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over sized bullets?

 
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  #1  
Old 09-22-2003, 09:00 PM
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over sized bullets?

Hello all,

In our never ending search to find affordable 50 BMG projectiles that are not steel cored surplus (fire hazard in So. kalif.), one of our buddies decided to have a bunch of brass turned projectiles made. One of the testers of the new projectile complained of "gas blowby" & the bullet diameter was changed from .510" to .5115". I had no problems w/the original .510" & wasn't too happy to hear that the specs had changed.

My 1st question is, has anyone heard of "gas blowby" before. 2nd question, is brass harder than copper? I've fired some surplus ball that had been resized & some of them meassured up to .512". There were never any issues w/rounds being over pressure due to the larger diameter, but since I'm now experimenting w/solid brass, I'm a little concerned about a tight fit in the barrel & possible dangerous pressures that might occur.

Any ideas/opinions would be greatly appreciated.

Thanks in advance.

Chris.
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  #2  
Old 09-24-2003, 12:47 AM
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Re: over sized bullets?

miltary jacquet are not in copper but in brass

hardness of brass can be close to the hardness of bronze depend what quality you use and heat treatement , pay special attention in bronze quality because as bullet raw material only use lead bronze ( bronze for bearing ) and avoid nickel bronze , aluminium bronze and phosphorous bronze they are far to tought for the grooves and you just sucess to smash the barrel grooves quick and some make easy galling in barrel .

Copper pure is nice but very difficult to machine clean .

try to copy some design as Groovebullet for drive band , they are copy of GScustom bullet so ..., this design is very sweet for pressure .

I turn my long range .50 cal in bronze and I use tight tolerance (as 0.015 millimeter on diameter )

on solid bullet moly coating help a lot for easy engraving

you shoot 50 cal in California ?

good shooting

DAN TEC
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Old 09-24-2003, 12:49 AM
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Re: over sized bullets?

what do you heard by gaz blowby , , your gaz espace by the side of the case look as no seal between case wall and case chamber ?

good shooting

DAN TEC
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Old 09-24-2003, 08:30 PM
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Re: over sized bullets?

Thanks DANTEC.

I was told that another 50 shooter was experiencing keyholed impacts on the target at 500 yards. He claimed that the cause was "gas blowby" de-stabilizing the bullet while in the barrel. The suggested fix was to increase the diameter of the driving band on the projectile to .5115". This is .0015" over what the "big" bullet manufacturers are producing.

My biggest concern is that the .0015" increase in diameter will wear my barrel out faster (and I just got the barrel installed) or increase chamber pressures (I don't like to play russian roulette just to save a few cents).

I will definitely moly coat the bullets & probably coat the bore w/Midway's Moly Bore Prep before I fire the 1st shot.

Any other thoughts would be greatly appreciated.

Chris.
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Old 09-25-2003, 05:34 AM
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Re: over sized bullets?

for some old hunting barrel in very un commun caliber I just make the first drive band ( front of the neck ) over size , by this way
you dont expand your neck to much
you get enought contavt to get good seal

some 0.50 cal are from miltary surplus and most of them are over caliber 0.510+++ even find some real machine gun in 0.518 cal ( old machine gun sec )

so best is to check with lead bullet / slug tight fit in the barrel what is your barrel caliber before to agjust bullet diameter

if you go with drive band design you can run over size bullet because radial pressure stay low yoy flow the bullet metal into the groove , no to much to avoid serious galling or fouling

good shooting

DAN TEC
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