Factory match tolerances

[JaysonCraig]

Out of curiosity last night i took the calipers to two boxes of Federal 175gr Sierra Matchking BTHP's one box of GM308M2 and one of XM308M2 (nickel plated) they both have the same packaging , 2 sets of 10

Anyway what i got was (in order)

GM308M2
pack1 pack2
2.806 2.811
2.814 2.809
2.811 2.808
2.807 2.811
2.806 2.807
2.805 2.805
2.811 2.804
2.800 2.808
2.806 2.806
2.809 2.810

I had a .14 inch variance in the 20 rounds
rearranged
2.800
2.804
2.805
2.805
2.806
2.806
2.806
2.806
2.807
2.807
2.808
2.808
2.809
2.809
2.810
2.811
2.811
2.811
2.811
2.814

Interesting groups develop. All of those were longer than 2.8 Now the XM308M2 box was typically shorter

XM308M2
pack1 pack2
2.803 2.798
2.809 2.789
2.803 2.798
2.793 2.797
2.795 2.805
2.799 2.802
2.799 2.799
2.797 2.797
2.798 2.801
2.797 2.805

here i had a .2 inch variance
reordered
2.789
2.793
2.795
2.797
2.797
2.797
2.797
2.798
2.798
2.798
2.799
2.799
2.799
2.802
2.803
2.803
2.805
2.805
2.807
2.809

these were 2 random box pulls, and i assume they were packaged randomly as well. How much do you think this affects shot placement? Is this typical tolerance?

 

[Silverado]

Are you talking about the overall length of the loaded cartridges?

Bullets vary in their length from base to tip. They all vary, some quite a bit. Bullets with polymer tips tend to vary somewhat less in my experience than HP or SP bullets.

Get a bullet comparator that measures the ogive of the bullet. I think you'll find that they vary a whole lot less in this dimension.
EDIT to add: the OAL I mean. I've measured whole boxes of SMK bullets with a comparator, and the tolerance from base to ogive was less than .001". The tolerance from base to tip was about .007". Remember that it is the ogive that contacts the rifling, not the tip of the bullet.

OAL or COL is a convenient way to measure, but is only important in terms of magazine length.

 

[JaysonCraig]

good tip

 

[Silverado]

Thanks.

I think understanding where variances in bullet construction occur would eliminate a lot of confusion for some reloaders.

It's not at all uncommon for my reloads to vary more than .005" overall, but the measurements to the ogive are very very close.

 

[Fassteel]

Thanks.

I think understanding where variances in bullet construction occur would eliminate a lot of confusion for some reloaders.

It's not at all uncommon for my reloads to vary more than .005" overall, but the measurements to the ogive are very very close.

I just got one of the comparators from Sinclair's very interesting way to measure your ammo, really the only way for accuarcy of reloaded ammo. FS

 

[Silverado]

Exactly Fassteel! A comparator and OAL gauge are a must for loading precise ammo.

The comparator really shows that decent seating dies like Lee's actually do a great job.

 

[Ganderite]

Like Silverado said.

A HP Match bullet has a lead slug in it, with the jacket formed to a point. About a quarer inch of the pointy end is hollow (no lead). It is difficult to hold a dimension to this section. The variaton in a box of 100 bullets (OAL of the bullets) can be 15 thou.

Your bullet seater has a hollow cavity in it so that it is pushing down on the ogive (shoulder) of the bullet - not on the tip. So your loaded ammo should be quite consistent in the dimension of bullet ogive and the rifling - even though the cartridge OAL varies.

It is real easy to make a tool that will measure cartridge OAL from the bullet ogive to the base. Ask your gunsmith for a 1" piece of rifle barrel in your caliber.

Drop this piece on top of your bullet, like a hat. The piece will sit on the bullet ogive. measure from the top of the hat to the base of the case.