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B&M Technical Support

Fortunately there are only a few issues I have found concerning the B&M rifles since they were conceived. All of which can easily be overcome. Sometimes by you, sometimes by going back to SSK Industries. We are going to discuss some of these, and what you need to do should you experience these problems or issues.

Basically I will break this down into two sections, first the rifle, dealing with issues concerning the rifle itself, and the second Loading, dealing with the actual loads, brass and other like issues.

B&M Rifle Tech

Anytime one takes a rifle and converts it into something more radical, such as taking a small bore rifle and converting it to a big bore rifle, there are going to be problems and issues to solve. There is no way around that.

When I chose the various platforms that I wanted to work with, I was careful to choose a similar or even the same cartridge case that the rifle was chambered in to convert. For instance, in the standard B&M cases from 9.3 to 50 B&M, I chose Winchester M70 WSM rifles, it does not matter, from 270 WSM to 325 WSM, all the same action. The WSM cartridge is very slightly larger in diameter than the RUM cartridge in which the B&Ms are based. Which meant the magazines were wide enough to accommodate the B&M based RUM case, the bolt face would work without modification, and really very little modification was needed at all to get the B&M RUM cases to work properly.

Cartridge Retention

The biggest issue of all is "Cartridge Retention", or very simply putting 3 cartridges down in the magazine and they stay as you operate the bolt, running the cartridges through the rifle. Most of the time you will experience this with 458 B&M, 475 B&M, 50 B&M and 500 MDM more so than the smaller bore 416 and less. The reason? Well, what you have done is taken a magazine that is designed to hold a cartridge with 150-180 gr bullets stuck in the front, and now you are putting a cartridge in that same magazine with a 450-500 gr bullet in the nose, as the bolt is drawn back, it wants to pull that cartridge out by the front. This is not something you can solve at home. If your rifle does not retain straight from SSK Industries, contact SSK and get it back to them. Brian at SSK can sort this out for you in short order.

Now, one other thing concerning retention of the cartridges, and that is changing the stock. Many times I have changed the stocks and all of the sudden this same rifle that has worked 100% of the time, now will not retain cartridges with the new stock! Sometimes you can put a spacer in the bottom metal front, or back, or both, which is simply a washer under the bottom metal screws, and this will lessen the pressure on the magazine just enough to work properly and retain. Sometimes this does not solve it, so send it back to Brian at SSK, and he can sort it out for you.....

Wes Chapman from Accurate Innovations came and spent a weekend with me to help solve this issue on the AI stocks. We believe now that we have the proper measurements for the bottom metal that should minimize this issue when changing stocks on the bigger bore B&Ms.

Feed and Function

No matter what magazine rifle or handgun you are working with, if you look hard enough you will find a bullet that it will not feed! However, a Winchester M70 is about as reliable feeding as anything I have worked with. The only thing you will start having trouble with is a Flat Nose solid that has a 70% meplat of caliber, then you will start having feeding issues. If you stay with properly designed 68% FN Solids, then you will not have an issue.

If you do, 99% of the time it is because of the position of the follower in the magazine. Winchester used a few different floor plates on the last Classic Control feed guns. Remember, we started this rifle off as a small bore WSM with little or no recoil. Now we are a big bore rifle, and we have introduced recoil into the equation. This recoil sometimes causes the flat spring that fits in the floor plate to move forward, and when it does it jumps over the hump that is molded in the floor plate itself. This places the front of the follower in a downward position, and causes the nose of the cartridge to take a dive into the feed ramp. See photo below.........


Spring over the hump in floor plate

When this happens, your rifle will not feed properly...............

Some of the photos I am going to show you below are some of the things I have done to my rifles only. I hope that you are more capable of doing nicer work than I am, as I have done some ugly things to accomplish what I needed to do, without having to send it back to Brian at SSK. Sometimes you can just take the spring out, bend it over close to the edge and this will keep it from jumping over. Sometimes I have taken and peened them in with a hammer and punch, and sometimes I have taken JB Weld and molded it in place to keep the spring from jumping. All will work, but I don't do the best looking work myself.

An interesting note, the new Winchester M70s coming out of Columbia South Carolina seemed to have addressed this issue for us, should you choose to use one of these rifles. In the front side the cut is very sharp and deep, it would be impossible I would think for the spring to jump over this. In the rear you see tabs that are made into the floor plate to also keep it from moving too far to the rear. This is the perfect solution and solves all feeding issues.


