260AI with 140gr. bullet is too slow?

[Billch]

Hi 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. 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 think I should be getting. 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 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

 

[SDDasher]

I am in a similar situation with my 260 Remington, 30" Krieger 1x8 twist Panda Action. I have used RL17 with some pretty good numbers using the Berger 140 Hybrid jumped .020 but nothing outstanding. I am considering trying some Berger 130's which show great speed and ballistic numbers in Quick Load. Is anyone using the 130's in competition?

 

[bheadboy]

I sold my 260ai for this very reason, i do not believe the case bbl dia. offers any significant improvement and holds the accurcy it should.

went to 7-08 AI and huuahhhhh
Bob

 

[Laurie]

Bill,

I think you're expecting too much from a 25.5" barrel that has been throated on the long side. 2,850 fps or thereabouts is a good MV with 140/142s from the standard .260 Rem in a properly throated 30" barrel and the extra AI capacity would give you somewhere between 50 and 100 fps. In your case, the extra AI capacity is mostly or entirely compensating for the loss of four and a half inches of barrel that would normally be on a long-range target rifle.

Throating the chamber out wasn't a poor move, but you usually find you need to use significantly higher charges than you'd expected to get the desired MVs and the data provided by Hodgdon etc becomes significantly understated being based on a short throated test barrel. On top of that, as is said again and again on this forum and elsewhere, every barrel (and one sometimes feels, every chronograph too) is different. I'd be happy myself with what you're achieving with your barrel length and wouldn't worry about what I see others claim.

QuicKLOAD doesn't list 260R AI, but I've input your 142gn SMK load and increased the case capacity to 57gn water. It calculates an MV very close to what you're getting, but at a chamber pressure of 62,886 psi getting on for 3,000 psi above CIP maximum.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Cartridge : .260 Rem
Bullet : .264, 142, Sierra HPBT MatchK 1742
Useable Case Capaci: 50.885 grain H2O = 3.304 cm³
Cartridge O.A.L. L6: 2.924 inch = 74.27 mm
Barrel Length : 25.5 inch = 647.7 mm
Powder : Hodgdon H4350

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.482% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step Fill. Charge Vel. Energy Pmax Pmuz Prop.Burnt B_Time
% % Grains fps ft.lbs psi psi % ms

-04.8 95 43.78 2741 2368 54335 9143 99.1 1.317 ! Near Maximum !
-04.3 96 44.01 2753 2389 55135 9176 99.2 1.308 ! Near Maximum !
-03.9 96 44.23 2765 2411 55947 9208 99.3 1.299 ! Near Maximum !
-03.4 97 44.45 2778 2433 56771 9240 99.4 1.291 ! Near Maximum !
-02.9 97 44.67 2790 2454 57607 9270 99.5 1.283 ! Near Maximum !
-02.4 98 44.89 2802 2476 58455 9300 99.5 1.274 ! Near Maximum !
-01.9 98 45.11 2815 2498 59315 9329 99.6 1.266 ! Near Maximum !
-01.4 99 45.34 2827 2520 60188 9358 99.7 1.258 !DANGEROUS LOAD-DO NOT USE!
-01.0 99 45.56 2839 2542 61074 9385 99.7 1.250 !DANGEROUS LOAD-DO NOT USE!
-00.5 100 45.78 2852 2564 61974 9412 99.8 1.242 !DANGEROUS LOAD-DO NOT USE!
+00.0 100 46.00 2864 2586 62886 9438 99.8 1.234 !DANGEROUS LOAD-DO NOT USE!
+00.5 101 46.22 2876 2608 63812 9463 99.8 1.226 !DANGEROUS LOAD-DO NOT USE!
+01.0 101 46.44 2888 2630 64752 9487 99.9 1.218 !DANGEROUS LOAD-DO NOT USE!
+01.4 102 46.66 2901 2652 65706 9510 99.9 1.210 !DANGEROUS LOAD-DO NOT USE!
+01.9 102 46.89 2913 2675 66675 9533 99.9 1.202 !DANGEROUS LOAD-DO NOT USE!
+02.4 103 47.11 2925 2697 67658 9555 100.0 1.195 !DANGEROUS LOAD-DO NOT USE!


