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 Post subject: Latest 7.62x39mm Subsonic Load Data
PostPosted: Wed Jun 11, 2008 8:27 am 
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Silent But Deadly
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I finally made it the range yesterday. I tested two different subsonic loads using 180 gr round nose bullets.

I recorded he following data, using 6.6 grains of Red Dot powder, CCI 250 primers, Winchester cases trimmed to 1.520â€

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PostPosted: Wed Jun 11, 2008 3:59 pm 
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Silent But Deadly

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tgbrowning,
Congrats on your load development. The velocity spreads look pretty good. Since you've developed these two loads, have you considered loading say 5 of each load in normal brass without the primer holes drilled out? If normal brass gives the same performance, then it would tell you that you don't need to drill out the primer holes.


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PostPosted: Wed Jun 11, 2008 7:19 pm 
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Silent But Deadly
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johndoe3 said:
Quote:
Since you've developed these two loads, have you considered loading say 5 of each load in normal brass without the primer holes drilled out? If normal brass gives the same performance, then it would tell you that you don't need to drill out the primer holes.


I haven't considered it because I started with 150 Winchester cases that I drilled out to 1/8 inch flash holes. However, I have 1,000 Remington cases with small primer pockets, so when I find a load I'm happy with, I plan on trying the load in Remington cases. Basically, I'm being very careful, because secondary detonation can destroy a rifle in one firing. Perhaps, by using Puff Lon ballistic filler I can eliminate this possibility. But, I am just beginning to experiment with Puff Lon, so this is fodder for future load development. I have some commercially loaded subsonic and I plan on examining the cases after firing to see if the primer pockets have been drilled. If they are not drilled, then I may try a loading without drilling the flash holes. It's just a matter of time until I find a load that suits me. Meanwhile, I will proceed carefully.

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PostPosted: Fri Jun 13, 2008 1:43 am 
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Silent But Deadly

Joined: Tue Feb 27, 2007 5:02 am
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Location: N. Colorado
tgbrowning,
The reason I brought up testing your load in normal unaltered cases, is because many people come to forums like this to learn how to do it. If the cases without drilled out flashholes worked just as well as those drilled out, then it would be beneficial for everyone who reads your data in the future to know this. They wouldn't go to the trouble of doing things that added no benefit. On the other hand, if the loads DO WORK BETTER as you've developed, then it would be beneficial for readers to know to do this step of drilling out flashholes.

For instance, I ignored all I had read on subsonic loading about drilling out flashholes, putting lard on the bullets, using a magnum primer instead of a regular primer, etc. I found with 308 subsonics that good subsonic loads require no difference in the brass from normal rounds. It just requires using a good powder precisely measured, neck tension, and jump to lands (depending on type of bullet used). And of course using a bullet weight/length commensurate with twist rate.

As Reagan said to Gorbachev ... Trust but verify! :-)


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PostPosted: Fri Jun 13, 2008 7:53 am 
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Silent But Deadly
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johndoe3

I can appreciate what you are saying and after I find a load that satisfies me, I will try loads without drilled flash holes. But, until I'm satisfied that the loads I develop are safe, I will use my brass with drilled flash holes. I prefer to err on the side of safety first. I've been reloading for many, many years, but if I am trying something new, I'll read everything I can find before proceeding. Drilling flash holes was the one thing I found most often referenced in my research of subsonic ammo. If I find I can do without drilling larger flash holes and get the same results, then rest assured it is a step I will gladly eliminate. It is, in fact, a pain in the ass to do. None the less, I really appreciate your input. I have observed that most of my posts on this subject receive a lot of reads, but very few replies. I am always open to new ideas and observations of anyone who has been there and done that. That said, I'm curious, what loading have you found to work the best for .308 Win subsonic loads? Most of the posts I've read indicate that Trailboss is the powder of choice.

Thanks,

Terry

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PostPosted: Fri Jun 13, 2008 8:55 am 
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Silent But Deadly

Joined: Wed Sep 21, 2005 2:55 pm
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Location: Southwestern NH
tgbrowning,

I confess to be one of the "readers without reply" on this as I have nothing relevant to add, but much enjoy seeing your research. Your other post about the C Products 30 rounders reminded me to start looking for an SBR (7.5"-12.5") upper in 7.62x39.

Could you provide some more details about your upper. Who made it, twist rate, accuracy with surplus ammo, reliability with steel cased ammo, etc.... THANKS!

Looks like a YHM forearm and AAC or YHM flash hider mount?


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PostPosted: Fri Jun 13, 2008 11:24 am 
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Silent But Deadly
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Howdy jandbj,

Thank you for the reply. Truthfully, this is the only forum that I make regular posts on. So, I'm happy to hear that my efforts are appreciated.

Image
This is the rifle in it's present configuration, for use in my subsonic load development.

