450Bushmaster.net

Looking for some subsonic load data for my 450 on a 20 in barrel 1/24 twist

I know we have some guys out here who have done some work on this. I'll try to find you a link.

I found four or five major threads that may help you out.

viewtopic.php?f=5&t=39&p=151&hilit=Subsonic#p151

viewtopic.php?f=5&t=719&p=4824&hilit=Subsonic#p4824


viewtopic.php?f=2&t=11083&p=29205&hilit=Subsonic#p29205

viewtopic.php?f=5&t=14263&p=44479&hilit=Subsonic#p44479

viewtopic.php?f=5&t=14190&p=43866&hilit=Subsonic#p43866

Thanks but I need some data for Imr 4227 on a 300 grain xtp-mag

540guns wrote:Thanks but I need some data for Imr 4227 on a 300 grain xtp-mag

450guns-
First, what have been your experiences so far with loading this bullet and powder with factory-recommended loads (30.5 up to 33.9 grains)? What have been the accuracy and velocities you have observed with various powder weights?

The Hornady manual shows a starting load for the 300-grain XTP mag of 30.5 grains of IMR-4227 for 1500 fps, as I posted on your earlier thread.

Given that nobody has worked out a subsonic load with 4227 & the 300 xtp-mag, this becomes a do-it-yourself project. If your work with supersonic velocities has proceeded as expected without hangups, then start with 30 grains and work down a grain at a time until your chronograph reaches a subsonic velocity of 1100 fps or whatever is a subsonic velocity at your location's temperature and air pressure. There may be some tweaking with fractional grains needed to produce a velocity close to 1100

Since 4227 is relatively slow and hence bulky for the 450B cartridge, you should experience few problems with inaccuracy caused by powder position in the case. However, it's difficult to predict what is likely to happen with ignition problems with decreasing powder charges. You'll almost certainly get case sooting, but that may be acceptable. It's also possible you may experience incomplete powder combustion caused by an insufficient buildup of pressure; this may leave a mess of unburned powder granules in your bore, chamber, and action. If this happens, then you will know that the powder is not compatible with this bullet for obtaining subsonic velocities.

Be sure to use a relatively hot primer for these trials. Also be sure to use a pretty firm crimp, although don't drop the mouth diameter below SAAMI specs.

Let us know how your trials work out.
--Bob

K thanks will do