Home Forums Reloading Big Game Rifles The Mauser M12 Extreme .308 Handloading Thread

Quite a few of us recently picked up Mauser M12 Extremes in .308, with the 20" barrel, for a smoking deal. We've been sharing some handloading lessons learned over on this thread,
Mauser M12 Extreme Opinions
but figured it's time to start a dedicated thread for this subject.
One thing that will help us rate the potential to share our data is information about our individual chambers, so we can get a feel for how consistent they are. Being production firearms, I would guess their chambers are finished with reamers that cut the throat in the same operation, so I am hoping we'll find them consistent in that dimension. Those of us who compared serial numbers found them to be close together so hopefully they're from a single production run.
Here are the Max OALs (bullet just lightly pressed into the lands such that it does not fall out when the muzzle is vertical) I measured for mine:

Nosler 165 BT, 165 AB, and 150 BT - 2.935"
Nosler 150 Part - 2.92" - 2.93" depending on the state of the exposed lead tip
Nosler 150 AB - 2.95"
Nosler 168 ABLR - 2.97"
Nosler 168 HPBT - 2.90"
165 Sierra Game King (probably 25-30 years old) - 2.90"
168 Sierra MK HPBT - 2.89"

What have others found in their measurements?

I'll post some data later when I get the time - I have yet to find "the load" I want. My goal is a load with a good hunting bullet in the 165 grain class (though 150 would be ok too) that will consistently shoot MOA or less and produce 2700 FPS from the 20" barrel, ideally with a powder that is pretty temperature resistant.
Up to now I have been concentrating on loads that will also fit in the ~ 2.85" OAL limitation of my magazine, but I have a Sauer 100 magazine (interchangeable) in 6.5x55 length inbound which will remove that limitation - should hold up to at least 3.2" OAL.

Looking forward to collaborating on some good loads for these fine rifles.

Cheers,
Rex

Try a 165-grain Partition over 45.5-46 grains of Varget over a CCI 200 primer.


Okie John

2700 with a 165/168 out of a 20" barrel may be a bit of a reach.

The load I listed above is right at 2,700 in a 22" barrel. TAC might go a bit faster.


Okie John

Thanks Sir, but I am finding it achievable while staying under published max(s).
2700 FPS is quite easy in my 20" M12 even a grain or two below max with PP 2000-MR.
In my 20" M12, I got 2739' with 49 grains/2000-MR and the Nosler 168 ABLR, but accuracy was not good.
In my 23" barreled '98 Mauser .308, 50 gr/2000-MR gives 2880' (really!) with the 165 BT, and excellent accuracy. 2000-MR seems to be a wonder powder with both 165 (and higher) in the .308, and 225 gr (and higher) in the 35 Whelen.

Back to the 20" M12 - Ramshot's max load of 51 grains of Big Game gives mine 2727' with the 165 BT. That load averaged .00053" Case Head Expansion (CHE) on the first firing in Lapua brass, and showed no additional CHE on subsequent loadings in the same cases, which is generally what you're looking for if using CHE as one of your pressure assessment tools.

45gr / Varget gives 2675' with the 165 BT, and that is a grain to a grain and a half below commonly used charges (Hodgdon's max is 46 - Mule Deer's go to load is 46.5), So I have no doubt it'll break 2700' as well. I've not shot above 45 gr yet though. But I don't have much Varget (hoping to save it for the 9.3x62, but do have an 8# on backorder), and I have plenty of Big Game, 2000-MR, and TAC. So if I can reach my goal with them, that'll be preferable.

Really glad to see the participation we're getting on this thread. I might as well list the one load I have ginned up that is actually significantly sub MOA (actually copied from the "most accurate .308 load ever" test):
168 SMK, 45/Varget, CCI250, Fed case, 2.88" (too long for the magazine, .010" off the lands). This put 7 of 8 shots inside 0.60". I pulled the 7th shot, opening it up to 1.33.
But this load doesn't meet 2 of my 4 objectives (hunting bullet, and 2700 FPS). It's got accuracy and temp stability. AND, it tells me there is nothing inherently inaccurate about my rifle - I just have to find "The Load."

Cheers,
Rex

How I wish I had some 165 Partitions!
Got most every other Nosler .308 - anybody want to swap 50 165 Parts for 50 "something else?"
Rex

Here's my work so far with Big Game.
First trip to the range with Big Game, snipped from our previous thread:
>>>>
I took 165 NBTs to the range loaded over Big Game on Wednesday. OAL was mag limited at 2.85", which put them .090" off the lands. Fed 215 primers, Lapua brass.
I took 48, 49, and 50 grains. Ramshot's max is 51 so I will also try that, as groups shrunk as charges increased. Three-shot groups.

