Interesting result using resized AK brass for testing.

[Arkhangel5]

Hey guys,

I was doing some testing AK 7.62x39 brass resized to 6.5G, just to see what it did. I had a mix of Winchester and S&B brass to test with. I was not shooting for accuracy, was only testing to see if it went bang with no issues.

I normally use IMR8208, but just for this test I decided to try TAC. I have never used anything other than 8208 in my Grendel for match shooting and hunting hogs. My normal 8208 match load matches up well with Hornady black velocities, right at around 2470fps out of an 18in barrel.

Now I was expecting TAC to give me slightly lower velocities vs 8208, but in the same ballpark. I was using a Nosler 123 cc as my test bullet, normally use this or a Hornady 123 ELD-M for match shooting.

I was shooting for function and over a chronograph to see what type velocities I got from TAC. I was using a Wolf LRM primer since I have quite a bit of it. All my test loads were under 28gr.

With the Winchester resized brass, I was getting readings of 2600+fps over a Caldwell optical chrony.

At first I thought maybe the chrony was misreading, so I shot a factory 123 Black to check, and I got 2480fps, what I was expecting. The rest of the TAC rounds gave me ~2600fps.

Rifle was working fine, brass was ejecting to 3-4o clock, bullets went where I was aiming, so the only thing is the velocity increase.

I chked the brass and they looked normal, chked again when I got home and shoulders were where I expected them to be.

So, my question, is this been anyone else's experience? And if this is normal, I may switch to TAC for matches if I can get it to shoot sub MOA, who doesnt like an extra 100+fps. I also have a lot of TAC.

I am going to load up some more to see if it repeats.

This AK brass is all range pickup, so it was free to me, and I can use this brass for plinking and hunting, where I don't have to worry about losing a piece of 'real' Grendel brass.

Anyway, is that velocity believable?

SY

[VASCAR2]

The case capacity for fire formed 7.62x39 brass is less than the case capacity of Lapua, Hornady or PPU 6.5 Grendel brass (more than likely less than Starline). When I load fire formed x39 brass I reduce my powder charge compared to what I use with Lapua or Hornady brass. I normally don’t load to max but my Western data for TAC with 123 grain SMK is 28.2 grains max charge. The higher velocity indicates to me your over the recommended pressure of 50,000 PSI. Western powders list 2424 FPS with 29.2 grains Tac with a 123 grain SMK out of a 20” barrel. Velocity translates to pressure so I would use less Tac with a 123 grain bullet.


I use even lighter charges of powder when using PPU large rifle brass as the primer pockets loosen quickly. I used my Fire formed x39 brass for varmint hunting where I might not recover my brass. My PPU brass is used for short range plinking or varmint hunting.

[Arkhangel5]

Vascar2,

Thx for the reply. Based on what you said about the capacity of resized x39 brass, I went back and weighed a few cases.

Winchester x39 brass resized - 120-125grs
S&B x39 " - 116-117
Lapua Grendel Brass - 111grs
Norma " - 111grs
Hornady " -116-117grs

My next test I will back off on the TAC.


SY

[VASCAR2]

You can fill brass with water and measure the weight of the water to get and idea about the difference in volume. I’ve never done this myself but comparing the weight of water between the x39 brass and 6.5 Grendel brass you could get a percentage of how much less volume x39 brass contains.


I read about the fire formed x39 brass having less case capacity than 6.5 Grendel brass so I’ve always reduced my charges to a moderate level and never worked up to close to a max load using x39 brass. There are threads where members have posted their results in using FF x39 brass. If your more interested you can use the google custom search feature to find mre info.

Here is a link.


https://cse.google.com/cse?cx=0163689474...cu1o&hl=en

[LR1955]

Hey guys,

I was doing some testing AK 7.62x39 brass resized to 6.5G, just to see what it did. I had a mix of Winchester and S&B brass to test with. I was not shooting for accuracy, was only testing to see if it went bang with no issues.

I normally use IMR8208, but just for this test I decided to try TAC. I have never used anything other than 8208 in my Grendel for match shooting and hunting hogs. My normal 8208 match load matches up well with Hornady black velocities, right at around 2470fps out of an 18in barrel.

