madppcs; looks like I'm late on this one but........I have an AR-50. I started loading 750gr AMAX w/215 grains of H50BMG at 5.68" OAL on my RCBS single stage. (Using once fired, neck sized, WW brass from shooting a ton of the Hornady 750 factory ammo over the years. ) It was barely 2400fps read with my Magneto Speed but easily 1/2moa 5 shot groups at 300 yards. So I agree with northern that 219ish is probably a good place to start.
I worked up gradually and now I'm at 235 grains which only yields 2600fps when the rounds are warm. Still 1/2moa at 300yds. I have absolutely no pressure signs so I'm going to try 240 grains next. Shooting for at least 2750fps and figure that should be no problem with the very long OAL I'm going with. I'll keep you posted but it may be awhile as I've been busy with other (gun) projects.
Might want to double-check that Magnetospeed because I easily get 2650 with 647-grain pulldown FMJs, once-fired Lake City cases and 210 grains of WC872 pulldown powder from 20mm cannon shells out of my AR-50. 200 grains gets me about 2250 fps. And those "plinking" rounds I load for $1-$1.50 a round are MOA or better at 500 yards. To get more than 2650 fps out of 647s I have to go to 50BMG. I haven't chronographed any "hot" ammo yet but I'm pretty sure I can hit 2900 or better with a nice, safe and sane charge of 50BMG. I rarely load any ammo for any gun anywhere near "max" because of the unnecessary beating it puts on guns, brass, powder inventory, budget and my body.
I've got a couple boxes of 750 A-Maxes but I haven't played with those yet. Hornady load data shows about 2750 with them and 200-odd grains of 50BMG. They list a "42-inch" barrel which I imagine is a Ma Deuce "test barrel". I don't know how "tight" those are in the bore but I do know that my once-fired Lake City won't come within a mile of chambering in my AR-50 until I FL size the cases so I know the mil-spec chambers are plenty loose and I suspect the barrels probably are as well. I'm not saying 2750 is easily and safely doable with an AR-50 but I damn well know they're good for a hell of a lot more than 2400 fps.
How did you go about mounting that MagnetoSpeed on your AR-50, by the way? And what is "WW" brass? And what RCBS single-stage are you loading .50 on besides an AmmoMaster? You mentioned a single-stage RCBS like its just a Rock Crusher. Pull the bushing out and they have the big die bore and threads but they don't have anywhere near the height for .50 which is why there is a much bigger RCBS press for .50. Lee Classic Cast presses JUST handle .50 and are far and away the best deal going for a .50 press setup. Press, adapters for priming .50 cases on top of the press and primer/die tools for "small-bore" rifle cartridges as well for about $200. And that's with an FL die set. Unfortunately you can't buy a Lee collet neck-sizing die separately so I had to buy another full set of dies and now have a duplicate seating/crimping die but for under $100 for THAT set I couldn't bitch a whole lot.
The only brass I've fired is 10 PMC cases from American Eagle 660-grain FMJ and that once-fired Lake City that's about 50 cents a case last time I checked from a few different suppliers. I've got at least a few hundred and annealing and mild loads are supposed to stretch case life to 15-20 reloads. Since .50 BMG is just "scaled up" .30-06 and is about a 54,000 psi cartridge max and very, very few commercial factory/reload loads even hit 50,000 psi, I can believe that kind of case life. Barrel life will be outstanding as well. The Fifty Caliber Shooters Association has classes specifically for "mil-spec" FMJ ammo and the top dogs shooting that "cheap" ammo ain't too far behind the "premium" ammo guys at 600 and 1000 yards. They shoot for "aggregate" group size if I'm not mistaken.
