01-29-2014, 07:22 PM
woohoo Wrote:I'll wade back into this one cautiously.
BW, A carbide reamer may last 400 chambers, HSS maybe 150- 200 if lucky.
What Dave at PTG said is correct more or less. He has a .001" tolerance on the reamers he grinds. When you send a print to him you need to keep that in mind and submit a print .0005-.001 larger than the minimum you expect. Another thing to keep in mind is the reamer will usually cut a hole .0005 larger than the tool and why I say .0005-.001 larger.
If the minimum Grendel chamber has a .2647 start to the compound throat, the drawings to be on the safe side should say .2657 or .266 to allow the reamer to wear .0003" if the reamer is made to the small side of tolerance. On the other hand if the reamer is ground to the large side of tolerance then the freebore could start at .2667"...huge.
Many chamber designs have a tapered freebore kind of like the tapered Grendel compound throat but they are freebore as in larger than the bullet. In the case of the .308 match chambers they start at .309 and end at .308 where the lands start ramping up.
Stuff happens, the good thing is they are stainless barrels and can be corrected easy enough.
Well I guess smaller is better than too big, right. You can always open it up if you want to but sure can't make it smaller.
One thing I thought of and due to the weather I have not had a chance to check. Will the chamber get larger, .0005 to .001 once the barrel heats up? Will the case fit better on a warmed barrel and not a cold bore measurement? The reason I was thinking this is if everyone starts opening up the throat, the throat might not be as tight after you have been shooting groups. Has anyone taken measurement after 20 rounds?
So like the 6.8 SPC, I have heard of tight chamber issues so they made a 6.8 II for the heavier, (larger) bullets. Maybe a 6.5 Grendel II will come out of this for heavier bullets and hunting but for the target guy, it might not be the ticket.