View Full Version : 50 BMG on an AR lower?

April 8, 2014, 12:02 AM
Hello all.
I have a question that maybe someone out there would be able to answer.
I see a few 50 BMG uppers available to put on AR lowers but I have seen plenty of light primer strikes on those ARs made up for 7.62X39 and firing hard mil-spec primers. This leads me to wonder how reliable such 50 cal rifles would be.
A long range high accuracy rifle needs a good trigger, but the ones I have used on 5.56, 6.5 Grendel and 6.8 SPCs have lighter hammers than stock ARs, and the stock AR hammer often doesn't hit a hard primer of a Russian round hard enough, so I wonder if the 50 BMG is going to be a problem also.
Does anyone out there have any experience with the various 50 BMG uppers set on AR lowers?

Feed back please.

April 10, 2014, 10:38 AM
You do realize that there's a whole selection of non-military loaded 50 BMG on the market?? I don't know what type of primers the commercial loads use but it's no big deal to swap in a heavier hammer AND spring if that's what it takes.

April 10, 2014, 11:32 AM
Well Mobuck, it really is a big deal. You see the rifle is made for long range high accuracy shooting. The stock AR "fire control group" is not good enough for that kind of accuracy. All good long rang target rifles need to have a good trigger.

So, coming back to the issue of misfires on hard primers (7.62X39) WITH stock hammer and hammer spring----this makes me wonder how hard the primers on 50 BMG rounds are. All the good aftermarket AR triggers I know of (and as a full time gunsmith who has made several hundred ARs, I think I probably know most of them) have lighter hammers than the stock ones that come on factory ARs.
As far as I know the reloader has only one choice and this is the CCI #35 primer. I have no experience with a 50 BMG upper (yet) on an AR lower, which is why I am asking if anyone out there does have such experience.

I have used Armalite and Barrett rifles this is not a problem but those rifles have pin-falls that are easily strong enough to pop the primers every time.
But the AR-15 was designed from the ground up as a rifle for the 222 and 223 cartridges, firing standard, and then later magnum small rifle primers.

So if I may, I’d like to ask the readership is any of you owns a 50 BMG upper AND you reload your own ammo, have you had problems? Also do any of you out there have a target grade trigger in your AR and use that trigger on the 50 BMG upper?

Please respond if you have experience.

April 10, 2014, 07:36 PM
No experience...but I have read about ignition problems you cite requiring heavy hammers and and hammer springs.

Just curious...on a platform that light it would have to tear your shoulder off even with an effective brake.

What's the attractiveness? Portability?

April 11, 2014, 04:42 PM
A buddy owns two .50 BMG bolt uppers set up on AR lowers. He hasn't had any issues with light primer strikes and he is using a stock, mil spec AR15 trigger (and he has used a wide variety of ammunition over the years).

tobnpr - They're not as light as you think. The barrels on both are incredibly thick. They both have large muzzle breaks as well. I'm not going to say that firing either of these rifles is pleasant, but it won't tear your shoulder off either. As for the attractiveness; I suspect that one reason is that a .50 BMG AR upper is a significantly cheaper route than something like a Barrett (not a .50 expert but I don't think there are a ton of other .50 BMG rifle options to be had). In my buddies case the biggest attraction was simply that he likes "big" guns (.500 S&W mag, tax stamped SERBU super short 870 "pistol", .338 Lapua mag, etc.)

I should also add...

I have encouraged my buddy to look into upgrading his triggers to Geissele units for not only the trigger weight reduction but also the reduction in lock-time (which is a big deal when shooting AR lowers for precision as you may already know). He never did call Geissele, but as I said to him, I'll bet someone over there knows if there are issues with their triggers and .50 primers.

April 11, 2014, 07:35 PM
Cheaper than a Barrett, sure.
Never been behind a .50, but been alongside plenty of them (well...at least two benches down, anyway to avoid the side blast :D) and popular opinion at the range is that the Barretts are unimpressive in terms of accuracy as relates to their cost.

Of course, I'm only talking accuracy for a casual, rec shooter- not durability nor appropriateness for professional or military applications.

I see a lot of Serbu's, probably because of their local manufacture, and at under $2500 seem to be priced about the same as an upper for an AR. Of course, I suppose there's always the point that the upper is not a "firearm", but I don't see that as being very relative over a $30 transfer fee.

Interesting subject, as I'm considering a "bigger gun" even though we only have 1K yards available...but leaning more towards a .338 LM or .300 WM because I think they're more practical for that range given that we're not taking out insurgents behind brick walls.

But I gotta admit, there is something really cool about that concussion that courses through your chest even 30 feet away ;)

44 AMP
April 11, 2014, 08:12 PM
While I don't have any way of knowing (or testing) it is (remotely) possible that .50 BMG ammo does not have primers any harder than "normal".

both the 7.62mm NATO and the 5.56mm were designed to work in rifles that had floating firing pins, the M14 and the AR. The firing pin actually bounces off the primer when the round is chambered. With most regular primers this is not a problem, BUT, to add to the safety the milspec primers are "harder".

