Thoughts on Bullet Seating Depth

[trodrig]

Hi all! I'm working up a new hunting load for my bolt action rifle in .280 Remington. I'm using the 139gr Hornady SST bullet. My question is on the overall length and bullet seating depth. This bullet has a cannelure, however, I do not plan on crimping the bullet. The overall length specified for this bullet in the Hornady manual (3.345") puts the cannelure well outside the mouth of the case. Using the Hornady Bullet Comparator and Overall Length Gauge I obtain roughly the same overall length specified in the manual to achieve 0.020" of free bore. I have always been under the impression that bullets with cannelures should be loaded with the mouth of the brass at about the middle of the cannelure. However, that is going to put my OAL at less than 3.330" which is way shorter than the both the book listing for this bullet and what I measure for 20 thousandths of free bore. Where do you all think I should start with my seating depth? Disregard the cannelure?

Thanks in advance for assistance!

[Guy Neill]

If you are crimping, then yes, you need the case mouth to the cannelure. Otherwise, you are free to vary the length as you see fit.

Remember, though, that the data was developed with the OAL listed. If you go shorter, it will increase pressure.

Also, while 0.020" off the rifling is the minimum, you should also be certain the rounds will go all the way in the magazine before settling on that length. Sometimes the magazine box isn't long enough to allow long seating.

Guy

[trodrig]

If you are crimping, then yes, you need the case mouth to the cannelure. Otherwise, you are free to vary the length as you see fit.

Remember, though, that the data was developed with the OAL listed. If you go shorter, it will increase pressure.

Also, while 0.020" off the rifling is the minimum, you should also be certain the rounds will go all the way in the magazine before settling on that length. Sometimes the magazine box isn't long enough to allow long seating.

Guy

The fact that the OAL in the book leaves the cannelure well outside the mouth is what concerned me a bit. The first thing I thought of is that if I need to seat to the cannelure I'm going to have to start very low on the powder charge because pressure is going to be increased. But, when the OAL gauge and bullet comparator gave me about the same length to be 20 thousandths off the rifling, I figured I was good to go with that. Again, if not crimping, cannelure should be irrelevant.

Good point about making sure the loaded rounds fit the magazine at that length. Hopefully the manufacturer wouldn't have put 3.345" in the manual if that wouldn't fit one of the most popular bolt actions around (Rem 700) but, it is something to verify!

Thanks!

[Guy Neill]

It's unlikely the load data people concerned themselves with the magazine length. Some because they rarely, if ever load the magazine, and because of the great differences in various makes of rifles.

Many have worked up a great load, only to find the magazine box would allow more than one round max.

Good luck.

Guy

[trodrig]

Double checked the magazine last night and there's tons of room with the bullets seated to 20 thousandths off the rifling. Loaded up 4 different powder charges last night and we'll see how they shoot this weekend. I'm getting a surprising amount of run out (0.005"+). Not sure why. I'm using the Redding comp seater die, everything appears to be adjusted correctly. Anyone have any suggestions on what to look at for bullet run out?

[Guy Neill]

Nice that your magazine box gives you the ability to play with the cartridge length.

Just to be clear, is run out dealing with concentricity, or overall length?

If concentricity (which I'm assuming it is), even with a comp seating die there can be play depending on how well the die fits the bullet (I don't recall at the moment if the Redding is a straight-line seater or not (I'm thinking not), but either can have tolerance situations). It also may relate to how well the seating punch fits the bullet nose/ogive. There is also the possibility that the seating punch is no concentric to the body of the die as it is set.

If the run out you are seeing is OAL, it's most likely do to variances in the bullet length. In general bullet length is not a closely held tolerance.

Guy

[trodrig]

The run out I'm talking about is concentricity. I'm seeing about 5 thousandths or more of run out. I was hoping to hold closer to 2 or 3 thousandths. I know variations in neck thickness can cause bullet run out problems. I believe the brass I'm using is not that great so that could be part of the problem. Some rounds will be around 3 thousandths with others 5+. So, a good amount of variation. I'm thinking I'll get a batch of Norma brass which is supposed to be better quality and see if my results are any better there. I'll also check on how well the seating stem matches the ogive of the bullets I'm using.