Currently have a 700 5R 300 WM that I would like to convert to RUM primarily to get away from the reloading of belted cartridges. I understand the bolt face is good to go. What exactly needs done to the side rails of the receiver and the mag follower and BDL magbox? I am running 208 AMAX so I hope the RUM will fit in the factory BDL magbox with 208's and get close to the lands. I am running 20 thousandths off the lands now with the 300WM. Any and all help appreciated, haven't found all the answers with the search.
Gunsmithing Rem 700 300WM tp 300 RUM conversion
- Thread starter wegner426
- Start date
A RUM chamber should clean up a WM chamber when you ream it. It should also feed fine with the rails but you will need to go to an RUM mag box which has windows cut out in it. I would make up a dummy round that fits in the mag box and have PTG grind you a reamer to match.
Thanks for the response, I tried to go down that road but the gunsmith said the chamber was too far out of round and didn't want to rechamber or guarantee accuracy, although the gun shoots really well now. He said the chamber was had almost 5 thousandths run out. He also wasn't sure whether the rails would need opened up so that is why I asked here.
Sounds like he is unsure of himself or just wants to sell you a bbl. .005" is nothing in this case. The only thing of the orig chamber that may remain is in the belt area. Granted the reamer pilot can't guide the reamer until it engages the bore. It should work out fine if it is done right.
As far as the rails go, they have to be opened up. Most will accept a virgin case but a fired/sized case won't go.
I very much disagree with your statement. The smith knows what he is talking about. .005 is a shitload of runout for a chamber!! Also The belted area may clean up, maybe. taking a chance on having too much un supported case is a good way to get case head separation and a face full of 50-60k psi of hot gas.
OP, listen to your smith. If he can cut off the old chamber of your barrel then ok, otherwise just get another barrel
By all means 426, listen to the loud fart. The Rigby case head is close to .020" larger than a mag belt in dia. The only thing that won't be supported is a lame opinion or smithing mistake.
No need to get upset because our opinions are different, If having a nice concentric chamber and a smith that has some good standards is lame then ill take lame all day, every day
You are talking about punching out an existing chamber. Measures can be taken to correct the runout during the process. Maybe your smith with such high standards should consider going back to school.
Thanks for the input gents. Not sure what I will do, I already had this barrel fluted, threaded, and a brake fit a couple years ago so I was hoping to re-chamber instead of throwing the investment down the drain. I will say that this gun will pretty easily hold 3/4 MOA now with handloads so it is a decent shooter. Ideally I guess I should have had this barrel checked more closely before I spent any money on it.
In your first post you said .005 was nothing, the belt area of the case MAY clean up and should work out fine if its done right. Now your saying that the runout can be corrected like its a problem? Sounds like your the one whos unsure and needs to go to school. Maybe that will do somthing for your standards
As a rule, I don't spout shit off if I don't know what I'm talking about.
I used the word MAY because I didn't know the dimensions off the top of my head. After measuring, I confirmed that .005" is not a problem in this case.
All you have to do is set it up and indicate the bore axis. Bore the chamber to shoulder dia w/ single point cutter as Turbo suggested deep enough for the pilot to engage the the lands and ream away. I would also cut the belt area until it cleaned up to avoid the possibility of it pushing the reamer. If you'd like, I can draw you a picture.
If you choose to go ahead with this, I have found that you can avoid major machining on the receiver by cutting the top of the mag box out like Winchester does on the WSMs. I've only done a few of these but the biggest prob I had was the rounds like to pop out of the mag prematurely. Cutting out the mag allows you to get function without committing the receiver.
Thanks for the responses. I will have to do some soul searching to decide what to do.