NB this is based on my guesstimate of what the AI case internal capacity might work out at and shouldn't be used by anybody except as an illustration, and certainly not for a standard 260 Rem chamber with standard throat based on 2.800" cartridge length or similar.

 

[alf]

For reference,

I'm running a regular 260 in a 23" 8 twist throated for the 140 Bergers.

My go to load is 44.5 grains of H-4350 with moly plated VLD's at 2850.

I found I ran out of room with 4831-SC as well.

I'd hunt for accuracy first, and take what it gives me for velocity......

 

[Billch]

alf,
That 44.5gr./H4350 load of yours is more of what I expected for velocity. Is it a 140gr. moly'd VLD you're using? As for your accuracy over velocity comment, I agree with that prioritization also. I'm happy with the accuracy of this barrel so far. I realized rather quickly that there wasn't any good reason to do any load development at the 100yd. range. Even my fire forming loads look great at that distance.

Laurie,
First off, thank you very much for taking the time to do the QL work-up.
YIKES!! Am I getting close to blowing something up? Not good, not good. I suspect my
saving grace in this regard is the remaining empty case volume after seating the bullets out so far. I haven't taken a measurement, but I'd bet I have room for another 1 to 1 1/2 gains of H4350. Not that I want to go there. My 47.5 gr. H4831sc/140 gr. VLD load is pretty much a full case and doesn't shoot bad at all either. Can I assume that the pressures for this load are more reasonable, safety wise? The biggest reason I went to H4350 over H4831sc was speed. If powder charge density plays a part in this maybe I should just stick with the H4831sc. Site member Techshooter Did an interesting primer study, magnum vs. standard. I may explore in that direction but am now more than a little concerned with the QL pressure predictions.
On the other hand, my RL-17/139 gr. Scenar fire forming load has a relatively huge jump and still shoots well. This makes me wounder if shortening my seating depth (with non-VLD's) will increase my MV without becoming dangerous. I'm having difficulty finding references to the charge weight spectrum for this powder in 260AI. My ignorance of RL-17 makes me leery of it.
I had an educated hunch that the shorter barrel length would give up some speed potential but still be able to produce 2900 fps without much problem.

I can resign to 2850-ish fps, grudgingly, for the 140 gr. weight range bullets.

Bob,
You sure know how to cheer a guy up.

6brmrshtr,
I'm relieved to here someone else is in the same, or simiar, boat as me, misery loves company. I too may try a lighter bullet just for kicks. My concern here would be the mismatch of a shorter bullet with my long throated chamber. I suppose there's only one way to find out. I believe that any trigger time is good practice. If that 130 works out for you, don't keep it a secret.

Thanks all

B

 

[Laurie]

YIKES!! Am I getting close to blowing something up? Not good, not good. I suspect my
saving grace in this regard is the remaining empty case volume after seating the bullets out so far. I haven't taken a measurement, but I'd bet I have room for another 1 to 1 1/2 gains of H4350.

I wouldn't worry unduly - QuickLOAD is very valuable, but is a computer model when all is said and done, not real life which varies a lot depending on various factors, in particular your barrel and chamber dimensions. If you still have some room in the case under a seated bullet, that in itself will reduce the pressure compared to the run I did which gave an exact 100% fill-ratio.


Your H4831sc load is calculated as lower pressure as follows:

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Cartridge : .260 Rem
Bullet : .264, 140, Berger VLD #26401- 504
Useable Case Capaci: 50.341 grain H2O = 3.269 cm³
Cartridge O.A.L. L6: 2.924 inch = 74.27 mm
Barrel Length : 25.5 inch = 647.7 mm
Powder : Hodgdon H4831 SC

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.467% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step Fill. Charge Vel. Energy Pmax Pmuz Prop.Burnt B_Time
% % Grains fps ft.lbs psi psi % ms

