300 RUM load development questions

[MontanaRifleman]

Hey Rifleman,
Help me out with this. I understand your point on at least 90% capacity. I may need help with my math. In the Berger manual 92 gr is at 100% capacity, 10% of that is 82.8. So if my math is correct, even the minimum load is at 90% capacity. 88 gr loads are by my calculation nearly 96% capacity. I'm seating a little farther out, so that capacity would be a little lower, but still well within 90%.
Help me out with my math if this is incorrect.
I appreciate all your input, and feedback, it can only help make me better understand, Thanks

Not sure where Berger gets their capacity calc?

Capacity is affect by a few factors, density of powder, bullet seating depth and volume of fired/sized case.

My experience... Up to this point, my process used to be neck size only and body bump back when needed. This makes for a little more room than a stnd FL sized case. When doing load work for 180 bullets, I usually load up to 101 gr of Retumbo in 1 gr increments. Right about 100 - 101 gr, with bullet seated to about the neck/shoulder junction, I start hearing and feeling crunching. Therefore, I consider 100 gr of Retumbo to be about 100% capacity.

If Berger is seating their 210's to SAAMI COAL, then their bullet is being seated fairly deep into the case and if the case is FL sized, that may take up some room as well. However, 8 gr difference sounds like a lot to me. I would guess maybe 4?

The best way for you to find out is to load a case with powder to just below the neck/shoulder junction, tapping a little for consolidation, and them pour it out onto a scale. Then you will know your Retumbo capacity in your sized case.

 

[Tidesloe]

Not sure where Berger gets their capacity calc?

Capacity is affect by a few factors, density of powder, bullet seating depth and volume of fired/sized case.

My experience... Up to this point, my process used to be neck size only and body bump back when needed. This makes for a little more room than a stnd FL sized case. When doing load work for 180 bullets, I usually load up to 101 gr of Retumbo in 1 gr increments. Right about 100 - 101 gr, with bullet seated to about the neck/shoulder junction, I start hearing and feeling crunching. Therefore, I consider 100 gr of Retumbo to be about 100% capacity.

If Berger is seating their 210's to SAAMI COAL, then their bullet is being seated fairly deep into the case and if the case is FL sized, that may take up some room as well. However, 8 gr difference sounds like a lot to me. I would guess maybe 4?

The best way for you to find out is to load a case with powder to just below the neck/shoulder junction, tapping a little for consolidation, and them pour it out onto a scale. Then you will know your Retumbo capacity in your sized case.

Thanks for the tip and tricks of the trade. That's why I'm here to learn that stuff. Finding the capacity of my cases rather than reading a book is probably a good idea.
That I will do. I'm gonna test up from 90 gr this week.

 

[Tidesloe]

Thanks for the tip and tricks of the trade. That's why I'm here to learn that stuff. Finding the capacity of my cases rather than reading a book is probably a good idea.
That I will do. I'm gonna test up from 90 gr this week.

I did check my case capacities, and it is right a about 100 gr. At 100 gr., there is no room left in the case.

Anyway, I went to the range, and tested on up from 90 gr, to 92. From 90 to 91 groups open up to 1 MOA, and a little over. At 91.5, & 92 its back to .5 MOA, not sub .5, but right on .5 I had 2 misfires today, but they both happened to be at the charges that were opened up. Using 215 primers. New lot with this round of tests. I pulled the bullets, saved the powder, and it appears that they partially lit off, but didnt ignite the charge. The bullet bases were smoked. On the ones that fire, I have excessive primer cratering. Maybe new firing pin / spring assembly needed?

What do you guy's make of the misfires?

 

[MontanaRifleman]

Which charges misfired?

Which charges had cratered primers?

Are the cratered primers flattened or do they have rounded edges?

Pics would be nice.

Any sticky bolt lift?

Did you chrony these rounds?

Cratered primers are usually sign of excessive pressure but not always. Could be a firing pin issue or something else. Retumbo is a good slow and stable powder and I have found it to be forgiving.

Size and decap the cases and set new primers in them, hopefully with a hand priming tool, and if they go in real easy or fall out, then you've got excessive pressure. How many firings on these cases?

Hard to say why the misfires. I would think that any primer that has started to ignite would finish but I'm not an expert on that. May a bad batch of primers? maybe some contaminated primers?

 

[Tidesloe]

Which charges misfired?

Which charges had cratered primers?

Are the cratered primers flattened or do they have rounded edges?

Pics would be nice.

Any sticky bolt lift?

Did you chrony these rounds?

Cratered primers are usually sign of excessive pressure but not always. Could be a firing pin issue or something else. Retumbo is a good slow and stable powder and I have found it to be forgiving.

Size and decap the cases and set new primers in them, hopefully with a hand priming tool, and if they go in real easy or fall out, then you've got excessive pressure. How many firings on these cases?

Hard to say why the misfires. I would think that any primer that has started to ignite would finish but I'm not an expert on that. May a bad batch of primers? maybe some contaminated primers?

