A friend wants to put together a .25 WSSM AR-15 upper. What bolt head diameter is needed, and where could he get one?

Check with D-Tech, he's the only one I know of still building WSSM"s. You also have to modify the upper but Mike can do it right.

I suggested that, but the price tag put him off. He asked me about building an upper. I think the mag is the only thing that has to be modified. If I can find a barrel and bolt head, the mag shouldn't be a problem to modify.

The ejection port has to be opened up.

I think Olympic Arms was making bolts and barrels but they were closing the doors last I heard.
Accuracy Systems also made them.

I don't know of anyone else.

Yep. I didn't think about the ejection port. More trouble than it's worth.

port is opened SO easy with a dremel...... its just AL....

It just always bugged me that the dust cover wouldn't close...

And I'll just add that in 223 WSSM, you can load 75 Amax's and I don't think any 224 cartridge will touch it.

Given that, the question now becomes, "Where can I get the proper bolt head?"

Have a few guns that have no dust cover, just never saw the purpose for some of my hunting guns.

Would not have had em on competition guns either if it wasn't the rule.

But if it's there it's gotta work!

http://www.predatormastersforums.com/forums/ubbthreads.php?ubb=showflat&Number=1470463

This might show a few things you are up against, even if you find a bolt.

So take it off. No reason for it to be there if it won't close.

You need a OLY bolt, Oly carrier, Oly barrel extension and a OLy receiver unless you modify a mil spec receiver. The bolt has a big head(lug diameter) and a big body. It will not work with a mil spec extension or carrier. The extension is 1.05" dia and will not fit a mil spec receiver.