The .50BMG was designed to run in the M2 machine gun, which does not have a floating firing pin. SO its possible that the primer spec isn't "hard".

Just a theory....

April 11, 2014, 11:33 PM
Yes 44AMP, it's quite possible. I for one do not know. The 50 BMG is not a cartridge I have reloading experience with personally. I have fired them, but not reloaded them.
That's why I am asking those that DO know.

April 12, 2014, 08:46 AM
Searched for a schematic on the design of these online unsuccessfully.
Typical bolt gun, FP is driven forward by spring tension within the bolt, when released by the sear.

How does this design work? Point to my question- if the hammer of the AR FCG is driving the FP forward into the primer with this AR bolt "conversion", isn't successful ignition also dependent on the hammer spring design being consistent with the mass of the FP?

If not, well...nevermind :o

June 10, 2014, 11:33 PM
Hello fellas.....I just bought a watson weapons "the boss" ar lower .50upper gun, which I have not fired yet, due to the fire restrictions and temporary shooting bans out here in Az, but, I HAVE checked out my firing pin assembly, and honestly, it DOES seem a bit weak, (and floating, I might add) at least for a primer that large. (Not to mention, small in diameter) I HAVE heard of, and seen online, a stronger spring for the fire control, yet I do not know what this would do for the accuracy...........I will keep all posted as I try out the ones I have loaded with the CCI 35 primers.

44 AMP
June 11, 2014, 10:12 AM
I doubt that a floating firing pin in a manually operated bolt is going to bounce off the primer of a chambered round in the same manner it does in an AR or M14.

Mechanically, a stronger AR hammer spring would have no effect on the accuracy of the rifle, but might have an effect on the shooter's ability to be as accurate, IF the heavier spring changes the trigger pull, or significantly changes the lock time.

June 13, 2014, 06:44 AM
You may want to look into Hiperfire triggers. I believe they have redesigned the springs as to assure better ignition while allowing for lighter trigger pull weights. Not cheap but in line with most of their competitors.

September 16, 2016, 12:50 PM
I've had similar experience as some of the other posters. I've used an AR lower against 7.62X39 (PMC and Russian surplus ammo) and didn't have a single problem with it. The mags sometimes lock up on the first round but feed fine after.

However, I bought a .50BMG from Valley Ordnance, new from their factory, and I can't get rounds to fire in that gun. They use a modified AR lower design but it's bolt operated (which is curious since a bolt gun should almost always go boom). With most ammo (Federal, Am Eagle, Sellier &B, etc.) I'll get 20% firing. If I buy top of the line Hornady, I'll get 4 of 5 to fire. Their primer strike is extremely light. My friend's McMillan and Barrett both have visibly deeper strikes.

I think you have to look at both the bolt and the trigger to make it function with a .50 but the most important thing is to buy quality parts/guns. Valley is NOT.

44 AMP
September 16, 2016, 11:08 PM
I bought a .50BMG from Valley Ordnance, new from their factory,

have you contacted them about your problem??

IF so, what did they say??

If not, WHY NOT??

September 17, 2016, 01:03 PM
Some of the 50 bmg uppers ship with heavy hammers and spring for the lower.

If I can find an example I will post a link. Ok here is one:


What's included:

Single Shot SHTF50

One(1) hammer and spring to replace the AR-15/M16 hammer and spring

50 shooter
September 18, 2016, 11:52 PM
Yes, you'll need a heavier hammer and spring to keep it reliable. Most of the manufacturers sell them or include them with the upper.

STAY AWAY FROM VALLEY FIREARMS! Do a search on BOHICA .50 uppers, same company just changed names.

A couple of the companies that make them are now making their own lowers to go with the uppers. Do your homework and if you have any questions just ask. Also, some MIL-spec ammo does have hard primers and need a second hit.

September 22, 2016, 10:18 AM
STAY AWAY FROM VALLEY FIREARMS! Do a search on BOHICA .50 uppers, same company just changed names

why? I have a Bohica in the 300 serial number range that has been great I was one of the first to buy one.

September 22, 2016, 10:20 AM
Mechanically, a stronger AR hammer spring would have no effect on the accuracy of the rifle, but might have an effect on the shooter's ability to be as accurate

this is the case. I was unable to get primer ignition without a heavy spring, and heavy springs don't work with some of the better light trigger groups.

50 shooter
September 22, 2016, 11:37 AM
Since you asked, the owner is a lying POS, his uppers have had more catastrophic failures then any on the market. Blamed everyone but himself for his problems, claimed that the .gov was going to put a halt to .50 uppers, is a lying POS.

Did I say he's a lying POS? Oh yeah, call up his new shop and ask if he has any parts for your BOHICA or will do any service on it. Then come back here and tell us what kind of response you got from them. (800)804-6473