The misfires were at 90.5 & 91. The primer cratering seemed to get worse at 90 and up. I already decapped and threw them away. Everything I've ever fired seems to flatten primers, even at moderate charges. This is also true with my 7-08. I have no sticky bolt lift. Other than the cratered, flattened primers everything looks good. Could it be that seating out near lands is giving higher pressure before max loads??? Also from 90 - 92 I didn't see velocity increases I expected. Another sign of pressure, I think. If I seat deeper would mean less pressure, less velocity, but maybe better able to work up velocity within pressure signs?
I'm at 4 firings on my cases. I hand prime, and pockets are a little looser than new.
I'm a bit frustrated, even though I have .5 loads, they are either underpowered, or over pressured.
I've been trying to get different bullets for about 3 months now. Maybe some day I'll be able to get more components. I'm wanting to go to a different bullet. I'm about out of everything now.
Being new to hand loading, when did this stuff become so hard to get?

 

[MontanaRifleman]

Sounds to me like you have conflicting signs of pressure. I don't ever remember not getting a sticky bolt within in about 1 gr of first seeing signs of cratered primers. Once I reached a sticky bolt I backed off about a gr maybe more. But not getting a sticky bolt doesn't mean your not getting excessive pressures.

I have read that sometimes too much headspace on a case can lead to flattened and cratered primers below max loads.

4 firings on RUM brass is getting up there if you have a warm load. My brass usually lasts about 4-6 firings. You might try separating out a dedicated lot of new or almost new brass for load development. if you think you are seeing pressure signs, checking primer seating on new or almost new brass is a good way to confirm that. Trying to read flattened primers is a fuzzy art at best.

 

[Tidesloe]

Sounds to me like you have conflicting signs of pressure. I don't ever remember not getting a sticky bolt within in about 1 gr of first seeing signs of cratered primers. Once I reached a sticky bolt I backed off about a gr maybe more. But not getting a sticky bolt doesn't mean your not getting excessive pressures.

I have read that sometimes too much headspace on a case can lead to flattened and cratered primers below max loads.

4 firings on RUM brass is getting up there if you have a warm load. My brass usually lasts about 4-6 firings. You might try separating out a dedicated lot of new or almost new brass for load development. if you think you are seeing pressure signs, checking primer seating on new or almost new brass is a good way to confirm that. Trying to read flattened primers is a fuzzy art at best.

I don't think headspace is the issue, as I'm carefully measuring cartridge base to whatever point on the shoulder my Sinclair bump gauge measures to on fired cases and bumping to .002. I measure over and over., and confident I'm not bumping back too far.
I've always had the primer cratering, it got worse above 90 gr. It could be more of a firing pin issue. The gun has a new bolt body with same old firing pin assembly.
I'm considering ignoring the primer cratering, as everything else appears normal.

I've never messed with pocket uniforming. I dug some of the primers out of the trash, and they are flatter than before firing but not sharp edged. Maybe they aren't too flattened out. I probably should do pictures maybe it can be seen in photos

 

[MontanaRifleman]

Pics would be good

 

[Tidesloe]

This shows that not all primers are cratered, and maybe they dont appear to be too flattened. The ones on the left have no cratering, but the ones on the right do. These were all fired yesterday from 90 - 92 gr. These primers have a very different look, I'm not sure why. I'm extra careful on my charge weight's, and check each one with a check weight set before and after I've charged each 3 round weight group.



In this view the case heads look good, I think.
Maybe I should ignore the primer cratering. The 3 case heads are from the 92 gr loads. The warmest. I'm not convinced that I'm seeing pressure signs, but the velocity increases that I expected weren't there.

Between 88 & 90 gr the velocities seem to be readable, but from 90 - 92, I cant read much of anything into the velocities. At 92 gr the velocities straighten back out, but not what I had expected.
So with 210 VLD's if I remember correctly without going back and looking. This thread has gotten a bit long. Were you running 92 gr?, if so what kind of velocities were you getting?

 

[MontanaRifleman]

Those primers do not look flattened. They still have well rounded edges and the cratering is inconsistent. It looks like a firing pin issue to me. You might want to consider a new assembly or at least a new spring and have it checked by a smith.

PTG Remington 700 Traditional Non-ISS Firing Pin Assembly Long Action

My new RUM build is getting a whole new PTG bolt and trigger assembly.

I did say 92 gr from memory but went back and checked my notes. The actual charge was 93 gr with an approx average velocity of 3130.

What were the light conditions when you were chronying these loads? Any clouds or shadows? Late afternoon - early evening? I have seen velocities flatten out when pressures get high and I have also seen them spike.

 

[MontanaRifleman]

These are flattened primers. This was a max load in my 7 RM. Notice the 2 factory cases with gold colored primers in the lower left

 

[Tidesloe]

;

These are flattened primers. This was a max load in my 7 RM. Notice the 2 factory cases with gold colored primers in the lower left

I have a new PTG bolt body, but the firing pin assembly is the original from factory. I will replace with a PTG firing pin assembly.
The light conditions were sunny, early morning. About 15 degree temp. I kept my ammo in my truck to about a 45 degree temp. About the same temp as the last round of testing.
I'm thinking that amount of flattening should not be a problem. Would you think I've reached max at 92? That max shot nearly as well as the 88 gr I started at.
At 92 gr. I chrono'd a 3090 fps avg.

 

[MontanaRifleman]

Your 92 gr velocity is in line with my 93 gr velocity. I think you'll be OK climbing another couple of half grain steps.

Or, you might consider starting @ 89 gr to the lands and climbing to see if you can tighten up the groups a little.