I built it using a DPMS Lower and Upper receiver. I matched the pair at a gun show for a good tight fit. The barrel is an E.R. Shaw that I bought from Model1Sales. It is sold as their 16'' C.A.R. 7.62x39mm Chrome Moly Heavy Barrel, 1-10'' twist, 11 degree target crown, with gas block front sight base. I also bought a 7.62x39mm bolt from Model1, but if I had known about MGI's enhanced 7.62x39mm bolt, I would have bought it instead. I had the barrel threaded to 5/8x24 tpi and recrowned for a Yankee Hill Machine (YHM) Phantom Q.D. mount/flashhider #YHM-3302A. The forearm is also a YHM part #YHM-5000 with a YHM Front Flip Sight Tower/gas block #YHM-9394. I removed the Model1 gas block so I could use the YHM Smooth Carbine Forearm and front sight. It makes a really sweet combination. The butt stock is made by Command Arm Accessories (CAA). I like it because of the built in battery compartment and permanently attached rubber butt pad. It holds 4 CR-123A lithium batteries. My Night Vision Scope is powered with CR-123A's. So backup batteries are always with the rifle. The scope on it right now is a Tasco Mil Dot target/varmint 2.5x10 power. It's a cheap scope but it works well. It's mounted in a very cheap UTG scope mount, but only because the Armalite scope mount I ordered is presently back ordered. The rear sight is a cheap Chinese copy of the A.R.M.S. Swan low profile 40L BUIS. I prefer the A.R.M.S. sight but, I don't expect to use the rear iron much on this rifle so I bought the Chinese copy at 1/4 the cost of the real deal. Admittedly, I'll probably buy another A.R.M.S. 40L to replace it, but not anytime soon. My next purchase will be the MGI Enhanced Reliability Firing system for7.62x39 -Firing Pin & Bolt. You can find it here:
http://www.mgimilitary.com/store/index. ... 0e05bea6f6
I have found the the standard firing pin in the AR-15 7.62x39mm bolt will not always reliably fire cheap ammo, for instance Wolf ammo. I was experiencing a failure rate of 50% or better with the standard bolt/firing pin combination. Yet, the same cartridges that would not fire in my AR function perfectly in my AK. The AK has a much larger firing pin face. This is what MGI has done with their bolt/firing pin combo, increase the diameter of the face of the firing pin and of course the hole in the bolt is larger, also.
To finish the parts list, I like the Hogue overmolded pistol grips and I install Rock River 2 stage trigger groups in my lowers.
ImageImage
ImageImage

Image
This photo is of the rifle, with my Gen 3 Night Vision Scope, before my CAA buttstock came in.

I think that finishes the parts list pretty much. And, of course, I'm using C Products magazines. I have a 10 rounder that works great. I'm waiting for my 30 rounders to arrive. All in all, I'm very pleased with the rifle. It shoots well, I like the balance of it, and the fit and finish of the parts I've chosen. As soon as I get my MGI bolt and C Products magazines, I'll be a happy camper. 8)

Oh, and I have a DPMS .308 carbine in the works. I'm waiting on a barrel to finish that project. Next, I'll be looking at .308 Win. subsonic loads, but thankfully, there's a lot more information on this forum on subsonics for the .308 Win. I'm already reading every post I can find from guys like johndoe3 and artful and a bunch of other users whose names I don't recall at the moment.

Later ya'll,

Terry

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"Genius may have its limitations, but stupidity is not thus handicapped."

Elbert Hubbard


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 Post subject:
PostPosted: Fri Jun 13, 2008 1:35 pm 
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Silent But Deadly

Joined: Wed Sep 21, 2005 2:55 pm
Posts: 995
Location: Southwestern NH
My SBR lower is nearly identical to yours, DPMS, CAA stock, I used David Tubb's springs on my trigger group and got a wonderful trigger pull for the $25 investment. Currently running a Bushmaster 11.5" upper in 5.56 with a first generation Bushnell Holosight, fixed front sight, cheapo flip up BUIS and Larue BUIS on order.


One stupid question, as I am new to the AR system... Can I use my .556 bolt carrier with a 7.62 bolt or do I need a specific 7.62 carrier to go with the bolt?


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 Post subject:
PostPosted: Fri Jun 13, 2008 2:42 pm 
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Silent But Deadly
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The standard 5.56 bolt carrier will work with the 7.62x39mm bolt. There isn't any difference in the bolt carriers, just the bolt itself. Do yourself a favor and buy the MGI enhanced bolt and firing pin though. It costs more than the standard 7.62x39 bolt, but it's worth it, because you get much greater reliability shooting cheap ammo, such as steel case Wolf.

Now, I have a question. Where did you get the David Tubb spring set?

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"Genius may have its limitations, but stupidity is not thus handicapped."

Elbert Hubbard


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PostPosted: Wed Jun 18, 2008 4:21 pm 
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Silent But Deadly

Joined: Wed Sep 21, 2005 2:55 pm
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Location: Southwestern NH
http://www.superiorshootingsystems.com/AR_15_Products-AR15_Trigger_Springs.html


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