Range Report 20"-24" 50BMGs ?

[Keith Johns]

Im soon to be barreling a 50 for myself. Ive read everything I can find about barrel lengths and have been amazed to find 50s dont seem to need much more barrel than most smaller catrdiges.


According to Dan Liljas article on it, FPS increases very minimaly after 28". Like 10-15fps.

From 24" to 28" They seem to loose only about 100fps.


So, a 24" barreled 50BMG is only behind a 34" barreled 50 by around 200fps.


Thats amazing to me.


If you then look at the time the bullet spends in the bore... shorter barrels are more forgiving on follow through.
Not to mention the shorter barrels with higher muzzle pressure, make the brake more effective and reduce recoil. Less recoil with shorter barreled 50s, all else being the same.

Shorter = more rigid. Especially with a smaller contour like the Navy contour. Id equate the Navy contour in .50 to a Rem Sendero contour in .30
The barrel only looks massive until the 50 round is laying next to it.


Now I see there are even 20" barreled 50BMGs out there!


Does anyone have experience with a 20-24" 50? Is it still very much a one mile capable rifle? On paper it looks like it should be 2000m+ capable. Easily.

 

[MitchAlsup]

Re: 20"-24" 50BMGs ?

Should anyone mention that the report doubles in volume with every 4 inches taken off the barrel?

 

[bohem]

Re: 20"-24" 50BMGs ?

The 50BMG is, in linear dimension, 1.6x's (50/30) larger than the 30-06. If it works well in the 30-06 it's not unreasonable to think it might work well in the 50BMG.

Volumes are increased by 1.6^3 across the board, base area by 1.6^2, etc. So why not give it a whirl...

Shooting Amax's with an Avg G7 somewhere around 0.49 (IIRC) it doesn't take a whole lot of velocity to easily reach a mile at sea level and the 750 Amax has lots of anecdotal evidence to suggest that it will remain repeatable during sonic transition.

Just off those "back of the envelope" numbers you'd need about 2400fps to stay above Mach 1 at 1800yds and ~2700 to stay above Mach 1-1.1 at 2200y, all at sea level.

Go up to about 3000' DA (which is reported to be pretty regular to attain in your general region) the 2650fps MV will get you crossing at 2000m/2250yd

 

[Keith Johns]

Re: 20"-24" 50BMGs ?

Doubles? So 24" is 4x as loud as 32"? 4x??
Muzzle pressure has not gone up <span style="font-weight: bold">that</span> much.

If thats true its damn good info. But can anyone else confirm that?

 

[Keith Johns]

Re: 20"-24" 50BMGs ?

Ive run the numbers too and it looks fine.

But anyone have first hand experience with a 20" 50?
I could see it being annoying to shoot for some reason. Either report like mentioned above or balance of the weapon.


Im leaning towards 24" right now. Shooting the 750 Amaxs. They claim to have been tested by Hornady in a 24"

2800fps they claim I think. 24" tube.


Anyone know if that's 24" true length? Or from the receiver face?
You'd think theyd go by distance from lands to crown

 

[bohem]

Re: 20"-24" 50BMGs ?

My experience shooting various length 50's is that I not only plug, tape, muff but I also put foamies in my nostrils because the pressure wave from the brake tends to cause a concussion headache after several rounds. My nose also runs like I have a nasty cold for about 12-16 hours.

Putting foamies in my nose (and keeping my mouth clamped shut when shooting obviously) makes that physical response non-existent.

 

[Keith Johns]

Re: 20"-24" 50BMGs ?

shit


So are you saying a 29" 50 would be much less punishing on the ears/sinuses than a 24"? Or you're hurtin' either way.

I shot one once and didn't think anything of it. But it was only once.


I see guys shooting Barretts with only ear foamies. Are they just deaf already? Or too bad ass to care.

 

[bohem]

Re: 20"-24" 50BMGs ?

Dunno, it could be that they don't have the issue I do.

I did a lot of scuba diving in all kinds of crap for years and one of the things that I've noticed is that my sinuses and eustacian tubes are very sensitive to changes in pressure. I never have trouble equilizing, but I can feel pressure changes quite easily.

If I pull the trigger 1-2 times no biggie, but a 10 round string will have me looking like I should be chugging on the Nyquil if I don't put foamies in.

