the rear of your cases? My WAGS might be wrong, I'm on my first cup of coffee and my psychic ability might not be fully awake.

 

[Xcount]

You mentioned that you had trouble pushing a round in the last bit, this tells me the case head is expanded. Are the cases new or previously fired. I have had trouble using multi-fired brass in a Compass Lake and Wylde chamber using a Dillon die with all the dimensions setup correctly. I had to go to a small base die and then it all worked fine again. I sense you are using reloaded brass that has a slight bulge at the base and since a Dillon die is not small base you are getting the same troubles I had. Try and borrow a small base die or try new brass in your current setup and see if there is a change.

 

[mtrmn]

So, is it fixed?

 

[TheGerman]

So, is it fixed?

It is.

Seems it was operator error (as is usually the case).

The shoulder measurement I had on my board was for my Mk12Mod1 where 1.457 is what the MK262 ammo shoulder is at, and I noted that my chamber was exactly there and bumped back to 1.455 or 1.454.

It didn't occur to me, even though its painfully obvious now, that on my reloading board, the Mk12 is a different rifle than my standard carbine AR I was using. The two things just did not register with me. So when I loaded the AR ammo to use, I loaded it with all of the correct 55gr components, yet with the MK12 shoulder dimension.

It finally hit me the other day as I kept wondering why a round with a much longer shoulder would fall free out of the carbine AR. Grabbed some fired brass, measured it, and sure enough it was all 1.465. Did some test cases bumping back to 1.463 and 1.462 and both chambered easily and both fell free with just a tap on the receiver. Will be out shooting them hopefully this weekend.

My guess is that since the shoulder was roughly .012 'short' in the chamber, the pressure when fired blew the case into size very unevenly and made it practically stick due to the rapid expansion causing the brass to swell and then have the extractor rip the rim off because the case was really fireformed in there.

 

[mtrmn]

Very good, glad to hear it worked out.