OK, tonite was the first time I`ve tried this powder. Shot 77grns under a 162grn A-Max in the 7 Wby. 4 shots cronied:
3185
3198
3201
3183.....4 shot avge 3191..just over an inch at 100. Shot were fired slow, but with no attempt to allow barrel to cool. Air temp was 45". I placed my hand on the barrel just after the last shot, and the barrel was cool..I mean not hot or warm, just felt at ambient twmp..never had a powder do that.

Just to check, I fired three rounds, same bullet, 75grns RL-25. Shots cronied,
3099
3078
3089......for a 3088 average. The lower end of the barrel was, as expected from prior experience, very warm.

So, why did RETUMBO act as it did?? Anyone KNOW?

My first thought was that if heat is a factor in barrel erosion, I just may stick with RETUMBO.

But I would like to know why.

don't know about a cool burn. but retumbo and the the 300 rum are a match made in heaven

You might want to try rl22.

I have done 22. Did OK.

Lay your hand on the barrel next time you shoot it. How does it feel?

Haven't shot Retumbo, but there's certainly a very clear barrel heat difference between some powders. 748 vs. 4198 or N133 (or most others) in the .223 Rem is another example of what you've experienced. The difference can be quite dramatic. If I were you, and if it shot well, I'd stick w/Retumbo for that cart.

Don't know, but glad to see test results with explanation. I'm REALLY wanting to try some Retumbo in the 264 WinMag once it's built along side the IMR7828, and Magnum! Thanks for sharing!!!

I have some Reloader 25, but might just have to try some Retumbo in the 8mm Mag

Good Timing!!! I ran Retumbo over a chrony just this morning.

73.0 gr Retumbo gave me 3100 fps in a 7mm Rem Mag with the 160 Accubond. That same bullet with 70.0 RL25 clocked a 9 shot average of 3041.

68.0 gave me 3250 out of my 26" .264 Win Mag with 130 Accubonds while 68.0 Magnum gave me 3078 with the 140 Accubond.

What I would like you guys to do when shooting Retumbo is check your gun barrel by touching. Interesting to learn if the powder responds the same in your guns.

I have been running 73 grs of Retumbo and the 168 Berger for 3050 in the 7 mag with great accuracy, 3 inch average at 500, 3/4 at 100, been running it ever since all the temp sensitive hype on RL 19 and 22, although I havent found such results, but Reumbo is a great powder, 75.5 under the 140 TTSX shouts bug holes

Here it's good too in a 30-378. Will give it try in that one when I burn up my H870. My luck is I find something that works well and they quit making it.

CG:

Your post doesn't say, but is that the only rifle you shot during that session? And with only that powder?

- Tom

tjm....no, I also shot the three loads with RL-25, right after the Retumbo, so I could compair the heat generated by each, by touching the barrel after each string.

MZ5,

Of the powders that you mentioned (748, 4198, N133, most others) which were hot and which were "cold"?

I love RETUMBO, I shoot it in my 30-378. but havent noticed the "cool". 113 grains warms the barrel right up!

I need to try it in my 7 WBY..RL22 has been so good I havent bothered yet.

Wismon, 748 heats my 223 barrel significantly less than either 4198 or N133. 4198 and N133 are close enough that I wouldn't claim a heat difference between the two.

I've been useing Retumbo under 200's in my 300 RUM for a few years now, at 95.5 gr. a pop I burn through a pound pretty fast.
When ever I shoot from a bench i always set up the crony. I havent seen any variation from Temps. or lot to lot variations at all.

Interesting. Either 748 or BLC2 was advertised as burning cooler than ohter powders which is why they claimed the military used it for machine gun ammo. I just assumed it was marketing hype...but maybe there's something to it?

CG-

I modeled your loads with QuickLoad and assumed a 26 inch barrel.

Remember, in this case more pressure=heat higher temp (see Ken Howells discussions).

69179 psi!!!!


57891 psi


Sleep well.

