300 RUM- early pressure signs?

[Big_Tex22]

Yesterday I fired my new 300 rum for the first time since getting it back from the smith. Its a tooley 700 with a 30" hart 10 twist.

I don't have 2g saved up for the scope I want yet, but wanted to go ahead and do a little barrel break in over a chrono and see were I start to see high pressure signs.

I'm going 210 bergers on retumbo with win lrm's (only primers I could get my hands on)

Sierra manual says max for retumbo with 200's and 220's is between 95-95.7 grains, so I loaded a string of 10 from 82 gr up to 95gr.

More load stats- this chamber was reamed for the 210's touching the lands and fitting in the wyatt's box. I actually started about .05" off the lands just to make sure I didn't have any extra pressure, i'm not real sure if that was significant or not. I have neck turned rem brass and loaded with 3 thou tension.

My results were linear with the veloctiy, but at 89.4 grains I was already reaching 3100 fps, which the manual said would be at 95 gr. I assume the 30" barrel could be the obvious reason instead of the 26" the manual used, but I also started with a little bit of sticky bolt and extractor mark on the case head, so I stopped there.

My problem is the early velocity because 3100 was tops of what I was expecting anyway, but should the high pressure at the medium charge be a concern and what could be causing it?

Sorry for the rookie question this is my first custom long range and I just wanted to make sure I'm going about it in a good way.

My plan is to ladder at 500 once I put the scope on within the range I tested yesterday.
Thanks

 

[barefooter56]

Yesterday I fired my new 300 rum for the first time since getting it back from the smith. Its a tooley 700 with a 30" hart 10 twist.

I don't have 2g saved up for the scope I want yet, but wanted to go ahead and do a little barrel break in over a chrono and see were I start to see high pressure signs.

I'm going 210 bergers on retumbo with win lrm's (only primers I could get my hands on)

Sierra manual says max for retumbo with 200's and 220's is between 95-95.7 grains, so I loaded a string of 10 from 82 gr up to 95gr.

More load stats- this chamber was reamed for the 210's touching the lands and fitting in the wyatt's box. I actually started about .05" off the lands just to make sure I didn't have any extra pressure, i'm not real sure if that was significant or not. I have neck turned rem brass and loaded with 3 thou tension.

My results were linear with the veloctiy, but at 89.4 grains I was already reaching 3100 fps, which the manual said would be at 95 gr. I assume the 30" barrel could be the obvious reason instead of the 26" the manual used, but I also started with a little bit of sticky bolt and extractor mark on the case head, so I stopped there.

My problem is the early velocity because 3100 was tops of what I was expecting anyway, but should the high pressure at the medium charge be a concern and what could be causing it?

Sorry for the rookie question this is my first custom long range and I just wanted to make sure I'm going about it in a good way.

My plan is to ladder at 500 once I put the scope on within the range I tested yesterday.
Thanks

Big_Tex22,
Our manual calls for a starting load of 82.5 grains and a max of 92.0 grains of RETUMBO for the 300 RUM using our 210 VLDs. Approximate velocities are 2636 to 2913 out of the 26 inch test barrel. Fill ratio at 92.0 was 100% so its a compressed load. Depending on how deep the bullet is seated in the case that could be the cause of the pressure issue. You may want to go to our website and read Eric Steckers "VLDs. Making them shoot" to get and idea of how to load test the 210 VLD. If you have any questions pleaase feel free to contact in this string or at [email protected].
Take care,
Phil Hoham
Berger Bullet Tech

 

[Big_Tex22]

Phil-
Awesome thanks for the reply. I'll go check the site out.
89.4 grains I would say looked maybe 85-90% case volume. Still quite a bit of room, even 95 grains still had a little room.

 

[barefooter56]

Thanks Big_Tex22. Let us know if you need anything else!
Thanks for using our bullets!
Phil Hoham
Berger Bullet Tech

 

[Deleted member 46119]

I experienced the same though some parameters are different. Still a 210/VLD.

IIWM Take the accuracy where you find it and the powder savings to the bank.

 

[Big_Tex22]

Fred kinda my thoughts also, little less powder no feelings hurt. But I guess my main concern is what is causing the pressure sooner than anticipated? Does longer barrel=more pressure? Is .003 tension too much for such little jump? I'm new to this level of reloading so learning on the fly here.

