TO all interested,
Took the day today to deliever a couple rifles and then spend some time with my wife and new little girl. She made it pretty clear that she was not overly impressed with me holding her!! [img]/ubbthreads/images/graemlins/grin.gif[/img]
This afternoon I headed over to the shop to machine up some case forming tooling so I could get my 50 Allen Tactical ammo formed and get a few high pressure fired cases off to get loading dies made.
This went very smooth and made a neck die to size the cornmeal formed cases properly for live ammo loading and also machined up a long tapered expander to take the 408 CT case up to 50 cal in one pass.
Once I got everything machined up and polished properly I headed over to the loading bench to see if my creations would actually work. I was a bit concerned about taking the 408 case up to 50 cal in one pass even though I was using a 5 degree tapered expander. This is still quite a step in one pass.
I lubed the case necks with graphite on 20 virgin TTI 408 Chey Tac cases and then adjusted the expander in the custom form die to open the case mouth up totally.
First round through the die expanded with ease, as did every one after that until #5 which felt a little sticky.
Case #6 collapsed the shoulder as did case #7, not good!!!!
I figured what had happened was there was still some cutting oil on the expander and it just took that many passes to get it worn off to the point the case necks started getting sticky. The TTI case necks and shoulders have a very soft anneal on them so if there is to much resistance, the shoulders collapse easily.
To solve the problem I grabbed some heavy case form grease lube and put an ample amount in one of the 408 case mouths. opened up perfectly and continued perfectly for 11 cases. THen I had a case neck split as I tried to expand it but all the cases after that opened up easily so I suspect that specific case that split probably had a flaw from the factory and would have let loose no matter what I did.
I found that with the heavy case lube, if I ran the case over the expander until it just made full case neck contact to the expander and then back it back off and then run it back up again, they case necks opened effortlessly. If I ran them up in one stroke, they would expand but required alot more pressure to do so, why, no idea but the really open up easily if you back off and hit them a second time.
This pic shows from start to finish along with the losses. First case is a virgin TTI 408 Chey Tac case. Next two cases are the collapsed shoulder cases followed by the split neck case.
After that is a necked up 50-408 CT case ready for corn meal fire forming and then a fully formed 50 Allen Tactical loaded with a moly coated 750 gr A-Max to an over all length of 4.860". This is seated 10 thou off the lands.
As you can see in the pic comparing the case ready for fireforming and the formed 50 Allen Tactical case, the shoulder position is significantly farther forward then the standard 408 CT. This is the same position as the 338 AM which allows it more case capacity then the other 338-408 wildcats on the market and this is about as much capacity as you can get on this case size with any decent neck length at all.
Moving the shoulder forward on the 338 AM is no problem as you neck the 408 case neck down just to the point where it will chamber in the rifle and seal solidly on the freshly formed 338-408 shoulder for case control during fireforming.
With the 50 Allen Tactical however, necking up the case poses a different problem as far as case control during fireforming. TO get a shoulder on the case substantial enough to control headspace during fireforming you would need to expand the case mouth up to nearly a straight cylinder case and then neck it back down and position the shoulder to the correct location you wanted. This would be a real pain in the rear and more then likely would require at least one annealing step during the necking up process of case forming even before the cases were actually fireformed. I did not want to do this.
So when I was designing the reamer I thought over how I wanted to solve this problem and the solution I came up with works pretty darn well so far.
A necked up 50-408 CT case measured roughly 2.990" in length ready to fireform using the corn meal method. As such, when I chamber the rifles, I use one of these cases so that I can set the chamber length so that when one of these virgin cases are chambered, the case mouth will actually be slightly compressed by the end of the neck in the chamber. This slight compression holds the case back solidly against the bolt face, ensuring proper primer ignition and also, since the chamber pressure with these corn meal forming loads is quite low, it controls chamber pressure quite nicely.
Once the case is fired, it will be to long to just seat a bullet and load full tilt loads because some of the cases may still contact the end of the chamber neck and could cause pressure issues, but all cases after fireforming need to be trimmed square and to length anyway so I figured if I trimmed 20 thou off the cases after forming, they would all be trimmed to the same length and also produce proper clearance in the chamber so there would be no pressure issues.
All in all, it has worked to perfection but it does require using the cornmeal case forming method but when your dealing with a 50 cal rifle, saving on bullets is not a bad thing in any way when fireforming.
Now that I have 20 cases necked up ready for fireforming I an going to try to get them formed after work tomorrow and trimmed up and ready for serious load testing with the 750 gr A-Max and also the 750 gr Short Baring Surface Wildcat ULD RBBT. More to come on actual load testing hopefully next weekend if I can get some work caught up in the shop and slip away for some 50 cal shooting.