48gr - 2556 FPS, SD 17, 1.29"
49gr - 2579 FPS, SD 12, 1.86"
50gr - 2619 FPS, SD 2, 1.25"

This makes 51 grains look promising. Also, I need to try the same loads with the 165 NAB.
<<<<
The next week I decided to try 51/BG. Here's what I got with it. For the record, I felt a little "off" this day, shooting -wise. Temp was 70-80F. 4-shot groups.
All loads were 2.85" OAL, New Lapua Brass (to take CHE readings), Fed 215.

51/BG, 165 BT - 2710 FPS average, 1.09" group. SD was 45, and this was entirely because the third round (of four) registered 95 FPS slower than the others on the Oehler 35P. Could have been a bad read. CHE was .00053"
51/BG, 165 AB - 2734 FPS, 2.41" group, SD was 4. CHE was .0008". This is a bit more than I prefer in a long-term use load.

So it seemed like 51/BG and the 165 BT had potential so I went to the range with 12 rounds loaded with the same load as above. 9 of them were new Lapua brass and 3 were the same cases I had measured the .00053" CHE on before - I was looking to see if there would be any additional CHE on those once fired cases, and to see if I could keep the good accuracy and avoid the one anomalous low chrono reading.
I got pretty large ES over the 12 rounds (which is unusual for Big Game) and the SD for 12 rounds was 39 FPS. The average speed was 2727 FPS. I may try standard primers, just for the heck of it. Also, maybe the 35P needs a new battery? I feel I may be getting some screwy readings.
I shot four 3-shot groups. The three groups with new Lapua brass were 1.38", 1.78", and 1.47". The group with the once fired brass was 1.26". Those three cases showed less than .0001" (not really measurable) additional CHE over the original .00053" CHE on first firing. So pressure is no big deal in this load and it is awfully close to all my criteria. I will start trying out some different seating depths and that may be "The Load."

Cheers,
Rex

Here's another observation:
I just added up my loads to date and, including both handloads and 19 of the Creedmoor Sports factory loads with the 167 Scenar and Lapua brass, I have 126 rounds down my barrel.
I have been using the Mule Deer "break in" technique of:

1. Take new rifle to range
2. Shoot new rifle 12-20 times doing sight-in and initial load development.
3. Clean barrel to bare steel.
4. Repeat 1-3.

I noted (with the Teslong borescope), when my barrel was new, that it was very, very, smooth. But running a patch through it it also had a lot of brown grunge in the bore, which others on our original thread also noted. I cleaned that out before starting the steps above.

I have noted (here's a news flash) that this barrel is "speeding up" a bit as it breaks in, and getting significantly easier to clean to bare steel between range trips. Nothing unusual here but good news all the same. Anybody else seeing the same?

The "Sauer 100" magazines in 6.5x55 length arrived. I put "Sauer" in quotes because, though I had seen an image online with the name Sauer embossed on the bottom, and expected that, these, happily, were unmarked, and the package listed them as generic to the Sauer 100, 101, and Mauser M-18. I reckon we can add M-12 to the list as they fit fine.

They actually sit a little more flush to the bottom of the rifle than the OEM mag.
Here is the extra length it gives. Can seat out to 3.2" + OAL.

The first thing I did was to grab 10 of the Creedmoor Sports factory rounds with the 167 Scenar in the Lapua brass and load up both of the new mags I bought, one with the rounds all the way aft, and the other full forward, as they might be after recoil.

I took them outside, put the safety in the middle position, and ran them through. All ten fed slicker than owl snot (that's an industry term).
So I took the load with the 165gr BT over 51gr Big Game, which had done the best previously but had been limited to 2.85", which put the ogive .085" off the lands. I loaded 3 each at .050, .025, and .005" off the lands respectively. The set at .050" off did this.

I will repeat it and see if it remains a sub MOA load, and also shoot more per group. I'd like to play some more with the 168 ABLR too, and see what sneaking it in closer to the lands does.
I loaded all these in Lapua cases that I had previously fired at least one or two times with the 51/BG load, so I could check again for any additional CHE over the .00053 average that load originally gave on virgin brass. Most were holding at .0001" more, and one had gotten up to .0002" more on the third firing, and it was one of the ones seated into the lands. So this continues to look like a load that, though at published max, will give plenty of firings before loosening pockets. The primers felt very tight on seating for this round of loads.
Speaking of primers I did switch over to the WLR (from my understanding, the hottest of the standard primers), from the Fed 215 I had been using. ES seems a little better but too early to tell.

Cheers,
Rex

P.S. Unlike many rifles, I have noticed this one shoots just great out of a squeaky clean bore. I have been cleaning to bare metal after each of these initial range sessions and it shoots fine right off - no need for "foulers." The group pictured above was the first of the day.

Excellent!

Great report and photos.

How full is the case with 51 grains of Big Game powder?

It's slightly compressed. IIRC, just barely above the neck-shoulder junction. I'll be loading some more of them soon and will try to remember to get a pic of the "fullness."
I decided to just keep shooting that load in the same ten cases so I can get some genuine data on how long they will hold up. The next round will be the 3rd or 4th loading with 51/BG depending on the individual case.

