FINALLY - 5 Underwood 10mm Ammo Disections

[The_Shadow]

I haven't test with the lighter bullets but in conversations with Mike Willard of SwampFox he mentioned the lighter bullets  achieved better results with LongShot than 800X.  However he used LongShot across all bullet weights in his ammo.

[REDLINE]

IMO that title would go to Double Tap, more specifically their 10mm line.  The key with Underwood is anything being in question or not, they are respected by the 10mm crowd as a whole (including me), even by those that simply aren't interested in ammo that powerful.  Double Tap, specificly regarding 10mm, is not.  So much so that they don't even get the respect of scrutiny anymore.

[Intercooler]

I never saw people going after DoubleTap or Buffalo Bore like Underwood. Even SwampFox didn't get much ink until later but not much in Kevin's ammo hasn't been tore down to almost the microscope level 

I would be kind of flattered 

[REDLINE]

Thanks for the info The_Shadow.

[Kwesi]

I had my first experience yesterday testing Underwood 200 XTP's which resulted in a very potentially dangerous outcome BUT it was fired in my CA89-10 (MP5 clone with a 8.85" barrel).  I reported what happened to Kevin.

If you feel it is pertinent to your thread let me know and I'll post.

[Intercooler]

Not my thread but always looking to learn.

Don't know much about your firearm.

[REDLINE]

Yes please.  Thanks in advance.  The more information we can all gather together, the better toward understanding what is, what might be, and/or what to consider as a possibility gets, helping all of us to make the most informed and safe decisions possible.

The more details the better.

[The_Shadow]

I had my first experience yesterday testing Underwood 200 XTP's which resulted in a very potentially dangerous outcome BUT it was fired in my CA89-10 (MP5 clone with a 8.85" barrel).  I reported what happened to Kevin.

If you feel it is pertinent to your thread let me know and I'll post.

Kwesi, If you don't mind, please elaborate as we are all here to understand and learn how any ammo is working or not working in a particular firearm.

I don't know if the MP5-10mm clone is using the same fluted barrel as the HK MP5, but if it does I suspect you saw the fluted chamber lines imprinted on the brass casings and possibly splits.  Why do I say this?  I have processed several thousand brass as shot from the MP5 10mm's, mostly Federal manufacture (gov. contract) and those conditions were seen as fire in those weapons.  The Federal ammo is high pressure but the velocity is not as high as Underwood's.

[sqlbullet]

I wanna hear too.  I tend to think The Shadow nailed it.  I can't imagine Underwood ammo getting along great with a fluted chamber. I haven't ever seen any splits in my CETME in 308, but rifle brass is very different than pistol brass.

[Kwesi]

I had my first experience yesterday testing Underwood 200 XTP's which resulted in a very potentially dangerous outcome BUT it was fired in my CA89-10 (MP5 clone with a 8.85" barrel).  I reported what happened to Kevin.

If you feel it is pertinent to your thread let me know and I'll post.

Kwesi, If you don't mind, please elaborate as we are all here to understand and learn how any ammo is working or not working in a particular firearm.

I don't know if the MP5-10mm clone is using the same fluted barrel as the HK MP5, but if it does I suspect you saw the fluted chamber lines imprinted on the brass casings and possibly splits.  Why do I say this?  I have processed several thousand brass as shot from the MP5 10mm's, mostly Federal manufacture (gov. contract) and those conditions were seen as fire in those weapons.  The Federal ammo is high pressure but the velocity is not as high as Underwood's.

It has the same fluted barrel as the HK MP5.  My 10mm cases in general sometimes have a black flute line but it has taken many loading before vertical case splits occur.  None of the Underwood ammo had any splits.  I will post the details in a few minutes and I'll try to post a pic of the remaining case that detonated out of battery.

