Thread: . 284 Winchester

Some related snippets of information on the .284 Winchester

From time to time I see mention of .284 reamers that are supposedly ground to cut chambers specifically for use with necked-up 6.5-.284 brass. Having looked into this I can find no evidence of any dimensional differences between the bodies of the two cases that would require this.

Below are the drawings taken from the QuickLOAD library showing just the metric dimensions for comparison. Other than the change in chamfer angle on the bottom edge of the rim there are no other differences below the necks that can be identified.





Here is part of the drawing of the .284 Winchester SAAMI reamer offered by Manson Precision where I have added some of the metric equivalent dimensions. The figures are the same as are given on the JGS drawing for their .284 Win SAAMI reamer also. The dimensions here may be cross-referenced to the case drawing dimensions. If a chamber was machined using this reamer to put the bolt face as indicated, then a standard case as above would have a 0.005” (0.12mm) crush on the necks.



Of particular interest is that the freebore and throat in the SAAMI standard chambering are combined into a single continuous taper running at 0.79°. This differs from the more typical 1.5° leade ahead of a cylindrical freebore. The drawing identifies that at this pitch, the diameter narrows to 0.284" at a distance 0.217" (5.51mm) ahead of the end of the neck transition - this being the touch point for the bullet. Also of note is the 1/8" radius on the neck shoulder junction (this might ease any donut issue, if only slightly), and the neck diameter of 0.323" tapering to 0.322", which has previously been identified as quite large, particularly for necked-up Lapua cases that have been turned, often then measuring down at a 0.310-0.312" loaded diameter.
If you think you have a chamber cut to this profile then from measurements on fired cases (and the CoL for just touching) the information above should be sufficient to confirm this. Maybe of interest to some? I imagine this standard profile reamer is the most common among gunsmiths here as the neck dimensions mean it is low risk, and being off-the-shelf from most suppliers may be purchased for the lowest cost.



Below is a reamer design from PTG, described as a 284 Norma Match #46114 that is interesting because of the comment recorded on it. I’ve only reproduced here the detail around the front of the case and the comment, as the body & head are all standard. Dimensions all in inches this time.



The shoulder neck radius remains at one-eighth of an inch. The neck tapers slightly - presumably for extraction purposes - down to 0.3185”. This time there is a length of more conventional freebore at the expected 0.2845” diameter. At 1.5°, the leade will narrow from this figure to the 0.284 nominal bullet diameter a further 0.0095” into the throat, which when added to the 0.208” freebore gives almost exactly the same touch point as for the previous SAAMI reamer, supporting the comment that this should be the case. Barrels so chambered will shoot better apparently.