Gas Port Browning BAR

[merbeau]

Posted on the reloading forum that I have just purchased my first Browning BAR in 7mm Magnum. After some research and from other forum members it is apparent that the BAR (just like for the M1 Garand) probably should not be shot with reloads using some of the newer slower burning powders like Retumbo because of the higher pressures at the gas port that could damage the rifle or cause a breech fire.

I was reading an article that Schemke (sp?) makes an adjustable gas port for the M1A rifle that can be adjusted - I assume if using a higher pressure powder make the opening smaller to use less gas.

Question: does any company make an adjustable gas port for the Browning BAR or can Browning Gas port pilots listed for example a 243 Winchester be substituted for the current 7mm magnum and allow for the use of slower powders.

Thanks

Robert

 

[Clark]

Here is a pic of a factory gas regulator for a BAR and my homemade one.

They are really just a bolt like plug with a hole in them that act as a bleed off by pass.

They are too much work to make, compared to buying one and drilling it out for hotter loads.

From my notes:

a) 7mm Mag is .066" hole
b) 300 Mag is .077" hole [p/n B3176146]
c) 338 Mag is .059" hole
d) My home made is .078" hole
e) recoil buffer [p/n B3176065]

 

[merbeau]

Clark

Thank you for the information. I assume the 7mm mag diameter is for hotter loads?

Robert

 

[Clark]

The hole is to dump excess gas pressure.
If the gun will not cycle, use a small hole.
If the gun is hammering the buffer, use a bigger hole.

From 2010 I wrote:
Is there any truth to this? - The Firing Line Forums

What does it all mean?
You want to load hotter, use a bigger hole.
You want to load wimpier, use a smaller hole

 

[merbeau]

Clark

First thanks for the clarification about the pilot venting excess gas. This is the best forum. People are willing to help. Thanks for the link which I just went to and certainly people have various opinions.

In my Browning Auto 5 shotgun manual (obviously they are not gas operated) but the manual clearly says not to shoot 3 inch magnums with only two rings (which is for 2 3/4 inch shells) because it will damage the receiver overtime.

I would suspect that more pressure would place additional strain on the receiver and perhaps for someone shooting just a few rounds a year probably not a problem but more than that overtime may impact the rifle.

If I can not find an acceptable load using the IMR 4350 like powders then I will go with a bigger gas port hole and try a few slower powders.

 

[Clark]

The problem with many semi automatics is that if there is not enough energy in the mechanism, it jams, and too much and it hammers the parts against each other.

You can tune the ammo to the gun. [change the powder charge]
You can tune the gun to the ammo. [change the recoil spring or gas hole size]
You could have an adjustable gun. [ turn on the gas adjuster knob on a FAL or invert the friction rings on an A5]
You could have a self regulating gun. [My father's 1982 patent 4,353,285 gives a formula for a parabolic taper to a hydraulic cylinder]

--------------------------------------
The hammering problem is separate and distinct from the over pressure problem.
It is easy to conflate them, because the more powder, the more hammering and the more pressure.
The guns are designed with huge safety margins on pressure, but the window between jamming and hammering is narrow.