 

[MitchAlsup]

Re: 20"-24" 50BMGs ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Keith Johns</div><div class="ubbcode-body">So are you saying a 29" 50 would be much less punishing on the ears/sinuses than a 24"? Or you're hurtin' either way.</div></div>

In my opinion, you are going to be hurting until the barrel length approaches 36" for 50BMG.
At 30" you can plug, tape, and muff your way to "acceptable body damage", but barely. As someone else noted above 50/30 = 1.6; 308 wants a 24" barrel so a 50 should want a 38.4" barrel.

Might also note, 30" 50BMG with brake at 5 feet away from an automobile windshield will concussively crush the windshield.

 

[Keith Johns]

Re: 20"-24" 50BMGs ?

I see a lot of 24" 50s out there. I saw a 20" too.

In fact, every "tactical" model Ive seen comes in 24" or 29".
Mcmillan and Robar offer only those two lengths, and my rifle is using all the same parts as Mcmillan and Robars rifles.(If Robar uses Lilja barrels)


So anyways, I know Im not going wrong looking to go between 24 and 29". This is NOT a BR50. This will be carried by a 140lb person. I want short, accurate, and 2000 yard capable. Keeping it under 25lbs with optics would be nice.

What I want to know is, are there any reasons 24" is a PITA to shoot? Seems to me it'd be nicer than a 29" to shoot. But I have no experience comparing the two.


I do not care about the lost velocity. I care about everything else. Accuracy and portability mainly.

 

[Keith Johns]

Re: 20"-24" 50BMGs ?

Ran the numbers again..

Even with 100fps less than I should be getting from a 24" tube, and with the BC knocked down to be realistic... Even in 30 degree weather the 750s will stay super sonic past 2000. Like 2300 probably... I only went to 2k.


24" it is.

I WILL be posting pics of it. Lots of pics. mid/late October

 

[Dylan in AZ]

Re: 20"-24" 50BMGs ?

I for one can't wait to see it...

 

[Keith Johns]

Re: 20"-24" 50BMGs ?

The APA brake Im going with..

Ammo and stuff for a different 50 build in progress for another company..

1/3rd of the chamber cut. 1-15twist Lilja Navy Contour barrel...

 

[Ledzep]

Re: 20"-24" 50BMGs ?

I have a 24" BOHICA 50bmg upper for my AR-15. I get about 2450 fps with 750gr Amax's. I'm using 225gr of H50bmg, and it's a pretty stout load, I wouldn't go much higher. Honestly it's pretty punishing on the shoulder and sinuses, too. I generally take some sort of padding (A fleece beenie usually) to put between myself and the gun when I shoot the Amax's. 610gr API's and APIT's I light load to also be around 2400fps, just for fun and the light show. Those are much more fun to shoot.

I don't believe 2800fps is possible out of a 20-24" barrel. From what I've seen and read, 2700-2900 fps is in the 30-36" range.

Even at 2400fps, the 50 cal bullets pack a huge punch. We found this core at 1050yd, about 6-7" inside a solid rock face (It broke material away behind it and to the left side, leaving it exposed).

 

[leadbullet]

Re: 20"-24" 50BMGs ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ledzep</div><div class="ubbcode-body">I have a 24" BOHICA 50bmg upper for my AR-15. I get about 2450 fps with 750gr Amax's. I'm using 225gr of H50bmg, and it's a pretty stout load, I wouldn't go much higher. Honestly it's pretty punishing on the shoulder and sinuses, too. I generally take some sort of padding (A fleece beenie usually) to put between myself and the gun when I shoot the Amax's. 610gr API's and APIT's I light load to also be around 2400fps, just for fun and the light show. Those are much more fun to shoot.

I don't believe 2800fps is possible out of a 20-24" barrel. From what I've seen and read, 2700-2900 fps is in the 30-36" range.

Even at 2400fps, the 50 cal bullets pack a huge punch. We found this core at 1050yd, about 6-7" inside a solid rock face (It broke material away behind it and to the left side, leaving it exposed).

</div></div>

that is an awesome pic and very impressive devastation indeed.

 

[dang472]

Re: 20"-24" 50BMGs ?

I have the same problems with my sinuses. My uncle and I have Armalite AR50s and we put 80 rounds down over 2 days. We were both hurting and our heads were all stuffed up. After the first few shots, I can definitely feel the pressure up my nose.

I load 214gr of H50BMG behind 750gr AMAXs. They have been extremely accurate but I haven't checked velocity.

 

[Keith Johns]

Re: 20"-24" 50BMGs ?

Hornady claims 2800 from a 24"

I'd hate to find out they're off by 300+fps!!!
It'd be letter written time just for the hell of it. Being off by 300fps isnt a barrel brand difference, its an outright lie.


