Extreme Spread

[@nd]

Are ES and S-D more noticeable in some reloading powders than in others?

Today I shot over a chrono 4 loads that I put together with two bullet weights and three different powders. One of the powders has a noticeably higher ES and S-D than the other two.

 

Load1; RL15 123gr SMK the ES was 13 the S-D was 5

Load 2; Varget 123gr SMK the ES was10 the S-D was 4.1

Load 3; N550 123gr SMK the ES was 52 the S-D was 20.3

Load 4; N550 130gr TMK the ES was 49 the S-D was20.2

 

All were fired over a magneto speed v3 in the same weather conditions.

All the powder loads were dropped from the same powder dispenser and trickled up to weight with a Target Master trickler. The same make/type of primers were used and new Lapua 6.5x47 brass was also used for all rounds.

I have tried to keep everything as uniform as possible.

Any ideas why the N550 have such a big velocity variation.

Thanks

And

[gbal]

And-others-like Laurie- will have empirical answers to your immediate question....

 

You don't mention range/target or group sizes,but here is some 'theoretical' figures for the effect of differences in SD consistency ( from 308,175 SMK @2600 mv),given 1mph wind accuracy,1 yard range accuracy,and .5 moa rifle/ammo precision:

 

10fps SD hits on gongs at 600y 5" 73% 10" 99% 15" 100%

 

15 fps ditto 5" 67% 10" 98% 15" 100%

 

20 fps ditto 5" 55% 10"96 15' 100%

 

 

by 800y,the 10fps 5" % is down to 34%;the 20fps 5" is down to 26%,and the 20 fps 5" is down to 20%

 

increasing fps SD degrades hit % with even very good rigs/shooting as range increases (and small target ,of course...it's still around 43 % on a 15 inch gong at 1000y with 20fps SD,though only7% with a 5"gong).

 

Out to 500y , 10" to 15" hits hold 100% (though 5" are 93%,91%,83% for 5.10,20 fps SD).

 

This might put the SD variation into some perspective....depending your desired/acceptable accuracy,how much need you 'improve'-compared to other variables (like moa,windreading......costs).

 

gbal

[Laurie]

ES / SD is affected by so many factors, it's difficult to be definitive. Ignoring physical things like neck tension levels and/or variations and the amount of bullet jump (yes - changing seating depths can change your ES significantly), it really comes down to how 'happy' a load combination is so far as your barrel / chamber is concerned.

 

In a case like this, it's most likely an ignition / charge burn behaviour issue. VarGet is well known as an 'easy igniter' as well as being a very flexible number within its limits. You don't say what the cartridge is, and there is also a significant difference in burning rates between VarGet and N550, more than enough to see the former ideally suited to an application while N550 could be sub optimal.

 

With VarGet being easy to ignite and generally 'unfussy' in proper applications, this also means it is reasonably primer and charge weight tolerant. N550 is a fine powder but can be 'fussy' at times resulting in some primers giving much better results than others. Many, but not all, true double-based (ie primarily ball types) and added nitroglycerin 'High-energy' powders such as the Viht N500 grades often need to be well into the 50,000s psi pressure range before they operate with optimum efficiency and consistency. This sometimes shows up as a velocity jump in a rising series of charge weights which is much larger than expected in relation to the charge weight increment.

[@nd]

Thanks for the replies

The cartridge is 6.5x47 Lapua,the bullet seated to maximum mag depth,the primers are CCI 450 small rifle.

my rifle has a 26'' barrel with a 1in 8 twist

The N550 was working up to Vihtavouri's maximum load on their website.

The RL15 and Varget are recommendations but being worked up to with no pressure signs.

i just couldn't see why keeping everything as uniform as i could there would be such a large difference velocity in one powder.

And

[Laurie]

Depending on how the rifle is throated and the resulting allowable COAL, QuickLOAD reckons Viht's Max N550 load with a 123 generates from just under 50,000 psi to around 54,000 psi. Typical H. VarGet 6.5X47 loads see around 60-63,000 psi, both having 100% or getting there case-fill ratios.

 

Although I'm very wary about QuickLOAD and this cartridge, in this case the program's predicted MV is close to that in Viht's data. Those pressures give you the most likely cause. Simply, the N550 combination is probably not running at a high enough pressure to get it to optimum efficiency for a 'high-energy' propellant.

[@nd]

Laurie Thanks

I don't have quickLOAD so was going on Vhits powder weights.

I think i have found good 123gr SMK loads with Varget and RL15 that i am happy with.

I will make up more loads with the N550 loads at higher powder weights to see if i get any better results with both the 123gr SMK and 130 TMK.

Andrew