Underwood 200 XTP Brass Blow OUT!

[REDLINE]

What model chronograph are you using?

Regardless, no doubt it was off.

I'll be interested in seeing your further results if you make it out this weekend to give it another go in the hopes of good chrono data and more brass to inspect.

Did you notice loose primers in the cases that split?

[The_Shadow]

Things to remember for best chrony use...
You need to have 10-12 feet of distance between the muzzle and the first sensor screen to eliminate blast effects and powder particles from yielding false readings.  Yes, lighting is important but usually that yields no readings error.  Battery voltage is also need for most accurate readings.

The sensor sees the bullet as a shadow to trip the timers, some actually blacken the projectile with a marker, as the shiny may be missed.

[Intercooler]

   Since changing my Sky Cloud (hoops) and using them every testing session my readings are very good with no odd readings. You can shoot without them and get readings but with them in place I think it's better.

[doverpack12]

I did not notice loose primers in the cases that split and the ones that passed inspection were actually harder to re-prime than most other starline brass.  I have an alpha chrony model.  I will try a new battery.  I always use the sky screens and I had problems when I was 10-12 feet away so I moved back to 20 and seem to get good consistent readings there.  I will try to blacken the bullet with a marker as well.  Any other suggestions are appreciated.

[DM1906]

For chrono (Chrony) use during low light (dawn/dusk, no direct sunlight), or on overcast days, I don't use the screens.  The screens block too much light.  A cloudy day is almost always the best, with no screens.  I also use a silver colored Easy-Up canopy over it on occasion during mid-summer.  Blackening the bullet does help during low-angle direct sunlight, but shading the chronograph (bullet path) works best.

[Intercooler]

  Just to be correct with the terms...

Sky Screens are the sensors (black boxes housing sensors) looking up through a window for a bullet shadow on the white/sky background.

Diffusers (simulated clouds) are the white plastic pieces positioned over the Chronograph in an Arc fashion to give a contrast of the bullets shadow as it passes through the Sky Screens at their set distance of 12".

You could actually take the Sky Screens out and put them in a table, etc... and it will function the same as in the box if you make the distance between them exactly 1'. 

[REDLINE]

Diffusers and skyscreens are the same thing.  Shooting Chrony calls them diffusers.  Competitive Edge Dynamics (CED) calls them skyscreens.

Different chronographs do not all have a 1' spacing for the skyscreens.  My CED M2 chronograph sensors are set exactly 2' apart.

The sensors are simply the sensors but always built inside of a general housing that varies among manufacturers of chronographs.

Some chronographs are better worse at reading velocities in low light and at being capable of reading a greater or lesser range of velocity depending on chips/circuitry/microcontrollers used.

[Intercooler]

Oh, a different unit than most use. I use the Chrony terminology because most people use it.

[475/480]

My chrony likes NO diffusers on a cloudy day. Here in Houston once the sun gets at a certain angle (. about 10 am in summer) I get high velocity readings-  ALWAYS.

Sean

[REDLINE]

And that makes the point on why the CED M2 chronograph is so awesome but also costs the wopping $200 it does.  Doesn't matter if it's 8am or just a bit before the sun rests on the horizon to the west, it has no problem giving accurate readings the whole time.  Whether it's cloudy or not it doesn't care if you leave the skyscreens on all the time.  Its sensitivity is awesome.

That's part of the reason it costs the $200 most don't want to spend on it in favor of $100 or less for lesser units.  You get what you pay for in this instance.  Plus replacement parts for the CED M2 are fairly inexpensive and readily available if you do shoot it, and you never have to worry about hitting the display/control buttons since they aren't part of the sensor/screen assembly.

I'm not saying the above to talk anyone into buying one for the reasons I listed above if they simply don't care about my above reasoning.  But I also think some people pass on the CED M2 because they can't imagine it could be much better than lower cost units.  In reality it is.   

[Intercooler]

Kevin buddy just keep banging them out and working the ammo! Thanks for all you do!

[Von]

Doubletap was the first to load full power 10mm like Underwood does and Swampfox did. Of course we know what doubletap did to their customers with the power levels and is now trying to get their customer base back from Underwood with hotter loads these days. The point I'm trying to make is Doubletap has always used Nickel plated cases and I've read opinions of reloaders on this forum that DT's caseings are the best quality for reloading with plated caseings. So nickel is not so unusual for 10mm.

[Intercooler]

I pick up a Double Tap Nickel case every 2-3 months at the range. Oddly, none have ever contained a primer 

[doverpack12]

I always use the diffusers then to use Intercoolers terminology.  Didn't have time between elk scouting trips today.  Maybe tomorrow.

[REDLINE]

IIRC the Double Tap 10mm ammo seems to be loaded to an awefully high pressure for the low(er) velocity they put out, as verified by pressure signs after firing.  Or maybe it's that they aren't always loaded consistently and it's a hit or miss kinda thing.  How often, if I even have a clue what I'm talking about I don't know.

I had disected the DT 10mm 135gr load and it contained what was guessed by Taterhead and The_Shadow to be Hodgdon Longshot powder.  It certainly resembles it.  The charge weight(s) seem to be in the ballpark to me, but I'm not 100% on that.

The thread is here - http://10mm-firearms.com/reloading-10mm-ammo/disected-hornady-155gr-180gr-win-silvertip-175gr-blazer-200gr-and-dt-135gr/

The powder charge in the DT 10mm 135gr load was 11.2gr and 11.4gr between the two I disected.  Those powder charge weights, if Longshot, seem quite reasonable to me if Longshot is the powder I found.  COL was 1.241" for both.

Here's the pic of the powder;


475/480 had worked up some Longshot 10mm loads with the 135gr Nosler, both loaded to a COL of 1.245", and chronographed them from both his G20SF (4.6" barrel) and his STI (6" barrel).  The velocity results were as follows:
G20SF + 11.0gr = 1470 FPS
G20SF + 12.0gr = 1497 FPS
STI 6" + 11.0gr = 1613 FPS
STI 6" + 12.0gr = 1698 FPS

Double Tap claims theirs at 1600 FPS from the 4.6" barrel of a G20.

475/480's thread (showing many more load comparisons) can be seen here -
http://10mm-firearms.com/reloading-10mm-ammo/10mm-longshot-loads-sti-6'-and-g20sf-4-6'/


The comparison of Underwoods 135gr 10mm loads using IMR 800-X powder (before this load has very recently been backed down) is as follows;

From Me http://10mm-firearms.com/factory-10mm-ammo/finally-5-underwood-10mm-ammo-disections/ -
The 4 rounds I disected ranged from 11.4-11.7 grains of 800-X and a COL ranging from 1.249"-1.252".

From The_Shadow http://10mm-firearms.com/factory-10mm-ammo/underwood's-lineup-135155165180220/ ;
1 round pulled had 11.8 grains of 800-X and a COL of 1.252".  After reassembly the velocity through his S&W 1006 5" with the 22lb recoil spring was 1738 FPS in which a light smile showed on the brass and the primer fell out.