[Nekekami]

A friend and I have been working on an off with an experimental cartridge, namely 6.5x70. We got hold of a box of empty .338 casings, and have been in the process of reducing the size of the neck, to fit the 6.5mm bullet.

Projectile: 6.5mm pprj 41(AP projectile)
Projectile weight: 7.3g
Propellant: Åkb 113
Propellant Weight: 4.5g (For the first tests, we'll use less propellant than the casing can hold, for safety reasons I'll explain later)
Primer: Federal 215

For this project, we've gotten some help from an armourer working at FMV. He's helped us build a prototype barrel with a very simple action. It's meant to be fired from a fixed mount especially for testing purposes, in this case a heavy tripod originally used for M2 machine guns. The first test will be in one month. Unfortunately, the test will have to take place on a military range, down in Karlsborg, and unless I get a permit, I will not be allowed to bring a camera in with me into that area. I have applied for a permit, but I have no serious expectation of being granted one. I'll post an update when we have data from the testing.

 

[Nekekami]

OK, I did not get a permit to bring a camera in, so I will be unable to take any pics. I guess the upside is that I won't have to spend time asking friends to let me borrow their cameras. (Being a poor student sucks, especially when you have bills to pay).

 

[mele]

This sounds interesting. I'm anxious to see how the results go. Keep us posted.

MEL

 

[Nekekami]

Will do. I'm quite excited about this, since it could be a really nice long range caliber if we got our calculations right, as well as our modification of the casings...

 

[Guest]

That sounds like it would be fun... but wouldn't you run into the same problem to be had with the 6.5-284 in that it'll burn the heck out of your barrel really quickly?

 

[Nekekami]

Jake:

I don't think so.
Especially since I hadn't heard about the problem until talking to you people across the atlantic. When talking to hunters and sports shooters over here, barrel burn isn't a problem for any of the 6.5 variants.

 

[mele]

I talked to a few more barrel pros and it seems to be that a big contributor to throat errosion is continued rapid firing of rounds with a hot barrel. Some people believe if you take your time and don't fire too many rounds in rapid succession, barrel life will be fine with the hot 6.5 variants. I'm not sure if this is why the Europeans do not experience this problem, or if they just know a secret that manufacturers do not know over here yet, but Nek is right, there is no reported problems in Europe about 6.5 barrel burn out, even with the hot 6.5's

MEL

 

[Guest]

Well, in that case it would sound as though you have something promising here!

 

[Nekekami]

OK, the first twenty rounds have been proof-fired.

With the amount of gunpowder exceeding normal 6.5x55 loads, thanks to the larger casing, we achieved an average muzzle velocity of almost 1030m/s, and as we increase the amount of gunpowder, it should reach even higher velocities. Due to the testing barrel we're using, we're not doing any accuracy tests yet.

 

[Nekekami]

We did have the time for some further testing of this round, before the accident.

We're now at the following stats, following some major changes:

Switched to the Lapua D343 FMJBT bullet. Weight 9.3 grams, BC is 0.635
Switched to Norma MRP-204, using 78 grains(Still safely within the safety margins of Lapua-manufactured .338LM casings. They are constructed to handle a pressure of 470MPa, CIP rating is 420MPa, and we're still below 400MPa)
Firing from a TRG-42 with a proper 27" barrel with 1 in 11 twist, instead of our home-built budget testing rig with a barrel that was not bloody expensive.

Firing conditions at the day was:
Temperature, 24 degrees Celsius in the shadows, 31 in the sun.
Humidity, 78%
Wind, 5m/s(roughly 11mph), coming more or less perpendicular to the line of fire(Yes, we were lucky).
Air pressure: 994hPa
Altitude, 65m ASL

We only had access to a short firing range, so we did our shooting at a range of 600m.
Zero at 300m
Average muzzle velocity: 1248.3m/s, following data taken from the median velocity bullet, 1250.2m/s

Bullet Drop in mm(Conversion for those who don't know the metric system: 1 inch=25.4mm):
100 200 300 400 500 600
45 61 0 -146 -386 -732

Energy in Joules
Muzzle 100 200 300 400 500 600
7268 6571 5928 5335 4790 4288 3828

Wind drift in mm, crosswind of 5m/s
100 200 300 400 500 600
10 42 96 176 282 418

Time of flight in seconds:
100 200 300 400 500 600
0.082 0.168 0.259 0.355 0.456 0.546

The best group for the day was 46mm, average around 58mm, so there are a few more things we need fixed before we make a super-accurate wildcat, but even now it shoots flat(flatter than even Lapua's 48.5gram .50BMG bullets with a BC of 0.930 loaded to a muzzle velocity of 930m/s, and the wind drift of that .50BMG load in the same conditions is 412mm, just 6mm less...), and it travels fast, increasing probability of hit. Armour penetration is good, due to the high energies involved(and Mel, energy matters a _lot_, since force is a function of energy over time), concentrated over a small area. It definitely penetrates vests and such better than the .300WM. The interesting thing is that our load delivers the same energy out at 600m that many 7.62x51 loads can barely achieve at the muzzle.

Next project will be to find some sabots and some gunpowder meant for the FSAPDS-T projectiles the Army uses for their 40mm autocannons on the Strf9040, and maybe we'll get the bullet to travel faster than 1500m/s...

 

[Shoe]

Perhaps I misinterpreted your statements Nek, but didn't I see the phrase "before the accident" in there? May I ask what happened and is everybody/thing alright?

 

[mele]

Remarkable results! This round obviously is an exceptional long range cartridge. Now, tell us why the sabot and different powder? I thought you had necked the .338 Lapua case down to 6.5, is this correct still?

MEL

 

[Nekekami]

Shoe:

Read my entry in the I'm Back thread in misc. :arrow:

Mel:

Yes, we're currently using a necked down .338LM casing, but he's still got the original barrel for the TRG-42 left, and we want to experiment with other variants. We think that we can get the bullet to leave the muzzle at over 1500m/s, but we need special propellant for that, and the sabots should help too.

 

[mele]

Ah! Gotcha.

How did you measure the 600 yard performance of the bullet, did you setup chronographs at the target down range?

keep us posted!

MEL

 

[Nekekami]

Two chronographs, and two testing runs. During the first, the chronographs were at 1m from the muzzle and at the 300 meter line. During the second, we had one chronograph at the 300m line and one lying down in the trench, almost right beneath the target, at roughly 599m.

We also had to sit down and do some calculations just to verify the data. I'd say the data is accurate to around +-1%

 

[Shoe]

Well doesn't that suck. Sorry to hear it Nek. I'm quite interested to hear about this ballistics experiment of yours...

 

[mele]

Nek,

Excellent work, thanks for going through the effort to get good data! Please keep us posted on the sabot experiments. I'll be interested to see if accuracy is still as good.

MEL

 

[Max338]

Mel.... a new caliber for a new rifle perhaps??? lol

 

[mele]

Hey, I'd love to! But I'd need to find a suitable action... .338 LM doesn't fit in a 700 Rem....

MEL

 

[Jeff_850]

too bad Remington didnt go ahead with their M700 in .338 Lapua they had a prototype of
what about the Win model 70 action? thats what Dakota uses and they offer the T-76 Longbow Tactical in .338 Lapua
thats a $4500 rifle so i woudlnt reccomend stipping one of those for the action
do these companies sell thier actions seperatley? even then id suppose the .338 would still be considerably more expenisve

could make a hell of a SC LR if there ever will be such a model