If the next trial with that same load that shot so well above continues to do so**, I will go back and try the same "everything" except swapping out 46/Varget and 49-50/2000-MR (both makers' published max). When I ran those two before I did not have a feel for what might be the optimum OAL. Now I just have a "hunch" what it might be, but will be gathering more data!

Cheers,
Rex

** when I read over this before hitting Post Reply I realized that was a pretty dumb thing to write. IF that same load keeps shooting under 1/2", I will not do ANYTHING else with that bullet. I will be DONE with load work for the 165 Nosler BT! Somebody else can test Varget and 2000-MR, LOL. I am not that good so I don't really expect it to. But if it does I will look forward to playing a little with the 168 ABLR. I don't think I will test any tougher bullets because I don't look at this rifle as more than a deer rifle (and the .308 165 BT is already a pretty tough bullet - real thick jacket base). When I get lucky enough to hunt elk, I have too many other rifles that are better than the .308 for that purpose.
Might fool around a little with the 150 Partition and 150 BT.

I have a hunt booked for BC (deferred from last year and likely again this year) for mountain goat, moose and elk (16 days) that I am now seriously considering bringing this rifle using the 168 gr TTSX. My 338-06 is good to go with the 185 gr TSX but it would be good to get this rifle out in the field. What are you using for optics and mounts? Also, where did you buy the magazines?

EdM,
That sounds like a real good hunt you have coming up - a dream hunt, in fact. I hope it goes great for you!
I bought the magazines from Chattanooga Shooting Supplies. I am an FFL and am registered with them - I don't know if they sell to the public. It is their item number BNS10502, at $45.66. Their were 19 of them in stock when I bought the three I ordered and they have 16 showing now, so I don't reckon they're flying off the shelves.
Just did a search for retail and there is ONE in stock for $53 at Wholesale Hunter
Seeing some other outfits in that price range too now, so I think you can find some.

Without any coordination at all SU35 and I both ended up mounting Burris Fullfield E1 4.5x14s on ours. To save weight, I skipped the nice steel rail that came with the rifle and just went with low Talley Lightweights and they're a perfect fit. I just learned that Burris will cut a custom turret to dial to range for under $50. Might try that, but with a 250 yard zero, the load above is predicted by the computer to be spot on the BDC tics in the E1 reticle at 300, 400, 500, and 600 yards.

Have you worked up loads for the 168 TTSX yet? I was just thinking about that bullet this morning wondering if I'll end up eating my words about not testing any tougher bullets for this rifle. That bullet is a true "kill anything you shoot at" choice.

Please share your loads here and anything else you learn about your rifle.

Good luck on that hunt!
Rex

EdM, et. al.
On an "FFL Not Required" item like magazines, I believe I can buy them through Chattanooga and have them sent to any address I want, So if anybody wants some of these 6.5x55-lenth mags and can't find them at retail, PM me and I'll see what I can do. When I ordered the three I incurred a $3 credit card fee and shipping was $10. So figure for two of them (seems like the right number to me to have a loaded back-up in my pocket) it'd be probably just under $105 shipped, which is actually cheaper than any of the retail prices I found.

Anybody that wants me to try to grab them a couple and have them sent to them, shoot me a PM and we can work it out. I'm pretty sure that'll work, and we know there are 16 available.

Cheers,
Rex

Rex,

PM sent on the mags. I am using the same scope in Talley LW's as well, but they are lows (already had them) and I cannot get the scope back far enough. I assume you are using mediums?

Make that 14, LOL

No, Mine are lows too, and I could actually get the scope back just a bit more than I have it now. Confirm you reversed the front mount - like the attached picture? Also that long LOP doesn't help. I just shortened mine, just an hour ago, and it is much better now.

I'll try that but mine were very near barrel contact is.

I just had one of those "doh" moments, looking through my Nosler #9. All along I hade been working off Ramshot's latest load guide for my Big Game data, and also referencing the comments on the thread Charlie Sisk started about how much he loves Big Game (which featured the .308). Both Mr. Sisk and Ramshot list 51 grains as max with the 165 SGK, and I had been using this max in the M12. I hadn't even realized Nosler listed Big Game in the most recent manual, and it was also their fastest powder.
Nosler's current .308 data
As you can see, they used 52.5 grains as max with their 165/168 and got a wicked 2910 FPS in their 24" barrel. Based on the .00053 CHE I already measured with my 51 grain charge, I'd not want to go much higher in my rifle, even though brass is holding up really well. I will be shooting this load for the 5th time in the same ten cases on my next trip out.
But there is the Nosler data for anyone who can use it.

On my most recent trip to the range yesterday with this rifle and load, 8 out of 10 shots nicely clustered sub-MOA, but one high and one low outlier opened the whole ten shots up to about 1.9 inches. Also the average speed dropped down to just under 2700, at 2689. I'll keep ya posted...
Rex