Oh, and btw, velocity is running a shade over 2900 fps outta the 20" factory barrel, with an SD value of 11, so in my opinion, the chrono numbers are pretty good as well.
338 RCM
- Thread starter gregsjt
- Start date
Help Support Long Range Hunting Forum
memtb
Well-Known Member
I may be incorrect……but I think that 100% is calculated at the point at which the bullet contacts the powder!
I've seated a 270 grain .375 into a case that was filled to within about 1/1"16" of the case rim….after using a 10" drop tube while lightly tapping the case to help settle the powder! You definitely have to seat the bullet "very" slowly as to not "bulge" the case!
memtbCalvin45
Well-Known Member
Not to derail the thread but @Seabeeken how temp sensitive have you experienced rl17? Is it like rl22 that way? Reason I ask is I live in Saskatchewan with it's crazy seasonal difference (yesterday, March 27, in the morning it was still -31 c or -24 F with the wind here) and am working on load development soon with it and 75 grain hammers in a .257 wby.
memtb
Well-Known Member
Calvin, I have some very interesting data on RL 17 used in my .375 AI. I realize that this is "apples and oranges" as I've read that powders respond differently in different cartridges and at different load stages…compressed vs non-compressed. I had heard about the extreme temperature sensitivity of RL 17…..and as that's what I use, I ran an experimen! Here are my findings.
I do all of my load development on hot days…..preferably above 90F. So, I chose a cool day to perform the test. During testing the temperatures varied very little……a cool of - 4 F to a -3 F. The rifle and ammo were left outside for several hours prior to test to achieve ambient.
I only shot a 3 shot group, allowing plenty of time between shots so the rifle would return to ambient. I do not remember the velocity spread, but the 300 yard group was pretty respectable, but here's the big surprise…..I gained an 8 fps average above my hot day load development!
Go figure! memtbCalvin45
Well-Known Member
Very interesting indeed.Calvin, I have some very interesting data on RL 17 used in my .375 AI. I realize that this is "apples and oranges" as I've read that powders respond differently in different cartridges and at different load stages…compressed vs non-compressed. I had heard about the extreme temperature sensitivity of RL 17…..and as that's what I use, I ran an experimen! Here are my findings.
I do all of my load development on hot days…..preferably above 90F. So, I chose a cool day to perform the test. During testing the temperatures varied very little……a cool of - 4 F to a -3 F. The rifle and ammo were left outside for several hours prior to test to achieve ambient.
I only shot a 3 shot group, allowing plenty of time between shots so the rifle would return to ambient. I do not remember the velocity spread, but the 300 yard group was pretty respectable, but here's the big surprise…..I gained an 8 fps average above my hot day load development!
I've posted a thread about this phenomena in the past and called it "reverse temp sensitivity" haha. Now a difference of 8fps either way is nothing, it plainly does not matter. But the fact that you were slower at all in the heat is weird.
I have observed this, much more severely, with SUPERFORMANCE and the discontinued 8133.
Some others had observed it with a few endurons and newer temp insensitive powders. "Too much pixie dust in there" was one consensus.
Superformance I haven't know what to make of. It's not particularly sensitive to heat but isn't marketed as temp insensitive, no "pixie dust" added. But like rl17 and 26 it is a true progressive burn rate powder, not just a double base powder. These things can allow for way higher velocity under ideal circumstances but they also don't play by the same rules regarding the pressure curve and they do some weird things (also more than other powders good luck nailing down what the burn rate is - again more than other powders they can be very different animals in different cartridges)
Going from June to February with both rifle and ammo at the ambient outdoor temp, not hot rounds in a cold gun, I saw a superformance load INCREASE by 100 fps and give stiff bolt. 8133 didn't increase by as much but still increased and I'm not the only one to observe it.
Now it's been noted that this can happen in extreme cold with any powder, and a very knowledgeable member put forward that it's not that the metal of the steel contracts in any significant way (we actually tested that too) but the metal itself loses elasticity in the cold and thus can not move and flex during firing the same way. Again, this only way below freezing. -20 to -30 territory.
