Retumbo and pressure

[Brent]

I've done some testing with the 300 Ultra and 220gr SMK's and 178gr A-Max's using Retumbo and noticed pressure signs to be pronounced at less than even 65,000 psi on the Oehler 43, ejector marks even started showing at 60,500 psi with the 220's at 88gr and 2930 fps. I am getting the same velocity as I am with RL25 with a couple more grains powder of Retumbo than RL25. Their are no pressure signs with RL25 at even 70,000 psi and velocity is much higher too, but the Retumbo causes stiff extraction and ejector button marks on nearly every load from where I started.

What I don't understand is, the peak psi is lower but causing brass to flow into the ejector bore??? I actually watched for psi signs to come quicker because S1 and some others said they showed signs earlier than RL25. I had expected the psi to jump high as well but it was way low when it showed clear signs of psi???

My first impression of this stuff is it won't work out like the RL25 has been. All my loads are temperature stable from 10-45 degrees so far with RL25, we'll see how they do at 70-80 deg this summer.

Anyone have observations along these lines with Retumbo?

 

[Guest]

Howdy Brent,

Got a chance to shoot Retumbo with 210 JLK's the other day, it was impressive. Much better than RL25. With the lighter 178 A-max the situation was REVERSED!

It seems RL25 likes the lighter bullets, and Retumbo performs with the heavy stuff.

 

[Brent]

I get the RL25 and RL22 powders for 19-21 bucks a pound and they want almost $60 for two pounds of the VV powder so I've never tried any yet. I have looked at the VV170 and it would be the powder to try, they don't carry it though. I'll wait and make a big order sometime the end of the summer and get enough to make it worth the shipping costs.

I'll load some 210 JLK's when the come in with Retumbo, but I'd have to say the 220 SMK showed more pronounced psi signs a bit quicker than the 178 did. What really perplexes me the most is, I've never had pressure signs on any case/gun until over 70k psi and neither one of these loads made it to even 65k psi, but both showed serious signs of psi. Velocity seemed to validate the pressure readings I was getting at about 60-65k psi though. I'll have to FL size some cases and try the same load range again that way. This could make a difference with them just neck sized with tighter headspace, but I doubt it, we'll see.

It rained out today, but I have some loaded up with RL22 I'll test in the morning. The case already seems too empty with RL25, with RL22 it just gets worse, H1000 or 870 is probably where I should be going but I'd like to stay away from the dirty 870 for now. Just tinkering now, the 94gr load of RL25 and the 178 works real nice, but still won't hold under 1/2 moa on a consistant basis, even though it always stays under 3/4 moa. I'm probably asking too much from the factory barrel but 1/2 moa would be a nice load.

S1,
when you say "much better", what department was it better in? Accuracy, velocity etc?

 

[djdcsi]

Brent, for what it's worth, all my testing has revealed pressure-before the velocity I needed using Retumbo. Ranks there with N-170 which gave the same results, with heavy bullets and large charge. But, it does burn differently depending on what capacity case your using. I've only used it in large capacity cases.

Still testing,
Dave

 

[speedbump]

Yes, I had more violent recoil & muzzle blast with sub-max loads early on in a 7mmRUM. Some minor pressure signs on the cases, but nothing excessive. This was in cool weather. With warmer weather here, I'm going to load up the two most accurate & go to it.....

 

[Randy in Va]

Brent,

Have you tried slightly faster than RE25?
If you could make VV170 work you would get clean and temperature insensitive at the same time.

 

[Guest]

Brent,

The most precise load in my Wolf so far is 93.8 gr. of RL-25 with a 178 A-Max, sub 1/3 Moa. producing 3,420 fps.

I have found several good loads with the 210 JLK, but am still looking for the GREAT LOAD with this bullet. Up until I Danzac coated the 210 JLK, 101 gr. of 50 BMG was the best overall combo of velocity and accuracy, sub 1/2 minute at 600 yards and 3,280 fps.

The other day I got to shoot Retumbo with the coated bullets (210) and it totally changed the pressure curve. The velocity was 3,330 fps. with no pressure signs, and accuracy was very promising. I need to shoot it some more and go through my load dev. sequence.

Remember that the Wolf has a completely different shape powder column than the UM and should act differently with the same powders. I will pass on more info with Retumbo as I do more testing.