What would cause difficult extraction?

[canezach]

Greetings, all! Let me give you the particulars first:

DTA SRS A1 26" 6.5 Creedmoor barrel
Silencertech Model X suppressor
Alpha LRP 6.5 Creedmoor brass 2x fired
140 ELDM seated for 20-thou jump
CCI BR2 primers
39.36 grains of Reloder 16
MV of 2805 fps
I full length size using Redding Type S with a bushing for 0.002" neck tension
After sizing, I run the necks through a mandrel to ensure 0.002" tension and push any deformities to the outside of the neck wall

Went to the range yesterday and found I didn't have particularly heavy bolt lift, but I really had to muscle the bolt to extract, like if the cases were overpressure. Inspect the brass and I had no cratering on the primer, primer was round, no extractor or ejector marks. Unfired rounds fed and extracted normally. Since the DTA is cock on open, bolt lift always has increased resistance as it cocks, but bolt lift wasn't heavy, per se.

When I got home, I measured the base of a few fired pieces of brass with a few unfired rounds and fired and unfired measured either identical or nearly identical (I want to say 0.470", but I can't remember for certain. Assume it was 0.470" and some measurements came in at 0.471" and 0.469", but that could be user error when measuring with calipers). I removed the barrel, cleaned the chamber, greased the bolt lugs, etc., but haven't been able to get back to the range yet. Assuming it wasn't just a chamber in need of cleaning, since I run suppressed 100% of the time, what else could it be?

 

[918v]

If your fired and unfired cases measure the same then your sizing die is defective.

 

[Brosome]

If you dry cycle a few times do you see any rub marks? if not you could always sharpie or dykem one and cycle it through a few times to see where its hanging up.

 

[J McGriddle]

Have you run that brass through that chamber before? Do you have the same issue with a different companies brass?

 

[canezach]

If your fired and unfired cases measure the same then your sizing die is defective.

By same size, I meant near the case head. It still sets the shoulder back 0.002", unless you mean it should also be shrinking the head diameter as well

If you dry cycle a few times do you see any rub marks? if not you could always sharpie or dykem one and cycle it through a few times to see where its hanging up.

I see nothing on the unfired cases that would indicate they're getting hung up somewhere, but I might have to break ot the Sharpie to check

 

[canezach]

Brass has only been fired through this barrel/chamber, so both firings of 400 have all been through the same chamber.

 

[Precision Underground]

Don’t see any rub/drag marks on the outside edge of the extractor do you? As if the extractor was pressed out against the inside of the action?

 

[canezach]

Don’t see any rub/drag marks on the outside edge of the extractor do you? As if the extractor was pressed out against the inside of the action?

I didn't, but I'll double check when I get home.

 

[Precision Underground]

I didn't, but I'll double check when I get home.

I’ve had that happen and the extractor lip wasn’t sitting correctly all of the time and the case riM would make it protrude out and drag the inside of the action. A little filing fixed it up.

 

[918v]

By same size, I meant near the case head. It still sets the shoulder back 0.002", unless you mean it should also be shrinking the head diameter as well

It should be sizing the body diameter at the head down about .002”, not right by the extractor groove but where the case has expanded, about .100” north.

 

[canezach]

It should be sizing the body diameter at the head down about .002”, not right by the extractor groove but where the case has expanded, about .100” north.

Assuming the die isn't sizing properly, any reason it would suddenly stop working? I was under the impression the die doesn't go all the way down the body, though I could be misremembering what I'd read or misinterpreting what was said. I'm measuring the case head right about the same spot you're indicating (let's call it the "line", where you'd check for a case head separation). I'll double check when I get home, but I seem to recall the numbers being fairly close for fired vs. unfired, like 0.470" or 0.471" for one and 0.469" or 0.470" for the other

 

[918v]

Assuming the die isn't sizing properly, any reason it would suddenly stop working? I was under the impression the die doesn't go all the way down the body, though I could be misremembering what I'd read or misinterpreting what was said. I'm measuring the case head right about the same spot you're indicating (let's call it the "line", where you'd check for a case head separation). I'll double check when I get home, but I seem to recall the numbers being fairly close for fired vs. unfired, like 0.470" or 0.471" for one and 0.469" or 0.470" for the other

The reason it would suddenly stop working is springback. On the first firing the cases expanded from their virgin diameter of say .468” to .470” and sprung back to .469”

Your die sized the case but prolly didn’t touch the bottom diameter. On the second firing the cases expanded from .469” to .470” and sprung back down to .4695”. Your die still didn’t touch the bottom.

On your third firing (second reload) the cases expanded from .4695” to .470” and had nowhere to spring back to. And they stuck.

 

[canezach]

The reason it would suddenly stop working is springback. On the first firing the cases expanded from their virgin diameter of say .468” to .470” and sprung back to .469”

Your die sized the case but prolly didn’t touch the bottom diameter. On the second firing the cases expanded from .469” to .470” and sprung back down to .4695”. Your die still didn’t touch the bottom.

On your third firing (second reload) the cases expanded from .4695” to .470” and had nowhere to spring back to. And they stuck.

Well, shit. I hadn't even thought of springback, so you might be right about it being a bad die, which wouldn't appear until third or later firings.

 

[canezach]

Just checked and it would appear @918v is correct. I measured about ten pieces of fired brass from yesterday. At the "case head separation" line, i'm getting consistent 0.469" measurements. After sizing, the shoulder is set back 0.002", but the line is still 0.469", so it would appear my die is not going far enough down the brass.

 

[Precision Underground]

Just checked and it would appear @918v is correct. I measured about ten pieces of fired brass from yesterday. At the "case head separation" line, i'm getting consistent 0.469" measurements. After sizing, the shoulder is set back 0.002", but the line is still 0.469", so it would appear my die is not going far enough down the brass.

Take a fired piece and chamber it to see if there is resistance as you get that part of the brass into the chamber.

 

[canezach]

There is resistance over the last third to quarter of the brass as it goes in and closing the bolt is noticeably difficult. Once the bolt is closed, heavy bolt lift to open and its extremely difficult to extract the case. Sized brass goes in and extracts with no issues

 

[spife7980]

Since it’s inline with the conversation

 

[canezach]

As expected, Redding said send the die in with a few pieces of fired brass. Assuming they find nothing wrong with the die, what are my options? Small base die? I've never had to use one, so how small do they size and how would I set neck tension?

 

[Sheldon N]

Get on the phone and call all the die manufacturers and ask them their spec for the base of the die at the 0.200 line. They'll all tell you, with the exception of Redding.

 

[canezach]

Thanks, guys! The guy who cut the chamber is no longer making DTA barrels, but I'll see if he remembers his reamer specs. I'll give the die makers a call first before jumping into a small base die

 

[Sheldon N]

I just went through this with my 7SAUM, turned out my Forster die wasn't a good match for my chamber. Great die just not a good fit with this particular gun. Called up Hornady and RCBS and both confirmed their specs which were sufficient to get the base sizing I was looking for. One of those things where you don't really know until you look into a particular caliber. For example, in a different caliber my Forster dies are the ones that give me the most base sizing.