.458 win mag throating

[adkennedy03]

I have an M1917 chambered in 458 Winchester magnum that I picked up for a pretty reasonable price a while back. I discovered that whoever chambered it somehow didn’t throat it long enough for me to load 500 grain bullets at the correct length. I can chamber factory 500 grain loads without any real issue, I’m not pulling bullets and dumping powder but the bullet is jamming into the rifling and leaving obvious marks on the bullet. When I used my hornady oal gauge with 500 grain partitions I can only load them to 3.280 before they start jamming. My question is would it be better to have the throat lengthened or have it rechambered for 458 Lott? If I go with lengthening the throat, how would I go about this? Is this something I can get a reamer for or would I pretty much need a gunsmith? I know if I go the route of the Lott I’ll need magazine work but it can still fire win mags.

 

[Nhoro]

You are correct to be concerned. With a specified 3.340 " COAL, you have a problem that needs investigating. How can you chamber be so much shorter than it should be ? Seems to me that someone reamed it short, maybe from a 45-70? Whatever they did, I reckon you should either ream it to win mag or to Lott. Lott gives you some more versatility with more powders and 500 gr monometal bullets so I would get a gunsmith to ream it out. I had a win mag and needed some work done on it. The gunsmith reamed it to Lott for free while working on the sights. I did a thread on the feed work I had already done to get flawless win mag feeding. The lott did not need any further work so you may be lucky.

 

[USMA84DAB]

I have had the same problem when I chambered .35 Whelen - the round nose bullets are too big at the tip/not spitzer-shaped, so they don't chamber -

If you are inclined/skilled at tinkering, you can get a throating reamer from Brownells and fix this.

Or, you could open it up to .458 Lott, allowing you to shoot .458WINMAG and .458 Lott. I am not sure you will need to "fix" the magazine to accommodate the Lott rounds - would have to check the numbers, but 1917s are "spacious".

This manual chambering-type activity is very doable - when I took a rifle into a gunsmith to be parkerized (I had no tanks) he looked at the chamber and was astonished at the smoothness of the cut and wanted to know who had cut it. I was quite happy to let him know I had reamed it by hand. Go slow and gentle, blow it out well for every headspace check, use lots of cutting oil each time.

 

[adkennedy03]

The

I have had the same problem when I chambered .35 Whelen - the round nose bullets are too big at the tip/not spitzer-shaped, so they don't chamber -

If you are inclined/skilled at tinkering, you can get a throating reamer from Brownells and fix this.

Or, you could open it up to .458 Lott, allowing you to shoot .458WINMAG and .458 Lott. I am not sure you will need to "fix" the magazine to accommodate the Lott rounds - would have to check the numbers, but 1917s are "spacious".

This manual chambering-type activity is very doable - when I took a rifle into a gunsmith to be parkerized (I had no tanks) he looked at the chamber and was astonished at the smoothness of the cut and wanted to know who had cut it. I was quite happy to let him know I had reamed it by hand. Go slow and gentle, blow it out well for every headspace check, use lots of cutting oil each time.

The 1917 is a massive action but the magazine box was designed for .30-06 length cartridges not full length 3.6 inch magnums, hence why it works with win mags. I’ll have to check out brownells and see if they have a reamer that’ll work with a 45 cal rifle. I was mainly wondering which would be an easier route as I’m perfectly fine with a 458 win mag but a Lott would be cool.

 

[adkennedy03]

You are correct to be concerned. With a specified 3.340 " COAL, you have a problem that needs investigating. How can you chamber be so much shorter than it should be ? Seems to me that someone reamed it short, maybe from a 45-70? Whatever they did, I reckon you should either ream it to win mag or to Lott. Lott gives you some more versatility with more powders and 500 gr monometal bullets so I would get a gunsmith to ream it out. I had a win mag and needed some work done on it. The gunsmith reamed it to Lott for free while working on the sights. I did a thread on the feed work I had already done to get flawless win mag feeding. The lott did not need any further work so you may be lucky.

I have no clue how the heck the thing was done, it’s headspaced correctly and fits win mag cases without issue but obviously throated short. I do think whoever built it intended it to be used with the lighter 45-70 bullets for some reason.