Too Much Powder Not enough 260AI Speed

[BillCh]

Greetings all,
I may be worrying about nothing.

I've got a 260AI (6.5-08 Improved) that I'm trying to work up a load for. Its a Savage LRPV, closed top, repeater action in the factory HS Precision stock. The barrel is a 25.5 inch Brux 1-8 twist, large shank, heavy varmint contour. My 'smith said it looked as good on the inside as any he's seen, for whatever thats worth. The chamber was cut with a PT&G reamer with a snug, .296 neck and a long freebore to accommodate 140gr. class bullets by seating them out ahead of the potential donut area at the neck/shoulder. I thought I new what I was doing when I spec'd this reamer out. I'm having second thoughts now. I'll be swapping this barrel into a single shot target action with an A-5 stock in the next couple of weeks.
I'm up to 46.2gr. of H4350 with a 140 gr. bullet and I'm still not getting the speed I want. Hodgdon lists the 260 Rem. max at 44.5 of H4350 so I'm well above that. For reference, Hodgdon also list 46gr of H4350 as max for the 6.5-284. My BR-2 primers are looking a little flat-ish but nothing abnormal. I've compared them to primers from my 43gr. RL-15 308 load and there isn't much difference. No ejector marks, hard extraction, or anything like that.

I did some more chrono testing a couple of days ago. These were all previously fire formed and fully prepped cases. The weather was overcast and about 55 F. The range alt. is around 1200 ft.

Berger 140gr. HPBT-LR
OAL 3.010 (2.300 to ogive)
46.2gr. H4350
Lapua brass
CCI BR-2
Av. 2863 fps., ES-11, SD-2

I've also given the 142gr. MK a go with about the same powder charge and gotten similar results.
Sierra 142gr. MatchKing
OAL 2.924 (2.319 to ogive)
46gr. H4350
Lapua brass
CCI BR-2
Two 5 shot strings, averaged.
Av. 2876 fps., ES-15, SD-8

One of the first bullets I tried was the Berger 140gr. VLD. I does pretty well but still not as fast as I wanted. A big drawback to this load is there isn't much more room for more powder. These are seated .020 into the lands.
Berger 140gr. Target VLD
OAL 3.020 (2.354 to ogive)
47.5gr. H4831sc
Lapua brass
CCI BR-2
Four 5 shot stings, averaged.
Av 2850 fps., ES-19, SD-6

I hesitate to invest in RL-17. I've mainly used it for fire forming. It blows the shoulder out nicely and provide for some pretty good groups to boot. I don't bother to chrono fire forming loads much. The extreme spreads are typically large. This load shoots fairly well dispite having a big jump to the lands.
Lapua 139gr. Scenar
OAL 2.850 (2.285 to ogive)
43.5gr. RL-17
Lapua brass
CCI BR-2
Two 5 shot strings, averaged.
Av. 2848 fps.ES-41, SD-14

I feel like I should be able to get more speed out of this setup, something in the low to mid 2900fps range. It seems like I'm having to use an awful lot of powder to get he speeds I'm getting. Am I overly concerned? Should I just say it is what it is and be happy with what I've got? I've checked in to getting QuickLoad to help me out, but being a Mac user, I'm out of luck there. I suspect my long seating depth is causing the low speeds. If thats the case, can I just keep adding more powder to get what I want? I feel like the pressures are still in the acceptable range. I fear I may have to have my reamer reground with a shorter freebore and rechamber. Bummer!

Any help I could get on this would be much appreciated. I'm not feeling all that good about this whole 260AI project right now. I probably should quit reading on the interweb about how everybodys stuff shoots better than mine

B

 

[Wolfish365]

Re: Too Much Powder Not enough 260AI Speed

Anything in the mid to upper 2800fps range is respectable, and with the Berger VLD's the standard deviation you have going seems great! Don't toss in the towel just yet. Let your rifle break itself in a bit and if you still aren't satisfied then by all means, send the reamer back to Dave at PT&G to get it adjusted.

 

[ChadTRG42]

Re: Too Much Powder Not enough 260AI Speed

2 things- 1st- let the barrel break in to about 150 rounds. After that, see what velocities you are getting. Most new barrels take this many rounds to get their true speed and accuracy. Also, load up 1 round each in about .5 grain increments as high as you can until you find pressure. This way you know how high you can go and can work backwards from there.
2nd- I've talked to several 260 AI shooters, and they all said the same thing. The AI part was not worth the little gain you get over a standard 260 Rem. You will get about 60 to 75 fps, maybe 100, if you are very lucky. But a longer barrel than 25" would help speed things up.

 

[Wolfish365]

Re: Too Much Powder Not enough 260AI Speed

One thing you might consider is David Tubb's Final Finish products. That might help speed up the break-in process. If you want more velocity, go with a longer barrel next time. A 27" is about as long as you'd want for the .260 though. Anything longer than that and you're going to see too much in the way of diminishing returns.

This is a little off topic, but I'm somewhat of a fan ChadTRG42. You've definitely got a gift and the hide is a better place for it with you're input and feedback.

 

[BillCh]

Re: Too Much Powder Not enough 260AI Speed

At a little over 200 rounds down this barrel now I think that its reasonable to believe that its bore is broken in. Yes? I'm not totally unhappy with the accuracy of this barrel at lower speeds. Tubb's Final Finish isn't a consideration for this barrel. Maybe for a factory barrel but not for this one. If I thought that the bore needed it I'd send it back to Brux and have it hand lapped - again.

I suspect the low speed issue is the result my compromise, the combination of long throat and thick brass and heavy bullets and 25.5 inch barrel. And yes, of course a longer barrel would run a little faster. Like the old carpenter joke that goes something like, " cut it twice and it's still to short." Next time around I may go with a 30 inch barrel, not uncommon in F/TR, then I'll be wanting it to shoot as fast as a 6.5-284. But, for now I have a 25.5 inch barrel to work with.

I'm working on getting QuickLoad to run on my Mac. Based on some models provided by some other posters It doesn't look like either H4350 or H4831sc will get me to the next accuracy node I want. A different powder may be the key. Although I haven't taken H4350 to the top, the 46.2 gr. load just seems like a lot. I guess I could load some up to see where I start to get pressure signs.

B

 

[ChadTRG42]

Re: Too Much Powder Not enough 260AI Speed

Thank you so much G Wolf! Very nice of you!

 

[Wolfish365]

Re: Too Much Powder Not enough 260AI Speed

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BillCh</div><div class="ubbcode-body">Tubb's Final Finish isn't a consideration for this barrel. Maybe for a factory barrel but not for this one. If I thought that the bore needed it I'd send it back to Brux and have it hand lapped - again.
</div></div>

Hand Lapping a barrel certainly smooths it out very well, but I suggest the FF because it's a bullet travelling along and fixing contours along the same track that other bullets travel. You can have the smoothest barrel in the world, with no burrs, scratches or anything but you'll lose velocity at the tiniest variation in flight path down that barrel. That's what I was trying to get at. From the sounds of it, you're highly satisfied with the accuracy but are trying to chase down higher speeds for getting further down the field with less drop and windage. Hopefully you find what you're looking for. Let us know how taking your loads higher works out.

And Chad, you're welcome. A little gratification to a person deserving of it is a sign of respect and costs nothing but the truth.