Throat erosion and double-based powders.

[Haagen Dazs]

Haagan Das,
I contacted Hodgdon powders about 10 years ago on this very subject.They told me that the double base ball powders like H380 burn at lower temperature than single base stick powders. I have unscientifically proven this by shooting 10 shot strings through a 22-250 with both types of powders loaded to close to the same velocity.

My barrel was significantly cooler to the touch with the H380 as opposed to 4895 when starting from cool barrel. It was enough to satisfy my curiosity as to which powder to go with.

Thanks for the answer, I had never heard of H380 before. I was about to settle on H4895 for my Garand but will look into the H380 for sure. I did manage to find the specific heat potential for both and these numbers don't back up your test but they may be wrong. I've got 3930 and 3970 KJ/Kg for H4895 and H380 respectively.

 

[hypersonic]

I want to start out on the right path, powder-wise. 25 is the slowest of the relaoder series powders (which others just can't match, performance wise)

Thats a pretty wide blanket statement without having used 25 in a 7Rum or other powders in a close burn range like H-1000, Retumbo or others. Rl-25 is not as temp stable as other powders and depending on your temps shooting dirtpigs versus your temps when you are deer hunting you could see a loss of 200 fps from summer to fall seasons. To say that other powders can't match the performance with your intended cartridge/ platform and bullet choice is not quite accurate. The rifle you are planning on bulding is going to dictate what powder is going to work the best with your chosen components. Here is a case in point with powder selection for 7RM. Worked up a load last year for my best friends 7RM using 150 Etips. Any powders that had proven to be excellent in the past with bullets in the 150-160 grain class did not pan out. Either accuracy was non existant or pressure was getting out of hand when accuracy was starting to form up. Went way out in left field on powder choice with Retumbo and " bing bang boom" got the accuracy and suprising speed without pressure issues. Yes the Etip is a different animal compared to a lead core bullet or a pure copper bullet for that matter on how they make pressure so it took a bit more work to get dialed in, but the desired results were achieved in a detailed and safe manner. To limit yourself to one powder is not the way to go when trying to find a load even if your chosen cartridge has a reduced barrel life because of cartridge capacity versus bore size. What is your intended barrel length for your 7 Rum build? as I see you have posted that you will be getting 3950 fps with the 120 Btip over 96.5 grains of Rl-25. I am not going to say anymore till you give a bit more info on barrel length and where your current velocity information has come from.

 

[Michael Eichele]

RL-25 shows 200 FPS between summer and fall? WOW!

Do you have any 1st hand proof of this?

 

[Thomas B.]

Thanks for the answer, I had never heard of H380 before. I was about to settle on H4895 for my Garand but will look into the H380 for sure. I did manage to find the specific heat potential for both and these numbers don't back up your test but they may be wrong. I've got 3930 and 3970 KJ/Kg for H4895 and H380 respectively.

4895 is the quintessential Garand powder. Thats all I use in the Garand except I use IMR4895. What you found out about H380 is the opposite of what they told me. It may have something to do with the burn rate that gave me the results I experienced. H380 is a bit slower than 4895 and is excellent in the 22-250, 220 swift and some of 6mm cases like the .243. It's real good in the 30-06 but I'm not too sure the pressure curve would be suitable for the Garand.

 

[Haagen Dazs]

I'm not too worried about the pressure because I've got an adjustable gas plug. I'm just looking for a good, reletively cool powder for gas guns.

 

[Bart B]

4895 is the quintessential Garand powder. Thats all I use in the Garand except I use IMR4895.

One of the arsenals (Frankfort, I think) tested the .30-06 for accuracy and barrel life with IMR4064. That powder had better accuracy with the 150 gr. ball, 165-gr. AP and 172-gr. machine gun bullet (also the match bullet in M72 ammo). And about 10 to 15 percent longer barrel life. Problem was, IMR4064 had to be weighed for each charge. The high speed powder metering machines didn't throw charges uniform enough to meet velocity spread specs. So they continued using IMR4895 as the standard powder as it metered more uniform charge weights.

When the Garand started being used in competiton, IMR4064 was the powder of choice when handloading new cases for the same reasons; better accuracy and barrel life. If you resize fired cases from your Garand for reloading, you probably won't see any difference in accuracy.

 

[Max Heat]

I used to run H414 in the 7mag with the 120's. But after I tried RL-19, I never used the H414 again. The RUM barrel will be 26", as that was the only option for the shaw group buy. That is the same length as what the guy who developed the 96.5gr of RL-25 with 120's clocked at 3950 used. The next one WILL be a 30 incher.

It is the 200fps difference between summer and fall temps that bothers me about RL-25 though (if true). I don't know at what temp the guy developed that load. But if it IS true, I'm wondering if that kind of number change would be similar for RL-19. If so, the 75gr charge (using 120's) that gave me 3680 in the 7mag HAS to be TOO HOT for warm weather, as it was developed at temperatures below 40 degrees F. I remember that my chrony F1 was giving me some fits down at those temps. The longer it sat set up out in the cold, the more it would be throwing initialization errors.

 

[RMulhern]

Absolutely infrickininsane!!

 

[Reelamin]

I have no idea about all this double base, ball, and other stuff eating barrels. My experience is the worst thing on a barrel is shooting it hot. I have seen guys litterally shoot guns to the point the barrel is smoking the gun oil. I believe not shooting a cool barrel is the worst thing a person can do on a barrels life.

I watched one guy ruin a .5" 308 in 200 rounds. He shot 5 shot groups one after the other continually as fast as he could. I have never seen a rifle barrel that hot ever. He was trying to prove that "modern" guns could be shot hot and it would not hurt them. Rifle would not group under 1" after he was done.

I shoot 120 Ballistic Tips out of my 7STW Sendero at 3600fps using RL22. I don't heat it and never shoot more then five rounds from a cool barrel. I have over 1600 documented rounds through it. Still shoots .5 or less for 5. This is my varmint gun and I use it for coyotes at 0 degrees and ground hogs at 90 degrees. I also do not clean until at least 100 rounds are shot through it. Same POI regardless.

Just a couple of my limited experieces.

 

[Freebore]

I have a 7RUM and RL-25 and 120 Nos B-tips along with some resized cases ready. I could run some velocity test with. It's a factory barrel LSS 700.
It shoots the 162's at 3350 with 93.0 of Retumbo into itty bitty holes at 100. The local gunsmith said he could make me another barrel with his custom min-spec reamer when I burn this one out! This might be my opportunity.

Hammonds' Rifles - The Hammonds' Hunter

His web site needs updated

 

[vegas steve]

i have a savage 112fv in 7 rem mag and shot only 71.5 grns of rl19 behind a 120 grn balistic tip and was seeing faster speeds than i imagined around 3680 fps. my barrel lasted about 700 rounds before the accuracy went south. upon bore scoping the bore,i found that not only did the barrel suffer throat erosion,i actually lost three lands at the front of the throat that seemed to have broke off completely and also had a bad case of fire cracking as well. the 7 rem mag is still my favorite caliberbut the next one i build won't be getting any rl19 fed thru it.gun)