6BR Powder Choice and Barrel Life

[Sheldon N]

Looking at doing a 6BR as my "trainer" rifle for PRS style shooting practice. It would be run as a switch barrel and I'd be running the 6 Dasher for matches.

I'm going to be loading the trainer rounds on a Dillon 550b with thrown powder charges from the Dillon hopper. Match charges get weighed to 0.02gr but I don't want to put that amount of time into practice rounds.

I'm looking for a powder choice that is suited for the 6BR with 105g bullets, that 1) meters well from the Dillon thrower and 2) maximizes barrel life. Since this is a practice barrel for PRS steel shooting, it's going to be run until it can't hold 3/4 MOA, well beyond when a bench rest shooter would call it "done". Leading contenders for powder choice right now are XBR 8208, H4895, and RL-15.

Are any of these going to have a barrel life advantage over the other?
Any other powders I should be looking at?

Thanks!

 

[perry42]

RL-15 should meter very well in the Dillon. I have found that going over 31.3 gr in my rifle the primer starts to show overpressure. RL-15 gives higher velocity than Varget in my rifle and the low SD's are causing me to switch from my 30.1 gr Varget load behind a 107gr SMK.

perry42

 

[walker2713]

Of the three you mentioned, I'd think the XBR8208 would meter best.....

 

[Sheldon N]

Of the three you mentioned, I'd think the XBR8208 would meter best.....

That's what I was thinking as well, and was leaning towards that. I just haven't been able to find out if there's any correlation with barrel life or throat wear since this is the fastest powder of the three according to burn rate charts.

 

[Delfuego]

I run H4895 in my 6BR in prs and field matches. I have been told 4895 is harder on the throat than varget, but I am getting good velocity and groups with H4895.

Why not just run slower load? Find a BR speed load for your training rifle instead of running 2 calibers? I just spoke to a friend and dasher shooter about this last night. You could probably find a slower node at around 2850fps or so in the dasher that would basically do the same thing and you wouldn't need all the extras that come with the 2nd caliber.

 

[Sheldon N]

Why not just run slower load? Find a BR speed load for your training rifle instead of running 2 calibers? I just spoke to a friend and dasher shooter about this last night. You could probably find a slower node at around 2850fps or so in the dasher that would basically do the same thing and you wouldn't need all the extras that come with the 2nd caliber.

I've been thinking about that option quite a bit as well. I haven't quite wrapped my head around the logistics of how I'd manage precision weighed match charges against powder thrown practice rounds from the Dillon and if I could do that all with one set of dies and the using the same sizing measurements between the two barrels. If I can't easily go back and forth between the two then I'm losing the time saving advantage of the Dillon and/or buying double sets of dies, etc.

Crunching the numbers in Quickload between 6BR and 6 Dasher to hit the lower OBT node using XBR 8208, it looks like the Dasher takes about 1.7gr more powder but hits the same barrel time node at 2k PSI lower pressure and with a velocity that's 60 fps faster.

Do you think burning the extra powder is going to result in shorter barrel life than the 6BR, despite the slightly lower pressure?

 

[Delfuego]

Sheldon, I wish I was smart enough to answer that question. I would guess wear and tear it is more about powder type, charge size and velocity. I know one or two guys are doing this with "trainer" barrels.

 

[Sheldon N]

Well, there's really only one way to find out. I think I may end up keeping it simple and doing Dasher for both barrels. Thanks for the suggestion!

 

[Delfuego]

Good call. Great reference too.

 

[offgrid]

Sheldon,

as Delfuego stated he and I were just talking about this. I'm in the camp of keeping it simple, shooting the same caliber for a training rifle as my match rifle. Here's some reduced loads through my 26" Dasher, Varget/105 Hybrids. Don't know how many rounds I'll get out of the barrel with the reduced load Dasher compared to a 6BR, has to be better then a full load Dasher.

 

[Sheldon N]

Those are some sweet groups, hoping for similar results as well. I think I've got it figured out how to set up the Dillon to do both match rounds and thrown practice rounds with the same set of dies so I can share brass between barrels. Will probably run cheaper bullets like the 105 Hornady HPBT on the trainer barrel with reduced loads.