-04.7 97 45.28 2680 2233 47814 9347 94.9 1.374
-04.2 97 45.51 2694 2256 48564 9394 95.2 1.364
-03.7 97 45.73 2707 2279 49330 9441 95.4 1.354
-03.3 98 45.95 2721 2302 50107 9486 95.6 1.345
-02.8 98 46.17 2735 2325 50897 9531 95.8 1.335
-02.3 99 46.39 2748 2348 51702 9576 96.0 1.326 ! Near Maximum !
-01.9 99 46.61 2762 2372 52521 9619 96.1 1.317 ! Near Maximum !
-01.4 100 46.84 2776 2395 53356 9662 96.3 1.307 ! Near Maximum !
-00.9 100 47.06 2789 2419 54203 9705 96.5 1.298 ! Near Maximum !
-00.5 101 47.28 2803 2443 55066 9746 96.7 1.289 ! Near Maximum !
+00.0 101 47.50 2817 2466 55945 9787 96.9 1.280 ! Near Maximum !
+00.5 102 47.72 2830 2490 56839 9827 97.0 1.271 ! Near Maximum !
+00.9 102 47.94 2844 2515 57745 9866 97.2 1.262 ! Near Maximum !
+01.4 103 48.16 2858 2539 58675 9905 97.4 1.253 ! Near Maximum !
+01.9 103 48.39 2871 2563 59619 9942 97.5 1.244 !DANGEROUS LOAD-DO NOT USE!
+02.3 104 48.61 2885 2588 60580 9979 97.7 1.236 !DANGEROUS LOAD-DO NOT USE!


Previous caveats apply!! But note, it doesn't give quite the MV you're actually obtaining. Again, it's back to remembering it's a theoretical model even if a good one and not the Oracle.

Seating bullets deeper doesn't affect pressures unduly in itself, unless you're currently running your VLD loads with the bullet pushed really deep into the rifling, a truly hard 'jam', which usually doesn't see good accuracy. Otherwise seating bullets deeper onto a full case load of powder may damage the powder kernels and over compress the charge affecting ignition adversely, if marginally. It's the throat configuration (length) that is important here. When the primer fires, it alone generates enough pressure to push the bullet out of the case into the rifling leade, expand the case almost to fit the chamber. It's the volume of the expanded case behind the bullet base at that point in the ignition burn process that is crucial in the first millisecond or so of the charge burn before the bullet moves down the bore expanding the total available combustion chamber volume.

 

[dennisinaz]

Don't be afraid to use R17. I find it a wonderful 260AI powder. I get very acceptable SD and ES. Velocity is close to yours with a 22" barrel.

I also have had good luck with Mag Pro. 4350 is a standby target powder and performs best with 30" barrels

 

[ShaneG.]

I'm shooting a 260ai with 140 Amax's. I ran some 4831sc up to 48.5g and was getting around the 2950 mark give or take a little depending on the brass. I did use some 4350 but didn't keep any of that data.

I had a lot of Alliant 2000MR so I started using that I ran up to 43.5 grains with it and it puts me in the same ballpark of velocity. This is with a 28" barrel and Rem. 308 brass necked down and Tula primers.

I also played with some Ramshot Magnum which pretty much filled the case way up into the neck and some reloader 22 also which filled the case very full.

 

[BoilerUP]

As another point of reference for a "standard" 260 Rem, my 26" 8 twist 260 Rem Criterion barrel gets 2820fps with 43.2gr H4350, 140gr A-Max @ 2.89" COAL, Lapua brass.

 

[Forum Boss]

For more velocity in a .260, as others have noted, RL17 works extremely well for many guys.

My solution with a shorter barrel was to run the Scenar 123. It is a very accurate bullet, not finicky. You should be able to get to 2950 without issues unless you have a very slow barrel. I reached 2950 fps with H4350 and 123s in a 24" factory barrel. Like you, I was stuck around 2830 with the 140s-142s. (This was pre-release of Reloder 17).

Another excellent bullet is the Berger 130-grainer, but I can't predict velocity on that.

