Quote Originally Posted by c310pilot View Post
Yes, I have noticed that also. That's Joe's transferable converted/ running 54r. It was test day and on the lowest gas setting it was still way to much. It also has the MKI single return spring. A MKII spring has since been installed and we are trying to figure out how to choke the gas down more. Evidently the mag didn't run as we'll at the Marietta shoot so back to the drawing board. If I could get my hands on some factory drawings for the 303 mag it would be helpful. We want to modify the follower and having the original geometry of both mag and follower would be very helpful. Peter?
C310,

IMO if you need less gas then you have to modify the holes in the regulator. The regulator has to be annealed to drill it. If you modify the barrel inlet the gas regulator will only work for the holes that are smaller than the inlet. If the inlet hole is smaller than the #1 reg hole the regulator will have no effect on gas pressure, at least that's my opinion.

On the Bren mag issue, I doubt modifying the follower on a Bren mag will help using the 7.62 x 54R. The modification of the ZB39 mag to run 7.62 x54R , including the one you were using essentially includes a helper spring to point the bullet tips up after about 12 rds. In order to maintain the high capacity the orig. mag spring is weakened so that the at capacity the total force of the helper and orig. mag spring are close to the orig. spring or the first rds. can't be stripped. That leaves later rds. (below about 12) with a weaker than design spring. It's all a compromise because the mag case does not have the right geometry (Radius) for 7.62 x 54r round.

Below is a summary of the single stack angle (actual mag is double but the proportions should hold) and the inside radius of the mag.

Magazine/cartridge---------- Stack Angle ---------- Magazine Inside Radius

.303 Britishicon Bren ------------ 9.78 ------------------ 6.31"

7.62x 54R ---------------------- 5.38 -------------------- ?

8x56R ZB39---------------------- 3.92 ------------------- 10.0"

You can see from the above table why the ZB39 mag is useful for the 7.62x54R because the stack angle is much closer to 7.62 x 54r than the Bren. When you put 54R in the Bren they start pointing up as more rds. are loaded. On the ZB39 they point downward which is much easier to counter with a helper spring.

Using the above table and the stacking angles you can predict an inside radius for a 54R mag of about 9".

Awhile back some pics. were posted of North Korean PKM's with hi capacity 54R box mags. Scaling the pic and making some reasonable assumptions since I doubt Kim Jung Il will send us one I came up with a inside radius of about 9". The pic is attached below.

IMO to get a 54R mag that really works you will need to design the mag case geometry to fit the 7.62x54R round. Helper springs, follower mods won't do it.

Joe

Attachment 57919