We shall see. First 50 will have a 28" barrel, for a customer.

Mine is planned to be 24" unless I see reason to go a little longer.

Both with be shot through a chrono.

 

[Ledzep]

Re: 20"-24" 50BMGs ?

There is some interesting ballistic data here for the .50bmg with both 36" and 45" barrels.

It says ~700gr M2 AP is going 2845 fps out of a 36" barrel. 2940 from a 45".

Out of a Lilja-barreled bolt gun using hand loads you could probably squeeze a little more velocity using the same bullets. But I would expect similar or slightly lower velocities with a 750gr Amax (all with a 36" barrel).

Back when the BOHICA forums were up and running, that was about in line with what people were reporting. 36" was maxing out around 2900fps, 30" about 2700, and 24" 2400-2500.

Various other sources put 610-625 API and APIT around 3100 fps out of a 45" barrel. I can't see lopping off 21" of barrel and maintaining 90% of that.

Personally, I doubt I'll ever go below 29-30" if I ever get another .50.

 

[Keith Johns]

Re: 20"-24" 50BMGs ?

Past 30", You gain VERY little per inch. 10-15fps.
I believe Dan Liljas article on 50BMG barrel length will confirm that.

So I can see a 30" being only 100-150fps slower than a 40"

Under 30", every inch means more. But only about 20-25fps per inch.

This is what I've read to be true. And what I've seen in real life confirms it with other cartridges(30-06 being a good example)


Getting way under 2800 would be a bummer. I expected around 2650 or 2700 out of 24", but like I said I care about accuracy and portability more.
Dan has another article on barrel rigidity. Amazing how much more rigid each inch removed makes it.

 

[bohem]

Re: 20"-24" 50BMGs ?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Dan has another article on barrel rigidity. Amazing how much more rigid each inch removed makes it.</div></div>

That's really a different topic, but I'm not in agreement with the consensus that a reliably accurate rifle must have the stiffest barrel possible.

 

[MALLARD]

Re: 20"-24" 50BMGs ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Keith Johns</div><div class="ubbcode-body">Even with 100fps less than I should be getting from a 24" tube, and with the BC knocked down to be realistic... Even in 30 degree weather the 750s will stay super sonic past 2000. Like 2300 probably...</div></div> I dont know what elevation your shooting at but supersonic past 2000 sounds unrealistic. If you look at the doppler radar results in byran litz book from a 750 amax, youll see the round goes subsonic around 1500y, that is at 2690fps. So subsonic at 2000y doesnt seem realistic unless you have a muzzle velocity above 3000fps with the 750 amax.

I have a 29in 50, i dont use plugs in my nose but i think im going to give it a try.

 

[BravoSector1]

Re: 20"-24" 50BMGs ?

I've been eyeing an Anzio Ironworks "Idaho Light Weight" 50 BMG. 18" barrel and 14 lbs before optics and ammo.

 

[Keith Johns]

Re: 20"-24" 50BMGs ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MALLARD</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Keith Johns</div><div class="ubbcode-body">Even with 100fps less than I should be getting from a 24" tube, and with the BC knocked down to be realistic... Even in 30 degree weather the 750s will stay super sonic past 2000. Like 2300 probably...</div></div> I dont know what elevation your shooting at but supersonic past 2000 sounds unrealistic. If you look at the doppler radar results in byran litz book from a 750 amax, youll see the round goes subsonic around 1500y, that is at 2690fps. So subsonic at 2000y doesnt seem realistic unless you have a muzzle velocity above 3000fps with the 750 amax.

I have a 29in 50, i dont use plugs in my nose but i think im going to give it a try. </div></div>

