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H4350 Burn Rate Change?

 
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  #1  
Old 09-17-2013, 10:57 AM
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H4350 Burn Rate Change?

I have been loading 165gr NP's ove 58.5 grains of H4350 for a few years and getting velocities in the area of 2950 fps. I started on a new 8lb jug and started low to rework the load. The best accuracy was at 57.5 grains. I built a few more to get velocities and was suprised to see an average of 3090 fps. OAL, gun, primer, bullets, and chronograph are the same. Drops seem to match the velocity at 620 yards. Any ideas why the velocities suddenly jumped?

The brass does not show signs of excess pressure. Bolt lift is normal.
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  #2  
Old 09-17-2013, 06:10 PM
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Re: H4350 Burn Rate Change?

All powders vary by lot, and it's good that you were cautious.
But it's hard to say anything about anything with so many changes going on at once.
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Old 09-17-2013, 06:12 PM
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Re: H4350 Burn Rate Change?

As best I've been able to determine H4350 is mythical, and therefore any burn rate changes are strictly theoretical.

Seriously though, lot to lot variation? Remember H414 and W760 are actually the exact same thing, though I've seen burn rate charts put them several powders apart.
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Old 09-18-2013, 07:28 AM
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Re: H4350 Burn Rate Change?

Quote:
Originally Posted by Mikecr View Post
All powders vary by lot, and it's good that you were cautious.
But it's hard to say anything about anything with so many changes going on at once.

The only change was 1 grain less powder. I may have to find someone who can loan me a different chronograph to check my results.
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  #5  
Old 09-18-2013, 09:39 AM
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Re: H4350 Burn Rate Change?

Bright sunny day and cloudy day causes about a 100 FPS difference in my chronograph. Bright sunny day is consistent, where cloudy day is not. Sensor screens need a consistent lighting. I do ALL chronographing for load workups on a sunny day, and shield the sensor slots from any direct intrusion of sunlight, which also makes a difference.

A load worked up on a sunny day and then rechecked on a cloudy day will show a velocity change.

Low sun angles on bright sunny days are also to be avoided. The first couple of hours and last couple of hours are not for chronographing.

A precharched pneumatic air rifle that is pumped up to the same pressure every time is consistent in velocity with match grade pellets. Unlike firearms, as long as air pressure is the same it is the same, as measured by an accurate gauge. Air can be added or bled off if there is a big temp change. Air pressure is air pressure is air pressure. When pumping up a PCP, the air chamber gets hot, and pressure will reduce in a few minutes. I take a couple of extra minutes and add air as pressure drops as the air chamber settles to ambient pressure.

If you have a high quality PCP air rifle (Benjamin Marauder, BSA, Daystate, FX, Air Arms, etc.), then it is a very accurate checker of your chronograph.

A string of a half dozen shots will vary by about 3 FPS in my BSA Lonestar .25 cal.

Powder can vary significantly from lot to lot, but I have not found that to be the case with Hodgdon powders lately. Liability issues and modern manufacturing practices make canister powders quite consistent.

Primers can change from lot to lot . I bought a lifetime supply of WLR primers during a short time period some time ago. That's one problem I don't have to contend with. Winchester primers of today are not the same as years ago, just like their brass.

Last edited by FAL Shot; 09-18-2013 at 09:40 AM. Reason: correct mistake
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Old 09-18-2013, 10:17 AM
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Re: H4350 Burn Rate Change?

"Low sun angles on bright sunny days are also to be avoided"

This may be a large part of the problem. It has been very hot and I was shooting early in the morning. I'll try a few later in the day when the sun's angle is a little less acute.
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  #7  
Old 09-18-2013, 03:28 PM
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Re: H4350 Burn Rate Change?

I have switched lots of H4350 with all other components identical with identical powder charge and blew primers. Had to pull the other bullets. I now back off and work up every time I change powder lots.
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