284 DAMAGED BRASS?

[2zero6]

I thought they always used the 7.62 bolts from the beginning of the production run to keep cost down. Is there any way to tell between the two with a caliper?

[wildcatter]

I thought they always used the 7.62 bolts from the beginning of the production run to keep cost down. Is there any way to tell between the to with a caliper?

See, that's why I wanted Hoot to clarify. I'm prolly not quite understanding. I designed the bolt. Bushy drew the prints to my spec. and to their production needs. The 7.62x39 has a nominal rim size of .447". The 284 has a nominal rim size of .476" The Russian Short spec would not allow the 284 to seat unto the bolt face, because the 284 is .026" too big. Until we hear for Hoot, I can only guess what he might have meant. But the facts are, we never used the 762 bolt and couldn't have, it's just too small to handle the larger rim. However you can open that bolt up as you can also open the 223 bolt, to except the larger rim of the 284.

I personally have used, on a custom basis, the 762 extractors on the 284 spec bolt, they kinda-sorta work, but you've got to let them slam seat on the case. Easing the bolt down, to the 762 extractor, requires copious amounts of force on the assist, to get the extractor to jump over the rim and thus is no real fun, but if you ruff-house them, you'll not have a problem.

I also do not know about this.."only feed from the magazine"..thing and the .."do not single feed"..thing. The AR Bolt has always been designed to single feed and feeding from the mag has no advantage to the extractor. This is NOT a controlled feed Mauser. The extractor jumps over the rim, when the case headspaces. Feeding from the mag, the rim does not slip under the extractor. However, there are several gents that have broken extractors. This is probably due to the rare instance that something was out of spec, such as, but not limited to, steel or machining specs or some combination thereof or maybe the stars were lined up, crud happens..t

But then again this is just tubular data, for as I said, I am prolly misunderstanding. In the mean time some of this might be helpful for future use..t

[pitted bore]

The 284 has a nominal rim size of .476"

The SAAMI drawings for both the 450 Bushmaster and the 284 Winchester cartridges give identical dimensions for rim diameter, extraction groove diameter, and base diameter:

Rim: 0.473, + 0, -0.010 inches
Groove: 0.409, +0, -0.010 inches
Base: 0.500, + 0, -0.006 inches

I've encountered a couple of pieces of brass that had an extraction groove diameter that exceeded the specs, but I atrributed that to sloppy quality control, not a systematic change in dimensions.

--Bob

[Hoot]

The 284 has a nominal rim size of .476"

The SAAMI drawings for both the 450 Bushmaster and the 284 Winchester cartridges give identical dimensions for rim diameter, extraction groove diameter, and base diameter:

Rim: 0.473, + 0, -0.010 inches
Groove: 0.409, +0, -0.010 inches
Base: 0.500, + 0, -0.006 inches

I've encountered a couple of pieces of brass that had an extraction groove diameter that exceeded the specs, but I atrributed that to sloppy quality control, not a systematic change in dimensions.

--Bob

The fly in the ointment is that Hornady manufactures their brass with a rim diameter of ~.465 and groove diameter of ~.400 to work with the smaller bolts that Bushmaster is using. Those smaller bolts have trouble engaging with the .284 brass available as it is actually made to spec. with .472 rims and .409 grooves. Strangely coincidental that the bolt and brass just so happen to be made slightly smaller, excluding easily using the less expensive, to spec .284 brass. I have to chuck each .284 case in my drill press and turn them down to make them cycle the same as the Hornady 450b brass with my current production Bushmaster upper. For a lot of folks, those extra steps are just enough dis-incentive to make them not use .284 brass. Mission Accomplished!

I do not consider myself a conspiracy theorist by nature, but...

Hoot

BTW, I have something like 250 Hornady 450b brass from folks all over the country. Most were first-fired and some were brand spanking new. Every single one is .465-.466 rim and .399-.400 groove. Not just a few out of spec exceptions. I have bought three 50 round bags of .284 brass from three different sources. Every one is .472-.473 rim and .409 groove.

H

[Siringo]

We need a simple tool that looks like a shell holder. Insert shell into drill press and slide the tool over the base to cut the proper dimension.

[BD1]

My guess would be that either you have a bolt with a slightly undersized face opening, or I have a bolt with an unusually large face opening as I have not experienced this issue at all. The next time I have my bolt out I'll measure the bolt face. I currently only use the Hornady brass for cast boolit loads. I use the .284 brass for everything else, about 700 rounds so far. Has anyone else experienced this issue? I'm sure glad glad I haven't had to turn down the .284 rims. Just cutting the stuff down is enough trouble already.
BD

[bushmeister]

Here is the thread where Hoot and Siringo discussed this and their measurments... viewtopic.php?f=2&t=802&p=5343&hilit=284+rim#p5343 (insert x files whistling theme song music here)