LiveLife
Member
+1. I think rcmodel's method is the best way to determine why your finished rounds are not fully chambering as different brand bullets (even though they are same FMJ/RN profile) can have different shape (ogive) with different length of bullet base/bearing surface that engages the rifling.rcmodel said:Different brands of bullets vary slightly in ogive shape, and will contact the rifling sooner or later then the bullet listed in the data.
Correct taper crimp should measure about .376" at the case mouth using .355" jacketed bullets.
I suggest you do this.
Completely 'color' a loaded round with a Magic-Marker or Dry-Erase marker.
And then force it into the chamber.
Where the marker ink rubs off the case, or the bullet, is your problem.
I not only drop the round in the chamber but also spin it side to side slightly to enhance the marking. If the bullet is hitting the start of rifling to prevent full chambering and/or the marking is rubbing off, then you need to decrease the OAL/COL until you can fully chamber the round and spin freely.otisrush said:And if it rubs off on the bullet - then reduce the COL?
Not really and also depends on several things: chamber size, out-of-round bullets, variation in case wall thickness and tilting of bullets during seating.So - if it rubs off the case: Then taper crimp needs to be adjusted down so as to reduce mouth diameter?
As rcmodel posted, I usually use no less than .376" taper crimp for .355" diameter jacketed/plated bullets. Some plated bullets are sized slightly larger than .355" as factory sizer wears and if not changed out frequently, could be sized .3555"-.356". So with some plated bullets, I will use .377" taper crimp so as to not cut into the thin copper plating.
Most SAAMI spec barrels will allow taper crimp up to .380" unless the bullets are out of round.
How can bullets be out of round? From manufacturing and/or from handling during shipping. With plated bullets, by the time copper plating is done and bullets tumble cleaned/polished, they could be out of round and many manufacturers double strike (push through size) to ensure roundness of plated bullets. And shipping companies/USPS will rough handle the bullets from tossing boxes to dropping boxes and the impact force will squish jacketed/plated bullets with softer lead/alloy core. So by the time you receive the bullets at your door, they could be out of round.
Out of round bullets will produce out of round finished rounds at the case neck. I experienced this with different brand bullets as bullet diameter measured with calipers will show oval shaped bullets instead of round (when I measure bullet diameter, I will measure at multiple locations not just one location).
How did I know that the out of round bullets was the problem and not the amount of taper crimp? Because verified round bullets did not produce out of round case necks and they chambered without rubbing the barrel. When I measured the rounds that did not fully chamber or rubbed the barrel, case neck measurements were different and pulled bullets were out of round.
Another thing that could produce out of round case necks is tilting of the bullet during seating. When I was in a hurry during one reloading session with Winchester 115 gr FMJ bullets, I saw noticeable bulging of case neck on one side only. Caliper measurements shows out of round case neck which was the result of tilting of the bullet during seating. After me slowing down and more carefully setting the bullet on flared case mouth, the one sided bulging was less of an issue.
But when I noticed the slight uneven bulging of case neck continue, I got curious and measured the case wall thickness. To my surprise, depending on headstamp, case wall thickness consistency varied quite a bit. They ranged from being thin on one side like .010" to thicker like .012"+. Since case neck gets formed by the taper crimp, I think case wall thickness variation is less of a contributing factor to out of round case neck but will stack on top of out of round bullets.
If your finished rounds' bullet is not hitting the start of rifling but the case neck is rubbing the chamber from being out of round, what can you do? One option is using Lee Factory Crimp Die to post size the finished round so the dimensions are within SAAMI specs. Another option is to increase the taper crimp to the point where the finished rounds will fully chamber. But extreme use of these two options may reduce neck tension by reducing the bullet diameter while brass spring back that will result in bullet setback.
So if you are resorting to these options to "fix" the finished rounds' being out of round, I would check the neck tension by measuring OAL before and after feeding/chambering from the magazine and releasing the slide without riding it. If the bullet setback is more than several thousandths and you are using near max load data, you have issues that need to be addressed or you could experience over max chamber pressures.
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