I do not think I have posted pics of the test rifle yet. Well here are a coule pics.
I think everyone should wake up on Christmas moring and walk out to the living room and see something like this!! [img]/ubbthreads/images/graemlins/grin.gif[/img]
Specs on the rifle are:
-BAT M 8.5" 1.55" diameter receiver single shot
-40 MOA BAT rail base
-Rifles Basixs 8 to 20 oz trigger adjusted to 1 lb
-Lilja "Allen32" contour 1-15 twist SS 50 cal barrel
-Defensive Edge four port 1.000" diameter muzzle brake
-McMillan A-5 stock
-APS Steel pillar bedding system
-Steel ADL trigger guard
-Nightforce Ultralight 1.000" rings
-ACI on rail base
-Super Sniper 16x mil dot for testing
Total rifle weight with Harris 9" standard bipod is 16.1 lbs but with a few modifications it could easily be Idaho weight legal!!
Only thing I will be changing on this rifle is to replace the current rings with a set of 0.875" high rings of the same make to drop the scope height just a tick more which should make it perfect for a solid cheek weld to the fixed CP A-5.
Also, if testing goes as expected, the barreled receiver and rail base will be shipped down to Shawn to get a nice matte black finish to really make this compact 50 cal look mean.
Here is a pic of the barrel engraving. You can see on the finish of the barrel that it has not been finished. as again it will probably be heading south for a coat of teflon.
As a side note, another 50 cal project I have been working on here and there when I have time has been my 510 Allen Magnum which is basically a 50 BMG case with an Allen Magnum shoulder and body configuration.
The shoulder has been set back very slightly for one simple reason, in the event the 50 BMG is outlawed, some areas may still allow 50 cal rifles as long as a 50 BMG round will can not be chambered in the rifle. Setting the shoulder back on my 510 Allen Magnum prevents a standard 50 BMG round from being able to be chambered but the design still offers dramatic case volume increases over the standard 50 BMG, just what we needed!!!
Here is a pic of one of my standard match 50 BMG rounds loaded with a 750 gr A-Max on the left. In the middle is the 510 Allen magnum loaded with the same A-Max and on the right is my 50 Allen Tactical for a size reference.
Because the 50 Allen Tactical has a much higher working pressure range then the standard 50 BMG, I am predicting my 50 Allen Tactical will nearly match standard 50 BMG performance with a much smaller powder charge, in much smaller and lighter and cheaper and more accurate rifles and with longer barrel life.
The 510 Allen Magnum on the other had is just for pure horsepower!! Initial loads I have tested at long range were with the 750 gr A-Max and 835 gr ULD RBBT and both shot well under 1 moa in quite windy conditions at 1000 yards with a less then solid rear support on the rifle.
My standard load in other 50 BMG rifles with the 750 gr A-Max has always been 212 to 215 gr H-50BMG with the bullet seated to just touch the lands. This load was just warm enough to just start showing slight ejector marks on the case head on fired cases.
In the 510 Allen Magnum, I loaded 25 rounds up with 245 gr H-50BMG under the 750 gr A-Max and got no ejector marks in any way and recoil was extremely comfortable. I have not been able to chrono test this batch of loads yet but this summer I did shoot a couple over the chrono and they produced around 2825 fps with the 835 gr ULD RBBT and 245 gr of H-50BMG so this same load under the 750 gr A-Max may be a very light load but I still suspect it is traveling over 2800 fps with potential to reach 2900 fps comfortably in the 34" barrel.
For those of you curious, thats just shy of 15,000 ft/lbs of energy at the muzzle for the 835 gr ULD RBBT and just over 14,000 ft/lbs for the 750 gr A-Max if we reach 2900 fps which I feel is pretty conservative from what we are seeing now.
Put another way, thats over 7100 ft/lbs at 1000 yards and still packing 3300 ft/lbs at 2000 yards where it still traveling over 1400 fps.
These are just number prejections so far but everything looks good for meeting or exceeding them so it should be interesting. Just need some middle of the day shooting time to get the chrono set up in good light conditions and get some bullets in the air.
More to come on both APS 50 cal wildcats very soon!!
As a comparision, my 36" barreled LAR Grizzly would top out at 2675 fps with the 215 gr load and the 750 gr A-Max so my 510 Allen Magnum should produce at least 200 fps more velocity with same bullet weights in a 2" shorter barrel length. I suspect top powder charges will top out in the 255 gr range with the 510 Allen Magnum and the 750 gr A-Max. If that is the case it will be a full 40 grains large powder charge then the standard BMG. Will have to see if the velocity will work out with the lighter 750 gr A-Max like it did with the much heavier 835 gr ULD RBBT.
More to come!!