50BMG velocity issues

[REELDOC]

Don't post often but I have one that I need to come to the masses for comment.

Running 750 Amax, LC brass (run through sizing die twice), CCI35 primers, 215 grains of BMG50 in an AR50 with 97 rounds on it. COAL is 5.590". Temp was 85 degrees. The load is around a half moa at 200 which is the longest yardage I have to work with right now.

Using an Oehler 35 chrono at 15 feet from the muzzle velocities are only running around 2450fps. Hornady book looks like this should be running in the 2650-2700 hundred range. However they are listing COAL at 5.730". I would think that I should be at least above 2600.

Barnes 750's were pretty much identical. 647 grain Barnes were only running around 2650.

Hope this enough info. Any comments will be appreciated.

 

[AIAW]

Your charge weight is a tad low. McMillan TAC50 with a 27" barrel would push the 750's AMAX at 2625 fps. I want to say it was around a 230g charge of H50BMG (don't use that of course).

I know the throating changed in the AR50's not too long ago. They got shortened. Have you tested to see how far off of the lands you are at your OAL? Seems a tad short to me.

 

[REELDOC]

Thank you. This is an older model AR50.

By my OAL measurements the max OAL for the 750's is 6.00 +/- 10 thousandths. As a comparison, max OAL for Barnes TSX647's is 5.856 +/- 10 thous.

I will go back and confirm these numbers based on your based on your observation.

 

[AIAW]

Thank you. This is an older model AR50.

By my OAL measurements the max OAL for the 750's is 6.00 +/- 10 thousandths. As a comparison, max OAL for Barnes TSX647's is 5.856 +/- 10 thous.

I will go back and confirm these numbers based on your based on your observation.

Excellent. Yeah you should be much higher velocity than that. That's going to be quite a case capacity difference if you reach out to nearly 6".

Verify that max OAL, seat back about .020" back from that and run a ladder test from 220g up to 230g - 235g (paying attention to pressure signs when you get up in this range). Typical reloading precautions.

 

[REELDOC]

Thank you very much.

 

[secondofangle2]

Don't post often but I have one that I need to come to the masses for comment.

Running 750 Amax, LC brass (run through sizing die twice), CCI35 primers, 215 grains of BMG50 in an AR50 with 97 rounds on it. COAL is 5.590". Temp was 85 degrees. The load is around a half moa at 200 which is the longest yardage I have to work with right now.

Using an Oehler 35 chrono at 15 feet from the muzzle velocities are only running around 2450fps. Hornady book looks like this should be running in the 2650-2700 hundred range. However they are listing COAL at 5.730". I would think that I should be at least above 2600.

Barnes 750's were pretty much identical. 647 grain Barnes were only running around 2650.

Hope this enough info. Any comments will be appreciated.

the Hornady book velocities are for a 40” barrel or something like that. Some have misprint. Check online and you will see. Figure 15-20 fps per inch barrel and there you go.

 

[secondofangle2]

I just checked my Hornady book. 36” barrel. Max load 214.9 grains H50BMG. That’s 6” longer than the AR50 so figure 120 fps. Plus they load them to 5.450” which will give more speed. That’s the length of their factory ammo which I have shot a lot of. They list 2700 fps in the book for that load
My buddy in Ohio has same gun and gets same velocity as you with his.
also you will find 50+ fps ES with cci35. They suck
The factory stuff uses 234 of RL50 or some use 869 I forget the charge.
that factory load in my 40” gets 2840 fps. Which shot the 5 shot group that is my pic.

 

[AIAW]

also you will find 50+ fps ES with cci35. They suck

Not much choice any more though. Back in the day you could find Lake City primers that were good. X-treme has some but they have been out of stock for a very long time.

RWS was absolutely the king of the hill - those are very difficult to come by. $240 for a 500 count if I recall IF they can be found here in the States.

Uniforming the flash hole on "non-match" brass helps a good bit. I could easily get a single digit ES with CCI #35's with once-fired non-surplus brass. Lapua and RWS brass, never have to do anything to the cases. At $5 each unprimed one shouldn't have to!

 

[REELDOC]

Thank you. I spent a couple weeks prepping the brass. Some was rifle fired and I separated it from the MG fired. Uniformed the pockets, deburred the flash holes, etc. Bought a Giraud trimmer head and several other tools that have come in handy. I also annealed the necks just to make sure everything was equal. I have a bullet sizer for the 660 pulls that I am working with. They were supposed to have been sized but weren't done well enough. Loading with a 50bmg press and RCBS dies.

I really appreciate your comments. I didn't expect the rifle to be a tack driver even though I think it can be a really good shooter. Need a place to stretch it out. I try to limit myself to no more than 20 rounds a session and have to shoot it when the range is essentially clear of folks. I have a friend and gunsmith that is guiding me through this. I don't like screwing around too much with a little stick of dynamite in my face