And at both 600 and 1000 with both mil-spec and premium commercial ammo the "world record" groups are way, way sub-MOA. Personally I don't think "premium" brass is worth the money compared to good, heavy-duty once-fired mil-spec stuff. Those Lake City cases are treating me very well. They take a lot of work in the primer pockets because the military ammo has ungodly tight primer pockets and super-duper crimps on top of that gbut once they're decapped and FL sized and annealed and trimmed with my Little Crow Gunworks "Big Boy" and have been wet-tumbled in stainless pins, you'd have to look at the headstamp to know its not "premium" brass.
I couldn't believe how tight the primer pockets and crimps are but de-capping is a big chunk of all the force it takes to decap/size "new" cases. I use a healthy coating of Imperial Die Wax on the cases and that makes a huge difference in effort required. One yahoo on YouTube managed to break his Lee Classic Cast press and in his "how-to" video I'm surprised he hasn't broken more than that. All because he insists on rolling cases on a "lube pad" or giving them a little squirt of liquid lube. I can't remember which he uses but it ain't anywhere near enough.
As far as "de-crimping" ALL my military brass (5.56, .308, .30-06 and .50 BMG) I don't "de-crimp" with any sort of made for the purpose tool. Tried my buddy's Dillon swager once on 5.56 and .308 and just didn't care for it. If the cases aren't all uniform in length they don't work very well. Now I just use the case neck ID reamer on my case prep station and "ream" the crimp out of the back end of the pockets. That leaves the rest of the pocket tight and undisturbed and puts a nice little chamfer on the rim of the pocket so those tight cases prime much more easily from then on. The case prep center DOES have enough smoke to do that on my .50 cases and that kind of surprised me given how tight and hard those pockets are.
They don't want primers popping out in machine guns I imagine. There's an RCBS primer pocket uniformer that is supposed to go on a case prep center but those things don't have anywhere near enough torque to ream out those primer pockets. I chuck it in a 1/2" 18V cordless drill. Mil-spec primers must be a little shorter than CCI #35s because I have to actually drill/ream the pockets quite a bit deeper to get #35s down to flush or just beyond. From time to time processing "new" brass I don't get the pockets deep enough and really have to lean on the Lee Classic Cast to get them in and flatten-flushed, lol. I mark those rounds with a Sharpie so I remember to hit them with the uniformer again on the next pass through.
Like I said, you might want to check your chrono because your ammo sounds way slow to me. I've got a Shooting Crony Gamma Master and it seems to be very "accurate" compared against a lot of different Hornady load data for several different rifles and cartridges I've shot over it. When I chronoed my .50 I had it out at least 10-12 feet in front of the muzzle when I was seeing 2250 and 2650 fps with those 647s and WC872. In my experience up to about 10,000 lb-ft. of muzzle energy - which is about where 647s at 2650 land - my AR-50 isn't even "working" the brake at all. I mean zero recoil. Plenty of blast but no kick at all. Above that starting at about 11,000 lb.-ft. I can finally feel the brake work and its just crazy to feel that brake grab the rifle and pull it back forward.
Lots of guys claim their brakes do that but I haven't seen any "small-bore" rifle that isn't still smacking them on the shoulder just a little bit at best and watching videos online its evident that some "one size fits all" brakes and even "custom" brakes aren't doing much of anything to decrease recoil. In many cases it appears they may actually INCREASE recoil. May sound crazy but if the brake tens to prevent the gas and ejecta "jet" from expanding rapidly and no redirection of energy rearward is achieved - which is the case with any and every brake that has ports perpendicular to the barrel axis - the recoil energy and its effects can be concentrated in front of the rifle pushing rearward for a longer period of time AND have a lot more SURFACE AREA to act against slapping the front of an ineffective brake rather than a small muzzle.
Proper brake design has to take the cartridge power and bullet design into consideration and the brake must be matched to the rifle and cartridge and bullets to be of maximum benefit and to justify the drawbacks that go with brakes. In particular the flutes have to "turn" the gas around and send it rearward at a significant angle and each "chamber" has less and less gas to do that with and must decrease in "volume" but also angle because there's more to the "energy" contained in the gas than just its volume alone. Proper design according to BULLET LENGTH is absolutely key because the bullet is the "plug" that must effectively "seal" each chamber as it passes through it and it must seal the FRONT of each chamber while "opening" the rear. Adding more chambers in front of ineffective, poorly sealed and over-sized or undersized rear chamber(s) does nothing but make the brake look more impressive and make it more expensive and a bigger waste of time, money, weight and lost benefits from having no brake at all.
