Saturday, July 18, 2015

300 Win Mag - Superformance - 208gr Amax - Playing with C.O.A.L (cartridge overall length)

Playing with case overall length

DISCLAIMER/WARNING FOR NEW RELOADERS:  Any load data in this article is for ONE particular rifle (mine).  If you try this load in your gun, it may not feed and worse, it may feed but blow up your rifle causing injury or death. Be very carefull when extending your Cartridge Length over the reloading book published values as there can be dangerously huge increases in pressure. 

If you have been following this blog, you may have seen that for other than the SIE HPBT 155gr,  and 175 TMK,  accuracy has been dismal so far with this bullet powder combination in my rifle.  Before I give up, I decided to play around with the COAL and see if things improve (usually they do).  I took a measurement using the loose bullet technique . This is where you take a fired case and lube the neck, put a bullet in seated just enough to hold it in the case and then put it in the gun and close the bolt. It may take a bit more effort to close the bolt but shouldn't be forced.

If you find you are exerting a lot of effort, you probably made the mistake of using a resized case (resized neck is tighter) or you forgot to lube the inside the neck. 

Another approach you can use is to just seat the bullet in a resized (unprimed) case and try to close it in your rifle. If there is any resistance, seat the bullet a little lower and try again. Keep going until you are able to close the bolt on the cartridge will little or no resistance. This should be close to your max overall length.

The first method will put you just over the max oal (lands tend to dig into the bullet and you definitely don't want to load at this length). I usually back off this .010 and then color the bullet with a dark sharpee (see picture right) and put it in the gun again to see if it makes marks on the bullet ogive.

If it does, I back it off another .010 and try again. I generally repeat this process until I can close the bolt on a cartridge without leaving marks on the bullet ogive. For my Savage 110 FCP, this measurement was 3.635".  I then back off another .010 and use that as my starting COAL. My max COAL I record at 3.640 which is the length where this bullet would be lightly touching the lands. I always record this info in my reloading notebook since this process is a pain to repeat.

I loaded 10rds at 3.625 which is way over my magazine length (3.510).  I wanted to try a light load and a heavy load so I used my min (66gr) and max (72gr) from my previous test results. I expected that the velocities would be lower since I was seating the bullets out quite a bit (creating more capacity). 

Next I wanted to load to the max length that would reliably work in my magazine.  I again made 10 rds at min and max powder charges using the COAL of 3.500. 


Things started off a bit rough as I my first 10 shots proved to be a  WTF load.  This is to say that groups were just over 4". Here is the data.

PPU 3x fired brass neck size only, Superformance, CCI #200, 208gr AMAX

5 shot groups fired at 100 yards


In summary, the trend I noticed was that as I increased the OAL , accuaracy seemed to get better however, if velocity was not above 2800, accuracy was degraded. The best load which was with 3.615" COAL and 71.5gr Superformance showed a little sign of over pressure. There was some slight cratering on the primers on about 3 out of 10 shots.

Here is a picture of those 3. You will notice a little cratering on the primer strike and some light circles on the "300" from the ejector.

For now I am done playing with this bullet powder combination.  I didn't seem to have much success without overpressure.  The 208gr amax seems to do better around the 2900 - 3000fps mark and I just can't get there safely with superformance.  I have had great results with superformance and 155s and 175s however and you can read about that in my other blog posts.

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