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Discussion Starter #1
I am building a 50 BMG bolt action rifle. I have been experimenting with firing pin springs to get as light a cocking pressure that will fire a primer. I have 10 XM33 rounds and have pulled the bullets from two rounds to test fire for springs. It's a custom design rifle and the barrel face is machined off for .290" protrusion from the face of the barrel because the bolt recess is .250" deep leaving .040" for a shim between the barrel face and the face of the breach to get correct head space.

When I fired the first empty case with the original primer the case protrusion was .290" and the primer fired just fine. I reprimed the case and the rifle failed to fire the primer. I measured the case protrusion and it is .210", .080" less than the unfired case. So I pulled the bullet out of another case and fired it and had the same results. It went from .290" protrusion to .210" protrusion in the barrel.

Why is it loosing .080" protrusion when firing just the primer, no bullet, no powder?
 

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Because the primer is driving the case into the chamber and pushing the shoulder back. DESTROY those cases!! Fired with a full load could wreck the rifle and you.

.290 is WAY too much unsupported case!! only have enough sticking out for an extractor to grab.
As a point of reference-- One of the valid criticisms of the 1903 Springfield was that too much case was unsupported by the chamber. It has .170 protrusion.

I suggest you re-think your design before shooting that beast.

I'd be interested in your action design. I have barrels and stocks for two .50 BMG but the Vulcan receivers were torch cut apart due to severe 'unsafe-ness'.
 
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Discussion Starter #3 (Edited)
JBelk, The bolt face design is a copy of the original single shot bolt action Barrett, except I designed the bolt with two lugs rather than the triangle Barrett used. Barrett recessed the head of the cartridge .250" into the bolt face to make the extractor rigid enough. Thousands or more of those Barrett's are using that design. The .290" protrusion of the cartridge face sticking out of the barrel is needed to seat the face of the cartridge against the bolt face and leave enough room for a shim between the face of the breach and the shoulder of the barrel. There isn't any more of the cartridge sticking out of the chamber than a stock unmachined barrel because you have to machine the face of the barrel off until you reach the angled relief in the chamber so the case is supported the same as in an unmachined barrel.

Keep in mind this is the same as a Barrett bolt face that the government has been using for sniper rifles since 1982 that they buy from Barrett. Its a proven design, I just don't like the triangle bolt lugs and prefer a two lug bolt for more face contact when in battery. Also, it's easier to machine a two lug bolt.

My testing has been without the extractor or ejector in the bolt. Today I am testing with extractor and ejector in the bolt and still working on firing pin spring strengths to fire the primer. I am also going to blue the chamber and spin a finish chamber reamer in it and see if the chamber is correctly machined. I am using the M3 36" barrels used in aircraft, not the M2 48" barrels used in ground machine guns.

I don't see or understand how a primer has enough pressure to fire form a case without a bullet or powder in it. I will keep posting updates.

By the way, the reason I designed my own rifle is I DON'T LIKE the Barrett design. A friend brought two of them to me and wanted me to build him another one. I refused and designed my own 50 BMG. I am working at making his two Barrett's work right. The original Barrett's have a lot of issues of bolt chamber alignment and scope barrel alignment.
 

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My mistake on the stick-out. The 50 is a scaled up 30-06 and .290 is still within the case web. The Ma Deuce is similar.

I have two actions to make and just looking for ideas. I'm with you on a 90 deg. bolt.

Remember the firing pin spring is a major factor in lock time. With a 90 degree lift you have more room to strengthen the spring and reduce lock time without making it too hard to cock.

Have you checked that barrel for a stellite liner? One touch destroys a reamer.

Why not just machine the barrel to fit and forget a spacer, or is the spacer also the recoil lug?

Think of a primer as just a reloading press ram without a shell holder. It takes surprisingly little pressure to push the shoulder back and create .030 excess HS. It's the exact same thing as trying to fireform Ackley brass with a reduced charge! If the primer is protruding from the case, the excess headspace is the amount of that protrusion!!! That's dangerous! Smash those case necks so nobody is ever tempted to load them.
 