When a company is making/selling "one size fits all" brakes by CALIBER (bullet diameter is "caliber" to most veteran shooters while chambering/cartridge is the actual "round" designation) and therefore is equating .308 Winchester to .300 RUM, that company and its "engineers" are either clueless and have no idea what they're doing by NOT developing different brakes for different .30-caliber cartridges or know EXACTLY what they're doing. Which is ignoring the FACT that a brake must be designed for the rifle/cartridge/bullet to be a net positive and taking advantage of the fact that so many "shooters" do NOT know that. Most of the time if there's a noticeable decrease in recoil, its due to the increased WEIGHT hanging on the front of the rifle. And the "placebo effect" ALWAYS comes into play.
If you pay a lot of money to install a brake on a rifle, you're going to "feel" the difference whether it exists or not. Of course that weight gain is going to produce a difference and how much of the difference is due to that weight gain could only be quantified by putting a "dummy brake" of equal size/weight/frontal area on the rifle and using "scientific" testing methods to actually MEASURE "recoil". Weird how we have chronographs and trigger pull gauges and a million different tools to "accurately" measure and quantify so many other aspects of guns and ammunition and components but nobody makes a "recoil tester", isn't it? Of course recoil is always subjective and when there are guys who talk about recoil and "kick" of ARs and there are even "brakes" for .22LR rifles, it goes without saying that there's no real interest from the "gun industry" in having a publicly available way to measure "recoil".
My AR-50 with "hot" ammo still WAY short of the 14,500 lb.-ft. or so "max" energy level I'm comfortable with had me thinking it was going to smack me the first time I shot it like that and felt it start sliding backward a touch but then the brake grabbed it, stopped it and did pull it back forward. I had a small plastic Plano "ammo can" on top of the bench for a "rest" so the rifle could easily slide back and forth and it never has kicked me at all. My Browning A-Bolt Stainless Stalker in .30--06 that weighs about 6 3/4 lbs bare is an absolute asskicker compared to every and any other rifle I own so I always get a kick out of shooting that .50 that's pretty much 5-6 times that rifle and cartridge in every way and not having it kick at all.
If you can really feel your brake working and especially can feel the concussion slap you in the face your MagnetoSpeed is WAY OFF since 2400 with 750s is under 10,000 lb.-ft. of muzzle energy. Get them to 2750 and you're well over 12,000 lb.-ft. And you'll feel 20%+ more energy/power every time. There are several serious "issues" that go along with a MagnetoSpeed when it comes to how they "measure" velocity or rather how they "sense" the passage of the bullet.
They're related to bullet MATERIAL(S) as well as the length and "mass" of the bullet and without some way to calibrate them, they're not "instruments" and their data is unreliable once whatever calibration parameters they left the factory with are exceeded. And being electrical devices and given how temperature affects electrical devices and "throws off" supply and signal voltages as temperature and resistance increase, there's no way for a MagnetoSpeed to remain "accurate" and "precise" over long strings when its sensors and conductors connecting them are continuing to get hotter and that heating affects voltages to and from the sensors.
LabRadars have their own issues when it comes to the material and size and "reflectiveness" of bullets traveling downrange and its pretty funny that all the online hype from "experts" and "reviewers" seems to go against "optical chronographs" and toward "magnetic" and "radar" chronographs giving how flawed and "new" and compromised the latter two are vs. the former. I say "funny" because optical chronographs have been around for many, many decades and are the "industry standard" for "scientific" ballistics testing and have been a known quantity and are widely trusted because of their consistency and the fact that only a few companies make them despite their relative simplicity and "easy" design/construction and because they are so easily "tested" and "calibrated" by putting two units "inline" with each other.
