Fired brass won't fit in the chamber

[rwh]

...

[bigbear_98]

I just finished reloading a batch of once fired brass and noticed that the fired brass was longer than my no go gauge by .004 inches. I am thinking this is because the bolt is unlocking before the pressure has dropped and the brass is expanding under pressure as the bolt slides back. I had a similar issue with my 223 AR and found that an adjustable gas block solved the problem. However when I tried the adjustable gas block in my 24" grendel I don't seem to have enough gas to cycle reliably when I have the gas block adjusted so that the fired brass will fit in the chamber. Anybody else seeing this? What are my options here? Low mass bolt carrier? Cut some coils off of the buffer spring? One of those JP silent spring kits with a lighter weight spring?

Are you not resizing the brass when you load it?

[dmsims21]

Is the brass 0.004 longer than the gauge after full length sizing?

[rwh]

I do resize the brass. I am talking about the brass before resizing. I have my 223 AR set up so that fired brass is about .001 shorter than the chamber, but the brass coming out of my grendel is more like .007 longer than the chamber. At almost $1 per case I would like to work the brass as little as possible when resizing.

[LRRPF52]

What is your fired brass length? I have yet to trim any of my Grendel brass, and I've been shooting it since 2009.

What chamber do you have?

[rwh]

I am talking about the measurement from the base to the shoulder. My unfired cases measure 1.155. The Hornady reloading manual shows 1.156, presumably that would be a max. My no go gauge measures 1.157 from base to the start of the shoulder, and I can't close the bolt on my no go gauge. My fired cases measure 1.162 from the base to the start of the shoulder, which is .005 longer than the no go gauge, and at least .006 longer than the chamber. With my 223 I can pick a fired case up off the ground, drop it into the chamber, and close the bolt with no issues. With my grendel I can't even begin to close the bolt on a fired case, and if I forget to take the extractor off the bolt before trying to chamber a fired case I usually have a tough time getting the bolt to open again after I try. My goal is to tune my gas system so that I can pick a fired grendel case up off the ground, drop it into the chamber, and close the bolt.

My chamber was cut with a Manson reamer.

[bigbear_98]

I personally think you are going to cause other issues by trying to achieve this goal. That is only my opinion but the gun functioning correctly would be my first goal.

[rwh]

I agree that function is most important, but if I can't fix the early unlocking problem then this rifle is headed for the scrap pile. I like the cartridge and really want to make this work. Most AR parts were designed around the 5.56 cartridge. It ought to be possible to reduce the gas enough to get the bolt to unlock after the pressure has dropped and still get reliable function with a corresponding change the buffer and springs.

[Variable]

I am talking about the measurement from the base to the shoulder. My unfired cases measure 1.155. The Hornady reloading manual shows 1.156, presumably that would be a max. My no go gauge measures 1.157 from base to the start of the shoulder, and I can't close the bolt on my no go gauge. My fired cases measure 1.162 from the base to the start of the shoulder, which is .005 longer than the no go gauge, and at least .006 longer than the chamber. With my 223 I can pick a fired case up off the ground, drop it into the chamber, and close the bolt with no issues. With my grendel I can't even begin to close the bolt on a fired case, and if I forget to take the extractor off the bolt before trying to chamber a fired case I usually have a tough time getting the bolt to open again after I try. My goal is to tune my gas system so that I can pick a fired grendel case up off the ground, drop it into the chamber, and close the bolt.

My chamber was cut with a Manson reamer.

I get what you are after, and I really wish I could chime in with an answer, but I'm not savvy enough on Grendels out of a barrel that long.

Thinking out loud here, you have a 24" barrel (long dwell time), a side charger upper and bolt carrier, and a buffer system I have no experience with either.... I presume your buffer system is rifle length? That limits the off the shelf weights you can play with buffer-wise (compared to a carbine). I probably wouldn't chop the buffer spring. Do you have access to a lightweight carrier you can try without having to buy one?

The devil is definitely in the balance between your carrier and buffer weight vs. available gas--- Both time-wise (dwell) and pressure-wise. That's a pickle, but you already know that... Dang.:confused:

Do you feel any extra drag (compared to your 5.56 AR) when you cycle the action?


If it were mine (and assuming your buffer system is rifle length) I'd pull some weight out of the buffer (add additional homemade spacers) and see what happens first before I started buying extra stuff. I could be guessing in the wrong direction though. Normally I'd add extra weight to keep the bolt closed longer (on a carbine), but your extra lengthy smokepole is outside my normal bailiwick.

However you go, I'd change the weight/spring-ratio (starting with the cheapest options first) and then cycle through the gas each time until you hopefully get it balanced out.

Hopefully some of the other "telephone pole" owners can chime in with better insight.

Good luck, and please keep us updated with anything you find.

ETA: At this link you can scroll down to see a pic with a disassembled rifle buffer in it. You'll see the weights I'm talking about. http://www.ar15.com/archive/topic.html?b...8&t=449161 HTH

[LRRPF52]

Check to see what your bolt face depth is for starters. Who made your barrel? What load are you using?

If the chamber and bolt are correctly matched, then I think you are having a harsh dwell time that is driving your bolt carrier to the rear too fast, and since an adjustable gas block is not working for you, you can go ahead and use more carrier weight, more spring weight, or both if one or the other does not work.

bwaites had this problem even more with his 28" RLGS Grendel, and some of his hand loads that are totally fine in a 20" RLGS would come out looking like belted magnums when shot through the 28" rifle.

[Drifter]

Resize the brass. Load it. Fire it. Repeat.

[wheelguner]

What measuring device/method are you using to measure your base to shoulder length?

[rasp65]

rwh The same thing happens with mine and as far as I know this is not abnormal for the Grendel. I can't close the bolt on a fired case. Size it to fit and you will be good to go.

[rwh]

I think I am ready to declare success on this, as I am getting decent reliability and my fired brass fits in the chamber.

My first experiment was to cut a few coils off of a buffer spring to see what difference it made. Unfortunately I took too much off the spring with my first cut, which left me without enough spring to reliably strip the rounds out of the magazine as the spring pushed the bolt forward. However I was able to verify that I could get the rifle to lock back reliably without stretching the brass by adjusting my SLR gas block.

Step 1, shut off gas completely and fire one round: fired case chambers, bolt does not unlock. This fired case becomes the baseline for measuring.
Step 2, open the gas block one click at a time until the rifle locks back consistently: fired case still chambers, case is .001 longer than baseline.

Once I knew it was possible to get the fired brass to fit in the chamber I ordered a JP silent buffer and a spring kit and installed the lightest weight spring in my rifle. I found that this spring is a lot lighter than the default spring that came with the JP buffer but was still stiff enough to strip rounds reliably. With this spring I went back to the range and opened the gas block until the bolt was locking back on an empty magazine every time and then opened the gas block one more click for good measure. Then I fired 60 rounds from magazines to check reliability with no hiccups. The fired brass does indeed fit in the chamber but just barely. It is actually the same size as my no go gauge but it has just enough spring that I can close the bolt.

I am sure there are other ways to approach this problem like switching powders or bullets. This worked for me.

[Variable]

Good fix. I'm glad you got it balanced out.

[Jakal]

RWH,

How many clicks on the SLR gas block did you come open?

[rwh]

I opened the gas block up 7 clicks.