Brown Bear 196 grain Subsonic 7.62 x 39 - Shooting Sports Forum


Ruger Mini-14 and Mini-30 Ruger Mini-14 and Mini-30 family of rifles

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Old 06-24-2019, 05:43   #1
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Brown Bear 196 grain Subsonic 7.62 x 39

Was reading about this round over at the AK-47 section of AR15.com
Surprised me that the decibel reading of the round fired through a suppressed AK was 131 decibels. Isn't that about the loudness of a normal, unsuppressed round ?
https://www.ar15.com/forums/AK-47/Ne...ngs/54-165487/
They said some rounds went supersonic, doesn't surprise me when they are going 1115 fps. They did mention the elevation at the test site might had had something to do with that.
Speed of sound at 5,000 ft. elevation would be 334 meters per second, or 1097 feet per second. So it figures that 1115 would have gone supersonic.

B.C. is high for a x39 projectile, .383.
Pressure is listed at 51,488. Sounds rather high. Lb/inch squared ? I wonder how that correlates to PSI or C.U.P. ?
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Old 06-24-2019, 13:37   #2
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The BAR pressure as I understand it is related to atmospheric barometric pressure. But the standard used in BAR can vary because of temp, humidity. So you have to have a standard to use, not sure what the standard is for BAR testing, actually there is no set standard so not knowing the exact standard used can skew results. There are BAR, PSI converters online. which converts the BAR 3550 to 51488 psi as shown in the AR15.com table.

The C.I.P. and SAAMI pressure maximums for the 7.62x39 are different. C.I.P (Commission internationale permanente pour l’épreuve des armes à feu portatives – Permanent International Commission for the Proof of Small Arms) is the equivalent of SAAMI for most of, but not limited to, European countries. The C.I.P member countries are Austria, Belgium, Chile, Czech Republic, Finland, France, Germany, Hungary, Italy, Russia, Slovakia, Spain, United Arabic Emirates and United Kingdom.

According to the official C.I.P. rulings the 7.62×39mm can handle up to 355.00 MPa (51,488 psi) Pmax piezo pressure. In C.I.P. regulated countries every rifle cartridge combo has to be proofed at 125% of this maximum C.I.P. pressure to certify for sale to consumers. This means that 7.62×39mm chambered arms in C.I.P. regulated countries are currently proof tested at 444.40 MPa (64,455 psi) PE piezo pressure.Pmax piezo pressure is yet another unit of pressure measure.

The SAAMI Maximum Average Pressure (MAP) for this cartridge is 45,000 psi (310.26 MPa) piezo pressure.

So there is a difference between SAAMI and the C.I.P pressure ratings. question is why. It may have something to do with the prevalence in the USA to use different bore sizes in the barrel of 7.62x39MM barrels, .308" (reported early mini 30 barrels) to .312" (groove dia). Both specs start with a 7.62 bore .300" but there are different specs for grooves dia. SAAMI being 7.87 (.310") And C.I.P 7.92 (.312). A smaller .308 (groove dia) will generate more pressure than a .312" barrel (groove dia) with the a .310" (or larger .311" or .312") bullet/cartridge. So I think the SAAMI spec is a safety margin for shooting bigger dia bullets in smaller bore barrels. I have never seen any real life figures for USA produced 7.62x39 cartridges that matched the velocities of true military surplus or military standard x39 rounds, which is right at 2,400 FPS, in a correct size 7.92 mm (0.3118" lets call it .312") barrel as per C.I.P standard.
Here is a link to the C.I.P standards of the 7.62X39mm cartridge.
The C.I.P standards carry with it the force of law, unlike SAAMI, member countries cannot produce firearms/ammunition exceeding or deviating from their standards. You can convert the MM to decimel using a online converter.

Also there is a slight difference in headspace, Hard to say what a USA chamber is cut to, SAAMI, C.I.P or bastard size except safe to say firearms from C.I.P countries will conform to their specs and USA companies can go either. Ruger most likely uses their own bastard specs, like the mini-14 and mini 30 which allow cartridges of different specs to be fired safely but with some sacrifices in accuracy/velocity.

I hope that's confusing enough
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Old 06-24-2019, 19:25   #3
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Interesting looking round. The question is, would it cycle the Mini-30, especially for those of us using reduced gas bushings. My gut says probably so, at least for 16” barrels, since C.I.P. uses 16.3” test barrels as standard for 7.62x39, and Mini-30s are over gassed from the factory. It would be worth buying a box to find out. Once SGAmmo picks it up I imagine it will be in the price range of the other Barnaul Bears at SG. PPU 182 GR x39 subsonic is only $11.95 per 20-round box at SG.