New Win M70 SC Rifle

All of the B&M Super Shorts suffer this problem more serious than the rest of the B&Ms. The WSM B&Ms are not so bad, one once and awhile. The JB Weld gun you see above is one of my 458 B&Ms, in fact the one that I have used on elephant, buffalo, hippo and other things, my favorite 458 B&M by far. I had one hell of a hard time stopping that spring from jumping over the hump. This last trip in July of 2013 I though sure I had beat and peened that spring in place that it would be impossible for it to move. However, after a hundred rounds or so, and then taking it to Zimbabwe I noticed one day it was feeding funny? I checked it, and sure enough the damned thing had jumped over! Simple, I just took a screwdriver and beat it back down right in the field hunting! I kept an eye on it the rest of the trip and did not have any problems, and it feed and functioned slick as can be. When I returned, I put the JB Weld to it, beat and peened it some more, and will see if it ever moves again!

If you have any of the Super Shorts, first thing, you might as well take that spring out and give it a good bend downward and see if that holds it. If not, do some of the other things until you get it to stay in place. I can just about guarantee that the Super Short will jump over if you do not do something.

These are the main two issues with any and all of the B&M Bolt guns. There really is not anything else, or other abnormal bugs that one needs to be concerned about, to the best of my knowledge. We have worked with a lot of these rifles now and other than some part breaking, which has nothing to do with the conversion, there is nothing else of concern.

B&M Cartridge Tech

Currently there are 11 B&M cartridges designed for bolt action, lever action or single shot rifles, and 2 cartridges designed for big semi auto actions. Most all these are really easy to load for, and with a few exceptions are some of the easiest cartridges I have ever worked with.

For the Standard B&M Series in 9.3, 375, 416, 458, 475, and 50 B&M I purchase mostly 300 RUM brass, but any RUM brass will work, have a close friend cut and trim all of it to 2.240 inches long.

For the Super Shorts we use any WSM brass, cut and trim to 1.640 inches.

B&M Super Shorts

All three of the B&M Super Shorts are extremely easy to work with, just lube and run them through the size die, trim 458 and 475 back to 1.640, load and shoot. New brass, fired brass, all of it, zero issues. Easy as it gets, if you have the basic brass already cut and trimmed.

Standard B&Ms

Most all of the bigger B&Ms are the same, size, trim back, load and shoot. With the exception of 416 B&M and 475 B&M. Both of these cartridges are notorious for head separation.


If you take basic NEW BRASS, run it through the size die that is set up so the cartridge goes easy in the chamber, then you give this case room to move forward when it is fired and forms to the chamber of your rifle. To prevent this from happening, set your size die back up a tad until you feel a slight bump as you chamber the cartridge or case. The shoulder of the cartridge is bumping in the chamber, when fired, it does not move forward, and therefore you get no stretch of the case, preventing case head separation in the future.

Now, with the 416 B&M, there are some exceptions that you can get by with. Most of the first loads used were with ball powders, and specifically AA 2520. The 416 B&M is very good with this powder. But when I started working with IMR 8208, more of a stick powder, I discovered that even if I sized new brass to chamber easy on the first firing, that with IMR 8208 I rarely got any case stretch, and subsequently rarely got case head separation issues. I also found this to be the case with lighter bullets, like the CEB 225 gr #13 and the 180 gr CEB using H-4198 as long as my loads exceeded 50000 PSI. No case head separation at all.

Naturally once the brass was fully fire formed to the chamber, then you could full length resize to chamber easy with no issues from that point forward.

With the 475 B&M I have not found a powder solution that would allow you to cheat case head separation. I still have to bump that shoulder on the first firing with all of these.

The 9.3 B&M uses a stick powder to begin with, IMR 4320 or RL 15, so it has not had any issues with case head separation.

The 458 B&M and the 50 B&M are the easy loaders here, size to chamber easy, trim, load and shoot, new brass, old brass, fired brass, it don't matter what you do with either of these.

50 B&M Alaskan

There are no known issues at all with the 50 B&M Alaskan designed for the lever guns and single shot rifles. Another easy loader.

500 MDM

The mighty 500 MDM..... 2.8 inch RUM case, made best from 375 RUM.

