Options for using PC boolits in tight throated M&P 9?

[jmac2112]

I ordered the new mold (35-126M) from Accurate Molds on Saturday, and it arrived today (Wednesday)! I've had speedy service from Tom before, but this is astounding.

I've already cast some boolits with it, and the measurements are right where they should be. I'll PC and load some up tomorrow and make sure they chamber. With any luck I'll get to shoot a Super Steel match this Saturday and I'll report back.

[DougGuy]

I can throat the MP9 barrel to work with .356-ish", but here's the deal.. All the salt bath hardened barrels, Glock, S&W, Poly framed Springfield, will only be throated by carbide tooling. No one stocks carbide throating reamers, they have to be custom ordered. 3 and 4 times the expense of high speed steel reamers, and the carbide goes away rather quickly, it wears quickly and cuts smaller and smaller throats, I only get about 10-12 barrels throated before they are only cutting .357" from .3585" when they were new. If you divide the number of barrels by the cost of the reamers, cost out of *my* pocket, runs about $30 per barrel before the reamer is just worn too small to throat any more.

I can take the barrel and throat it to whatever the reamer will cut, and you size until they plunk, and this will get you a great deal of improvement over the stock barrel. Send me a PM here on this forum.

I also throat them out quite long so that I can use a 1 degree leade angle, and the freebore actually acts like the front half of a Taylor Throat job done on a revolver, it gets the same effect in that it allows the boolit to exit the case and enter the throat which is smaller in diameter than the expanded case mouth, so it holds the boolit more concentric to the bore, and square with the centerline of the bore before it engages rifling leade ins which generally improves accuracy, these longer throats shoot lights out. They also provide less resistance which can translate to lower pressures so you can adjust with powder charges. It's just a smoother much more gradual transition from pulling crimp to engaging the rifling.

[jmac2112]

Just an update on my new mold, Accurate Molds 35-126M. Everything works great! I've put a few hundred rounds through my M&P Pro with no signs of leading, and even though I haven't tested the accuracy by shooting groups from a bench, it seems to be at least as good as it was. This is the first mold I've had that has allowed me to size the boolits to .358 AND get a decent OAL, and I'm loving it so far.

Even though the nominal weight is 126 grains, my boolits are averaging 129.5 grains. I recently bought a chronograph as well, since I'm tired of not really knowing what kind of power I'm making. I've heard that powder coated boolits move faster than jacketed for a given powder charge, and it must be true. I can reliably make 125 PF with room to spare using 3.6 grains of Win231. Extrapolating from the the load data that I have for 125 grain jacketed bullets, I was expecting to need around 4.2 grains, but that gives me 140 PF. I'll be loading for an upcoming Steel Challenge match using 3.4 grains, which makes for a very soft load. The brass lands only 2 feet away, but it runs the gun, so looks like all is well.

Anyway, thanks to all who contributed, and I'll post and update if I run into any problems with this boolit!

John

[fredj338]

IMO, no such thing as published data regarding OAL. The loaded round MUST fit your gun, regardless of what the book tells you. So 1st get your proper OAL then work the load up. If you do not want to ream the throat, then shorter OAL is the fix.
FWIW, you can not really extrapolate lead bullet vel from jacketed data. A lead bullet will go faster, coated or lubed, than a jacketed of the same weight, same powder charge. IMO, it is the better seal the bullet makes in the bore. I have found any slight vel gain using PC is very minimal, within deviation from day to day reloading.

[jmac2112]

Thanks for making those excellent points! I hadn't thought about lead giving a better seal, but I'll bet your right.

As to the other issue, it isn't so much the OAL per se that I'm concerned about, but the seating depth. I had a 125 gr. mold that made boolits requiring an OAL of 1.010, and a seating depth of about .285 (I may be mis-remembering, but it was something like that). It may be irrational of me, but it made me nervous to have to take a wild guess as to the start grains. I've heard numerous times that pressure does not increase in a linear fashion as you seat the boolit deeper and deeper.

What I would like to know is why do all the load manuals give the OAL when it's really the seating depth (plus bullet weight) that matters in terms of the charge? If they would at least give the dimensions of the bullets they are referencing, then you could figure it out for yourself, but they don't do that.

End of rant!