Velocity & Pressure Spike

[live2huntmt]

My "go to" load for my 300 RUM was a 230 Berger Hybrid over 96.0 grains of RL-33 jumping .010" off the lands. This load would produce 3025fps Digital Pro Chrono velocities and 3042 magnetospeed velocities in new virgin Nosler brass.

Now I resized that same brass, setting the shoulder back .0015" with a Redding Type S Match Full Length Bushing Die, using a bushing that was .0015" smaller than the loaded neck diameter. Trimmed to min trim length using a forster trimmer. Chamfered & deburred case mouth after trimming. Uniformed primer pockets and flash hole deburred the brass.

Same Fed215 primers, same powder, is now way overpressure and blew a primer at 96 grains. I checked the powder charge on 3 scales, all match. I now have to load down to 92 grains to get where I was before. All case necks were brushed and dry lubed prior to dumping powder in on both new and resized brass. I went and bought a new pound of RL-33 today and got the same results.

Is there something that I am doing during resizing that would cause this? Or is there something going on with my rifle? This has 100 rounds on it since it was blueprinted and rebarreled. it was cleaned 20 rounds ago.

 

[codyadams]

Was temperature different on the two different days?

Do you have the same lot of bullets?

Did you measure your OAL to the ogive to ensure your die didn't get accidentally adjusted and you're now jamming your bullets?

Could your neck tension have possibly increased during sizing? Measure your sized cases and fired cases and see how much your sizing down your necks, and if you still have any virgin brass, compare it to that

 

[Mikecr]

Now I resized that same brass,

This implies that your go-to load was with unsized/fire forming brass, and this was the 'change'.
Is this true?

 

[FearNoWind]

Was temperature different on the two different days?

...

That would be my first guess too.
Appears to me that you may be working too close to the edge of the max load for that rifle. When you do that the slightest change in any of the variables can make a very big difference.

 

[live2huntmt]

This implies that your go-to load was with unsized/fire forming brass, and this was the 'change'.
Is this true?

Yes...this is correct

 

[live2huntmt]

Was temperature different on the two different days?

Do you have the same lot of bullets?

Did you measure your OAL to the ogive to ensure your die didn't get accidentally adjusted and you're now jamming your bullets?

Could your neck tension have possibly increased during sizing? Measure your sized cases and fired cases and see how much your sizing down your necks, and if you still have any virgin brass, compare it to that

Ambient temperature is within 5 degrees. I have documented the change in velocity and temperatures in the first 100 rounds and have plenty of data to compare these loads to...I can guarantee you it is not a temp sensitivity issue. Max pressure on this load is producing around 3175 fps(ejector mark and barely stiff bolt). I am trying to achieve 3025 fps (150 fps below max). Using virgin brass I could do this using 96 grains of RL-33...using resized brass I now have to use 92 grains.

I measure my bullet seating off of the ogive using a Hornady bullet comparator.

New virgin Nosler necks measure .337", loaded they are .339" and fired they are .341"

I am using the same lot of Berger 230's.

 

[dsculley]

Has the brass grown in length?

Just doesn't make sense that going from virgin brass to once fired and resized for that much difference.

Same lot of brass, powder, primers and bullets require 4 gr. adjustment? That doesn't make sense to me either unless the brass is now too long.

FWIW

 

[live2huntmt]

Has the brass grown in length?

Just doesn't make sense that going from virgin brass to once fired and resized for that much difference.

Same lot of brass, powder, primers and bullets require 4 gr. adjustment? That doesn't make sense to me either unless the brass is now too long.

FWIW

After I fired the first 100 cartridges...I deprimed the cases and brushed the inside of the necks. I then tumbled them in walnut media for 2 hours. I then lubed the cases and resized them in a redding type s full length bushing due using a .337 bushing. I only resized the top 3/4 of the neck...alliwowing the bushing to float. I set the shoulder back .0015". I then trimmed with a Forster precision trimmer to min trim length. I then chamfered and deburred the case mouth. I then uniformed the primer pockets and deburred the flash holes. Next I tumbled them again for 3 hours. Pulled them from the tumbler and brushed the case mouths again. Then I primed with the same lot of Fed215 primers...dry lubed the case necks, wiped off the outside of the neck and charged with 92 grains of RL33. I seat the bullet .005 long and then individually seat each bullet .010" off the lands

 

[codyadams]

What brass was your load fired in prior to getting this new brass? Have you weighed your old brass compared to your new brass? I have seen nosler brass vary ALOT from one lot to another, among the lot they are usually pretty consistent, but from one lot to another can vary substantially.