[Kwesi]

In anticipation of my first hog hunt and based on the recommendations of more experienced hunters I purchased this Underwood Ammo. I loaded my CA89-10. I attached a E&W brass catcher and inserted an HK mag with the HI impulse LP installed. This is some of the most stout 10mm on the market & is loaded in Starline brass. Rated at 1250 FPS fired from a Glock pistol.

I chambered the 1st round then removed the mag as a safety precaution. Round one fired & sounded fine so I reinserted the mag and proceeded to fire 4 additional rounds on semi. No problems yet.

Time for full auto. I squeezed off a quick short burst of 4-5 rounds then I noticed a lot of smoke exiting the ejection port, the brass catcher was falling off AND my mag blew out onto the bench! I noticed two pieces of a brass case lying on the bench. One was the primer end and the other twisted shrapnel. The CA89 and myself were fine. I took her apart and found a live round not fully seated. After dislodging it I confirmed the barrel was clear. Reassembled her and attempted to resume SEMI ONLY but she would not go into battery.

When I got home I was expecting to find some small brass slivers in the flutes that prevented the round from fully seating. What I found was 50% of the length of the case (minus the primer end) stuck inside the flutes. I was fortunate to be able to tap it out.

I notified Kevin at Underwood and he was very concerned. He stated that they have only tested these rounds in a Glock barrel. He offered to replace it with ammo of my choice and pay the shipping. My guess is the FPS was closer to 1400 FPS.

Guess I'm going to use my 180 grain FMJ loads.  Pic below of the case that detonated out of battery:

[The_Shadow]

Thanks for sharing your experience in this situation and glad to hear you and the gun are OK. 
Several things do come to mind when firing in full auto...
Chamber gets dirty...that's why the fluted design was added if I recall.  However the flutes also lessens drag on the cases for easier extraction, if the softer Starline brass was used by Underwood and it was imprinting the cartridge case into the flutes, that may have add to the drag/friction factor.  Due to the very high impulse and pressure of the Underwood ammo and the dynamic nature of the CA89-10, cartridge cases may have started extraction before pressures could drop to safer levels, thus holding the cartridges pressed to and/or into the flutes, causing the case heads to be ripped off during this ejection phase.

The picture appears that the casing was being pulled out of the chamber while under great pressure, as eveident of the rolled pressure formed ring from unsupported area ahead of the start ejection cut. Further cycling ripped the case head apart as a result of the weakened area which allowed the jets of high pressure combution gases to leak out.  Leaving the forward segment (the thiness part) of casing stuck in the camber shows it was pressed tightly to the chamber walls, also tearing apart.

The Federal cases I have retrieved as shot from the MP5 10mm, many do split on their initial firing.  I think their brass is somewhat harder/brittle, as not to expand as much in those applications, thus many crack and split length wise between the fluted chamber walls. 

I am no expert...just some observations and my opinions, taking in the facts and dynamics of the situation.

BTW, I still kick myself in the ass for not buying one of those clones when opertunity knocked!  Instead I left my money on the VLTOR Bren Ten ~~~~~"vaporware"~~~~~

[sqlbullet]

My take is the same as The_shadow.  Looks to me like the ammo separated and partially extracted while pressure was still high.

[4949shooter]

I would like to see some of the other fired cases. As kwesi mentioned, the chamber flute marks usually appear as burn marks. They do appear to be more metalllic in color on the case pictured. The chamber flutes are not only to make extraction easier as Shadow mentioned, but they will also provide for extraction in the event the extractor becomes broken or otherwise disabled.

My take on this is that the MP10 and clones are designed for FBI spec 10mm ammo.

[The_Shadow]

BTW Kwesi, is not the first to have experienced issues in the MP-5 and Clones, I have read other post about issues.

I'm not sure exactly how much of 10mm casing is unsupported as chambered in the MP-5 10...looking at the cartridge in the chamber would indicate if there is some unsupported areas of concern.

One thing that did concern me with the fluted chambers is that it allows gasses to by pass because the chamber doesn't seal off like a normal chamber by the casing expanding to seal to the smooth chamber walls.