10mm...too hotly loaded?

[hifiwasabi]

I went out yesterday to pop off some more of my reloaded 10mm in my TD carbine. I had done some load development in October, but haven’t gotten out until now. Anywho, I started where I left off; at 9.2 grains of Longshot pushing 180 grain hollow points from a Winchester once fired case. When I was looking at the brass after firing I noticed that the case had bulged somewhat just above the case head. For reference, they chrono’d at roughly 1530 fps out of my 18.6” barrel at -10 degrees. Once I saw the brass, I shot a couple of 9.1 grain loads to compare; they too had some bulging. I’ve read of people running 9.5 grains of Longshot, but I don’t want to push it if the loads are unsafe or brass life goes in the terlet.



Are these primers and cases telling me that I’m in the danger zone?

 

[B]

I ran my Glock handloads through a TD I owned years ago and one of the cases failed doing significant damage to the gun. After that I spent a lot of time with their engineer thinking of and testing different changes to ensure it held up to full pressure ammunition.

I don't know if they went back to older and simpler buffers but I'd say they took a step backwards somewhere... Your load is not hot but those cases sure look like they are close to a rupture.

 

[hifiwasabi]

That’s what I thought too. I’m happy with the velocity, but not if I damage anything. I think I’ll pull all my loads down and start over and hang out closer to 9.0 grains.

 

[jimbo14]

180gn @ 1530fps is a power factor of 275!!!!
Crazy hot!

 

[220]

Blue dot is faster burn rate than long shot by 2 to4 steps depending on where you look 9.2 grr blue dot is start load
How often do you clean or care for brass as one looks like it has green corrosion spot
Primers are not too flat for 10mm

 

[Suther]

Is the TD Carbine blowback or locked breech?

180gn @ 1530fps is a power factor of 275!!!!
Crazy hot!

That is from a carbine barrel though, not a handgun. Minuteman loads 180gr to 1300fps from a 5" barrel : https://minutemanammo.com/collections/10mm

An extra 230fps from a barrel more than 3 times longer doesn't seem entirely unreasonable?

 

[jimbo14]

Is the TD Carbine blowback or locked breech?



That is from a carbine barrel though, not a handgun. Minuteman loads 180gr to 1300fps from a 5" barrel : https://minutemanammo.com/collections/10mm

An extra 230fps from a barrel more than 3 times longer doesn't seem entirely unreasonable?

I think I was thinking PF based on .40, but I think a rifle can boost fps by 10% or so? Still seems hot by another 10%.

 

[hifiwasabi]

TD’s are blowback. The brass looks green and grungy because I had to pick them out of the snow/ice. I was going out of the Lyman book, but I just got a Lee book so will look in there too.

 

[B]

My 180grn Longshot hand loads ran nearly 1700 feet per second with published data. I also run 9.6 grains of Longshot under a 180 grain jacketed hollow point in my pistols. His load is fine in almost any gun but as I also found out the Thureon Defense just doesn't handle some loads properly.

I had a very long thread I started detailing my issues and my work with Thureon. It would be about 8 years old at this point though.

 

[Suther]

I think I was thinking PF based on .40, but I think a rifle can boost fps by 10% or so? Still seems hot by another 10%.

Im pretty sure the case capacity factors into how much velocity increases. A bigger case like 357mag can see 25-30% increases or more from what I'm reading here (and 10mm has a decent case size for a handgun round): https://www.ballisticstudies.com/Knowledgebase/.357+Magnum.html

Factory loads for the .357 are produced by all major ammunition manufacturers and are generally available in two base weights, a 125 grain bullet at 1400 - 1500fps depending on handgun barrel length and a 158 grain bullet weight at 1200 to 1300fps. From a 16 to 20” rifle barrel, velocities increase by an average of 500fps.

My 180grn hand loads ran nearly 1700 feet per second with published data. I also run 9.6 grains of long shot under a 180 grain jacketed hollow point. His load is fine and almost any gun but as I found out the thureon defense just doesn't handle some loads properly.

Being a blowback I wonder if the action is opening too early? That would explain the bulge wouldn't it?

 

[B]

Being a blowback I wonder if the action is opening too early? That would explain the bulge wouldn't it?

Yes the bolt thrust is high enough that the mass holding everything in place is insufficient. Were he to keep increasing the powder charge I have little doubt that his cases would rupture very soon

 

[B]

I would be very curious to see the bolt and buffer set up on the Thureon Defense rifle the OP has. I'm thinking they just went back to their standard design.

 

[jimbo14]

Im pretty sure the case capacity factors into how much velocity increases. A bigger case like 357mag can see 25-30% increases or more from what I'm reading here (and 10mm has a decent case size for a handgun round): https://www.ballisticstudies.com/Knowledgebase/.357+Magnum.html

Thanks for that.

 

[hifiwasabi]

I haven’t played with the buffer setup, and I’ve not thought the look into it until now, B. It really flings the cases with authority! I pick them up from two shooting lanes over.

 

[B]

Post a picture if you can. I can't seem to find my photos, I imagine the ones in my thread would be no good by now since Photobucket went lame.

 

[bigedp51]

If the fired case has bulged completely around its base above the extractor groove the case could be close to the minimum diameter and the chamber close to max diameter. Meaning this is not "Glock bulge" caused by the feed ramp not supporting a small section of the case. When the bulge is around the circumference of the case the amount of the bulge is the difference in the diameter of the case and the chamber. meaning how far the case can expand before contacting the chamber walls.

SAAMI case manufacturing tolerance diameter .425 to .420

SAAMI chamber base diameter tolerance .428 to .432

A simple check would be to fire factory loaded ammunition and measure the base diameter before and after firing.

 

[B]

Looking at the pictures closely they don't seem too bad. The left case in the second pic looked bad but seems like it could be a trick of the light. I would consider anything over .430" to be a bulge if it's uneven. I found the pictures, here is my bulge...

 

[Suther]

Looking at the pictures closely they don't seem too bad. The left case in the second pic looked bad but seems like it could be a trick of the light. I would consider anything over .430" to be a bulge if it's uneven. I found the pictures, here is my bulge...

Wow.

 

[VanMan]

I worked up a 9.5gr Longshot load for my 610. Brass ejects cleanly, so not over-expanded.

 

[hifiwasabi]

I popped off a few factory loads as well, I’ll try to compare tonight. I see that Thureon offers different buffer weights, but I’d like to not add more weight to an already beefy carbine.