Help with Mauser Action

[LRich]

I rebarreled a Remington 798 action from a 375 H&H to a 375 Weatherby. This action has been described to me as a modified Mauser action.

The problem I'm having is that on occasion, the rounds that are in the action pivot up from the rear when I open the bolt. A gunsmith called it "porpoiseing".

He also said because of the Weatherby case design, that the rounds may not be stacking properly. BTW he said he didn't know a proper fix.

Does anyone have a suggestion as to what can be done to fix the problem?

 

[Bwanabob]

I am n0t a gunsmith but my first question would be whether the action rails were modified when the rifle was rebarrelled? The .375 H&H and .375 Weatherby have exactly the same headsize (the .375 Weatherby is basically an improved .375 H&H) so one would expect the rear of the case to be retained without problems.

However, it is possible, as your gunsmith suggested, that the Weatherby case is not stacking properly because the shoulder of the case is fatter and this is causing the rounds to project out from the action side rails and this allows them to stick up at the rear. The solution would be to have the feed rails reworked to suit the .375 Weatherby. What I have found is that many Mauser 98 owners (and this includes many gunsmiths, too) don't fully appreciate the importance of the size of the magazine box and the shape of the feed rails when rebarrelling for cartridges of a different size or shape to the original round. Having played with a lot of Mauser 98 projects, I have learnt the hard way about the importance of magazine box size and feed rail shape - I still do not understand it fully, but know that it is something that is vital to any rebarrelling project.

To illustrate this point, if you can get hold of a copy of the book "Original Oberndorf Sporting Rifles" by Jon Speed, Walter Schmid and Reiner Herrmann, and go to page 127, you will see that the Mauser factory had different magazine box sizes for each cartridge that they made. While the same dimensions can be used for cartridges that are very similar in size and shape, when you change the shape substantially, such as blowing out the front of the .375 H&H to make a .375 Weatherby, then the dimensions become marginal and changes need to be made - in this case the magazine box is probably ok, but the feed rails will not be ok.

If you decide to get the feed rails re-worked, make sure you get someone who knows what they are doing, or you will never get reliable feeding.

The other option, and in my opinion the better option, is to rebarrel back to .375 H&H. What isn't generally appreciated is that the .375 H&H is more than adequate for most hunting purposes and if you need more gun than a .375 H&H, then you need to look at a .416. 404 or .458. Also, if you read some of the gunsmithing publications in relation to Mauser 98s, you will find that the standard length Mauser 98 and some of the newer Manufacture M98 clones, such as the Zastava M70 magnum (and the Remington 798 is based on the Zastava action) are still only standard length actions and are not suitable for cartridges that operate at greater pressures than factory .375 H&H rounds.

If you really have to have a .375 Weatherby, then you really need a true magnum length action such as a CZ 550 Magnum.

 

[sestoppelman]

Why was it rebarrelled when all that needed doing was re cutting the chamber? Same caliber.

The action used on these is perfectly suitable for magnum cartridges as regards pressure as long as max is not exceeded, same as with any action. The only issue with the Zastava action that Bob refers to is the length. In order for those actions to accept long rounds like the .375 H&H the feed ramp has to be cut forward, shortening it (to make room for the magazine box) which at the same time removes metal from the lower locking lug recess area. Its not a problem if done right. I have a Whitworth (Zastava) .375 that I have been shooting for nearly 40 years, no problems and with full power loads. The slightly fatter round is the likely culprit as mentioned above so getting a good smith is essential.

 

[LRich]

I am n0t a gunsmith but my first question would be whether the action rails were modified when the rifle was rebarrelled? The .375 H&H and .375 Weatherby have exactly the same headsize (the .375 Weatherby is basically an improved .375 H&H) so one would expect the rear of the case to be retained without problems.

However, it is possible, as your gunsmith suggested, that the Weatherby case is not stacking properly because the shoulder of the case is fatter and this is causing the rounds to project out from the action side rails and this allows them to stick up at the rear. The solution would be to have the feed rails reworked to suit the .375 Weatherby. What I have found is that many Mauser 98 owners (and this includes many gunsmiths, too) don't fully appreciate the importance of the size of the magazine box and the shape of the feed rails when rebarrelling for cartridges of a different size or shape to the original round. Having played with a lot of Mauser 98 projects, I have learnt the hard way about the importance of magazine box size and feed rail shape - I still do not understand it fully, but know that it is something that is vital to any rebarrelling project.

To illustrate this point, if you can get hold of a copy of the book "Original Oberndorf Sporting Rifles" by Jon Speed, Walter Schmid and Reiner Herrmann, and go to page 127, you will see that the Mauser factory had different magazine box sizes for each cartridge that they made. While the same dimensions can be used for cartridges that are very similar in size and shape, when you change the shape substantially, such as blowing out the front of the .375 H&H to make a .375 Weatherby, then the dimensions become marginal and changes need to be made - in this case the magazine box is probably ok, but the feed rails will not be ok.

If you decide to get the feed rails re-worked, make sure you get someone who knows what they are doing, or you will never get reliable feeding.

The other option, and in my opinion the better option, is to rebarrel back to .375 H&H. What isn't generally appreciated is that the .375 H&H is more than adequate for most hunting purposes and if you need more gun than a .375 H&H, then you need to look at a .416. 404 or .458. Also, if you read some of the gunsmithing publications in relation to Mauser 98s, you will find that the standard length Mauser 98 and some of the newer Manufacture M98 clones, such as the Zastava M70 magnum (and the Remington 798 is based on the Zastava action) are still only standard length actions and are not suitable for cartridges that operate at greater pressures than factory .375 H&H rounds.

If you really have to have a .375 Weatherby, then you really need a true magnum length action such as a CZ 550 Magnum.

Bwanabob,

Thanks for taking the time to reply.

BTW, I do have a 404 Jeffery. I wanted the 375 Weatherby just a for a little more flat shooting gun than the H&H. Notice I said wanted, not needed. The gun shoots 1/3" groups at 100 yards so it's a keeper but it needs to function properly of course. With a round in the chamber and one in the magazine it's fine but then it's a 2 round bolt action rifle. I could also shoot 375 H&H ammo in it, albeit at reduced velocity.

I am talking to a gunsmith that knows how to properly work on the side rails.

Thanks again

 

[LRich]

Why was it rebarrelled when all that needed doing was re cutting the chamber? Same caliber.

The action used on these is perfectly suitable for magnum cartridges as regards pressure as long as max is not exceeded, same as with any action. The only issue with the Zastava action that Bob refers to is the length. In order for those actions to accept long rounds like the .375 H&H the feed ramp has to be cut forward, shortening it (to make room for the magazine box) which at the same time removes metal from the lower locking lug recess area. Its not a problem if done right. I have a Whitworth (Zastava) .375 that I have been shooting for nearly 40 years, no problems and with full power loads. The slightly fatter round is the likely culprit as mentioned above so getting a good smith is essential.

Thanks Sestoppleman.

I rebarreled it because I had the barrel and didn't want the 375 WBY to be stamped with 375 H&H. And yes the magazine box is not long enough to get the most out of the Weatherby round, but I do get 2675 FPS using 300 gr North Forks and 1/3" group at 100 yards.

Thanks again for the reply.

 

[sestoppelman]

I see. What is the length inside, of your mag box? OAL is essentially the same for the two rounds, so if it was long enough for the H&H, its should be long enough for the Weatherby.