Best method to delay the breech opening of a Colt Delta Elite

Mello2u · 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.

croc4 · August 8, 2009, 11:23 AM

Are you sure its not just the ammo?

Croc4

Mello2u · 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.

croc4 · 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

Croc4

drail · 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.

Mello2u · August 10, 2009, 12:23 AM

drail,

Thanks for explaining the square bottomed firing pin stop. That sounds like some thing to try.

Hunter Customs · 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.
Regards
Bob Hunter
www.huntercustoms.com

drail · August 10, 2009, 02:30 PM

Mello2U, you are very welcome. You be careful with that thing now.

Jim Watson · 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.

brickeyee · August 11, 2009, 01:01 PM

The bullet is out of the barrel before link down starts to occur.

drail · August 12, 2009, 05:46 AM

That's the design theory anyway.

brickeyee · August 12, 2009, 10:29 AM

Quote:

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.

HammerBite · 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.

**Unclenick** · 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.

drail · 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.

saltydog452 · 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.

salty

August 8, 2009, 10:46 AM	#1
Mello2u Senior Member Join Date: February 21, 2009 Location: Georgia Posts: 1,424	Best method to delay the breech opening of a Colt Delta Elite 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. __________________ NRA Life Member - Orange Gunsite Member - NRA Certified Pistol Instructor "When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that justifies it." Frederic Bastiat

August 8, 2009, 01:58 PM	#3
Mello2u Senior Member Join Date: February 21, 2009 Location: Georgia Posts: 1,424	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. __________________ NRA Life Member - Orange Gunsite Member - NRA Certified Pistol Instructor "When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that justifies it." Frederic Bastiat

August 8, 2009, 08:33 PM	#5
drail Junior member Join Date: February 2, 2008 Posts: 3,150	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. Last edited by drail; August 8, 2009 at 08:38 PM.

August 10, 2009, 12:23 AM	#6
Mello2u Senior Member Join Date: February 21, 2009 Location: Georgia Posts: 1,424	drail, Thanks for explaining the square bottomed firing pin stop. That sounds like some thing to try. __________________ NRA Life Member - Orange Gunsite Member - NRA Certified Pistol Instructor "When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that justifies it." Frederic Bastiat

August 12, 2009, 04:03 PM	#14
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	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. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

August 8, 2009, 11:23 AM	#2
croc4 Senior Member Join Date: March 9, 2006 Location: Idaho Posts: 191	Are you sure its not just the ammo? Croc4

August 8, 2009, 06:04 PM	#4
croc4 Senior Member Join Date: March 9, 2006 Location: Idaho Posts: 191	Before changing anything on the gun, I would try a different brand of ammo and a different gun for comparison. just my 2c Croc4

August 10, 2009, 08:18 AM	#7
Hunter Customs Senior Member Join Date: March 26, 2005 Location: Osborn, Missouri Posts: 2,697	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. Regards Bob Hunter www.huntercustoms.com

August 10, 2009, 02:30 PM	#8
drail Junior member Join Date: February 2, 2008 Posts: 3,150	Mello2U, you are very welcome. You be careful with that thing now.

August 11, 2009, 11:58 AM	#9
Jim Watson Senior Member Join Date: October 25, 2001 Location: Alabama Posts: 18,543	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	#10
brickeyee Senior Member Join Date: December 29, 2004 Posts: 3,351	The bullet is out of the barrel before link down starts to occur.

August 12, 2009, 05:46 AM	#11
drail Junior member Join Date: February 2, 2008 Posts: 3,150	That's the design theory anyway.

August 12, 2009, 03:04 PM	#13
HammerBite Senior Member Join Date: January 11, 2006 Location: Northern VA Posts: 429	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, 07:39 PM	#15
drail Junior member Join Date: February 2, 2008 Posts: 3,150	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	#16
saltydog452 Senior Member Join Date: August 16, 2004 Posts: 516	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. salty