New brass and pressure

[BillyGoatGruff]

Starting load work on a re-barreled 7mag.
Using new nosler brass. After first firing on the new brass, the shoulder has moved .015" and I still don't think it has fully filled the chamber. I can easily chamber the once fired brass. I'm going to set up my FL bushing sizing die to just neck size it for this next firing.
My question is. How much will the pressure change. I ran a pressure test with the new brass. If the brass is not moving as much the 2nd time around. Will that increase or decrease pressure? I'm going to repeat the test on the next firing. Just curious how close I can start to the max pressure I reached in the first test?

Hopefully that makes sense..

 

[milboltnut]

the load wasn't enough... try near max and see

 

[dok7mm]

It will usually increase pressure. I will drop back about 2 grains and redo a small pressure test @ .3 gr per load. I am looking for a charge weight that will expand the case fully, but doesn't show excessive pressure. I am checking base to datum measurements to find a load that needs a shoulder bump after second firing. I'll use that charge weight to load up the rest of the cases.

I also use second firing to do a rough seating depth, as they are really close to fully formed and no sense in wasting components.

 

[milboltnut]

It will usually increase pressure. I will drop back about 2 grains and redo a small pressure test @ .3 gr per load. I am looking for a charge weight that will expand the case fully, but doesn't show excessive pressure. I am checking base to datum measurements to find a load that needs a shoulder bump after second firing. I'll use that charge weight to load up the rest of the cases.

I also use second firing to do a rough seating depth, as they are really close to fully formed and no sense in wasting components.

and a complete waste of time ! Talk about a waste of components...

 

[QuietTexan]

So in general expanding the brass does suck down part of the energy budget and reduces pressure signs. That said I can normally find a load on the lower edge of a speed or vertical dispersion node and have it shoot well for a loading or two before shoulders start bumping. If you're laddering up go ahead and find the top again, but I'd rather shoot a decent, well-shooting load instead of trying to run it hot. Cases grow either way at any reasonable pressure level. Let it level off, then do the serious stuff.

You're already on top of the biggest issue with the 7RM, not bumping the shoulders at all until they grow.

 

[tonyf3]

My belted mags (7mm and 300) have about a 1.5-2 grain reduction from virgin to 1x fired brass with Retumbo.
I stopped doing any real load dev work on virgin brass especially if the barrel is new because the barrel will speed up as well. With a new barrel I load to a moderate velocity. Load up 100 and shoot the brass and let the barrel start to speed up.

 

[BillyGoatGruff]

Quick question. Will a similar bullet have similar pressures using same powder?
I tested a 175eldx. I'm going to do a seating test with a charge that showed promise in the middle of the charge weights from that test.
The real question, can I do a seating test at that same charge weight with a different bullet? A 175 nosler ABLR?
The chosen charge is 2gr lower than the charge that showed first signs of pressure. 67gr. Pressure signs , stiff bolt lift at 69gr.
I'd like to run both tests at the same charge mainly for an apple's to apple's comparison.

 

[vancewalker007]

Quick question. Will a similar bullet have similar pressures using same powder?
I tested a 175eldx. I'm going to do a seating test with a charge that showed promise in the middle of the charge weights from that test.
The real question, can I do a seating test at that same charge weight with a different bullet? A 175 nosler ABLR?
The chosen charge is 2gr lower than the charge that showed first signs of pressure. 67gr. Pressure signs , stiff bolt lift at 69gr.
I'd like to run both tests at the same charge mainly for an apple's to apple's comparison.

It will likely be safe as far as pressure, but you can't be sure 67gr is in a powder node for the ABLR without shooting a ladder. Maybe shoot a short ladder like 66.8, 67, 67.2 with the ABLR just to check the node. One thing about some guidance for seating depth on those bullets. I've tried the ABLR in several 7mm LRMs and in a 6.5 PRC. I found in all of them the ABLR shot the best around 100 thou off. The ELDX shot the best much closer to the lands, like 20-40 thou.

 

[QuietTexan]

Quick question. Will a similar bullet have similar pressures using same powder?

In theory yes, but "similar" in this case means things in addition to weight like bearing surface length and the ogive radius. Same weight but drastically different other specs will make them engrave and shoot differently enough to the point where as a practical matter IMO it's best to treat each new bullet as a new project and not try to carry over information from one bullet to another.

The real question, can I do a seating test at that same charge weight with a different bullet? A 175 nosler ABLR?

If the charge weight is several percentage points below max you can start at above a starting charge to test with, but if you've never worked with the bullet before best to start from a more conservative place, and run the full ladder so you don't miss anything. I don't necessarily use slow nodes, but it's nice to know they're there if you can't find a fast node. You can always check the slow node and confirm a bullet does shoot well somewhere, just not where you want.

I found in all of them the ABLR shot the best around 100 thou off. The ELDX shot the best much closer to the lands, like 20-40 thou.

Back before Nosler redid their website there was a disclaimer on the ABLR page to use book COL as a starting point because so many guys were having trouble with them shooting poorly sat out long. My 300 RUM shot the 210 ABLR best at the book COL spec of 3.600", which was 0.072" off the lands in my rifle. Even though that sat the base of the bullet past the neck shoulder/junction, which is another bit of conventional wisdom that didn't work in that case.

 

[BillyGoatGruff]

Thanks for the quick replies.
I run a ladder for the noslers. Then seating test.
Am I wasting components Taking the eldx out past .075" off?
I was going to go from -.025"--.125" in .025 increments on my seating test.

 

[BillyGoatGruff]

It will likely be safe as far as pressure, but you can't be sure 67gr is in a powder node for the ABLR without shooting a ladder. Maybe shoot a short ladder like 66.8, 67, 67.2 with the ABLR just to check the node. One thing about some guidance for seating depth on those bullets. I've tried the ABLR in several 7mm LRMs and in a 6.5 PRC. I found in all of them the ABLR shot the best around 100 thou off. The ELDX shot the best much closer to the lands, like 20-40 thou.

I ran the ABLR in the previous 7mag barrel @.060" off with good results.
I'll have to look at my notes, but I might start the seating test at like -.040" and nit waste components closer to the lands if the consensus is they like jump

 

[QuietTexan]

Am I wasting components Taking the eldx out past .075" off?

I don't think so, what is BTO if a bullet sat to book COL, and how does that related to your lands measurement?

Normally the older magnums are based on deep seated bullets and this isn't an actual problem. But if you're seating really deep into the case you're looking at messing with pressure, charge weight, and powder selection possibly. If you compress the load before you should by seating deep, that's a problem. But if you're in the range of book data shouldn't matter much.

 

[BillyGoatGruff]

Here's another question for the collective.

Bullet seating. Will a particular bullet like a similar seating depth with a different powder in the same rifle?

Example, 175 eldx likes -.040" w/ RL26. Will it like -.040" w/ H1000 or Retumbo? Giver or take 5-10 thou.

Obviously I'll run a separate test but I could shorten it and save components if I had an area to shoot for.
RL26 is hard to come buy. I'd like to use as little of that as possible until I can locate some more.

 

[BillyGoatGruff]

I don't think so, what is BTO if a bullet sat to book COL, and how does that related to your lands measurement?

Normally the older magnums are based on deep seated bullets and this isn't an actual problem. But if you're seating really deep into the case you're looking at messing with pressure, charge weight, and powder selection possibly. If you compress the load before you should by seating deep, that's a problem. But if you're in the range of book data shouldn't matter much.

At a .125" off I'm. 027" longer than book