FINALLY - 5 Underwood 10mm Ammo Disections

[REDLINE]

Is this a correct depiction of your setup?  If so, and if this very basic image is correct for your specific application and scenario, it would definitely seem your cases are being extracted before pressure drops to a safe level for the spent casing to be extracted (as has been suggested earlier by others).  Well, with the pressure level of the UW 200XTP loads you were shooting anyway, compared to other lesser loads you also shot.

Otherwise it does seem like there is plenty of case support if this pic depicts anything close to your actual setup, aside from a generally loose chamber to begin with.

I got the image from http://commons.wikimedia.org/wiki/Category:Roller-delayed_blowback

[The_Shadow]

Thanks for the pictures Kwesi...It appears that there is a fair amount of unsupported casing as it sits in the chamber.  Underwood's ammo is at the very upper end of performance as well as pressure.  That MP clone being a longer barrel that the ammo was originally tested in could add to the subjected pressures to the casing.

The info from Swampfox/Mudrush was copied even with the mispellings.  I agree that the peak pressure is spiked before the bullet moves from the casing, but in that short time it travels to the barrel opening, it is still quite high.  I also mentioned about the type testing using the strain gauge on the exterior of a barrel chamber as opposed to those being used inside the chamber as SAAMI discussed in Publication 205.

I still stand on the premis that Star Line brass is soft (this is done with the purpose of reloading and reworking in mind) and at the upper limits of performance it will start to flow.  I know that it was mentioned that Star Line provide brass to several other manufactures.  Does the specs if internal case dimentions remain the same? Does their brass get other treatments to make them tougher?  (they don't load to the levels of Underwood, SwampFox & Double Tap)

Look at what happens in the Delta Elites using the Underwood, they also needed a reduced loading to keep the brass from expanding and bulging so bad, this maybe what the MP clone will need as well with relation to timing and ejection.

[REDLINE]

I still stand on the premis that Star Line brass is soft...

Look at what happens in the Delta Elites using the Underwood, they also needed a reduced loading to keep the brass...

10mm brass on it's own, outside of a barrel chamber, is gonna handle what?  5000 PSI or so?  Maybe less?

I'm not seeing that any available commercial 10mm brass by any manufactuer can be made hard enough or strong enough, within SAAMI specifications, to overcome the beyond-poor chamber support of a Colt Delta Elite.

And lets say Starline brass is the softest of any available.  I'm not saying it's not.  But by the same token, by how much?  1%?  20%?  50%?  Enough that the brass brand is gonna make a noticeable difference?  I'm having a hard time seeing it.

Am I missing what you're suggesting?

Do you disagree?

[Kwesi]

Sorry for the poor pics.  Just could not get a better close-up:

[Intercooler]

Damn. That's a Delta x2! 

[The_Shadow]

What I am suggesting is that the stuff being loaded Underwood, SwampFox & Double Tap (of earlier years) were at the upper level of pressures & performance for most semiauto guns, they have had to back off the loads or change powders to eliminate the serious bulging as seen by many shooter with various guns.  These same rounds as shot in barrels like the TC with heavy walled, tight chambers of full support can with stand more, also they don't have the dynamics of ejection phase while pressures are still present like the semiautos.  As in this case, not all guns are equal...

This is why I load my own ammo, I control my own choices in every aspect of a load as related to my guns and the way they are set up to handle it.

[Intercooler]

Yea. You are going to need Delta-Lite or worse ammo in that puppy!

[4949shooter]

Damn. That's a Delta x2! 

That's kind of what I thought at first as well. But if you look at Redline's diagrams, the bolt should enshroud the case head when it locks into place.

Edit: Though I do agree, he will have to use something less powerful than Underwood 200 grain XTP. The Delta Elite load sounds like a good compromise.

[The_Shadow]

Thanks again Kwesi, the pictures do tell a story of less chamber support and add to that the dynamics of things in motion during the ejection cycle, pulling the casing further out of the chamber, the expanding casing, also acting to push it self outward from the chamber all add up to the situation you have experienced.

Conclusion; I don't know enough about the HK system to say recoil system could be adjusted with different spring rates, therfore utilizing loads with slighltly less peak pressures provide you with safer operation.

I did just read you post over at GT where you decided on the Delta Elite tuned loading, sounds good.  Please advise how this works from your gun when you get a chance!  Best of luck! 

