High performance 7.62x39

[Slamfire]

Developed a high performance load for my 7.62x39 Ruger No.1 using Hornady 123gr .310" SST (Super Shock Tip) bullets. Bullet speed corrected at the muzzle is an impressive 2700 fps with reasonable accuracy. No apparent signs of excessive pressure in my rifle (only!). It's a strong action coupled with generous freebore in this particular rifle. This level of performance wouldn't be achievable in my bolt action 7.62x39.

A significant improvement over the nominal 2350 fps muzzle speed of factory loads. Doubles the range at which it makes 1000 ft-lbs in this nicely balanced, lightweight and compact rifle. Deer slayer.

7.62x39 Ruger No.1-A with Leupold VX-2 2-7x28mm

 

[xdmer]

Nice numbers and I like the bullet, but details needed. Powder, weight, primers, brass? Definitely looks beyond overall length.

 

[Slamfire]

"Developing a load to match your rifle is one of the most fun and rewarding things you can do as a handloader..."

https://www.nosler.com/blog/news-and-articles/2013/6/4/beyond-the-basics-developing-your-own-loads

 

[Slamfire]

The No.1 action locks up with a massive breech block. A comparatively strong design. The designer of the rifle purportedly never did succeed in blowing apart the action with extreme pressure loads. In destructive testing the barrel sheared off first so it isn't the action strength that's the weak link in the design.

For illustrative purposes only (not for design), I thought it would be interesting to estimate the chamber and barrel stress levels at chamber pressures up to the SAAMI-specified pressure limit. For a thick-walled cylinder the hoop stress (assumed to be the design-limiting stress component) equation is -

(reference: Advanced Mechanics of Materials, 3rd ed., Boresi et al)

Where -

p1 = internal pressure = P
p2 = external pressure (atmospheric so negligible = 0)
a = bore radius
b = barrel outer radius
r = barrel wall location

By inspection of the equation, hoop stress is maximum where r is minimum, or where r = a, so at the inner surface of the bore.

Approximate dimensions of my 7.62x39 barrel -

muzzle outer diameter = 15mm so b1 = 7.5mm
breech outer diameter = 22mm (? estimated) so b2 = 11mm
bore diameter = 7.62mm so a1 = 3.81mm
case head diameter = 11.35mm so a2 = 5.68mm

Estimated hoop stress level at the muzzle end (1) and breech end (2) -

Muzzle: P * (3.81^2 + 7.5^2) / (7.5^2 - 3.81^2) = 1.70P

Breech: P * (5.68^2 + 11^2) / (11^2 - 5.68^2) = 1.73P

SAAMI-specified pressure limit is 45,000 psi for the 7.62x39 so for published maximum loads chamber and barrel stress levels are about 75 ksi. Unknown what the yield strength of the No.1 barrel actually is, but 416 stainless steel - a typical stainless barrel material - yield strength is 65 to 85 ksi.

http://www.schmolz-bickenbach.us/fileadmin/files/schmolz-bickenbach.us/documents/Ugitech/416RS.pdf

 

[xdmer]

Thanks for the details.

 

[Slamfire]

AISI 4140 appears to be a commonly used material for rifle barrels -

"Common Gun Metals

Carbon Steels

1020 and 1520—Common, “plain” or cold-rolled steel. You’ll find it in trigger guards, floorplates, sights, sling swivels and other steel hardware.

4140—Ordnance steel or chrome-moly steel, it has 0.4 percent carbon and is really strong while still being cost-effective to machine. You’ll find this in barrels, bolts receivers and high-stress items like muzzle brakes."

http://www.rifleshootermag.com/rifles/ar-15/guide-to-gun-metal/


According to this website, barrel steel is hardened to between 25 and 32 on the Rockwell C scale -

http://firearmshistory.########.ca/2010/06/barrel-making-making-modern-steel.html


According to the Lilja website, 4140 steel yield strength varies according to hardness -

http://riflebarrels.com/a-look-at-bolt-lug-strength/

So my No.1 barrel yield strength is probably around 135,000 ksi if it's made of AISI 4140 hardened to about 30 on the Rockwell C scale.

