Hi carsten,
There are other, better ways to soften the blow between slide and frame than
using a heavy recoil spring...and the best way is to go back to Browning's original design on the firing pin stop itself. The other factor that has an effect is the mainspring.
EGW markets an oversized firing pin stop that allows the installer to size it for a light press fit. The benefits are preventing the stop from dropping out of position...which can and does happen when the firing pin spring gets tired...
and keeping the extractor stable in its channel. The EGW stop also comes
with square at the bottom, on the area that contacts the hammer. This lets the installer cut a smaller radius on the bottom to reduce the mechanical advantage of the slide when it recoils and cocks the hammer.
The radius on your stop is probably industry standard...or nominally 7/32nd inch. The original stop had a much smaller radius...very nearly square...and
was .075 to .080 inch...nominally .078 inch. It makes a tremendous difference in the slide's velocity, and there are two mechanical reasons for it.
One...as noted...in the reduction of the slide's mechanical advantage in cocking the hammer, and thus absorbing part of the momentum imparted on the slide under recoil. The second factor is in delaying the slide's movement for a fraction of a second, and thus delaying the barrel's unlock timing.
The slide and barrel move backward as a unit for about .100 inch while the bullet is still in the barrel. The necessary momentum for the complete recoil cycle is established in that first one-tenth inch of travel. (You'll need to convert that to metric in order to see just how short that distance is.)
If the slide is delayed from movement at that critical point, the momentum
imparted on the slide dissipates somewhat, and is absorbed by the mainspring
rather than relying on the recoil spring to slow it down AFTER the slide is moving at full speed. Simply put...it acts much like applying a brake for a second just after pushing an accelerator pedal. The recoil spring has very little effect on slowing the slide in the first thenth-inch of travel, and has
the most effect when it approaches full compression. With the "brake" applied
early on in the stroke...while the recoil spring is barely more than at pre-load
tension,(about 3.5 pounds) the slide's rearward movement is more rapidly
dissipated than by the recoil spring's small pre-load. Less momentum remains to complete the cycle, and the slide doesn't hit the impact surface as sharply.
Install a 23 or even a 25 pound mainspring along with a small radius stop...
and I'd be willing to bet that your brass will barely dribble out of the port
with your 20-pound recoil spring...if the slide even makes full travel. I've
induced short-stroke malfunctions using that combination with 18-pound springs.
After hearing your description of your pistol's operating characteristics, I also have to suspect that the barrel is unlocking a bit too early in the cycle...maybe at around .080 inch of travel. That doesn't sound like a lot, but it can make a big difference in the slide's rearward speed.
Standin' by...
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