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Discussion Starter #5
The ramp up to cock the firing pin is 45 deg with a lift of 5/16". When the bolt is closed the cocking lever drops 1/16' to engage the sear So I have 1/4" firing pin travel.

I designed this rifle like a Mouser design but its big. I have revised it a few times because what you conceive in your mind and draw on paper doesn't always work.

The barrel is a M3 aircraft barrel. It was made by a quality maker and is a higher grade than the normal Military specs. The barrel has a stellite liner. In most the military grade barrels the stellite riffling doesn't line up with the rifling in the barrel.

A friend brought two knockoff Barrett bolt action rifles for me to make them chamber better. I don't like the bolt carrier rails mounted in the bottom half shell and the barrel mounted in the bottom shell and top shell. It was hard to get the bolt liked up to enter the breach and even then there is no way to know if the bolt and barrel are concentric. When I checked his rifle head space I found it had about .020" so the cartridge was loose in the closed bolt. The Barrett used set screws to set the head space and tighten.

I had already made all my parts before trying to fit it up. That's when I saw that I had to make a shim to set the head space rather than modify anything. because I didn't want to use set screws to lock the barrel in. All the cases I have test fired get destroyed.

Have you designed the rifles you plan to build? Don't even think about using a M2 land machine gun barrel.

How do I post a photo here to show you some photos or drawings?
 

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Carl--

You're dealing with a VERY short FP motion. The Remington 700 has about .310 of 'stroke' and uses a very strong spring to get reliable ignition. You can get more stroke by simply moving the sear back. Notice a Remington sear does NOT re-set by simply opening the bolt. The bolt has to be withdrawn some for the sear to rise. Look at a M93 or M94, 95 or '96 Mauser that cocks on closing. Some have nearly a half inch of 'stroke'. Their cocking notches are actually a disconnector safety feature.

I have chrome-moly 50BMG barrel blanks to work with so will thread and chamber to the action I build just like any rifle.
My customer doesn't know yet if he wants a bolt action or some kind of SS. I have the tools to build whatever he wants. We're in the negotiation stage right now. He wants two rifles built.

To post pictures--- click on 'go advanced' and scroll down to 'manage attachments'. Click on the picture you want to load and click 'upload'. It'll show up as a thumbnail at the bottom of the post. I'm interested in your project.
 

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The Shadow (Super Mod)
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The barrel is a M3 aircraft barrel. It was made by a quality maker and is a higher grade than the normal Military specs. The barrel has a stellite liner. In most the military grade barrels the stellite riffling doesn't line up with the rifling in the barrel.
That was certainly true in 1967, as detailed in Springfield Armory memo SA-TK1-2075.
But given the testing and rejection outlined in that report, I'm not sure I'd buy that they are continuing this far along with the same limitations.

Interesting.
 

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Added weight works. That's why dangerous game Mausers have a longer cocking piece.
 

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Discussion Starter #14 (Edited)
I've only had one failure with on of my Vortex scopes and they fixed it, the cross hairs moved with each shot. what do you recommend for a scope for the 50 BMG rifle?

attached is a photo of the assembled rifle. its not finished yet, it needs some massaging to get it ready to fire. i wanted a photo of what it will look like finished. I've been working on it for two years, should be ready to fire in a week or two. I'll need taller scope rings to get the scope up so i can see through it and for longer range shooting. that scope is a Vortex PST Tactical scope. well, that didn't work its upside down.









IMG_0889.jpg
 

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The Shadow (Super Mod)
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Just remember that drops get "wonky" when you start getting large scope/bore height offsets.

Depends on what distance shooting you are going to do, and how good your eyes are.
The Weaver model# 800363 is light-years more durable than that PST, and frankly better optically; it also doesn't hurt that it's cheaper.

Cheers
 

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I took the liberty of cropping your photo and turning it right side up.
Where's the locking lugs?
 

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I have a gallon can of X-283 powder if you want to reload for it.
 

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Discussion Starter #20
I am considering doing reloads. I'm thinking about buying a full set of dies and using my arbor press to resize and load the rounds. I think the cases may get 3 reloads out of them. My 22-250 at 3600 fps only gets about 3 reloading's.
 
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