Trying to reduce SD

[ScottMcc]

What about Varget in 308?

 

[Laurie]

What about Varget in 308?

It works with 210-230gn bullets but is a bit too fast burning especially for the 230. As a result, maximum safe loads produce lower MVs than powders in the Re17 / 4350 / N550 class. Re17 and N550 are also double-base 'high energy' (nitro-glycerine added to the nitrocellulose base) and give more energy = MV, but usually at the expense of more rapid barrel throat wear.

 

[Boisblancboy]

I don't care what my MV would be as long as I can keep the bullet super sonic at 1000 yds.

 

[amlevin]

I gave up on RL17 because of temperature problems with hot barrels and attendant velocity variation.

Temperature is certainly a "variable" that needs to be considered yet how many shooters pay attention to how long the cartridge sits in the chamber soaking up heat from the barrel/action?

I've found that when working up a load or "speed testing" I get better results when I pay attention to how long I have had a round chambered. If the winds are erratic I may not chamber a round until they steady down or have a momentary lull.

I find the biggest changes when it's cold outside and the barrel has a couple dozen rounds through it already.

As for RL-17 in my .308, I've only had success using it with Berger 185 gr Juggernauts. Now if I could only get more of each

 

[Keith Glasscock]

I'm using a RCBS ChargeMaster 1500 Powder Scale and Dispenser that I set to .3 gr short of what load I'm looking for and hand trickle the rest in.

I think we just found your problem.

The scale on the Chargemaster is not sensitive enough to allow you to hand trickle slowly.

Try this, set scale to 0, then trickle powder very slow (I used Omega trickler for this test), you can get a few grains of powder in the pan without the scale ever reading higher than 0.

I have an Ohaus built old RCBS scale that does the same thing. The trick is that it has a zero holding function to avoid the scale drifting away from zero when empty. If I do the same test with a 5gr calibration weight in the pan, the scale dutifully clicks off a tenth every 4-5 kernels of powder...

Sadly, I think the problem is RL-17. Out of curiosity, is the slowest shot in the first 2-3? and the fastest near the end of the string?

I ask because we can get quite wound up in statistical measures over a number of shots, but here is the test: can you, as a shooter, see a pattern wherein you can predict accurately the fall of the next shot? For example, I can shoot a perfectly waterline 20 shot string with an ES of 100 *if* every shot is 5 fps faster than the prior shot. The bullets would simply climb the target, and I could simply hold a little lower each shot. On the other hand, I couldn't even guarantee hitting the target board if there was a 100 ES and the velocity was erratic.

As for fixing your problem: Are you still jumping those big Bergers? Try backing down and working back up with the bullet jammed (mine liked the 215's jammed). Be sure to go slow because the pressure can build fast.

Why jam? In a nutshell, the powder has X amount of room to burn and will build pressure over a given curve. When the bullet first moves, the game changes. If the powder isn't all burning, it will not necessarily burn consistently from shot to shot. If we increase the pressure built before the bullet moves, we give the powder a split second more to get lit before the bullet moves.

Give QL a look with a start pressure of 10600 psi before you start. The max pressure and total velocity can change quite a bit. As always, go a bit lower than QL thinks is safe. It is just a computer program after all.

 

[Laurie]

Sadly, I think the problem is RL-17.

.................. + 1 on that.

As for fixing your problem: Are you still jumping those big Bergers? Try backing down and working back up with the bullet jammed (mine liked the 215's jammed)

Reading German Salazar's recommendations for .30-06 loads on his Rifleman's Journal Blogspot, I was struck that he jams everything including the old faithfuls that we all *know* will happily jump a half-inch such as the 190gn Sierra MK. Anything German does, he does for a reason, usually a very good one!

FWIW, my experience of the lighter Hybrids in 308W has made me think that on balance, it's easier to treat them as VLDs rather than assume they behave in a similar way to an MK, Berger BT, or other traditional tangent ogive bullet. Combinations that just wouldn't perform were transformed by moving to 15-thou *in* seating.

 

[Boisblancboy]

I've got about .009 to reach the lands right now. One thing for I know would help is if I could turn the necks on my win brass, but with the Sammy spec neck chamber ill just be going through brass way too fast.

 

[Erik Cortina]

I've got about .009 to reach the lands right now. One thing for I know would help is if I could turn the necks on my win brass, but with the Sammy spec neck chamber ill just be going through brass way too fast.

You don't need to turn necks. Follow the advise given and your ES will be reduced.

 

[Boisblancboy]

So turning necks is not going to show any improvement?

 

[Erik Cortina]

Not as much as the other things mentioned.

