Hi guys,

First time post here.  I have been loading shotgun shells for years, and I'm finally just getting into hand loads for my 10mm and have a few questions.

I've seen that some reloaders use mixed brass - so I take it reload recipes aren't specific to a particular make of brass?  I plan on using Starline, but don't really see the type of brass listed in loading data. 

Does it matter what brand of primers I use?  I know in shotshells they can have a dramatic effect on pressures.

I recently got some Rushmore 180gr coated bullets.  Has anyone here used them? 

The big question I have is about Longshot powder.  I use it for my shotshells and love it.  I'm seeing that about 9 grains behind a cast 180 grain bullet has given some good results. 

Based on the Starline brass, 180 grain cast bullets, and Longshot powder, what primer has worked well for folks here?  It also sounds like a chronograph is a good piece of tuning gear.  I'll pick one up.

Oh, and I'm shooting a Springfield XDM 5.25. 

Like I said, I'm totally new to this part of reloading so any info you can share will be greatly appreciated.  Thanks!!

For low-power plinking, mixed brass is no big deal. But for a high pressure cartridge like 10mm, variations in internal capacity can make a big difference. It's always best to segregate your brass and work up to max loads conservatively, realizing that a max load with one brand of brass could easily be above max with another.

I load mixed-brass medium-power plinking 10mm loads, but for serious work I bought new Starline cases.

LongShot is an excellent powder for 10mm, especially at the upper end. I use it with fmj and jhp bullets, so no experience with coated/cast.

Since cast bullets can vary greatly in hardness I'd start a work up well below 9gr of LongShot. Cast bullets obturate more than jacketed bullets and seal the bore better, thus more pressure.

Good luck with it. Let us know how the coated/cast bullets work out.

Welcome to the forum BenTen!  Starline Brass is one of the very best brass cases and they start out on the softer/malleable side being a true handloaders brass for reuse.
I have run CCI 300 and 350, Remington and Winchester primers without issues, even with my heaviest loads.
Using 8.8 - 9.0 grains of Longshot would be a good healthy dose for your 180gr Truncated Flat Point .401".

Yes a Chronograph can provide you good feedback on how your firearm is doing with a particular load!

Quote from: Pantera Mike on January 07 2021 12:09:17 AM MST
For low-power plinking, mixed brass is no big deal. But for a high pressure cartridge like 10mm, variations in internal capacity can make a big difference. It's always best to segregate your brass and work up to max loads conservatively, realizing that a max load with one brand of brass could easily be above max with another.

I load mixed-brass medium-power plinking 10mm loads, but for serious work I bought new Starline cases.

+1...I do exactly as Pantera Mike

Great information guys, thank you!

Is there a good Velocity vs Pressure rule that I can apply while chrono testing?  Like, how to know what velocity corresponds to a max load for my combination?  I definitely believe in a conservative starting charge and laddering up in small increments. 

Thank again!

1287 is Hodgdon's max velocity for a 180 grain bullet.  Their data is for a JHC design, not a cast bullet.  The higher density due missing copper jacket and the lack of a hollow-point will give you a bit of extra case capacity.  So...1287 is the max "by the book" but I would not be nervous at 1300 fps personally.

Great - thanks again everybody!

One last question - what would be a good starting charge to start with for Longshot?  Like, what's the lowest number of grains that would still function well?

I would probably start at 8.2gr and work up in.2gr increments to 9.0gr. Without a chronograph, I'd really start looking for signs of overpressure at 8.8 and not even shoot the 9.0 load if 8.8 showed any. Best accuracy will probably not come with highest velocity, but you never know.

Good luck with this!

The lowest I used was 8.5 gr in 180gr Brazos coated bullet.  I've pushed this bullet in a Longshot load just over 1,300 fps in my XDM with no issues. 

Very cool - thanks again!  It may be a bit, but I will post results when I get some testing done. 

Have a good one guys!

Okay, I think I have chosen my combination. 

Rushmore hard cast 180gr truncated bullet
8.6 grains Longshot
Remington Magnum Primers
New Starline Brass
OAL 1.240"
Mild crimp

1313 FPS average
High of 1325 fps
Low of 1301 fps

Shot with a Springfield XDM 5.25, 22lb Wolff recoil spring.  Brass went about 15 feet. 

It's very accurate, and showed no signs of excessive pressure.  That said, if there is a reason to back it off a bit I would love to hear about it. 

Thanks again for the great input!

BrenTen, you had asked whether there was/were any indicators suggesting a maximum load when choreographing your load development. There seems to be a point reached with most powders where an increase in powder charge does not produce any, any significant increase or in a paradoxical indication velocities have been reported to decrease with an increase in powder. I personally have not seen a decrease in velocity but I have seen where an increase in powder charge produces little or no change in velocity.
Some powders especially double based powder, which most are today, are designed to function within a narrow set of parameters where too much or too little can both have bad results. Spiking pressures are the most common result.