A puzzler for y’all...

[Dkcampbl]

This one has me scratching my head...

I acquired a 300NM last winter, ordered a box of Lapua brass and a batch 230 Bergers. This thing shoots nearly one hole at a hundred with 96.5gr of R50, no pressure signs. Shot a group at 325 that measured just over .750” with the new brass. I am tickled pink.



Now fast fwd to once fired brass, same load and I get obvious pressure and 2”+ groups at a hundred. Back too new brass, one hole again and no pressure.



Once fired trimmed to same length, also tried .010 under, shoulders bumped back to no resistance on chambering. Full length sized with no expander then opened back to .002” neck tension.



I’ve been reloading for 50yrs and not run into this one before. Looking for somebody smarter than me to explain what the hell is happening. Thanks

 

[Aftermath]

That is a strange one.
Have you checked velocities?
Try annealing your once fired brass.

 

[Jmkjr87]

Do you have chrono? Is there a change in velocity from once fired to fired. I had a sweet load on Virgin brass this year that was just too easy to obtain. Thought I was good. Well when I reloaded them, even tho the cases grew about 2 tho it was enough to have to tune it to get it back shooting great

 

[TheOfficeT-Rex]

Define: obvious pressure.

 

[ZY100]

Wet SS tumble or ultrasonic Clean? Anneal? It's probably a neck tension thing somehow.... How did seating the bullets in the new brass feel compared to the 1x?

ZY

 

[Mbaysinger89]

Has to be different velocities. Have you checked H20 capacities before and after firing? Sometimes too low pressure can show pressure. It would take extreme growth in width, but all I can think of accept jamming into lands accidentally.

 

[Texasflyer]

Hmmm, if it was me i would be trying another set of dies just to see

 

[jakelly]

Exactly what pressure signs are you seeing?
How tight is the neck?
Case neck OD of loaded rounds vs case neck OD of fired rounds?
Can you drop a bullet freely into a fired case?

 

[2aBaC̶a̶]

What exactly did you do to the 1x fired that you didnt do to the new brass?

 

[918v]

New brass is annealed. 1x brass is hardened a little. The springback characteristics between the two are completely different. If you annealed your 1x cases after sizing they would behave like virgin cases.

I would redo your ladder test with 1x brass and check for bolt lift and velocity.

 

[Dkcampbl]

Wow, thanks for all the responses.

Pressure signs are severely cratered and flattened primers, heavy bolt lift and very light ejector marks. The first rnd of once fired recoil was enough more than virgin it shocked me. I actually went back to the house, pulled bullets and verified charge weights which were fine.

I didn’t anneal but bullet seating didn’t feel any different from virgin brass. Using a carb 30 cal Sinclair expander before loading on both virgin and once fired brass.

I haven’t chronoed the once fired loads, virgin was right at 2975fps.

I did back off the charge and try to get a new load with the once fired. Got down to two full gr under but could not find the sweet spot again, yet.

 

[Dkcampbl]

Bullet slips into the fired case with minimal pressure like you would expect. Id of sized brass runs .306-.307.
I typically anneal every other loading but may punch a few live primers out and anneal a few too see what happens.
Being Lapua brass I wouldn’t expect hardening issues from one firing.

 

[orkan]

Did you answer whether you were stainless tumbling or ultrasonic, or did I miss that?

 

[ShtrRdy]

From my limited experience new brass uses up some of the energy/pressure during the first firing. Then if you use the same load the velocity will be higher as well as the peak pressure.

 

[918v]

It’s not a hardening issue. It’s a direction of spring back issue.

 

[Dkcampbl]

Brass was vibratory cleaned with walnut media. No stainless tumbling.

I’ll anneal and play around with it. In the meantime I do have 90 some rnds of the new brass left that will shoot great.

 

[2aBaC̶a̶]

What is the headspace difference between new and sized 1x? Is it possible fire forming the new brass obsorbs some of the energy as it expands??

Velocity difference between the two would help.

 

[hafejd30]

Confirmed the OAL of the round isn’t changing between the two? I know it shouldn’t but off the lands vs in them could cause this drastic of a pressure increase

Otherwise I’d say the virgin has room to expand where the once fired has less. Thus increasing pressure.

I usually find a good load with virgin Lapua brass. Then tune it in with fired brass to keep everything as consistent as it will be for the life of the brass. I’ve never seen a .5 MOA gun go to 2 MOA though

 

[jakelly]

OP, what is the neck OD of new loaded brass, once fired brass, once sized loaded brass, and twice fired brass? Measured close to the neck shoulder junction.

