Gunsmithing What is up with my (DTA) chamber?

[dbooksta]

I have been shooting and reloading for a DTA SRS .308 16" factory bbl. I am only in the mid-hundreds on this barrel. I started with factory-loaded LC brass and after first firing only neck-sized the brass. I'm now into my second reloads on that brass.

On my last batch of reloads I fed a round that I couldn't get into the chamber, and actually had to tap out with a rod. I pulled out my Wilson .308 case gauge and discovered that round as well as about a third of the reloads were no longer in spec!

I kept shooting the ones that fit the case gauge, and had a lot that were hard to close the bolt on. Then another one got stuck and had to be tapped out.

Now the barrel won't chamber <span style="font-style: italic">any</span> .308 case that passes the Wilson gauge, including:
<ul style="list-style-type: disc">[*]Brass originally fired in it and neck-sized only[*]Factory rounds[*]Small-base full-sized cases[/list]
This is even after scrubbing and inspecting the chamber and throat area as best I can. I don't have a bore scope, but it looks smooth and clean.

What could be going on?

(NB: I haven't seen excessive pressure signs on any round fired in this barrel.)

 

[RWSGunsmithing]

Re: What is up with my (DTA) chamber?

So factory fresh new brass/ammo will not chamber in it?

 

[dbooksta]

Re: What is up with my (DTA) chamber?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RWSGunsmithing</div><div class="ubbcode-body">So factory fresh new brass/ammo will not chamber in it? </div></div>

Correct. Not anymore!

 

[LRI]

Re: What is up with my (DTA) chamber?

As a general rule:

Size your brass and cycle it prior to finishing out your reloads. This way you KNOW it works. It's a pain sometimes, but it sure beats going to the range and beating cases out of your chamber in front of a big crowd of people.

Next. If your neck sizing only your running on the assumption that your cases are sized perfectly to the chamber. They might be, but it sounds like they are too tight.

Body dies resolve this.

If your rifle is a repeater, load your ammunition so that it runs as a repeater. Minimal neck sizing, body sizing, shoulder bumps, etc are all fine and dandy as we sit and talk about them. It also becomes a rather significant source of frustration when the gun won't run reliably.

Treat brass for what it is: a consumable. get your 3-4-5-maybe six reloads and then pitch it. If you figure your time invested in trying to get 10x+ reloads from brass a bag of the stuff becomes rather affordable. Especially when you consider the time/fuel expense of going to the range.

Just sayin. FL resize the stuff, gas it up, seat your bullet, and run it till the necks get hard.

C.

 

[dbooksta]

Re: What is up with my (DTA) chamber?

This is a bolt-action rifle, and the cases have only been fired in it twice.

I have never heard of a closed action expanding cases to the point that they won't chamber, nor have I heard of a chamber increasing in size so it won't fit properly-sized brass. Both of those seem to have happened, and I can't figure out how that's possible or what I should do about it.

 

[bward]

Re: What is up with my (DTA) chamber?

So you can't take a piece of brass that was fired in your chamber and bump the shoulder back and make it chamber?

 

[-Snyper-]

Re: What is up with my (DTA) chamber?

Have you taken the barrel out and looked to see if there is anything restricting the brass from clearing. I say this, because I had the same thing happen to my DTA and it actually ended up being a very thin layer of Alu. film in the chamber.

Remember the action of a DTA is alu. And it takes time for the bolt to correctly work its way in, brake in period. With that said the wear of alu from the bolt in the action works it way into many areas. By the naked eye, the thin layer of alu looks like part of the extension/chamber. After an extensive clean, my was back to normal, and after the brake in period the alu film never returned. Every .001 counts when it comes to clearance. Hope this helps.

 

[dbooksta]

Re: What is up with my (DTA) chamber?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bward</div><div class="ubbcode-body">So you can't take a piece of brass that was fired in your chamber and bump the shoulder back and make it chamber? </div></div>

Correct!

 

[dbooksta]

Re: What is up with my (DTA) chamber?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Snyper</div><div class="ubbcode-body">Have you taken the barrel out and looked to see if there is anything restricting the brass from clearing. I say this, because I had the same thing happen to my DTA and it actually ended up being a very thin layer of Alu. film in the chamber.</div></div>

This is the only explanation that I could even imagine as to what is going on. Didn't realize there was aluminum in the bolt!

Just to be clear, though, the bolt will close on an empty chamber, so I don't think it's a problem in the extension area, but rather in the chamber itself.

What did you do to clean yours out? Any particular solvents or abrasives, or just a lot of scrubbing? Also can you see or detect the film without a borescope?

 

[-Snyper-]

Re: What is up with my (DTA) chamber?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dbooksta</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Snyper</div><div class="ubbcode-body">Have you taken the barrel out and looked to see if there is anything restricting the brass from clearing. I say this, because I had the same thing happen to my DTA and it actually ended up being a very thin layer of Alu. film in the chamber.</div></div>

This is the only explanation that I could even imagine as to what is going on. Didn't realize there was aluminum in the bolt!

Just to be clear, though, the bolt will close on an empty chamber, so I don't think it's a problem in the extension area, but rather in the chamber itself.

What did you do to clean yours out? Any particular solvents or abrasives, or just a lot of scrubbing? Also can you see or detect the film without a borescope? </div></div>

No the bolt is steel, the action, if that's what you want to call it, the part the bolt tracks/rides in, is alu. Therefore you have steel riding in alu. The alu has been hard coated so it will last for the most part all over, but the areas with extra tight tolerances, will wear to the desired amount. With this wear you get very fine alu particles, that when mixed with the oils/solvents/heat, harden the more rounds fired.

As for how I found it, I had a piece of the build up, peal back at the perfect time, and seen the remaining amount build up all over the chamber. I didn't try the borescope idea, but I bet you will be able to see the build up with it.

For the cleaning, I eventually had to go with a SS chamber brush, and some copper cleaner. With a lot of elbow grease and time it did come out.

I've yet to run into this problem, and currently have 3000 rounds fired through this chassis, but you can bet your ass, I still look to this day.

 

[dbooksta]

Re: What is up with my (DTA) chamber?

For those following this mystery: I sent the bolt and barrel back to DTA. They determined that the ejector was sticking, so much that the bolt couldn't close on a Go gauge! After reworking the ejector the gun is functioning normally.

Which, I deduce, means that previously the ejector had been applying enough pressure on the cases to keep them slightly out of battery during firing!

 

[ss10ring]

Re: What is up with my (DTA) chamber?

glad it was an easy fix, Thanks for the update