New ELR bullet testing

[jmason]

This post is rooted here on sniper's hide but I thought some of you guys would like to see it as well. I was lucky enough to get to shoot some new projectiles.

Today I ran some maximum safe velocity testing with the ZA 338 280.5 grain Match bullets. No accuracy testing was done at this time. All shots fired from a 338-408 Improved with a 30" barrel.

Distance to first Chronograph screen: 13'4"
Temp. 39F
Humidity 69%
Station Pressure 28.59

Based on other data I'd collected I thought 142 grains of RL-50 would be a safe place to start. Below are my sample charges and velocities.

142gr = 3278fps
147gr = 3377fps
152gr = 3479fps
154gr = 3518fps

I got a maximum velocity of 3518 w/ RL-50. The Primer was still round around the edges but some firing pin hole puckering was becoming evident. Given this is well over 100 FPS faster than I could run other 300 gr conventional, and solid bullets, I saw no reason to push. I Highly doubt I'm burning all the powder I'm putting through it. I feel pretty strongly a longer barrel would offer some increase on the top end.

Without any other test firing I simply loaded what I felt was the maximum safe powder charge(not knowing if it would produce an acceptable ES). I chose 153 Grains of RL-50 for 6 shots. It produced an ES of 8 and avg velocity of 3508 fps. Even though these bullets were not designed for my barrel they did produce sub MOA groups at 100 yards.

338 MK--280.5 ZA--325 rock mountain
https://www.dropbox.com/sh/80y90zuwjy23tu1/9NhAxk_f0B
/2014-02-08%2014.58.02.jpg

https://www.dropbox.com/sh/80y90zuwjy23tu1/TR3VKjZA2u/2014-02-08 14.58.13.jpg

https://www.dropbox.com/sh/80y90zuwjy23tu1/e-XOT-9O-u/2014-02-08 loaded_round.jpg


https://www.dropbox.com/sh/80y90zuwjy23tu1/ZPqlZyQoku/2014-02-09 Accuracy_testing.jpg

https://www.dropbox.com/sh/80y90zuwjy23tu1/MmysZ5gYmb/2014-02-09 100_yard_range.jpg

 

[supercrossbmx69]

What twist rates do these bullets require to keep them stable?

And who makes them? Never seen them before.

 

[Sling]

Gain twist for sure. Look for the ZA system soon.

 

[jmason]

The bulletin barrels are available at this time. They can be obtained through Noel Carlson. He'll probably end up posting in this thread.

 

[noel carlson]

I am not a paid advertiser on this site... so in keeping with forum rules, my comments will be limited to a technical discussion.

John has graciously offered to contribute his time/resources in assisting with the development of a Mach 3+ loading for the ZA projectile/barrel "system".

All who have read the link to Sniper's Hide know that the issue of bore heat-erosion at extreme velocities has been addressed. Common barrel alloys will have a reasonable life, perhaps even above that of normal loadings, with the ceramic bore-lube currently used in conjunction with the solid copper ZA projectile. What has not been established (yet) is the possiblity of reaching the next velocity accuracy node within the MV potential afforded by RL-50. It seems pretty clear to me that 3,600 fps is obtainable with an additional 4-6" on John's barrel. If he can obtain a sub-half MOA accuracy with the 280 grain projectile between 3,400-3,600 fps, I will consider his experiment a success. We may have to adopt a bull pup configuration to make it ergonomically practical, but the overall goal is well within reach.

Any questions?

 

[jmason]

The bulletin barrels are available at this time. They can be obtained through Noel Carlson. He'll probably end up posting in this thread.

I meant bullets and barrels. I gotta quit typing on my phone!

 

[ELR Researcher]

What twist rates do these bullets require to keep them stable?

jmason - open question (above).

 

[noel carlson]

ELR Researcher,

"What twist rates do these bullets require to keep them stable?"...

The ZA338 used in this test is compatible with standard bore/groove dimensions, and is a two year old design that will never be publicly released. Therefore; in a strict sense, the specific answer to your question has no consumer utility. However; within a generalized context, a 16-18 caliber exit-twist will stabilize any 6.4 caliber ZA projectile regardless of diameter (the bracket spread is to accommodate a variable Reynolds number). I hesitate to dwell on that piece of information due to the fact that I am actually using a 14 caliber exit twist-rate rifling geometry in a proprietary bore/groove dimension. There are reasons for this that go beyond projectile stabilization, and focus upon drag reduction. The engraving bands require full effacement to achieve potential aeroballistic efficiency.

 

[jmason]

Noel you gotta put that in English for the rest of us.

I think maybe the question that is better to ask is what kind if barrel do I need to stabilze your new offering and what kind of twist is it?

Can I run your bullets through a conventionally rifled barrel?

 

[noel carlson]

"I think maybe the question that is better to ask is what kind if barrel do I need to stabilze your new offering and what kind of twist is it?"...

The barrel needed to stabilize the new ZA338 is a variable gain-twist, in an .008" oversize 338 bore dimension. Rifling geometry is in a twist configuration greater than that required to stabilize the projectile, and much faster than a jacketed bullet can safely be put through... in this case, a 1: 4.7" exit rate.

The purpose of such a high gain function is to eliminate the engraving bands, and produce a smooth projectile shaft in .338 diameter at muzzle exit. This adds ~18% to the ballistic coefficient.

 

[noel carlson]

"Can I run your bullets through a conventionally rifled barrel?"...

No.

 

[Kiwi Greg]

Looks very interesting Noel, keep up the good work