 

[Dkcampbl]

New brass loaded - .338”
Once fired loaded - .342”
Once fired empty resized - .337”
Twice fired empty unsized - .341”

new and fired loaded rounds same length per Hornady comparator.

I’ll try and get out with the magnetospeed tomorrow. Got two rnds of the once fired loaded I didn’t shoot.

 

[sirhrmechanic]

Following with interest!

 

[918v]

New brass loaded - .338”
Once fired loaded - .342”
Once fired empty resized - .337”
Twice fired empty unsized - .341”

new and fired loaded rounds same length per Hornady comparator.

I’ll try and get out with the magnetospeed tomorrow. Got two rnds of the once fired loaded I didn’t shoot.

Your loaded necks can’t be that thick

 

[GrumpyOleFart]

I'm surprised this is happening with Lapua brass.

 

[jakelly]

There’s probably .001” of variation in those necks, but the bottom line looks like a tight neck situation revealing itself after one firing. My guess is that a small donut is forming after one firing, and the neck is fairly tight.

 

[jakelly]

@Dkcampbl Has every once fired loaded round been high pressure? Have some been more stout than others?

 

[Mbaysinger89]

Chrono numbers would tell alot again. Maybe the 4 thou loaded neck growth. You run an expander mandrel can you find a donut on the exterior after pushing the neck out?

 

[Dkcampbl]

Your loaded necks can’t be that thick

Yea, never even paid attention to the differences when I was measuring those and punching numbers. Just double checked and they are right down close too the shoulder. At the case mouth new and fired loaded brass both measure .338”. No donut but there appears to be a slight cone type thing going on.

Hmmmm maybe has something to to with the spring back @918v was talking about???

More tomorrow, thanks guys.

 

[orkan]

New brass loaded - .338”
Once fired loaded - .342”
Once fired empty resized - .337”
Twice fired empty unsized - .341”

new and fired loaded rounds same length per Hornady comparator.

I’ll try and get out with the magnetospeed tomorrow. Got two rnds of the once fired loaded I didn’t shoot.

Need a new battery in the ol caliper? Those numbers seem a bit haywire.

 

[kblack583]

I think that .342 loaded neck diameter is where to focus attention. Do you know what the neck size was for the reamer used on your gun? Not sure off top of my head what standard is for 300NM but mine is .343. My new and 1x fired Lapua with 230 Hybrids loaded is .338+-.001 with no issues or changes in velocity.

 

[Dkcampbl]

OK, only two rnds once fired reloads thru the magneto speed but if it’s true it explains the high pressure. 1st rnd, 3128 FPS, 2nd 3123 FPS, scary shit! Remember the new brass loads avg of 2975. I’m sure somebody with the right program can figure approx chamber pressure. Not sure I even want to know.

Hard to imagine the new brass would absorb enough energy fireforming to make that much difference. Same brass, same lot powder, bullets and primers.

 

[Dkcampbl]

Need a new battery in the ol caliper? Those numbers seem a bit haywire.

Numbers are right but as I said there is a slight taper from mouth too shoulder. I’m going to punch primers and anneal a few too see if they size with straighter necks.

 

[Dkcampbl]

I think that .342 loaded neck diameter is where to focus attention. Do you know what the neck size was for the reamer used on your gun? Not sure off top of my head what standard is for 300NM but mine is .343. My new and 1x fired Lapua with 230 Hybrids loaded is .338+-.001 with no issues or changes in velocity.

Don’t know what reamer dims were but I’d guess similar too yours.

 

[Precision Underground]

This one has me scratching my head...

I acquired a 300NM last winter, ordered a box of Lapua brass and a batch 230 Bergers. This thing shoots nearly one hole at a hundred with 96.5gr of R50, no pressure signs. Shot a group at 325 that measured just over .750” with the new brass. I am tickled pink.



Now fast fwd to once fired brass, same load and I get obvious pressure and 2”+ groups at a hundred. Back too new brass, one hole again and no pressure.



Once fired trimmed to same length, also tried .010 under, shoulders bumped back to no resistance on chambering. Full length sized with no expander then opened back to .002” neck tension.



I’ve been reloading for 50yrs and not run into this one before. Looking for somebody smarter than me to explain what the hell is happening. Thanks

How much bump are you talking here? What’s the headspace diff between new and 1x brass? Do you have a headspace gauge? You can use a spent .45 case if not.

 

[Dkcampbl]

How much bump are you talking here? What’s the headspace diff between new and 1x brass? Do you have a headspace gauge? You can use a spent .45 case if not.