Pound-force per square inch (lbf/in2) is PSI. Same thing, but the Brown Bear specs are using the symbol rather than the abbreviation. 3550 BAR is 355 MPa (Megapascals). So both numbers, 3550 BAR and 51,488 lbf/in2 (psi) are right at standard C.I.P. pressures for 7.62x39.

Silencers aren't really that silent, but they cut the decibel level down quite a bit. 131 dB is pretty good for rifles, which are typically in the 160s dB range without silencers, and the lower 130s dB range with silencers.

A 30 dB reduction in sound level is perceived as about six times quieter, but I'd still wear ear plugs at 130 dB. An unsuppressed Ruger 10/22 is in the 140 dB range. A 10 dB reduction in sound level is perceived as about two times quieter. So you could look at it as a suppressed Mini-30 shooting a subsonic round will be quieter than a 22 rifle shooting 22 LR in practical terms.

I wish silencers actually worked like they do in old James Bond movies, but that’s just Hollywood.
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Old 06-24-2019, 19:38   #4
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Originally Posted by Walkenbear View Post
Also there is a slight difference in headspace, Hard to say what a USA chamber is cut to, SAAMI, C.I.P or bastard size except safe to say firearms from C.I.P countries will conform to their specs and USA companies can go either. Ruger most likely uses their own bastard specs, like the mini-14 and mini 30 which allow cartridges of different specs to be fired safely but with some sacrifices in accuracy/velocity.
In the beginning with the .308 bore, the Mini-30 used the "Lapua Chamber" which is C.I.P. approved. I'm not sure if the .310 bore Minis still use it or not.

As I’ve mentioned in a few posts in the past, the Mini-30 is sold in some C.I.P. regulated countries, so it’s required to meet the more rigorous C.I.P standards. That’s one of two reasons I ignore SAAMI and follow C.I.P. The other reason is that SAAMI spec for 7.62x39 has always been wrong. Finland (a C.I.P. country) helped Ruger establish the SAAMI spec for 7.62x39, but there was a miscommunication from the start when translating the way C.I.P. measures pressure and the way SAAMI measures pressure.

I read an article back in the late 80s about the development of the Mini-30. The author said Ruger estimated .311 bullets fired through their early .308 bore Mini-30 barrels would raise pressures by about 5000 psi. That may be another reason SAAMI specs started out lower. But Russian made weapons chambered in 7.62x39 aren’t made any better or more robust than US made weapons chambered in 7.62x39, so SAAMI can take a flying leap as far as I’m concerned when it comes to x39.
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Last edited by Beck; 06-24-2019 at 21:04.
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Old 06-25-2019, 19:51   #5
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Old 06-26-2019, 09:55   #6
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I load 13gr 2400 behind a 160gr Ed Haris home cast Lee bullet. It is really quite in my non suppressed SKS.
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Old 06-26-2019, 11:28   #7
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Hey 51colt, Any idea on the velocity of that load? sound interesting, I have always wanted to play around with heavier bullets in the 7.62x39.
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Old 06-26-2019, 12:05   #8
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Beck,
If the mini 30 is still being sold in the C.I.P countries then it would have a approved chamber. Knowing Ruger's business practices they don't change unless they have to.
Pretty sure it was Ed Harris who said that at the beginning they were using .308 barrels that were on the large size in the first mini 30's. That's Ruger for ya, they used the skinny barrels they had left when they retooled for the new 580 series mini 14, it had the skinny barrels until @ 580-50xx. good business practice for a company, not so good for consumers.

You are correct that they used the Laupa chamber specs because well, that's all that was available at the time. SAAMI didn't get on the bandwagon until later. Don't know for sure but the mini 30 was probably the first American rifle designed around the 7.62x39. I have an old article on the mini 30 and sks that said Ruger used a "forcing cone" at the front of the chamber necking it down from .311 to .308 so that a bullet as big as a .311 would safely go bang. Shooting Times mag, interesting article, did accuracy tests with various factory and hand-loads for each rifle. I'll see if I can find it, One of the advantages of getting older, you have a lot of old stuff

At the bottom of this article are a few different sub-sonic loads, spendy but pretty interesting, up to 220 grain. According to Kvar the 196, brown bear load will cycle an AK.
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