Trying to understand my jump and minimum seating depth

[aussiepaul]

Hi all, I'm new to reloading and have come across an issue that I would appreciate some advice on. I measured my cartridge base to Ogive to determine how high to seat my projectiles and realized I have a large jump. I have a Mossberg MVP 5.56 Nato, and I'm shooting .223 brass and shot around 1500 rounds through the rifle. I have been shooting Blitzkings 55gr, so I have heaps of once-fired ADI brass that I will be using. The issue is I used a Hornady OAL Gauge with the full-sized ADI brass (measured 1.750") with using a Hornady ELD-Match 52gr projectile. This measure to 1.988", but that means the projectile only is sitting in the case by 0.166 without factoring for any setback. I thought something was wrong, so I did the Alex Wheeler method and got pretty much the same result. Even a 20 thou setback means the projectile is only sitting in the case by 0.188 thou as the projectile is only 0.802 long. I spoke with a guy down at my local gun store, and he said to set it back enough, so it fits in my magazine, but I bench rest, so I am happy loading the ammo one at a time directly into the chamber. My question is compared to a blitzking, the difference in the CBTO is massive, the blitzking CBTO is 1.836" compared to my rifle, which is 1.988" but factor for a 20 thou setback and call it 1.968", this is still a difference of 0.132". Is this jump too long, and why is it so long? Is it a quality issue? And what would be the minimum seating depth for the 52 gr?

 

[cajun]

What your finding is quite common in an off the shelf rifle. I usually like to keep one caliber,.224 in your case, of bullet in the neck. Also know that a lot of precision rifle competitors are finding that great accuracy can be found quite a ways off the lands. Granted these guys shoot a lot of rounds but it is a very interesting theory.

Bullet Jump Research: Executive Summary & Load Development Tips

This is the last post in a series of articles focused on bullet jump research that has been conduct...

precisionrifleblog.com

 

[aussiepaul]

Thanks for your advice. I might start at a safe seating length and then start moving forward after I play around with the projectiles and powder weights

 

[338 dude]

Welcome to the forum from Tennessee

 

[aussiepaul]

Welcome to the forum from Tennessee

Thanks 338 dude, glad to be here.

 

[Leadriver]

I wouldn't drive yourself crazy chasing the lands, if you have a magazine I would load them to fit in there. Adjust your powder, bullet or primer combo to see what will tighten the groups. You would be surprised at just changing the primer will do, everyone I have talked to says it doesn't make a big difference, but in my testing it can take a 1 moa group to a .750 or a bit less. It's all about tweaking one thing at a time until you get your desired results. Also a wood of advise, if you get to 1/2 moa stop and be happy.

 

[Varmint Hunter]

While it's a "rule of thumb" to have one caliber (.224") in the case neck it isn't needed. It's more important when bullets are rough handled like having cartridges in your pocket or loading for a semi-auto rifle. Carefully single loading from the receiver makes .224" of neck bearing contact completely unnecessary IMO. Look for an accurate node and shoot.