There is a fundamental issue with large cross sectional area cases, operating at low pressures, burning smokeless powders, in autoloading rifles with a direct gas impingement operating system!

This is the 50 Beowulf's bore and chamber (viewed from the breech). I did not shoot any "low pressure" (for the Beowulf anyway) loads today. What you see is a wholelotta H110 that never did anything useful (except maybe jam up the gun, but that ain't useful )



This is NOT a good situation with an autoloading rifle operating on the direct gas impingement system!!!!

Here are some pics of the rest of the rifle torn down for cleaning. It fired off 77 rounds today. The last 30 rounds were H110, there ballistics are tallied in the thread dealing with 50 Beowulf load work.

Bolt carrier and bolt assembly:


Bolt carrier and bolt assembly (disassembled)


The bolt face was full of H110 powder balls too! I couldn't get a clear picture though, so I gave up. I believe that the issue is the case design itself. The case's pressure envelope is TOO low to allow for efficient burning of smokeless powders, which are appropriate for case's expansion ratio. If Alexander Arms had departed from the 50 AE case and reinforced the web (added to the case head bulkhead) the operating pressure of the case could have been dramatically increased. However, it is also true that the AR 15 series locking lugs and barrel extention are near the limits with the 50 Beowulf's current operating pressure envelope. Perhaps, on an AR 15 anyway, there is no happy medium.

For the record 44 grains of IMR4227 burns very cleanly, and with low heat generation. It doesn't provide optimum velocity however. Accuracy is a missing entity with the cartridge so we shall not even go there! Having said that, the IMR4227 load of 44 grains is the best accuracy performer so far. I have tested about 40 different loads now with 3 different bullets and 4 or 5 powders. It has been fun, if somewhat frustrating.

Even with all it's shortcomings, it is fun to shoot, and always attracts onlookers (who usually think it is a 308 Win ). It most certainly would not be my first choice for a combat rifle/cartridge combo though (or second, or third, or fourth, etc, etc).

Scott

Scott -

During initial load development we saw some similar issues with the .458 SOCOM and there are certain powders that we suggest not to use. However, in the .458 guise (perhaps due to the venturi effect of the necked case? This is a theory that has been postulated elsewhere), we find that we can get complete and clean burn, with maximum velocity and good load density - if you're willing to shop for powder and pay a little more. Powders that turn in the best numbers are Lil Gun, Norma 200, Win 296, Re7 off the top of my head.

Even the 500 and 600 gr subsonic, LOW pressure, loads run like a champ ... in barrels from 7.5" up to 24" ....

H110 will work but is far from ideal ... as you can see. Muzzle flash tends to be horrendous with H110 and we tend not to use it to please our brethren that use these rifles when going "in harms way". Loosing once night vision due to muzzle flash is detrimental to survival ..

Marty,

I agree with your postulate concerning the "venturi" effect. I am convinced that the excessively high velocity and pressure variation is a direct result of HIGHLY inefficient powder combustion, due to burn dynamics existing in the short, stubby, wide open, 50 Beowulf case.

I have used all the powders you have listed, with the exception of the Norma and Lil'Gun powders. I shall use Lil'gun next. I have heard rave review of about it in the 50 Beowulf, but then again I have heard these same statements made about W296 and H110!

My obvservations on the following powders:

Rel 7 - extremely bad . Large quantities of unburned powder with both 325 and 334 gr bullets and powder charges weights of 48grains - 52.5 grains. 59 grains of Rel7 burned cleanly but also provided 0.007" case head expansion and a blown primer! Could not seat the bullet to full depth either since the powder column was approximately 120% compressed!

IMR 4198 - not very good . Small quantities of unburned powder with 334 grain bullets and powder charge weight of 51.5 grains. There were some unburned powder kernels. Pressure was at maximum levels with this load, as case head expansion was a factor. I did not measure it directly, but the sizing dies sure did!

W296 - very similar to H110 . With the exception that is seems to be even more temperature sensitive! On my second rapid fire string of 10 rounds (full SA80 magazine), I experienced stuck cases on round number 3 (lucky number 13 ). This load was 42 grains of W296 and a 334grain Rainier HP. Initial shots looked fine, no extractor marks, bolt face rim rings, etc. I had considered this a top load for daily useage, I WAS WRONG! After that little hair raiser, I do not care for this powder, nor H110.

IMR4227 clean and cool burning . Best accuracy, but mediocre velocity. As with all the other powders very erratic velocities, but this powder seems to suffer the least.

Again, I think it is a function of the combustion process in a short straight walled case of such large cross section. I think your shouldered cases are a better approach to the solution of a large diameter round being fired from an AR platform.

All of the powders tested generate a MASSIVE fire ball at the muzzle. I would not want to ever shoot this thing in the dark! If asked which powder produced the worse muzzle blast fire ball I would have to say it was Rel 7. Makes since to me, Rel 7 is a slow powder, relatively speaking, so a great deal of it is till burning when the bullet leaves the muzzle. To observe the muzzle blast, I typically ask someone else to touch a few off. There is usually no shortage of volunteers. Most of the volunteers dislike the rifles obnoxious recoil. It isn't so much that is kicks hard, as it smacks you in the face. At least that is how I would descibe it. I suspect everyone's description will vary slightly depending upon fit of rifle to shooter.

Will post my results with Lil'gun.

Also, I will post results of swaged down 450 Barnes Originals fired with IMR4198 and IMR4227. I was going to start with Rel7, but I think I will skip that one, as I believe it is still going to be too slow.

Rel 7 works best in the 458 Win and 405 Win. Their expansion ratios seem to be perfection for that powder.

Scott

Scott -

The is not my data, but one of my customers (actually, the QL data is mine, and two of my customers did the load testing, but Spongeman was quite methodical, and maniacal (look in the HOT tab). One hole groups is not unusual, and we have run in full auto without issue.

One note, JD at SSK and I were talking, and he lamented my decision to stick with the PISTOL primer as he felt that in the lower ambient temperatures (such as the ones in your test) they did not provide sufficient ignition. Now, down here in Texas, where 40 is c..c..c..c..cold, I don't seem to run into this problem Perhaps test again when things have warmed up and see if it improves?

Here is the link

http://www.mylittlespark.com/ar15/458Socom.html

Marty you have a PM

Scott