This likely does affect things, HOWEVER it should affect things things the same way with all powders across the board if that's all there is to this and the actual burn chemistry is not involved. It does not. No, something weird goes on with some of these newer "super powders" when the mercury drops!
memtb
Well-Known Member
Calvin, Yep a -3 or -4 is a lot warmer than a -30……but, still raises some interesting anomalies! memtb
Calvin45
Well-Known Member
Calvin45
Well-Known Member
Yeah that's what I'm thinking…like I'm wondering if you took that same rl17 load
Into that -20 -30 territory if something truly wild might happen like my superformance experience.
Maybe it's common to progressive burn rate powders too…now to start a separate thread haha
Into that -20 -30 territory if something truly wild might happen like my superformance experience.
Maybe it's common to progressive burn rate powders too…now to start a separate thread haha
memtb
Well-Known Member
I'll have to consider that test……but, I'm gett'n soft in my old age! Maybe I can "muster" the courage!
I have about 10 months to talk myself out of it!
memtb
The last time that I was in Specialty Sports in Colorado Springs, they still had Hornady brass for the 338 RCM:
Specialty Sports & Supply
www.specialtysportsandsupply.com
Website
Directions
Facebook (86) · Sporting goods
4285 E Fountain Blvd, Colorado Springs, CO 80916 · ~13.3 mi
(719) 391-2556
Open · Closes 7 PM
Specialty Sports & Supply
www.specialtysportsandsupply.com
Website
Directions
Facebook (86) · Sporting goods
4285 E Fountain Blvd, Colorado Springs, CO 80916 · ~13.3 mi
(719) 391-2556
Open · Closes 7 PM
Seabeeken
Well-Known Member
Speer data with a 5 gr lighter bullet
Attachments
memtb
Well-Known Member
Correct! It's not always he bullet weight…..often the the "bullet surface to bore contact area. I don think that the computer program is capable of factoring that in! When Barnes "grooved" their bullets it reduced the bullet to barrel contact area…..greatly reducing pressures! JMO. memtb
Calvin45
Well-Known Member
I'll have to consider that test……but, I'm gett'n soft in my old age! Maybe I can "muster" the courage!
I have about 10 months to talk myself out of it!
That's interesting for sure. And I'm not suggesting that the load in question isn't over 65kpsi. It almost certainly is though these progressive burn rates like rl17 and superformance do weird things sometimes in your favour…sometimes NOT! Total area under the curve can be way greater without a higher peak pressure. And honestly I don't think exceeding 65k by a little is that big of a deal. Hard on brass. Not "catastrophic failure in your face" territory. And the guy's primers not only aren't cratered, but the edges ain't pancakes. That does tell me something. Yes different headspacing and chamber tolerances will show pressure at different levels (I had a .300 win that Showed cratering and ejector swipe with most factory ammo) but that edge of primer flattening out isn't part of that same equation I don't think. Same with stiff bolt lift. If his primers look fine, his brass is fine, he's not loosening pockets in just a few firings, the bolt can easily be lifted with one finger (my personal practice, the one finger rule!) and his velocity isn't something simply impossible at sane pressure then if I were in his shoes I wouldn't worry at all. That's just me tho.
I sure wish more sources of data from large companies would spring the extra cash for some real pressure data like hodgdon does for theirs. Thanks for sharing that tho it certainly does raise an eyebrow.
Having another 338 RCM built and it should be in my hands in a couple more weeks. This one started out being a Bergara Highlander model in 6.5 PRC. Having it re-barreled with a Bartlein 3b contour 24" long. Also having the magazine box lengthened with a 3.100" Wyatt's extended box so that I can try loading some 250 Bergers at a more appropriate seating depth. Did some mock-ups with brass already and for the 250 Elite Hunters it appears around 3.060" is where the boat tail aligns with the neck/shoulder junction. On my Ruger (same smith; same reamer building this new one) the 250 Bergers jam the lands at 3.150" so there is definitely gonna be plenty of free-bore but not a ridiculous amount. Was wondering if anyone has tried the 250's in the 338 RCM with an appropriate cartridge overall length seating them out I mean to maximize the potential performance with 250 grain bullets yet? I'm also betting N550 or RL-17 will be the best powders but wanted to hear from others who have any real world experience with this cartridge in the 250 grain class of bullets?