 

[Jay Christopherson]

I use RL-17 in my .260AI with 140gn. Bergers and I'm able to easily get 3020fps without maxing out my load. Of course, I have a 30" barrel too, which makes a big difference. You might give RL-17 a try though. I'm guessing that while you probably won't break 3000fps with a 25" barrel, you should be able to get more velocity than what you are seeing with H4350.

 

[BoilerUP]

[quote author=Forum Boss]Another excellent bullet is the Berger 130-grainer, but I can't predict velocity on that.[/quote]

Same rifle/barrel I mention above gets 3000fps+ with 43.5gr RL17, Berger 130gr VLD @ 2.94"COAL, Lapua brass.

 

[Billch]

Laurie
I suppose this low speed issue is the result my compromise, the combination of long throat and thick brass and heavy bullets and 25.5 inch barrel.
I don't mind not having to consider the doughnut that may or may not form in the case during fire forming. However, I keep thinking that the next time around I may shorten up that free bore a bit. I've got an internal neck reamer that I can use to remove doughnuts if need be. Using another brand of brass has crossed my mind. Your thoughts on this? I'm not sure if it would help me any. I've used Win. Fed. and L.C. brass in my 308 F/TR rifle. Its all seemed to move around a lot, relatively. I kept coming back to the Lapua. The rest I've relegated to the ammo feed bag for my M1A where it can die an honorable death. One thing is plainly evident, this particular chambering is providing for some very stable brass. Despite the high pressures indicated by you QL simulations I'm not getting much case deformation. It takes very little to get it back in shape for the next go 'round. I'm loving that. My barrel length was originally supposed to be 26 inches long. During the finishing process, It was decided that the last half inch at the muzzle end should be trimmed of to remove a slight bit of belling to maximize accuracy potential at the expense of speed potential. I'd rather have the accuracy than the speed. Wouldn't we all?
Thanks again for the QL for H4831sc. Same speed - lower pressure, It makes me feel better! 47.5 gr. of H4831sc is pretty much a full case, with maybe room for another 1/10 or two. I've never been convinced that compressed loads were the way to go unless as a last resort, especially these days where in there are so may different powders to chose from.
As mentioned by others, perhaps a few more rounds down the pipe will show some speed gain. I'm at around 200 now. Time will tell, but I'm not holding my breath for that. I think it may be time to just work on fine tuning for what I've got.

B

 

[Billch]

For more velocity in a .260, as others have noted, RL17 works extremely well for many guys.
My solution with a shorter barrel was to run the Scenar 123. It is a very accurate bullet, not finicky. You should be able to get to 2950 without issues unless you have a very slow barrel. I reached 2950 fps with H4350 and 123s in a 24" factory barrel. Like you, I was stuck around 2830 with the 140s-142s. (This was pre-release of Reloder 17).
Another excellent bullet is the Berger 130-grainer, but I can't predict velocity on that.

I've got an unopened box of 123 gr. MK's on the shelf. One of these days I'll give them a try I'm sure. My main point of this whole project was to be able to use the bullets with the higher BC's. Not that the 123 gr. Scenars or MK's are slouches by any means. While speed diminishes, BC is forever.
The 139 gr. Scenars haven't done bad for me in this rifle, contrary to the 155 gr. Scenars I've tried in my 308. I may end up melting those down to try to extract the gold that's in them, certainly there's some in there somewhere!

BoilerUP,
You and jaychris seem to be having favorable results with RL-17. That's encouraging. My worry with the RL-17 is two fold, I suspect that there isn't any powder out there that'll be able to get me to the low 2900's, and I'm having a tough time finding much information about it. I guess I'm being a little self defeating here, but my previously high pressures are holding me up from trying the RL-17. The 4831sc is better than the H4350 for me, pressure wise. It could be that RL-17 is better yet.

If I may relate a bad joke that comes to mind:
A guy goes to his bookie to pay out on a loosing bet he'd made on several professional basketball games. At the same time, he places bets on a few more upcoming NBA games. The bookie takes the guys money and records the new bets. Having a sympathetic urge the bookie says to the guy, "Hey, your a great customer all, but I hate to see you lose all the time. Why don't you bet on something else for a change, like some other sport. Maybe you'd have better luck."
The guy replies, "I would but I don't know anything about other sports. All I know is pro basketball." ???

