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Bullet seating question

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GSMAlifer:
I have been trying to get my mind around a seating issue that I am having currently, with 9mm & .357 Mag bullets, where the C.O.L. varies by several thousandths of an inch.  The manual calls for the C.O.L. to be 1.075”, so I set the Redding micrometer seating stem for that measurement.  Of the first ten rounds, the COL measured from 1.080 to 1.073, with most being 1.0755 (on a Frankford Arsenal digital caliper).  Since the die was locked in with nothing seeming to be loose, I couldn’t grasp why the different seating depths.  John Kies suggested I measure the bullets and I found that while the diameters of the 9 mms were exactly .355”, the lengths varied by as much as .006”.

Even though this variance could account for most of the swings in seating depth, I found it hard to grasp how that would make a difference.  If the seating stem pushed all the bullets the same distance, by the bullet nose, the COL should be the same ..... with the longer bullets just going further into the case.  This would be worrisome because of the resulting higher pressures on some rounds, but this apparently was not happening.  Since the bullet seating stem is supposed to be pushing on the bullet’s ogive, not the nose, I figured that the different bullet lengths must also result in differing ogives, resulting in bullets being seated to the same depth in the case, but giving varying COLs.  But the 1.073” measurements made me suspect that in some cases, the longest bullet lengths may be getting pushed on the nose, which results in the shortest COLs; those below the 1.075” setting.

Would some of you old hands at reloading care to comment on my conclusions?  The bullet being used is the Winchester  115 gr JHP, WB9JHP115, and I was surprised that the length varied by so many thousandths.  My biggest question, if the above reasoning is valid, is what do I do now, to insure I don’t set any bullets too deep?

winchester:
According to Redding:

There are many factors that can cause bullet seating depth to vary when using our Competition Seating Die. First, make sure you're comparing bullet seating depths correctly. You cannot check bullet seating uniformity by measuring cartridge overall length off the bullet point. You must use a bullet comparator, like our Instant Indicator, to compare bullet seating depths. A comparator contacts the bullet at the bore diameter contact point. This is important, as bullets can vary slightly in overall length.

We have designed the seat stem in our Competition Seating Die to contact the bullet ogive as far down as possible. Our Competition Seating Die features a bullet guide that is only .0005-.001" larger than bullet diameter. This tight fit between the bullet guide and bullet ensures that the bullet is seated straight in the case neck. It also limits how far down the ogive the seat stem can contact the bullet. If the ogive of your bullets aren't uniform, you may notice a slight difference in seating depth. Generally, this isn't a problem as modern bullets are very uniform. In rare instances, when using inexpensive bulk bullets, you may find that the bullets were made on several different machines and then blended.

If your loading press is worn, the ram may not stop in exactly the same spot each time you raise it. Obviously, this will cause variations in bullet seating depth. Although our instructions warn against it, raise the shellholder and adjust the outer, threaded die body to make light contact with the shellholder. (Make sure you keep the contact light, so you don't damage the die.) This creates a "dead length" seating chamber that is unaffected by where the shellholder stops. The only disadvantage to using the die adjusted this way, is that it may be awkward to read the micrometer if it ends up on the back side of the die.

Inadequate or excessive neck tension can also cause bullet seating depth variations. If you're using a bushing style sizing die, make sure you've selected the correct diameter bushing to size the case necks. Our current recommendation, is to select a bushing that is .001" smaller than the neck diameter of your loaded cartridges. (See the bushing selection newsletter in the "Tech Line" section of our website for more information.) As cases are fired over and over, their necks become progressively harder. This can cause the necks to "spring-back" excessively when they are sized, which reduces the neck tension on the bullet. Either anneal the case necks after several firings, or discard the cases and start with new, soft ones.

Heavily compressed loads can create problems when seating bullets. Our Competition Seating Die is not a powder compression die. The excessive force required to seat a bullet on a compressed load can damage the die and may cause seating depth variations. Switching to a faster burning or ball powder may eliminate the need to excessively compress the powder charge.

GSMAlifer:

--- Quote from: winchester on January 19, 2015, 09:48:47 PM ---According to Redding:

You cannot check bullet seating uniformity by measuring cartridge overall length off the bullet point. You must use a bullet comparator, like our Instant Indicator, to compare bullet seating depths. A comparator contacts the bullet at the bore diameter contact point. This is important, as bullets can vary slightly in overall length.
--- End quote ---

Whoops!  There it is ...... exactly what the problem would be.  Since I don't have a comparator, I'll have to look into getting one.  But that begs another question:  do loading manuals present the C.O.L. as measured from the "bore diameter contact point" or the nose of the bullet?   If they give the "nose measurement", how do you convert that to what the comparator reads?  I'll have to get one of those and read their instructions.

Thanks, Winchester, for the good info. 


--- Quote from: winchester on January 19, 2015, 09:48:47 PM ---In rare instances, when using inexpensive bulk bullets, you may find that the bullets were made on several different machines and then blended.

--- End quote ---

I believe this could be the case with mine.  Though I ordered the bullets from MidwayUSA in bulk, they arrived in bags of 100 and they could have been from different lots, from different machines, and then I just dumped them all into a container before I began, so they are now "blended".

Thanks again.

GSMAlifer:
Followup to last post:   In a "senior moment", I seem to have forgotten that I already have a bullet comparator, but they are only for rifle cartridges.  So I am back to square one on measuring C.O.L. with these bullets.  Since the only measurement available seems to be from the nose of the bullet, I need to determine the best way of setting up the seating die and trust that it will then seat all the bullets to the proper depth, without regard to the actual overall length of the cartridge.

I am sure I'm not the only person to have had this issue.  Or is it really an issue?  Am I worrying over something that isn't of much importance?  I never load to the max powder charge anyway, so maybe the fact that some bullets get seated a tad deeper than others wouldn't make a lot of difference.  After all, I've been loading for a lot of years and I'm sure it's been true before and I just ignored it.

cquist:
I really dont think its an issue. Thats about as short of a COAL as I see in 9mm but have some factory ammo much longer. If they function in your gun and group alright I dont think you have anything to worry about.  The load I have using seems to work well with a 1.080-1.085  (HP) COAL and functions in all 6 of my different brand 9mm guns. No brand loyalty here.

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