The first design of the 500 MDM was probably actually a better cartridge design in and of itself, than the current cartridge with the shorter neck. The old version had a very long and tapered neck, and I could see a bullet bulge at the bottom edge of every bullet, and I did not like that at all. It was totally aesthetics, and had nothing to do with function, but I changed it anyway, and probably introduced some of the issues we have with it today because of that... OK OK.. My Fault for making the change and I take responsibility!

What we have today really looks pretty good, and it most certainly works just fine, and is a hell of a good cartridge and the biggest cartridge one can "easily" convert a Winchester M70 to. Full .500 caliber. In 20 inches it can run 500 gr bullets to 2400 fps, 450 NonCons to over 2500 fps, and even 300 gr bullets to 3000 fps. It is a power house on still a small package for what it is capable of doing.

But it can be somewhat troublesome with making new brass from 375 RUM. And it can also suffer case head separation just like the 416 B&M and 475 B&M can.

Forming brass is not quite as easy as any of the other B&Ms. With the other B&Ms we are going down in caliber from basic 50 B&M brass or 50 B&M Super Short brass. With the 500 MDM we have to go UP from 375 RUM Brass. I find its always easier to go DOWN in caliber, than to go UP in caliber, especially if you have to go a long way up or down. Going from .375 to .500 is a LONG way!

Nearly from the beginning I have used corn meal to blow the 375 RUM out to 500 MDM, and this method still works great, and so good in some rifles that the finished case looks nearly fire formed and ready to load.

Corn Meal Case Forming

But this is a lot of work and is very time consuming. Sam Rose recently made a set of punches and dies for me to take the brass up in steps, first step from 375 is to around 416, and then to 458 and then final to .500 caliber. I then resize this brass back to spec, load and shoot. Now this method is causing some issues with head separation, and I might be able to solve some of it by not sizing the case as much, which I am going to work on in the near future. But, I can make brass very quickly and much easier than using the corn meal. While it is not as nice and formed as a true fire formed case, it is functional, for the most part, especially if I could reduce the number of cases I loose to head separation, which currently is only 4-5 per 100 cases. See below......


Once you get that ring around the case, about 3/4 inch up from the base, you might as well toss those in the trash. They will separate completely probably on the next firing.

Another thing that you should note is that these cases show extreme flattened primers, which to some would indicate extreme pressures. This is NOT THE CASE HERE. What is happening is the case is moving forward when fired, forming into the chamber, during this the primer is backing out some, when the case slams back against the bolt after it has formed, then the primer is getting flattened against the head. These are all low pressure loads, less than 50000 PSI........


What you see is not caused by high pressures, but simply brass flow when being fire formed. You will see this on this first firing on some cases that don't have case head separation as well. And, in addition this also occurs with some of the corn meal formed brass that works so well too.

In addition, I have seen some of the 375 RUM brass that has a bevel at the top of the primer pocket, this allows primer to flow into that, and get flattened as well, looking like a high pressure load, but with the exception the rifle action works slick and this is not caused by pressures, just primer flow in this case because the primer pocket is enlarged.

If you are forming from Corn Meal loads, then when you size your case, leave it some short so it bumps the shoulder, and the same I believe if you are forming from dies as well, this should eliminate most of these issues with the 500 MDM.

Another little thing about the 500 MDM, since I changed the length of the neck, and brass is thinner at 2.8 inches than it is on the standard B&Ms at 2.25 inches, the 500 MDM requires a crimp to hold the bullet in place. Now, you can't over crimp, or you will crumple the case just below it's tiny ghost shoulder. This can be an issue with heavy recoil pushing the bullet back into the case on that 3rd round down in the magazine. It is always best to use a compressed load with the 500 MDM. The compressed charge, along with the crimp, will hold the bullet in place, not allowing that 3rd round down to seat deeper during recoil.

I am a fan of compressed loads anyway, and this is just an added bonus for compression, and also comes to play with most of the other B&M cartridges as well.

Final Conclusion To Date

In truth, there really are not too many issues with either the rifles or cartridges of the entire B&M family. None that cannot be solved easily.

While I would like to take some of that credit, the truth be known that most of the credit belongs to SSK Firearms, JD Jones, and Brian Alberts! Without SSK I can promise there would be many more problems to over come than there is.

If you have something going on with your rifle that is not part of what I have talked about above, please contact me, and let me know. This way, we can figure out what the issue is, and how to solve it.

If you have a rifle tech issue, such as retention or feeding, contact Brian at SSK Firearms either by email or by phone.



When and if I learn of any other tech issues I will report them on this page.

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