View Full Version : Best method to delay the breech opening of a Colt Delta Elite
August 8, 2009, 10:46 AM
I chronographed 10 rounds of DoubleTap 200gr XTP ammo out of my Colt Delta Elite a little while ago. The average velocity was only 1075 fps at 10 feet from the muzzle. The extreme spread of the velocities was a bit over 100 fps.
I read on Buffalo Bore's website that a wide spread of velocities was an indication that:
"When the cartridge fires, it generates enough pressure/recoil to prematurely open your breech face in some guns. When this happens, the opening breech face has an effect on the burn rate of the powder. This can result in some fairly high extreme spreads in velocity. If you are experiencing extreme velocity spreads of more than 50 fps, simply install a stiffer recoil spring."
I have also read that stiffer recoil springs will not delay the opening of the breech. That post suggested getting a flat bottomed firing pin stop to delay the slide movement.
Does anyone have real knowledge of this issue?
I want to see if I can get a narrower spread of velocities with this ammo in this gun.
August 8, 2009, 11:23 AM
Are you sure its not just the ammo?
August 8, 2009, 01:58 PM
I do not know whether it is the ammo. I have not chronographed it out of other guns to see if the extreme spread in velocity is repeated.
August 8, 2009, 06:04 PM
Before changing anything on the gun, I would try a different brand of ammo and a different gun for comparison.
just my 2c
August 8, 2009, 08:33 PM
Installing a heavier recoil spring will very slightly delay unlocking. The down side to this method is it will return the slide to battery with greater force and can batter the locking lugs on the barrel and the frame. A much more effective and less abusive method is to install the Evolution Gun Works firing pin stop with a square bottom edge. This will give the slide less mechanical advantage in cocking the hammer when the slide starts back. You can either leave the bottom edge of the stop fully square or radius it slightly to get less effect. It also will make it harder to pull the slide back manually if the hammer is forward. (you can cock the hammer first and then pull back the slide) John Browning's original design for the firing pin stop used this type of stop and was subsequently changed at the Army's request to make it easier to pull back the slide. I have installed the EGW stop on all of my bull barrel guns and they are softer shooting and have less muzzle dip when the slide returns on firing. It also will tighten up your extractor fit and stop it from rotating resulting in more consistent ejection patterns. John Browning knew what he was doing.
August 10, 2009, 12:23 AM
Thanks for explaining the square bottomed firing pin stop. That sounds like some thing to try.
August 10, 2009, 08:18 AM
I agree with what drail told you. I recommend putting a small radius on the edge of the stop, a .062 radius will work just fine.
Another thing you can do is put a stiffer mainspring in the mainspring housing, a 25 pound one seems to work well.
August 10, 2009, 02:30 PM
Mello2U, you are very welcome. You be careful with that thing now.
August 11, 2009, 11:58 AM
While I think a 10mm Colt needs all the help it can get from stout springs and small radius firing pin stop, the stuff about "the opening breech face has an effect on the burn rate of the powder" is pretty hokey. If the breech was open far enough to affect the burn rate of the powder, it would be blowing caseheads left and right.
August 11, 2009, 01:01 PM
The bullet is out of the barrel before link down starts to occur.
August 12, 2009, 05:46 AM
That's the design theory anyway.
August 12, 2009, 10:29 AM
That's the design theory anyway.
Multiple high speed movies of 1911s firing show the slide AND barrel recoiling about 0.1 inch and still locked before the bullet exits and unlocking occurs.
August 12, 2009, 03:04 PM
If the barrel and slide were to unlock before the bullet is gone I imagine that the resultant high-pressure event occurring in your ejection port would get your attention.
August 12, 2009, 04:03 PM
Agree with the 0.1 inch, but that is shortened by the square (with radius) firing pin stop. This lowers the total inertia in the slide and significantly reduces muzzle flip. Three of us put them on our 1911's (two full size, one Commander) and were all impressed by how much less muzzle jump there was.
As to affecting velocity extreme spread, though, that's a try-it-and see thing. The slide and chamber would have to back up at pretty different rates, shot-to-shot, to cause it. If that extreme spread is greater than firing, say, an Encore chambered for the same round would produce, I would think it's more likely to turn out to be uneven firing pin action on the primer due the the round headspacing on the extractor and shifting a bit variably in the chamber because of that.
August 12, 2009, 07:39 PM
I would almost bet that if a high speed film was made of a 1911 firing a really hot 10mm or .38 super duper it would be considerably less than .01. You are quite correct about the normal ACP timing though Brickeyee, but some folks just have to push the envelope and try to bend the laws of physics. I know I did when I was young and stupid.
August 14, 2009, 10:46 AM
Up untill reading this post, I had a high opinion of the folks at Buffalo Bore. Now, I'm not so sure.
I did have an OM that left firing pin drag marks on the primer and a bloom that was visible from the side in dim light behind the chamber though.
This is interesting.
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