I think I'll give my jug of RL-17 another look.

If I do some thinking I could figure how your 2.940 COAL for the 130 relates to my 3.020 COAL for the 140. Obviously I have a longer throat to fill. I'm afraid the 130 gr. VLD is just too short for me. What is the length of the 130 gr. VLD? I'm wondering if they aren't possibly the same. I'm not firmly apposed to going with a lighter bullet.

B

 

[BoilerUP]

My experience has been you can match a given charge's H4350 velocities with about 1gr less RL17...and run RL17 very close to the H4350 charge without pressure.

My experience has also been RL17 isn't outrageously insensitive to ambient temperatures, but leaving ammo in direct sunlight (like this guy stupidly did) can make it spike. I've experienced something like a 120fps extreme spread with RL17 across many different range trips (ES each trip around 10), but 3000fps is my average for the 130 VLD/43.5gr load (about 0.010" off lands) through multiple tests.

Although, vast majority of that huge 120fps spread came from me leaving my ammo box open, in direct sunlight, for about 90 minutes prior to shooting on one particular trip. IIRC they went across the chrony at an average around 3090fps, though brass showed no pressure, and while POI obviously shifted due to velocity all 5-shot groups at 2970fps thru 3090fps were always 0.5" @ 100yd (about all I can do as the rifle's driver right now).

...and 44.0gr RL17 will drive a 123gr A-Max at 3100fps in my rifle...again, no pressure.

 

[.260 james]

To Billch:
Give the Reloder 17 a fair shake. With good working pressure loads should give you around 100 fps over the H4831 and H4350 loads. A 130 gr. Berger give give you even more velocity.

 

[XTR]

I can't help you with the 260 loads, I don't shoot one, but I will tell you that based on what I've read on the internet I must have the slowest Krieger and Rock Creek barrels ever made. I've seen guys post MVs out of a 20" 308 using the same load I do in a 30" barrel and they get 50 to 100 FPS more than me. I guess we just have heavy air here or something.

[/sarcasm]

In all seriousness, the brass makes a big difference, Lapua is much thicker than WW. Us F class shooters have been known to use that extra case capacity to drive light bullets really fast. I didn't notice in your posts, are you using the same brass as was used to develop the tables?

Seating long effectively gives more case capacity, and if you work up to it it can be used to load more powder to get more MV.

I guess the real question to answer is why do you need the extra 75 FPS?

 

[Billch]

QuickLoad on the way.

After doing some reading, and scouring the internet, I've come to the conclusion that I need a different powder to get me to my goal of the 2950 fps range. The QuickLoad models Laurie has so kindly provided, and the work of Chris Long, have inspired me to consider optimal barrel times. My load development thus far has nearly coincided with those predictions and my actual accuracy nodes. With H4350 and H4831sc, it doesn't appear I can get there with a 140 gr. bullet.

I ordered QuickLoad and Hopefully I'll be be able to get it up and running for next weekend. It can only help. I'm curious as to what the QL predictions will be for RL-17 (and others), as so many people are reporting success with it.

I've got some Hunter loaded up for a round-robin target session this morning. Its a fine day for shooting.

Thanks all for the help.

B

 

[vervi1jw]

You velocities are definitely low. I shoot a 28inch Criterion on a savage action. Load data as follows

Lapua case
140 amax
FGGM primer
47.5gr of H4831SC
COAL 2.83
Velocity-2905 fps

This is not a max load and is very very accurate.

42gr of H4350 has netted me 2800 fps with an SD of 7, it is very very accurate and way below max.

I am thinking that you just have a slow barrel. ow has the accuracy been? Also, I backed mine down from 2900 because the 100fps gain doesn't do a whole lot and also significantly reduces barrel life. Also, is the Chronograph you are using reliable? May try another Chronograph and you might get different results. I had this issue before.