Don’t have the gauge and no spent .45 brass but did use a spend .44mag spent brass ;{)

brass measured several
New - 3.337”
Fired - 3.349”
Sized - 3.348”
So I’d say only bumped back .001ish

Is that what you were looking for?

thanks

 

[2aBaC̶a̶]

Don’t have the gauge and no spent .45 brass but did use a spend .44mag spent brass ;{)

brass measured several
New - 3.337”
Fired - 3.349”
Sized - 3.348”
So I’d say only bumped back .001ish

Is that what you were looking for?

thanks

So your new loaded rounds are .011" under your 1x fired sized?

 

[Dkcampbl]

So your new loaded rounds are .011" under your 1x fired sized?

No the .337” is new unfired brass, new loaded is .348”.

 

[jakelly]

You have a donut issue. If you turn your necks, including the top of the shoulder, the problem will go away.

 

[2aBaC̶a̶]

No the .337” is new unfired brass, new loaded is .348”.

Am I missing something? were talking headspace right? How does your headspace grow .011" from loading?

 

[kblack583]

Don’t have the gauge and no spent .45 brass but did use a spend .44mag spent brass ;{)

brass measured several
New - 3.337”
Fired - 3.349”
Sized - 3.348”
So I’d say only bumped back .001ish

Is that what you were looking for?

thanks

Nothing there is out of line. Also think you are getting early doughnut formation. I'd try a couple 1x fired with the expander ball in and see what result you get.

 

[Dkcampbl]

Am I missing something? were talking headspace right? How does your headspace grow .011" from loading?

Ah fat fingered it, once fired sized .348

 

[Dkcampbl]

Can you explain what the donut is and what’s causing it please?

 

[Dkcampbl]

I punched the fresh primers and annealed a few rnds, just gotta wait for them to dry.

 

[2aBaC̶a̶]

Ah fat fingered it, once fired sized .348

I guess what Im getting at is that your virgin brass is .012" under your chamber so some of the pressure energy is being obsorbed into fire forming the case and not pushing a bullet down the barrel. Sort of like a shock obsorber.

You could try sizing a couple 1X fired cases back down to 3.337 if you can even get that low and see if it more closely matches the virgin brass on speed.

 

[918v]

But then he would stretch the case a lot, again.

 

[Dkcampbl]

I guess what Im getting at is that your virgin brass is .012" under your chamber so some of the pressure energy is being obsorbed into fire forming the case and not pushing a bullet down the barrel. Sort of like a shock obsorber.

You could try sizing a couple 1X fired cases back down to 3.337 if you can even get that low and see if it more closely matches the virgin brass on speed.

No way I’d get that much without milling the shell holder and @918v is right. Would sure work the heck out of the brass.

 

[Steel head]

Don’t have the gauge and no spent .45 brass but did use a spend .44mag spent brass ;{)

brass measured several
New - 3.337”
Fired - 3.349”
Sized - 3.348”
So I’d say only bumped back .001ish

Is that what you were looking for?

thanks

Pressure difference between .012 of growth (new) and .001 growth (resized) is noticeable.
You just need to back off the load for reloaded brass to match the speed of new brass if that new brass load is working for you.

With that much initial growth I’d be looking at a false shoulder or mild load with jammed bullet if you want maximum case life on new brass loadings.

 

[jakelly]

.012” of extra headspace will not absorb much energy. No where near 200 fps worth.

@Dkcampbl The donut is a ring of thicker brass that forms at the base of the neck. When the case is moved during firing and sizing, thicker brass from the shoulder is moved into the neck, which forms a donut.

Your rifle has little neck clearance, so the beginning of a donut is becoming evident immediately, although not immediately evident . When I FF Lapua .243 brass into 6 Comp Match in my rifle, I get baby donuts after only one firing that effect accuracy. In your case, the bullet is being pinched in the neck, building pressure. A lot of pressure.

To fix the problem you need to ream the inside of the neck or outside neck turn extending all the way down into the shoulder some. So the brass isn’t thicker there.

 

[Precision Underground]

I guess what Im getting at is that your virgin brass is .012" under your chamber so some of the pressure energy is being obsorbed into fire forming the case and not pushing a bullet down the barrel. Sort of like a shock obsorber.

You could try sizing a couple 1X fired cases back down to 3.337 if you can even get that low and see if it more closely matches the virgin brass on speed.

This is why I asked. Not sure if it’s true but my thought has always been that growing brass that much will use a lot of energy that will have to go somewhere else once the case fits the chamber. I’d back the charge off and check your base to ogive.

 

[918v]

You’re not going to get doughnuts after only one firing of a factory case in a factory chamber.

 

[jakelly]

Think about what you’re suggesting, that a load that is over pressure in an Ackley Improved case would be safe in an unimproved parent cartridge, because expanding the brass uses energy.