440gr. Sub Sonic 450 Bushmaster

[Weazelwacker]

Ladies, Gents, or Whatevers.


I received the recommendation to join this site yesterday, while on 450Bushmaster.net. I have build a Ar15 .450B with a 10" barrel, and am looking to suppress it.

I believe that cast bullets might be the way to go as it is the only way to get the bullet weights I am looking for (ideally 420gr.), while staying within the proper diameter (without swaging). The attached photo is what I am looking at right now, which does not have a gas check, and I am told that with the velocity I am looking at it should not be a problem.


So this is where I am at so far. My idea was to use a heavy bullet and the right powder (Lil Gun maybe??) to get around 950fps. It may be obvious that I have never cast bullets before, but I do have a small amount of experience in reloading. I am looking for what ever knowledge the collective community has. Also I have no problem with reading material so please (past experiences speaking), if you are just going to tell me to read the forums, don't bother it would take years to get through them. If you have a particular page in the massive database of forums, then please point me in the right direction.

[jmorris]

I run my 458 socom with 405gn JSP subs using HS-6 and HS-7 closer to 1050 FPS, good hog killers. Only ran my 450 BM with supers but there isn’t a lot of difference between the two other than bullet choices.

You won’t need a gas check but I only run jacketed or coated lead through my suppressor because it’s not one I can easily take apart to clean (I welded it vs threaded the end cap).

[6.5 CM]

Many 450 BM barrels have gain twists which IME didn't do well with cast.

[longbow]

Can't help with 450 Bushmaster specific questions... or really much on subsonic but still might have some useful info on boolits and casting.

You should slug the bore to determine groove diameter. You want your cast boolit to be at least 0.001" over groove diameter after sizing (or as cast if you are not sizing). You might want to order 0.002" or 0.003" over groove diameter then experiment with sizing to get best performance. I like to run a couple thou over groove diameter.

That looks like a Accurate Molds design in your post. If so Tom will make what you want... exactly to diameter and weight.

What is the rifling twist? If not fast enough you will not stabilize a long heavy for caliber boolit at low velocity. I would think you'd want a pretty fast twist for that boolit. A quick look at an on line twist calculator says 1:19" for minimum stability so you'd want faster like maybe 1:16". Not sure what's available. Hmmm... on the other hand the JBM calculator says twist is marginal at 1:30" which seems slow to me but...? That may be a good question to ask here and on other sites... what is the minimum twist rate for your 420 gr. boolit at subsonic velocity.

You have the rifling twist you have so if not fast enough to stabilize the long heavy boolit then you either use a shorter boolit or buy a faster twist barrel.

I agree that you should not need a gas check at that low velocity or even into supersonic velocities. I use all PB boolits in my .44 mag. Marlin and run up to max. jacketed load data with no issues so your Bushmaster shouldn't need a gas check... unless the supressor is an issue as small bits of lead may blow off as the boolit passes porting.

Not sure if you will find 450 Bushmaster info but you might try searching for "cat sneeze" or "mouse fart" loads. There are a number of threads with light load/subsonic load info that may be helpful.

Most important out of the above is determining your groove diameter then get a mould to suit (0.001" to 0.002" over groove diameter) and rifling twist.

A bit generic but I hope of some use.

Longbow

[Weazelwacker]

I'm currently running a twist rate of 1:18. Ill have to slug tomorrow when I get off work. hope I have a fishing weight the right size. You are correct the cast is from Accurate Molds, its not exactly what I'm looking for but it does a good enough job for now.

Another question now that I have seen the coated boolits; does the cast diameter change if you coat them, or is it a small enough difference not to worry about it?

[kbstenberg]

Like longbow said you have to know what the throat is sized at before ordering a wrong sized bullet. I could send you some carosafe (sp) to make a cast of the chamber. You Tube has some videos on how to making a chamber case. Send me a PM if interested.
PC adds some to the dia of the bullet. Generally .0015 Tom at accurate molds is first class tell him your needs and he can make what you want. His molds are a little on the pricey side but they are very high quality.

[longbow]

Here is a design I was looking at (maybe still am) for a .44 mag. "Whisper" load. I scaled it down to .434" diameter at about 400 grs..

As is it may be a bit heavy but you could get Tom to drop a little weight keeping same basic design. Not real clear by the info but this is a Dr. Richard Gunn design shown on "Gunwriters on the Web":

http://guns.connect.fi/gow/QA7.html




Heavy subsonic .45 bullet & nomenclature of special loads

Thank you for the information that you sent. I e-mailed NAMMO-LAPUA Oy about their trans-sonic research but have not yet received a reply.

Attached is a copy of a 480 grain .45 caliber bullet that I designed for use with the .45 Colt or the .45-70. The bullet mould is going into production at N.E.I.

According to the computer, 10 grains of 2400 should push this bullet to 900 fps from a 24" barrel with a maximum pressure of 35,000 psi and a muzzle pressure of 650 psi. Maybe it will qualify as a heavyweight "cat's sneeze?"

Dick

Accurate could make this for you in a size to suit your groove diameter. On that note, I'm not a semi auto guy so usually size boolits to just fit the throat and be at least 0.001" over groove diameter. If fitting the throat means 0.002" or 0.003" over groove that works for me. With a semi you need clearance for feeding and a large nose or too close to throat fit may cause chambering issues. The Gunn design if seated deep to the crimp groove shouldn't be an issue as there is no throat diameter nose sticking out. If seated out further that could be an issue so the portion in the throat would need a bit of clearance.

I've posted this drawing before but so far no-one has had a mould made that I know of anyway. If I get some toy money to get a rifle made up I'll try it in .45-70, 444 Marlin or .44 mag.

Should be a good boolit design. Just a thought.

Longbow

[GARD72977]

Many 450 BM barrels have gain twists which IME didn't do well with cast.

I have not seen Gain Twist in AR barrells. What Manfacture are using them?

[Tackleberry41]

Ill be watching, want a sub load for my 450bm. Where I went looking for a mold was accurate. Any mold heavy enough in that cal comes with a crimp groove for use in revolvers. Need one wout a crimp groove for the BM.

Going that slow can usually get away without a gas check, but never know w some powders, lil gun tends to burn hot. Wonder if there is a 4198 load that will work with heavy bullets.

[longbow]

I should note that since 450 BM headspaces on the case mouth any crimp groove is meaningless. Tom can set up the driving bands to give you a spot for the case mouth at the seating depth (nose projection) you want.

[jmorris]

Another question now that I have seen the coated boolits; does the cast diameter change if you coat them, or is it a small enough difference not to worry about it?

I size after I coat, so diameter is always the same.

My 450 BM cases hold 59gn of H20 so a little less volume than 61gn for the 458 socom but I use 14.3gn of HS-6 and 15.4 of HS-7 averaging right around 1000 FPS using 405gn bullets.