Bend...thanks for the printout. Interesting..
Barrel length on my rifle is 24 inches. COL 3.627 Wby chambering in a Remington Classic.
Both loads are a grn short of max, per the latest Nos manual.
The quickload print out suggests I should be getting more out of the RL-25 load, and the reverse is the case. I am not getting the velocity the book suggests either, slow by about 30 fps.
With Retunbo, I`m over the suggested book velocity by almost 50 ft. So much for book stuff, tho it is in the ball park.
Neither load showed any signs of excess pressure. At least mone I could see or feel, and looking at the pressure curve caused by RL-25, I should have had a hard bolt lift.

Think I`ll stick with common sence and my crony...:)

I am going to shoot the same load again tomorrow...I`ll tell you how it goes.

WHOA NICE!!

Retumbo is the only powder I use in my 300 RUM these days.

Hmmmm....interesting....I may have to try some Retumbo.Looks good!

Butch Searcy told me many years back that in general the double base powders (R22 and 25,etc) have a " higher " flame temp than the single base powders(7828,Retumbo?),and will give somewhat longer barrel life....by how much I dunno.

Edited: I screwed up above;it's the double base stuff that has the higher temp;Sorry!

Bob,

I need to re-shoot the 73.0 load. Only loaded up three with that charge, out of a clean barrel the first was low, the next two touching.

May be a moot point though. I hung three targets, one behind the other and shot three, three shot groups. The last target (which had all 9 bullet holes) measured just over an inch, all 9 shots touching. That was with the 70.0 load of RL 25.

I mounted that S&B on her last night, yowza!!! Hoping to sight her in Sunday and re-shoot the Retumbo load.

Could be. I don't know how exothermic the combustion of nitroglycerin vs. nitrocellulose is, but according to some calcs done by others here and here, nitroglycerin's expansion ratio is around 3.5 times that of nitrocellulose's. If the combustion of nitroglycerin is less than 3.5x as exothermic, then a double-base powder would show lower temperatures (as well as lower charge volumes) than a single-base.

MZ5: Sorry I screwed up;see edited post above.I got it backwards.

Could still be the exothermic vs. expansion ratio issue, if things are reversed from what I had posted.

My observations, though, are that Ball rifle powders (yes, I mean Winchester) run cooler than stick powders. I don't yet have enough experience with Ramshot vs. the stick competition to comment on them. It is frequently (always, IIRC?) the case that Ball powders are double-base, whereas stick is generally single-base (that's becoming more of a mish-mash these days).

So, either someone somewhere got it backwards, or else there's something about the inhibitors in the specific powders I've compared that's responsible.

In the case here of Retumbo vs. Re-25, the issue could be mainly the pressure difference. I don't really know.

Well, thought I`d call the Horse on this question, so did this morning. Talked to a very nice rep. He didn`t have a clue, and said they, Hodgen, does not check for barrel heat, or heat generated from any powder manufactured or tested by them. At least he was honest!
I would think cooler burning propellants would be something one could "crow" about?
Didn`t get the chance to reshoot last nite, will try again tonite after work.

I'm sure they will be working on a new "coolness" add now

Winchester literature did crow about that when Olin was selling its own propellants.

I'm not sure how to put this delicately, so I'll try to be politely direct:
Some of the people who answer the phone at Hodgdon have proven to be somewhat 'variable(?)' or even unreliable in the information they share with me. I have spoken to the same person on various occasions, and received exactly contradictory info from that person.

My point is merely that I'm not surprised at all that you received the reply you did, nor would I be terribly surprised if you got the opposite response at another time.

Yea, I wondered about that....tho after my explanation of what I`d felt..he came right back to say they didn`t test for barrel heat. He also mentioned Retumbo was not considered to be applicable powder for the 7 Roy. by Hodgen...told him the load came from the latest Nosler book.

Come to think of it, Sierras` tech people seem to be the best with hands on experience.

Then again, how many people do touch the rifle barrel??

Wonder if I get a pay-off in powder for the rest of my life for the new "COOL" ad???