Win. M70 .300wm OAL vs. magazine length

[Maverick26]

Hey guys, a few weeks ago I got my rifle back from a local smith/machinist who is known for awesome work around here and I am more then happy with the rifles I have had them build. I had them build and install a new barrel on my M70 long action post 64 push feed. I had them chamber in 300wm in the new 22" barrel. They test fired the rifle once before letting me have it. I then started in my quest to develop a load. This is my first time doing all this stuff but reading on here and other sites may have given me enough confidence to do so. I started my measuring the chamber case length and then went on to measure the chamber to find the OAL. I measured from end of barrel to bolt face with a cleaning rod and rod stops, set the stops and then I seated a 208 Amax about .20" long in a case and slowly eased it into the chamber tell I felt it touch the lands then repeated with cleaning rod and lowered the bottom rod stop to the barrel. Measured between the 2 stops and I am getting 3.540". Book spec says OAL should be 3.420" and my factory box magazine measures 3.4" max and thats tight, all measurements done with calipers.

It seems to me that in order to seat my bullets close, jammed or just off the lands my chamber is about .140" too long. Or is my factory BM and internal mag not long enough for this kind of round? I have not talked to the smith about this yet but plan to soon, but I just wanted to see if I was doing anything wrong or see if anyone could provide a standard 300wm chamber length. Im kinda scratchin my head tell I talk to someone better at this then me. Thanks.

 

[Maverick26]

No help or ideas on this? Im going to stop by the smith today and see if he can get me back on track.

 

[Engine 22]

I will be able to measure the chamber of my M70 .300WM for you when I get home tomorrow. I'd strongly suggest you invest in a Hornady COAL system as it is much easier to make this measurement of OAL more ACCURATELY. Which bullet are you going to use?

 

[rcamuglia]

Pretty normal not to be able to reach the lands with the Mod 70. Mine was out of the Winchester Custom Shop chambered in .300 WM and was the same. Had it re-chambered with a different reamer and set back. Also removed the little "dead space" in the Mag box to accomodate more length. Bolt stop will have to be altered as well.

Just develop the load at mag length and see how it shoots

 

[Fuzzball]

"It seems to me that in order to seat my bullets close, jammed or just off the lands my chamber is about .140" too long."

That's obviously true. But your rifle is a magnum hunting rig, not a BR rig. Load it as it needs and shoot the thing.

 

[Maverick26]

Ok so I talked to my smith that did the work on the rifle to get it to this point and he said the same things, load to mag length and see how it shoots. If things dont work out he can do some milling on the recever and bolt stop and lengthen my mag box a little to give me more room for a longer OAL. So I went home and loaded up a test round with no powder just to see how it would work. With an OAL of 3.390" (this is .01" shorter then mag length) the 208gr Amax ogive is pushed inside the case neck. The ogive caliper adapter hits the case neck before stoping on the bullet. Is this normal?

Oh and I also had the smith verify and measure my chamber OAL and I was correct at 3.540".

Im thinking it may need the additional machining to lengthen the mag and bolt travel since I dont think there is any realy good way to shorten the chamber to mag length.