Now I was expecting TAC to give me slightly lower velocities vs 8208, but in the same ballpark. I was using a Nosler 123 cc as my test bullet, normally use this or a Hornady 123 ELD-M for match shooting.

I was shooting for function and over a chronograph to see what type velocities I got from TAC. I was using a Wolf LRM primer since I have quite a bit of it. All my test loads were under 28gr.

With the Winchester resized brass, I was getting readings of 2600+fps over a Caldwell optical chrony.

At first I thought maybe the chrony was misreading, so I shot a factory 123 Black to check, and I got 2480fps, what I was expecting. The rest of the TAC rounds gave me ~2600fps.

Rifle was working fine, brass was ejecting to 3-4o clock, bullets went where I was aiming, so the only thing is the velocity increase.

I chked the brass and they looked normal, chked again when I got home and shoulders were where I expected them to be.

So, my question, is this been anyone else's experience? And if this is normal, I may switch to TAC for matches if I can get it to shoot sub MOA, who doesnt like an extra 100+fps. I also have a lot of TAC.

I am going to load up some more to see if it repeats.

This AK brass is all range pickup, so it was free to me, and I can use this brass for plinking and hunting, where I don't have to worry about losing a piece of 'real' Grendel brass.

Anyway, is that velocity believable?

SY

SY:

You are heading for blown primers and cracked necks. Range AK brass? Not a good idea.

The 7.62 X 39 brass has a much lower case capacity so yes, you can get higher velocities. Even lower if you didn't blow it out with a light load before loading it up.

Am pretty sure your pressures got up there very quickly and you probably weakened the primer pocket significantly.

Run a search because there are probably a dozen threads on 7.62X39 brass converted to Grendel.

'Real' Grendel brass remains a much better bet.

LR-55

[lazyengineer]

I'm the one guy who actually likes 7.62x39 brass. I like the thicker neck wall thickness, myself. That, and I have a surplus of LRP, so it's a good way to use those up. And finally, being "free" brass, great for field trips where brass recovery may be spotty.

That said - as everyone notes, you don't really want to use the exact same load as used with Grendel brass, as you'll pressure spike more. I generally just run cheap 90 TNTs in mine - great combination and that's a very forgiving bullet.

Have fun, thanks for the post!

[JASmith]

QuickLoad can be your friend in this situation.

Use the as-measured case volumes for the Grendel head-stamped brass and your "go-to" load for the Grendel to calculate velocity and pressure. Even though they might not closely match (reasons will be a much longer discussion) one can use the calculated velocity and pressures as baseline.

Then do the same with the resized and firefored 7.62X39 brass. Now note the CHANGE in velocity and pressure from the baseline. I have determined that QuickLoad does an excellent job in determining increase or decrease in pressure going from one load to another. This is in spite of QL occasionally not predicting the same pressures as we see in published load data.

That change will tell you how close you are to dangerous pressure levels with the x39 brass when using your favorite load.

Then, determine the new charge weight needed to match what QL calculates for the Grendel brass. That load should also be close but slightly below the velocity you get with your favorite load in Grendel brass.

- - - and yes, start below that "matching load" and work up, as always with new combinations.

[Klem]

angel,

Hand-loaders are more interested in the capacity of cases when working up pressures, not the case itself. You are weighing different brands of cases and they will vary slightly, but you cannot assume much from the differences.

With capacity, size a case and seal the primer hole somehow. A spent primer works. Weigh the case. Then fill the case to the mouth with water and weigh again. The difference between empty and full is the capacity or volume in water. Be careful to get rid of any bubbles and don't have too proud a meniscus at the mouth.

If you have Quickload you can replace the default case capacity (35.99 grains H2O) with your converted brass. See how the change in volume affects predicted pressures.

[StoneHendge]

I shot thousands of rounds of Starline x39 brass converted to 243 LBC (basically 6mm Grendel) back when primers were nonexistent and I had a backstock of LRPs. In addition to what everyone says above, my main takeaway was that the LRP gives faster powder ignition and hence an earlier pressure peak which is less than optimal for the cartridge and results in lower velocities for the LRP brass vs. SRP brass at any given peak pressure.