[REDLINE]

I also mentioned about the type testing using the strain gauge on the exterior of a barrel chamber as opposed to those being used inside the chamber as SAAMI discussed in Publication 205.

Can you provide a link to where you mentioned this?  Was Swampfox using a strain gage setup?

[REDLINE]

The Delta Elite load sounds like a good compromise.

I agree.  That setup doesn't look appealing by any measurement for full power 10mm loads.  And it clearly you've proved it with the UW ammo you ran through it.  Those pics are worth 1000 words, even if the bolt face shrouds the case head to some extent.

[The_Shadow]

Redline, the remarks were made on GT, when XmmAuto, was buying the Pressure Trace system and the TC with a 10mm barrel to conduct pressure testing.  As we discused the accuracy of such testing and calibration.  He has since sold off the equipment and the TC pistol if I recall.

I also mentioned it here on this form as concern.
http://10mm-firearms.com/factory-10mm-ammo/10mm-ammo-history/

[Kwesi]

Thanks again Kwesi, the pictures do tell a story of less chamber support and add to that the dynamics of things in motion during the ejection cycle, pulling the casing further out of the chamber, the expanding casing, also acting to push it self outward from the chamber all add up to the situation you have experienced.

Conclusion; I don't know enough about the HK system to say recoil system could be adjusted with different spring rates, therfore utilizing loads with slighltly less peak pressures provide you with safer operation.

I did just read you post over at GT where you decided on the Delta Elite tuned loading, sounds good.  Please advise how this works from your gun when you get a chance!  Best of luck! 

The HK roller locked system does not utilize different recoil springs other than each caliber has a different spring.  They utilize, in the 10mm and 40, two different locking pieces ( LP ).  One is for low impulse ammo and the other is for high.  I had the Hi LP installed which is what I also use for my 1200 FPS loads.

BTW: the Delta Elite rounds are a trade out and intended for my Delta Elite.  I doubt I'll run any more UW in the CA89-10.  She purrs out full auto with my loads.  Remember the reason I purchased these were for my 1st hog hunt.  I going to use my 180 loads.   **** I forgot to mention that the UW was also for my G20 that I'll carry as a backup.  I tested these with the OEM barrel and a KKM and had a few failure to feed's.  I have a Wolf 22# spring and metal rod installed.  I'm not prone to limp wristing but switched to my loads and had no issues at all.  I did note that the OAL of UM were either 1.251 or 1.255 mostly whereas my are 1.255 - 1.260.

I was thinking of trying some original Black Talons - have about 8 loose rounds...

[REDLINE]

Redline, the remarks were made on GT, when XmmAuto, was buying the Pressure Trace system and the TC with a 10mm barrel to conduct pressure testing.  As we discused the accuracy of such testing and calibration.  He has since sold off the equipment and the TC pistol if I recall.

I also mentioned it here on this form as concern.
http://10mm-firearms.com/factory-10mm-ammo/10mm-ammo-history/

TYVM for the link.

My interest lies in what issues there are or aren't using a strain gage setup as opposed to the copper crusher system or the piezoelectric transducer system.

I did see at the link you provided in reply #21 where you said;  "Using that system would be better than those which use the strain gauge wrapped around the out side of a barrel."  But I saw no additional or other comments regarding the same, either to agree, discuss, or spell out where your thoughts are coming from on that.

So what I'm trying to find is any discussion or general writeup regarding, as you put it;  "the accuracy of such testing and calibration" or the like, negatively toward the strain gage setup.

Can you give me anything toward that light or point me in a general direction?

[Yondering]

The HK roller locked system does not utilize different recoil springs other than each caliber has a different spring.  They utilize, in the 10mm and 40, two different locking pieces ( LP ).  One is for low impulse ammo and the other is for high.  I had the Hi LP installed which is what I also use for my 1200 FPS loads.

If the high-impulse locking piece works correctly with your 180gr 1200 fps loads, I'd say you'd need an "extra high impulse" locking piece (if there were such a thing) for the Underwood loads. 180@1200 is relatively weak, compared to the Underwood stuff, or any "full power" loads, especially considering that 1200 fps is out of your 8.8" barrel. Just off-hand, Underwood 180's are probably at 1400+ from the same barrel?

Looks to me like that gun is just not designed to handle full power 10mm loads.