Question re: JHP vs FMJ RN

A

aridan

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I ran out of the Canadian BDX 124gr FMJ RN bullets, so I picked up some 147gr JHP Zeros. These JHPs are significantly longer than FMJs I used. Looking at Lapua reloading data for VV N320, I see that the same OAL of 1.142 is recommended, with 3.4-4.0gr for 124gr FMJ-RN Lapua, and 3.1-3.9gr for 147gr HP/XTP Hornady.

Since the recommended OAL is the same, and the JHP is a longer bullet, and the recommended charge is almost the same volume-wise, won't I be compressing the powder with the JHPs, causing excessive pressures?

Up to now, I loaded the FMJ-RNs at 4.0gr of N320 - I found that less than that caused occasional FTEs. The OAL is 1.155 which works well in my Shadow.

I was planning to go with 3.7-3.8gr for the 147 JHPs, is this about right for minor loads?
 
that is why you need a chrono. start at the minimum load and work up. if the longer bullet does raise your pressure then it should also increase your velocity and you shouldn't need as much powder. however the only way you can know this is with the chrono. do not assume that you can switch bullets and not have to work up a new load.
 
If your pressures are so low that you have fail to ejects the bullet will not make a big enough difference to cause any damage. Just start low and work your way up.

Personally I always stay well under max and use the same load for almost any bullet. Just start with a couple and look for pressure signs.
 
Thank you all.

This morning I determined the OAL for those JHPs using the barrel of my Shadow. The OAL is huge at 1,168". I had to back off to 1.160" just to have the rounds clear the mag walls. I then loaded 4 groups of 10 with 3.2, 3.4, 3.6, and 3.8gr of N320 and headed for the range.

I haven't had a single FTF, even with 3.2gr. Surprisingly, the 3.2gr also gave me the best accuracy, same as 3.6gr. I don't have a chrono, but I suspect the 3.2gr won't make the minor PF, it feels very soft. 3.8 was too snappy for my liking.

At the end, I'll probably settle on 3.5gr, and will shrink the OAL down to 1.155 or so, I had a couple of rounds catch the mag while loading it, but they all shot fine.

I am VERY impressed with the bullet, not only how soft it shoots, but also the ease of seating it in my Hornady die. The bullet has a shallow recess at the bottom which makes it stay on the case without belling the case too much. I think this should be perfect for a bullet feeder once I get it.
 
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