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More 303/25 testing
Old 02-08-2014, 10:19 AM
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Default More 303/25 testing

Having had issues with this rifle and round recently after having a few years break I took a similar but slightly different approach this time. My new Frankford Arsenal digital scale arrived so I decided to test it against my Lee Safety Scale which is a balance scale. After zeroing it I carefully measured 10gn of AR2209 (H4350) into the Lee scale and then put it on the digital scale (which has also been calibrated by the included weight.) The digital scale said 9.9gn.

So, it seems, there's nothing wrong with the Lee scale. Nonetheless, I used the digital one to be sure. This time I neck sized 12 of the once fired 303/25 brass and then, starting at 38.5gn, loaded 3 rounds per weight to load up to 40gn of ADI AR2209 powder behind the usual Sierra 90gn HPBT I prefer. I figured it was all safe with AR2209 having a guide max of 41gn.

It was a hot day at the range, already over 30ºC (86ºF) when I reached there but under the cool shelter at the firing line it was ok. Today the rifle, or ammo, had a new trick for me. The first 3 rounds, 38.5gn, shot ok, 1.304", and although the pattern was vertical the shots weren't consecutive - 1, 3, 2.

It was encouraging. The next 3 with a charge load of 39gn were less encouraging....the shots spreading wide in no particular order to 2.455".

The following 3 with the 39.5gn load were equally poor at 2.17":

But the final 3 with a 40gn load seemed to be getting better with shots 1 & 2 almost touching and a group 1.742".

But the really screwy thing about all of the cases was that all of them had a good deposit of soot on the case neck and shoulder:

This screams "cases not sealing due to too little pressure." The bolt was easy to lift but required a little additional tug to pop the cases, clearly because the soot was causing friction between the case neck and the chamber. So, where to go. I discussed this with some really experienced mates who've reloaded for many years and they came to 3 possible conclusions.
  1. The case neck and shoulder were work hardened while being necked down from .311" to .257" and accordingly the charge was not pushing out to seal the chamber.
  2. The powder charge was very mild. The maximum charge for 303 Brit of AR2209 is 48gn compressed and it's about 43,500 CUP. While 25 cal is necked down a fair way even the 41gn max is quite possibly too low to seal the case at the neck.
  3. AR2209 works best when loaded almost full and needs sufficient resistance from the bullet to ensure all the powder ignites in the case before the bullet leaves. If the bullet is seated too far out this does not happen and boat tails provide even less resistance because they have less surface bearing on the inside of the case neck per length of bullet.

That leaves me with the following solutions:
  • Anneal the neck and shoulders before reloading to soften them and ensure they seal.
  • Try hotter charges up to and over the recommended maximum.
  • Seat the bullet further in to make sure the powder ignites properly and burns efficiently rather than having blow-by down the neck and shoulders.

Any thoughts, lads? I'm sure I can count on Paul, Don, RJ and others for wisdom in this quandary. Remember, before suggesting issues with the rifle itself, this rifle shot sub-MOA for many years with previous brass and never suffered the issues I'm currently experiencing. I have not touched any of the mechanics or bedding between then and now.
Cheers & God Bless
22lr ~ 22 Hornet ~ 25-20 ~ 303/25 ~ 7mm-08 ~ 303 British ~ 310 Cadet ~ 9.3x62 ~ 450/400 N.E. 3"

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