Originally Posted by benchracer
GREAT writeup! Thank you for taking the time to post your experience with the SERBU. Your proposed mods would be interesting indeed.
I am disappointed to learn that a semi-auto cannot be used with the 750g AMAX. That would be my bullet of choice in a .50. Can the SERBU 50A be fed single shot, if desired? I am given to wonder if there is such a thing as a single shot follower for the Barrett Mags.
There are a lot of guys that load up match ammo using the 750 gr A-Max and single load them in the Serbu and the Barrett. You do get a decent ballistic advantage with these bullets and some accuracy improvements as well with some rifles.
Its a little tricky because there is no "Last round bolt stop" on this rifle. Would be nice to have one and then that would really make it easy to single feed the Serbu 50A. Still, it can be done. The bolt is surprisingly easy to pull back on this big rifle. With a bit of practice, its no problem to single load a round.
Still, these rifles are not made as precision BR class rifles. They are made to be accurate Utility rifles and for this, from what I have seen in comparing these to other semi-auto 50 BMG rifles, they are very near the top rung of accuracy performance.
The biggest issue with these rifles and accuracy is that most people buy a $7000 class rifle and then go and try to find the cheapest ammo possible to shoot it. That does not make a lot of sense....... If someone paid even $3000 for a custom rifle chambered in a more conventional chambering, I would say 90% of them would want to handload their ammunition to get the most out of their rifles.
With the 50 BMG however, most spend MORE on the rifle and then try to get the cheapest ammo possible. In this case, that is usually mil surplus ammo. Now, there is nothing wrong with this ammo but the 50 BMG owner needs to realize that this ammo has a "Dispersal" factory built into it for an intentional purpose. In the military, they do not want every round fired out of an M2 Browning to land in a tight group, instead they want to saturate a target area to do as much damage as possible to the intended target, which is generally a hard target or vehicle. This is done mainly with variations built into the bullets with weight variation and some powder charge variation.
The ball projos are not all that consistant and some even have loose cores. When I get ready to load ammo using these projos, there is bench work that needs to be done. First thing I do with a new lot of Ball projos is to take each one and shake it aggressively next to my ear. Many would not believe it but in some lots of bullets you can actually hear the core rattling around. Some lots are much worse then others but its not unusual with mild steel core ball bullets. Those bullets that are found to have loose cores are sorted out and set aside.
Next, now that you have all the bullets with solid cores, I weigh each bullet and short by weight. Now a 647 gr ball or 700 gr AP projo does not need to be sorted to +/- 1 grain in weight. Remember that most will use a 1 grain weight range for most match bullets that weight 1/3 that of these projos. As such, I like to sort groups of bullets into groups that are all within 3 grains.
Now remember this is for match BALL ammo, not true match ammo that will be used in a precision single shot rifle like the one below:
This rifle is one of my rebuilt AR-50 rifles that has an accurized receiver, match grade barrel and chamber, usually in my 510 Allen Magnum. This rifle is made for precision at long range. For a rifle like this, you want bullet weight variation to be as little as possible. You want that with any rifle but its easier to get a good supply of 750 gr match bullets to weigh within 1 grain then it is to get a good supply of 647 gr M33 ball bullets to be within 1 grain. There is no sense buying 500 M33s and shorting them to get a few small lots of bullets that are within 1 grain of each other.
For that reason, for what I call match BALL rounds, I will live with a 3 grain variation in group size. We also need to remember that a semi auto rifle will generally not have the ability to tell the difference between a 3 grain variation in bullet weight, in all honesty, even a 5 grain variaition is probably just fine.
After I get the bullets sorted into groups that are within 3 grains, I will then measure the baring surface of the bullets in these goups. This will help with vertical stringing at longer ranges. If your shooting under 500-600 yards, this step is really pointless. In all honesty, in a semi-auto rifle, this step is probably overkill but its something I do just to sleep better at night.
Once these bullets are all sorted by weight and baring surface length they are labeled and stored in their sorted lots.
In the 50 BMG, primer seating pressure can have a significant effect in consistency. This is because the 50 BMG primers take a HUGE amount of energy to ignite. It is for this reason that a 50 BMG rifle should NEVER be dry fired as its very easy to damage a 50 BMG firing pin while dry firing because of the energy in the firing pin. It takes nearly 10 times more energy to consistently ignite a 50 BMG primer then even the toughtest large rifle magnum primer. I used to know the exact ft/lbs required or recommended but that numbers eluded my mind now!!! Simply put, its ALOT!!!
Because of this, the 50 BMG primer needs to be seated to consistant pressures in the primer pocket to consistently reload the anvil legs inside the primer. There are many tools available to do this properly and for a match rifle or any 50 BMG rifle for that matter it can be a significant improvement in velocity consistency.
Another aspect that is related is case sizing. You want a case that is easy to chamber but not one that is loose in the chamber. If a case is loose, you will get similar results as you would with inconsistent primer seating because when the firing pin hits the primer, it will drive the cartridge forward in the chamber until the case shoulder is stopped by the chamber shoulder stops it. The more distance there is, the more energy is robbed from the firing pin. In a match rifle, you want the case to be lightly touching the chamber shoulder but still allow the bolt to close with very little resistance if any.
In a semi-auto, we can not do that for functionality, we need a bit more room but as little as possible to maintain function is what we are looking for. Again, consistency is the key, all cases need to be sized the same.
Then obviously we need a consistant powder charge, that's a given.
We also need consistant neck tension. The 50 BMG case neck is very thick. Most often, match handloaders will use some kind of bullet surface lube on their bullets to help in some way with copper fouling which is always a problem with a bullet of this size. as such, a coated bullet will help with bullet pull forces. I generally clean the inside of my necks, debur very well with the proper tool for the given bullet I am using and then lube the inside of the case necks with a quality dry lube. Same as with any conventional match ammo.
Finally, as with any rifle, we need to seat the bullets straight into the cases with as little run out as possible. Still, we need to remember what we are loading for, a semi-auto rifle will not show the benefits of true match ammo nearly as well as a precision single shot rifle. Just the way it is with the mechanical system with the semi-auto rifles.
This all brings me back to the point that many pay a load of cash for a 50 BMG rifle but then get the cheapest ammo they can find and then wonder why their rifles do not shoot well. Put a bit of time in on the bench, save up and get the proper tooling to make good 50 BMG ammo and you will be impressed with the consistency and accuracy the big girl can produce.
Good brass can be had for less then $2 a piece which is pretty cheap compared some conventional chamberings. Powders for the 50 can be had pretty cheaply if your using surplus powder, in the $50 per 8 lb keg range. Bullets are the largest investment, especially for match ammo but again, not much more then the more expensive 338 or 375 match projos.
Benefits are huge. If you spend the money on a 50 BMG rifle, invest in the ability to load quality ammo for it and you will be much happier with your big 50.