Lack of pressure signs with Retumbo

[BLC3128]

Good day all,

I've been developing a long range elk load for my 300 WBY. Before I explain my concern, allow me to provide the details of my development. The rifle is a Mark V Terramark w/ 26" barrel, brass is Norma (once fired, fully resized), primers are federal 215, powder is Retumbo, the bullet is Berger 210 VLD hunting.

I started at 80 gr. with a COAL of 3.560" and worked up half a grain at a time. Once I reached 84 gr (which is well past the listed max of 81.5 gr), I seated to bullet out a tad for a COAL of 3.593" (hoping to reduce pressure) and to my findings This load shot the tightest

There were no signs of pressure whatsoever!! So I went back to the bench and loaded up some more, increasing half a grain at a time.. I went back to the range and shot loads from 84.5 all the way up to 87 grains my COAL was 3.70" for all the loads and I did not hit any signs of pressure until the 87 grain load (there was a slight raised brim around the firing pin indentation on the primer). The most accurate load for this range session was 85.5gr with a COAL of 3.70"



I did not have a chronograph available, but does anybody have an idea of the approx velocity of the 84gr and 85.5gr load, possibly the 87gr as well? (temps were around 70 degrees at an elevation of 1,600'). Is anyone here willing to share how hot they loaded a similar setup and list the velocity. Also, how in the world was I able to go so far beyond the max without any signs of pressure?!

On a side note I did load up 9 loads for the 84gr and 85.5 gr and will compare them again today at 100 and 200 yards.

Thanks in advance,

Brandon

 

[TwoMore]

without any velocities it is hard to tell if your loads were weighing correctly. could your scale be weighing heavy?

 

[BLC3128]

without any velocities it is hard to tell if your loads were weighing correctly. could your scale be weighing heavy?

I checked, rechecked, calibrated, recalibrated my scale like a mad scientist! I do not think the scale was weighing heavy whatsoever!!

 

[TwoMore]

bergers load data is pretty conservative I just looked at nosler and their top load for a 210 is 86 grains
https://load-data.nosler.com/load-data/300-weatherby-magnum/

 

[BLC3128]

bergers load data is pretty conservative I just looked at nosler and their top load for a 210 is 86 grains
https://load-data.nosler.com/load-data/300-weatherby-magnum/

From my research the Berger VLD has more bearing surface than the nosler accubond. This may be why the nosler data for charge weight is much higher than Berger data ( it's for nosler accubonds). Although I could be wrong!

 

[TwoMore]

yea i would keep that in mind for sure

 

[Doublezranch]

One thing to keep in mind when working with Retumbo is that is goes critical without any warning. You maybe at 86 grains with no pressure signs at all and the next .5 grains your blowing the primer completely out of the pocket. Excellent powder, just unpredictable at the upper charge loads.

 

[BLC3128]

One thing to keep in mind when working with Retumbo is that is goes critical without any warning. You maybe at 86 grains with no pressure signs at all and the next .5 grains your blowing the primer completely out of the pocket. Excellent powder, just unpredictable at the upper charge loads.

This was the group at 87 grains

With pressure issues beginning to appear at 87 grains and the group "opening up" I'd say it's a good idea to not go any further! I'm very curious at the estimated velocity with the 2 loads I'm testing (84 and 85.5)

 

[Ksmirk]

I've been playing this same game with my 300wm! I've used Retumbo before and when you think your getting close I'd inch up in .2 cause it won't let you know your getting close to pressure until your there.

 

[Deleted member 46119]

Get a chronograph, cost of a couple boxes of bullets.

No one can tell you with any accuracy what your speed is. Only guess withing +-200fps maybe more.

However, if everything is "normal":

Your 84 grain load at 3.583 COAL is probably going in the low 2900fps range. This matches book data predictions.

Your 85.5 grain load at 3.7 COAL is only around 10fps faster.

Your 87 grain load at 3.7 COAL is probably in the high 2900fps range.

 

[BLC3128]

Update:

I spent some time at the range shooting groups during the week and settled on this..

SPECS
Bullet - Berger Hunting VLD (210 grain)
Brass - Norma
Primer - Federal 215
Powder - Retumbo (84 gr.)
OAL - 3.593" (w/ WBY freebore, I still have .328" jump)

PERFORMANCE @ 100 yards
Best 3 shot group - .445"
Velocity (from the best 3 shot group) - 3025fps, 2975fps, 3007fps (AVG. 3002 fps)

I was extremely satisfied with the results and headed to a friends property yesterday to shoot a little farther. Steel plates (12"x12") are set at 445 yards, 585 yards, 690 yards, 735 yards, and 805 yards. The loads worked flawlessly at all ranges, connecting on all attempts at all ranges, and my ballistics chart needed minimal adjustments (Vortex LRBC). I did pick out a nice sized boulder (about the size of a microwave) at 1,303 yards, dialed up, eased into the trigger, and sent that Berger bullet from the 300 Roy airborne. 1.88 seconds later, I watched the boulder erupt into a cloud of dust! Confirmed hit 1" low and 3" left from dead center. I took a second shot and hit just below the rock or about 8" low from dead center. Nonetheless, I am extremely pleased. My rifle will be joining me on an elk hunt this October in Colorado and I am really beginning to gain an dramatic amount of confidence in how the rifle/load performs. I owe a lot of thanks to the various members who contribute to this forum. I have learned so much hard data and practical knowledge from my readings.

Thanks!

 

[MudRunner2005]

My issues I had with Retumbo was having a lack of accuracy signs with it, in multiple cartridges with different bullets... I couldn't get any sort of consistency or accuracy with it at all. So the rest of the 2nd pound of it is still sitting on the top of my bench collecting dust.

 

[JTB]

Retumbo is my go-to powder for heavier bullets in calibers from 6.5-06 to 338 edge. It seems to produce higher relative velocities with less pressure signs vs other comparable powders. I admit I have gone through several 8 lb kegs of it and may just be more comfortable with its characteristics but I generally find a consistent, high velocity round using Retumbo as my first choice for heavies. Temperature stability is a priority for us in the desert so I like to utilize the Hodgdon extreme powders when possible but when venturing toward maximum loads/pressures even extreme powders will produce critical pressure if these highly charged cartridges are not guarded from high temperatures.