 

[Cakes]

++ to Steve's comments on the lower ES's coming from the peak of the pressure curve. I also agree that on the statistical side of all this SD is not as important as ES, IMO. Yes they are related to each other but if you can get your ES's day in and day out 5-15fps (large sample) you have found a load with the minimum vertical. I personally would start with powder charge/change and neck tension. I'll also agree that RL-17 is a likely culprit. I started using RL-17 on my .284 when it first came out and could not get acceptable ES"s. Switched powders and with a little tinkering settled into ES's of 8-12. Leave a round in a hot chamber for more than a few seconds and yes you'll throw one high. Good Luck with your adventure! Eric in DL

 

[mpumulanga]

Hi Laurie

You underestimate the Match Rifle fraternity. H4350 has been used for years, especially by the Australians with 208 AMax and 210's. Because its not a High Energy powder, it cant compete with R17 and N550 for velocity so as a result lost favour

 

[Laurie]

You underestimate the Match Rifle fraternity.

NO! .... that I would never do! I often wish I knew more of what you guys have done as I'm sure we F/TR shooters are often attempting to reinvent the Match Rifle wheel.

MR is something I'd like to try one of these days. Living in York, I'm in between the two MR shooting centres of Bisley and Blair, but who knows when the pressure eases a bit on F-Class activities?

 

[wolfman]

Out of curiosity, has anyone tried N160, or N165 with the heavier .308 bullets?

 

[Steve Blair]

Out of curiosity, has anyone tried N160, or N165 with the heavier .308 bullets?

[br]
I've tried N550 and 230s with good results. The N16X powders seem too bulky for .308 powder capacity.

 

[wolfman]

I can see N160/165 being too bulky for the 230's, but I was thinking about the 200 and 215's. I shot N150 under the 185 BT's for a couple of seasons and did well with it. I'm about to start testing a new rifle, and I'm really hoping to come up with an optimum 215 load.

 

[Erik Cortina]

I can see N160/165 being too bulky for the 230's, but I was thinking about the 200 and 215's. I shot N150 under the 185 BT's for a couple of seasons and did well with it. I'm about to start testing a new rifle, and I'm really hoping to come up with an optimum 215 load.

The 200's and 215's take more powder than the 230's.

 

[Laurie]

I've heard of the occasional person who has tried N160 with 200/210gn bullets, but velocities were very low even with heavily compressed charges.

Here's what QuickLOAD suggests for the 210gn Berger VLD in a 5% compresssed load, 30-inch barrel and using the water overflow capacity I get from a Winchester case fireformed to my rifle's chamber and at 3.00" COAL. Shot start pressure has been set at 10,000 psi + assuming the bullet will be seated into the lands:

Cartridge : .308 Win.
Bullet : .308, 210, Berger M T VLD #30415-515
Useable Case Capaci: 48.743 grain H2O = 3.165 cm³
Cartridge O.A.L. L6: 3.000 inch = 76.20 mm
Barrel Length : 30.0 inch = 762.0 mm
Powder : Vihtavuori N160

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.249% 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

-02.5 103 44.17 2322 2513 48380 5270 93.5 1.584
-02.2 103 44.28 2327 2525 48693 5283 93.6 1.580
-02.0 103 44.40 2333 2537 49009 5297 93.7 1.575
-01.7 103 44.51 2338 2549 49328 5310 93.8 1.571
-01.5 104 44.62 2344 2561 49647 5323 93.9 1.567
-01.2 104 44.74 2349 2573 49972 5336 94.0 1.563
-01.0 104 44.85 2355 2585 50297 5349 94.1 1.559
-00.7 104 44.96 2360 2597 50627 5362 94.2 1.555
-00.5 105 45.07 2366 2609 50958 5375 94.3 1.551
-00.2 105 45.19 2371 2621 51293 5388 94.3 1.547 ! Near Maximum !
+00.0 105 45.30 2376 2634 51629 5401 94.4 1.543 ! Near Maximum !
+00.2 105 45.41 2382 2646 51969 5414 94.5 1.539 ! Near Maximum !
+00.5 106 45.53 2387 2658 52313 5427 94.6 1.535 ! Near Maximum !
+00.7 106 45.64 2393 2670 52659 5439 94.7 1.532 ! Near Maximum !
+01.0 106 45.75 2398 2682 53007 5452 94.8 1.528 ! Near Maximum !
+01.2 106 45.86 2404 2695 53359 5464 94.9 1.524 ! Near Maximum !

Results caused by ± 10% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 10% relative to nominal value:
+Ba 105 45.30 2491 2894 60138 5455 98.7 1.463 !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba 105 45.30 2235 2329 43957 5125 87.2 1.642


MVs under 2,400 fps are poor for this bullet in a 30-inch barrel. The key value is the % of charge burned. Figures in the low 90s show it's an inefficient combination.

Switching to an only slightly lower charge weight of N550 reduces the fill-ratio to just below 100% (due to the powder's smaller kernels and increased density from the N-C infusion) raises peak pressures up to 308W max allowed ~60,000 psi and MVs to the 2,550 fps level while estimating there will be complete combustion of the powder charge.

 

[wolfman]

Thanks Laurie and Eric- I'll cross those two off the list!