I'm kind of at a loss but it may be possible that your first initial firing in virgin brass was actually overpressure or right on the borderline, and it didn't manifest itself until your second firing. And heavy bolt lift doesn't always come before blown primers...I was loading a .270 one time and in a half grain difference it went from a half smiley on my case head with no heavy bolt lift to a blown primer.

Do you still have any of your once fired brass to closely inspect for pressure signs? Possibly measure primer pocket size of once fired brass to virgin brass and see how much a single firing stretched it, in conjuction with weighing the new brass compared to old. Other than that, I just don't know.

On the bright side your using less powder to get the same performance...that's a good thing. Ha ha.

 

[live2huntmt]

What brass was your load fired in prior to getting this new brass? Have you weighed your old brass compared to your new brass? I have seen nosler brass vary ALOT from one lot to another, among the lot they are usually pretty consistent, but from one lot to another can vary substantially.

I'm kind of at a loss but it may be possible that your first initial firing in virgin brass was actually overpressure or right on the borderline, and it didn't manifest itself until your second firing. And heavy bolt lift doesn't always come before blown primers...I was loading a .270 one time and in a half grain difference it went from a half smiley on my case head with no heavy bolt lift to a blown primer.

Do you still have any of your once fired brass to closely inspect for pressure signs? Possibly measure primer pocket size of once fired brass to virgin brass and see how much a single firing stretched it, in conjuction with weighing the new brass compared to old. Other than that, I just don't know.




On the bright side your using less powder to get the same performance...that's a good thing. Ha ha.

This is a newly blurprinted and rebarreled Rem 700. I had a 3 groove 1:9" Lila screwed on it. I wanted to use virgin brass in the new barrel and could only find nosler. I fireformed the first 100 pieces during barrel break in and load development. I then resized the fired brass and started having problems. I went and bought a different lot of powder and the problem remained. I just got back from the range from trying virgin nosler and virgin Remington brass... both approximately 15-20 fps slower than fireformed brass...but way faster than the first 100 rounds. I am now guessing something is going on with the rifle...I am going to give it a complete cleaning and see what happens

 

[Mikecr]

That's too many changes at once for troubleshooting.

It's common that fire formed brass would produce different results over new,, and that differently sized brass would produce different results,, and the same with different brass. Two things here that can lead to results going either higher or lower in MV: capacity, or chamber fit.
Given same chamber fit, lower capacity brass will go higher pressure.
Given same capacity brass, tighter chamber fitting leads to higher pressure.
Higher pressure is not a problem -provided you load developed under the condition you have.
So load develop with fire formed brass, that you intend to stick with.

Depending on your load density you might end up going to different powder than you had planned beforehand.

 

[243winxb]

Same bullet lot number?

 

[live2huntmt]

Same bullet lot number?

Yes

 

[orch]

That's too many changes at once for troubleshooting.

It's common that fire formed brass would produce different results over new,, and that differently sized brass would produce different results,, and the same with different brass. Two things here that can lead to results going either higher or lower in MV: capacity, or chamber fit.
Given same chamber fit, lower capacity brass will go higher pressure.
Given same capacity brass, tighter chamber fitting leads to higher pressure.
Higher pressure is not a problem -provided you load developed under the condition you have.
So load develop with fire formed brass, that you intend to stick with.

Depending on your load density you might end up going to different powder than you had planned beforehand.

I have to agree with what Mike is saying...

If the virgin brass is quite undersized compared to the chamber, the brass expanding to fit the chamber will absorb some of the energy from the expanding gas and reduce the amount of energy driving the bullet forward and sort of acts like a pressure buffer...

the next time you use the fireformed brass that fits tight in the chamber the brass doesn't have any room to expand and absorb energy and there is more energy to drive the bullet hence the higher speed....

i have seen the same sort of thing in my 2506ai, had some weak fire forming loads that left me with only partially fireformed cases without the shoulders pushed out all the way, loaded them up with my regular load and fired them along side properly formed brass from the same lot and they always shot 50-100fps slower, after they were properly formed they shot exactly the same as the brass that formed right the first time...

Orch