Anybody who says that's not "accurate" for testing/calibration because they're not "seeing" the projectile at the same speed and point in its flight is either forgetting or ignoring or just never realizes because they know nothing about "calibration" of instruments that you can SWITCH THEM AROUND and put the far unit in front and vice versa after checking them the other way around. And they're ALWAYS subjected to exactly the same operating conditions and the shooter, gun and bullet and location can all be removed from the testing and you can test them with ANY object you can "shoot" through them. Being on the same "axis" there's no "parallax" and they either "pick up" the object or they do not. And you know precisely when and where that occurs.
With a MagnetoSpeed or LabRadar all of that goes out the window and you're stuck comparing "identical" units to each other. There's no "competition" for LabRadar or MagnetoSpeed. And they're supposedly "accurate" and "precise" despite the former having a LOT of "issues" over the MANY years its been marketed/available and the LATTER being in its third "generation" with supposed "improvements" to what is/was also supposedly an "accurate" instrument to begin with.
There are multiple "models" and "generations" of Oehler and Shooting Chrony optical chronographs as well. But both have been around for many, many decades and they're all fundamentally "identical" in design and operation at the basic level. Newer "generations" and "models" simply add more features and functionality. For example, a "Gamma Master" Shooting Chrony like mine has a "timer" function that records the "splits" between shots fired which in and of itself can help "investigate" why differences in velocity from shot to shot in a string exist.
If the "harmonic theory" of barrels/bullets is true and the barrel is "bending" as it "vibrates" then it must continue to "vibrate" for a period of time after each shot. A "rapid-fire" string could have shots occurring while the barrel continues to "vibrate" and that would tend to create more "spread" in velocity even though the effects of heating might be "reduced". Shooting several strings of "identical" loads at different time intervals with varied but consistent (within a string) "splits" shot to shot and overlaying that data over velocity is a "scientific" way of determining whether "harmonics" or "heating" has more effect on "ES".
Of course you get lots of "optical chronographs suck because...." crap from the MagnetoSpeed faithful but most of their claims are complete b.s. Especially when they talk about the sensitivity to light and not having "enough" light to make an optical chronograph work correctly. Most of that is b.s. because TOO MUCH LIGHT is the major "issue" with an optical chronograph. The "sunshades" are actually diffusers and keep the sensors from being "dazzled" by ambient light because the sensors do not "see" the object. They "see" its "shadow" as it passes over them.
The brighter the ambient light the harder it is to "see" shadows because there is reflected light all around and some light even reflects off the "eyes" of the sensors themselves. That's only a problem with "overhead" light of high intensity because they're located quite a ways down into the "sensor" body itself. But when the light is directly overhead, it "dazzles" the sensors and a small and or fast-moving projectile may not cast a strong enough "shadow" to be "seen".
Fortunately with an optical chronograph, you know with the FIRST SHOT (if you know how to operate it correctly and have it set up correctly) what the "problem" is and the chronograph isn't affected by anything BUT the projectile and its "shadow" so when there's an "error" its a "lighting" or "location" issue. And you can install the "diffusers" OR auxiliary lighting above the sensors/projectile path to be able to use an optical chronograph pretty much ANYWHERE and with ANY projectile and "gun" propelling it. I would only take a MagnetoSpeed or LabRadar if it were given to me and only to immediately sell it to the first available "fanboy" of those chronograph types.
And the REAL reason so many "shooters" prefer them to optical units is pure LAZINESS. They want "plug and play" while sitting on ass at the "bench". And not a few of them are plain and simply scared of shooting an optical chronograph or have already done so and invariably because they're too LAZY to read the instructions and make sure they're set up correctly and shoot enough and practice enough to be "good" enough to "hit" the sensing "window" of the chronograph without hitting the chronograph itself. So they want something "foolproof" because they regard themselves as...fools.