XBR 8208 continues to look like a promising powder choice. I noticed in Quickload that the "Heat of Explosion / Potential" field is actually lower than Varget/H4895/RL-15 despite it being a faster burning powder. I think that means it burns a bit cooler in temp which would be helpful for barrel wear.

We'll see if I can get it to shoot well once I get everything tooled up.

 

[RonAKA]

If you download the barrel life calculator spreadsheet from the main Accurate Shooter site, and play around with different powder choices I suspect you may find VV N140 provides the longest barrel life, due to the lower heat content, compared to other alternatives. That is if you trust the method used by the calculator...

 

[savagedasher]

I don't think it all about heat of the charge
I think it's how much barrel lingth the heat is at highest pressure .
My dasher varget rl15 4895 And several others the pressure is in the first 10""
Changing to 4350 the highest pressure and temperature is in 16 "
So I have 6" more barrel exposed to the heat.
I can say it takes longer to heat a 16" piece of steel then a 10" Larry

 

[mikecr]

I wrote the calculator, and dammit you can trust it!
Anyway, I'll email latest to anyone interested

 

[RonAKA]

I wrote the calculator, and dammit you can trust it!
Anyway, I'll email latest to anyone interested

To be clear, it makes sense to me. However it does conflict with a lot of theories about barrel life. I keep meaning to check the calculations, but do you just take powder weight and multiply it by energy content by weight of the powder to get total available energy? If so, that makes a lot of sense. The other side of it is the size of the bore that the energy has to expand/escape into. The combination of the two, must basically determine heat erosion potential in the throat area.

 

[Sheldon N]

That's very interesting, I hadn't seen that calculator before. It does follow the same lines of thinking I was going after, with keeping pressure low and choosing a powder that burns cooler. It actually suggests that N135 would be a very good choice for extending barrel life, given that its temperature is much lower than the others.

Only downsides seems to be that user reports suggest that N135/N140 are only so-so in terms of accuracy of thrown charges from a Dillon and that the price of powder is $45 more per 8lb'er.

 

[X-Caveman]

For metering, I'd look at alliant MR-2000. It's cheap, available, made in the USA and flows like water.

I have no 1st hand knowledge regarding barrel life, but if 3/4 MOA is the standard, I'd expect several thousand rounds regardless of powder choice.

 

[mikecr]

My calcs are based on heat potential(including that from pressure and shot rate) applied to a given bore area.
'Accurate' life in this case is best from a bore, whatever that happens to be.
This is a tricky standard separated, because accuracy is so relative to the beholders that there are many disparities reported about it. Took me over 10yrs filtering through it all, finding credible reporting from shooters who actually reach best from their bores, and immediately detect departure from that best, amidst a myriad of cartridge capacities and powders and loads.
For example, a competitive 6PPC, in competitive use, will provide best for ~900rnds. That's 1s to low 2s.
But someone with a 6PPC could easily claim accuracy to ~5000rnds, if their standard were 1/2moa and they had loaded it no hotter, for slower shooting (say small varmint hunting). They probably didn't detect an accuracy shift, from ~3/8moa, around 3600rnds.

The true killer is not erosion. It's carbon impingement leading to bore constriction at some distance nearer the throat(the heat).
If you don't manage carbon, it can sooner reach a point where fixing it breaks it. That's the point where 'best' is forever gone.
That don't mean the barrel is dead. It means passing 'accurate barrel life' as a line in the sand.

 

[mikecr]

Oh yeah, there are a lot of new powders lately, and I don't have a latest QL update. I don't even have QL installed yet on this particular laptop...
If someone could send me the latest QL powder file, I could update the barrel life spreadsheet. Would greatly appreciate it.

 

[stacy]

If you download the barrel life calculator spreadsheet from the main Accurate Shooter site, and play around with different powder choices I suspect you may find VV N140 provides the longest barrel life, due to the lower heat content, compared to other alternatives. That is if you trust the method used by the calculator...

MY 6BR SURE LOVES N-540 4 SURE!