 

[Slamfire]

Update: 170gr NP & 180gr RN performance

Curious to see how fast I could safely fire .308" 170gr Nosler Partition and 180gr RN Hornady bullets. Results as shown. Not bad considering the best I could do with the 174gr RN bullet in my SKS is about 1800 fps MV.

Now to decide on what load to use for hunting.

 

[rosconow]

What powder you using. I use h4198, h335 for x39. I also load out past the canelure in my bolt gun.

 

[Slamfire]

"Developing a load to match your rifle is one of the most fun and rewarding things you can do as a handloader..."

https://www.nosler.com/blog/news-and-articles/2013/6/4/beyond-the-basics-developing-your-own-loads

 

[legi0n]

let us know how long the brass lasts at these numbers

 

[time4t]

....

 

[MiG25]

Congratulations, you have a heavy, single shot 30-30.

 

[Andy]

Congratulations, you have a heavy, single shot 30-30.

Well essentially, but running at much higher pressure, as the 30-30 has about 25% greater case capacity than the 7.62X39. Must be using a slow pistol powder, as I don't think you could stuff enough of even a fast rifle ball powder in to get those MV's , except perhaps CFE BLK which is extremely dense.

Goes to show though that you can load to the lesser of brass or rifle strength, and not be restricted to SAAMI. Another good example is 303 Brit in the P14 or Ruger #1.

 

[buffdog]

Congratulations, you have a heavy, single shot 30-30.

AH, but an interesting one at that. I once had a Russian SKS that we played around with one day and shot off the bench on a silhouette range. Using Norinco standard Chinese hunting loads, we got a surprisingly large number of hits on the 500 yard Rams and knocked most of them over, so the cartridge itself can be accurate. And this cartridge is souped up a bit over the standard 7.62x39 velocities.

As far as the single shot goes, most times you have only ONE chance at a game animal, and most of the game is shot within 200 yards out in the West, and less than half that distance in the Cedar swamps of the East.

 

[rosconow]

https://www.nosler.com/blog/news-and-articles/2013/6/4/beyond-the-basics-developing-your-own-loads

You wouldn't last very long on The Handloaders Bench with that kind of response...

 

[Ganderite]

Does Ruger mention whether the #1 has a 308 barrel or a a .310" barrel? A 308 would have a greater selection of bullets.

 

[Slamfire]

Not heavy. The rifle weighs 7.5 lbs as shown. Nicely balanced as the No.1 rifles are with light (and medium) weight barrels.

Chrony is positioned 6m from the muzzle. So add ~25 fps to the reading to correct at the muzzle. Chrony was checked against a Caldwell G2 - close agreement.

.310" groove diameter barrel. Accuracy improves a little bit with .310 bullets. Besides better selection, what's the other advantage of using .308 bullets?

Brass life is fine. Several reloads to a case.

One shot. One dispatched target.

 

[Ganderite]

I asked about the barrel because my Ruger Mini-30 was a 308.

The advantage of 308 would be larger selection of bullets and to me, because I have a few thousand on hand.

I have a 45-70 on a Martini-Enfield action. I have carried it on a few hunts, but never got to fire it. I have no problem with a single shot action for hunting. Only once have I required a second shot, and that was just a coup de grace after I got up to the deer.

 

[madtrapper143]

Hodgdon's new CFE BLK powder is likely the secret. Going to try some in my American Ranch 7.62x39. Claims of 150 to 200 FPS gains in velocity with safe pressures is the manufacturers claim.

Darryl

 

[saskgunowner101]

Did you walk it up until signs of pressure showed themselves, or ran out of room for powder, or just hit good enough for me levels? That's some turbo charged cartridge now, that's for sure!