http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi









Input Data
Ballistic Coefficient: 1.050 G1 Caliber: 0.500 in
Bullet Weight: 750.0 gr
Muzzle Velocity: 2700.0 ft/s Distance to Chronograph: 10.0 ft
Sight Height: 2.50 in Sight Offset: 0.00 in
Zero Height: 0.00 in Zero Offset: 0.00 in
Windage: 0.000 MOA Elevation: 0.000 MOA
Line Of Sight Angle: 0.0 deg Cant Angle: 0.0 deg
Wind Speed: 10.0 mph Wind Angle: 90.0 deg
Target Speed: 10.0 mph Target Angle: 90.0 deg
Target Height: 12.0 in
Temperature: 48.3 °F Pressure: 26.82 in Hg
Humidity: 0 % Altitude: 3000.0 ft
Vital Zone Radius: 5.0 in
Std. Atmosphere at Altitude: Yes Pressure is Corrected: Yes
Zero at Max. Point Blank Range: No Target Relative Drops: Yes
Mark Sound Barrier Crossing: No Include Extra Rows: No
Column 1 Units: 1.00 in Column 2 Units: 1.00 MOA
Round Output to Whole Numbers: No
Output Data
Elevation: 28.411 MOA Windage: 0.000 MOA
Atmospheric Density: 0.06998 lb/ft³ Speed of Sound: 1104.9 ft/s
Maximum PBR: 362 yd Maximum PBR Zero: 307 yd
Range of Maximum Height: 172 yd Energy at Maximum PBR: 9764.3 ft•lbs
Sectional Density: 0.429 lb/in²
Calculated Table
Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yd) (in) (MOA) (in) (MOA) (ft/s) (none) (ft•lbs) (s) (in) (MOA)
100 24.8 23.7 0.3 0.3 2623.2 2.374 11457.4 0.113 19.8 18.9
200 47.1 22.5 1.2 0.6 2545.1 2.304 10785.6 0.229 40.3 19.2
300 64.0 20.4 2.7 0.9 2468.4 2.234 10145.3 0.348 61.3 19.5
400 75.2 18.0 4.9 1.2 2393.1 2.166 9535.3 0.472 83.1 19.8
500 80.3 15.3 7.8 1.5 2319.0 2.099 8954.2 0.599 105.5 20.1
600 79.0 12.6 11.4 1.8 2246.2 2.033 8401.1 0.731 128.6 20.5
700 70.8 9.7 15.7 2.1 2174.7 1.968 7874.7 0.866 152.5 20.8
800 55.2 6.6 20.9 2.5 2104.5 1.905 7374.3 1.007 177.2 21.1
900 31.8 3.4 26.9 2.8 2035.6 1.842 6899.3 1.152 202.7 21.5
1000 -0.0 -0.0 33.7 3.2 1968.0 1.781 6448.9 1.302 229.1 21.9
1100 -40.8 -3.5 41.5 3.6 1901.8 1.721 6022.5 1.457 256.4 22.3
1200 -91.2 -7.3 50.2 4.0 1837.1 1.663 5619.5 1.617 284.6 22.6
1300 -151.9 -11.2 59.9 4.4 1773.9 1.605 5239.2 1.783 313.9 23.1
1400 -223.7 -15.3 70.7 4.8 1712.2 1.550 4881.3 1.956 344.2 23.5
1500 -307.3 -19.6 82.5 5.3 1652.2 1.495 4545.3 2.134 375.6 23.9
1600 -403.6 -24.1 95.5 5.7 1594.0 1.443 4230.7 2.319 408.1 24.4
1700 -513.7 -28.9 109.7 6.2 1537.7 1.392 3936.9 2.511 441.9 24.8
1800 -638.5 -33.9 125.2 6.6 1483.3 1.343 3663.5 2.709 476.8 25.3
1900 -779.1 -39.2 141.9 7.1 1431.1 1.295 3410.1 2.915 513.1 25.8
2000 -936.7 -44.7 160.0 7.6 1381.1 1.250 3176.2 3.129 550.7 26.3




That program claims mach 1.25 at 2000 yards.

50BMG rounds going subsonic at 1500 yards? The BC is 1.050... even at 2500fps, how can you expect them to fall short of any other round with that BC?? I think your 50 stays supersonic a little further than you think but please correct me if Im wrong.

 

[Keith Johns]

Re: 20"-24" 50BMGs ?

And here's the BC knocked down .050, only 2500fps at muzzle, and 48 degrees outside...

Says it supersonic at 2k. Im not saying I expect the program to be right on. But arent you saying its off quite a bit?