I didn't mention earlier my chamber is .342 neck my loaded rounds are .336 neck (brass turned to .014). Not a tight neck I know that, but is it too much space- will that hurt my accuracy?

Another thought- were do the win lrm primers rank as far as pressure compared to the others?

Thanks again.

 

[Deleted member 46119]

Fred kinda my thoughts also, little less powder no feelings hurt. But I guess my main concern is what is causing the pressure sooner than anticipated? Does longer barrel=more pressure? Is .003 tension too much for such little jump? I'm new to this level of reloading so learning on the fly here.

Neck tension is about right for me. As far as I know barrel length does not effect pressure that way.

I didn't mention earlier my chamber is .342 neck my loaded rounds are .336 neck (brass turned to .014). Not a tight neck I know that, but is it too much space- will that hurt my accuracy?

I don't believe it will. IIWM on the next batch go .015.

Another thought- were do the win lrm primers rank as far as pressure compared to the others?

Thanks again.

I am using Win LRM in one of the 300 RUMS. Should be middle of the road. No way it should push your pressures that much.

If I get a chance I'll load a pressure ladder with the same parameters you have and see what I get.

 

[MagnumManiac]

Your chamber may be tighter than others, therefore the early pressure signs, not all rifles can take the book max, it is afterall only a GUIDE.
I would be happy with my projected velocity with less powder and leave it at that, but if there are ANY excessive pressure signs, I would back off that load at least one grain.
I have a 25-06 and a 300WM that have very tight chambers and reach max pressure below most manuals max loads, it happens.
If my neck was that loose, I would only be skim cutting the necks, .006" clearance is right at my limit for good accuracy, wouldn't want anymore than that amount.

Cheers.
gun)

 

[Big_Tex22]

Update on my pressure testing, after my first string showed early pressure I remeasured everything, and I had them .010" into the lands. I'm glad I started with light powder charges to help protect my mistakes in measuring. I know .01 into the lands is probably not a big deal with the bergers, but I set the rest of my string exactly touching the lands, and had no pressure all way up to 95 grains of retumbo! No tight bolt or ejector pin marks at all, got up to 3224 fps. So I guess I'll go with the same charges and start my first "ladder test."

I did have what I guess you would call a firing pin "crater" of some sort, not much but a little, but I had that in my light charges as well. Could it just be a characteristic of the firing pin since there was no other pressure signals? The primer didn't look necessarily flattened at all.

Thanks for the education.

 

[mrultramag]

first off the data in the manuals is for factory rifles using SAMMI chamber and throat. The 300 rum is designed with a long throat (free bore). The factory magazine on a model 700 will only allow your cartridge overall length to be 3.670 or thereabouts. in a factory rifle 300 rum you cannot seat the bullet far enough out to reach the lands usually.
You are using a custom rifle and using a longer COL to place the bullet closer to the lands or your barrel was chambered with a shorter throat than SAMMI. Also your chamber may be on the tighter side since its a custom. Also your using a longer barrel.

All of this adds up to you experiencing max pressure at a lower charge powder weight than the manual indicates. Nothing surprising about that.

If the manual's testing was done with a 26" bbl. Look at the velocity they reached. Now to be safe, figure 25 additional fps for each inch of additional bbl length. So for 4 additional inches add 100 fps.
Don't worry about the fact that you are reaching this velocity with a mid level charge.
You will either hit your target velocity and be happy or you will see pressure signs which will tell you to back your load down some.

In your situation, always start your load at starting load level and progress up in charge weight carefully. A chronograph is a must for you. You have removed the "free bore" which is one of the ways the RUM cartridges and Weatherby's get their performance at acceptable pressures.

 

[barefooter56]

Big_Tex22,
If you are having slight cratering of the primer you are right on the edge as far as the load. If you did your load development at low temperatures you will want to back the load off about 3-4 grains and work it back up in hot weather and note the powder charge in your load book along with the temperature. When you change LOTS of powder do the same. If you have any more questions please feel free to contact us in this string or at [email protected]
Take care!
Phil Hoham
Berger Bullet Tech