39 gr of little gun with 200 XPB too hot?

Talk about your 450b reloading experience, ask questions, etc...

Moderator: MudBug

Forum rules
Please try and keep it safe!

This information is the responsibility of the community, not the forum. 450bushmaster.net is not responsible if you blow yourselves up.

Re: 39 gr of little gun with 200 XPB too hot?

Postby mcb » Fri Sep 01, 2017 11:01 pm

I got very similar results with that bullet when I tested it a few weeks ago. Nearly identical load to yours.

20-inch Bushmaster 1: 24 barrel
Bullet: Barnes 200gr PBX
Brass: Hornady (once fired)
Primer: Winchester Small Rifle
OAL: 2.240
Crimp: .475
Powder: Hodgdon Lil'gun
Charge 2: 39.0gr
Average: 2614fps (3033.9 ft-lbs)
Std Dev: 36.63 (5-shot)

From my earlier thread: viewtopic.php?f=5&t=15306
User avatar
mcb
 
Posts: 70
Joined: Fri Apr 07, 2017 10:22 pm

Re: 39 gr of little gun with 200 XPB too hot?

Postby Hoot » Sat Sep 02, 2017 9:03 am

I've said this before and its not just my anecdotal opinion, as many other reloaders have noticed it as well. Regardless of what they publicly say, Hodgdon changed the formulation of Lil Gun several years ago. It is definitely hotter than it was back when I first began reloading this caliber. There are other factors as well that impact resultant velocities. Back then, I was using a factory Bushmaster 20" upper with its chromed chamber and bore. I made a Cerrosafe cast of my chamber the first time I ever removed the barrel from the receiver. (Its a lot easier with the barrel off). Anyway, barrel revealed two noteworthy observations. My chamber was a little loosey goosey compared to three other brands of barrels and it was slightly out of round, IE not totally coaxial to the bore on all sides. The barrel still threw some amazing groups. A roomier chamber causes lowers chamber pressures as it allows the brass to expand more during ignition. Another factor that's not discussed much around here is the fact that new barrels have more friction in the bore until they're broken in. New actions too, but that's not the thrust of this discussion. I mentioned that because AR cycling smooths out the more they're cycled. Anyway, that bore resistance contributes to higher pressure and velocities as well. About the only way to shorten the break-in time is too clean often and include some JB compound or Remington 40X solution treatments in those cleanings. There's the Tubbs abrasive bullet thing but I've never tried it nor feel absolutely good about trying it. Old, blackened, neglected bores would be a different thing however, though they can be dealt with also by using JB compound and the Armstrong method. ;) Copper jacket fouling buildup contributes to more stiction in the bore and it builds up faster on new bores that haven't been broken in. Abrasive cleaners like JB add Rem 40X are very effective at removing copper buildup before it becomes a problem requiring a lot more work to remove. Remember the drag of copper on copper vs copper on steel is significantly higher and even more so as the barrel heats up. Clean after every use. "Ounce of prevention, pound of cure".

All of these lesser factors can contribute to more pressure and resultant velocity regardless of which powder you use. Think "Tolerance StackUp". I haven't even brought up ambient temperature, the "800 pound gorilla in the room".

Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.
User avatar
Hoot
 
Posts: 5083
Joined: Tue Feb 09, 2010 9:34 am
Location: Minnesota

Previous

Return to Reloading for the 450b

Who is online

Users browsing this forum: No registered users and 26 guests