Input Data
Ballistic Coefficient: 1.000 G1 Caliber: 0.510 in
Bullet Weight: 750.0 gr
Muzzle Velocity: 2500.0 ft/s Distance to Chronograph: 10.0 ft
Sight Height: 2.50 in Sight Offset: 0.00 in
Zero Height: 0.00 in Zero Offset: 0.00 in
Windage: 0.000 MOA Elevation: 0.000 MOA
Line Of Sight Angle: 0.0 deg Cant Angle: 0.0 deg
Wind Speed: 10.0 mph Wind Angle: 90.0 deg
Target Speed: 10.0 mph Target Angle: 90.0 deg
Target Height: 12.0 in
Temperature: 48.3 °F Pressure: 26.82 in Hg
Humidity: 0 % Altitude: 3000.0 ft
Vital Zone Radius: 5.0 in
Std. Atmosphere at Altitude: Yes Pressure is Corrected: Yes
Zero at Max. Point Blank Range: No Target Relative Drops: Yes
Mark Sound Barrier Crossing: No Include Extra Rows: No
Column 1 Units: 1.00 in Column 2 Units: 1.00 MOA
Round Output to Whole Numbers: No
Output Data
Elevation: 33.768 MOA Windage: 0.000 MOA
Atmospheric Density: 0.06998 lb/ft³ Speed of Sound: 1104.9 ft/s
Maximum PBR: 335 yd Maximum PBR Zero: 284 yd
Range of Maximum Height: 159 yd Energy at Maximum PBR: 8364.3 ft•lbs
Sectional Density: 0.412 lb/in²
Calculated Table
Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yd) (in) (MOA) (in) (MOA) (ft/s) (none) (ft•lbs) (s) (in) (MOA)
100 30.0 28.7 0.3 0.3 2422.9 2.193 9774.9 0.122 21.4 20.5
200 56.6 27.0 1.4 0.7 2344.6 2.122 9153.3 0.248 43.6 20.8
300 76.9 24.5 3.2 1.0 2267.8 2.053 8563.0 0.378 66.5 21.2
400 90.4 21.6 5.8 1.4 2192.3 1.984 8002.6 0.512 90.2 21.5
500 96.7 18.5 9.2 1.8 2118.2 1.917 7471.0 0.652 114.7 21.9
600 95.3 15.2 13.5 2.1 2045.6 1.851 6967.4 0.796 140.0 22.3
700 85.5 11.7 18.6 2.5 1974.5 1.787 6491.2 0.945 166.3 22.7
800 66.8 8.0 24.8 3.0 1904.8 1.724 6041.5 1.100 193.5 23.1
900 38.5 4.1 31.9 3.4 1836.8 1.662 5617.7 1.260 221.8 23.5
1000 -0.0 -0.0 40.1 3.8 1770.4 1.602 5219.0 1.426 251.1 24.0
1100 -49.7 -4.3 49.4 4.3 1705.8 1.544 4844.8 1.599 281.4 24.4
1200 -111.3 -8.9 59.8 4.8 1643.0 1.487 4494.8 1.778 313.0 24.9
1300 -185.8 -13.6 71.5 5.2 1582.2 1.432 4168.2 1.964 345.7 25.4
1400 -274.2 -18.7 84.4 5.8 1523.5 1.379 3864.5 2.158 379.8 25.9
1500 -377.6 -24.0 98.6 6.3 1467.0 1.328 3583.2 2.359 415.1 26.4
1600 -497.1 -29.7 114.2 6.8 1412.9 1.279 3323.8 2.567 451.8 27.0
1700 -634.1 -35.6 131.2 7.4 1361.3 1.232 3085.6 2.784 489.9 27.5
1800 -789.9 -41.9 149.7 7.9 1312.5 1.188 2868.3 3.008 529.4 28.1
1900 -965.9 -48.5 169.6 8.5 1266.6 1.146 2671.2 3.241 570.4 28.7
2000 -1163.6 -55.6 191.0 9.1 1223.8 1.108 2493.6 3.483 612.9 29.3

 

[Ledzep]

Re: 20"-24" 50BMGs ?

I'm going on leave for a month in October. Ill run a pressure/velocity test in my 24" 50 in 1gr increments up to 233gr h50bmg (obviously stopping if i get signs). Ill post it and we'll see what happens.

I doubt ill get over 2550fps but I may be wrong.

 

[Jig Stick]

Re: 20"-24" 50BMGs ?

I hope I never shoot next to Keith. The muzzle blast and report are going to redefine obnoxious. But I love it! My 300winmag is loud as hell with the brake on.

 

[hofhine1]

Re: 20"-24" 50BMGs ?

When you get done come down to Tucson and we'll set it next to an 82A1 and try side by side where it ends up.

We have a mile to work with, and I'd like to see what the report is like, maybe some strippers will come and we can see an actual skirt blown up like some of the folks have posted up above.

I shoot mine with cheap ass earplugs I steal from jobsites, and although a lifetime of listening to Iron Maiden may have dulled my senses, I seem to be fine.


PM me anytime, we can see about some range time.


sean