404 Jeffery conversion issues

[Matthias5662]

All,
I bought a 404J that started life as a 375 H&H. The action is a left hand, M70, post 64, long action clone - I think it was originally from MRC. I can load three rounds down (barely) but the third round will not stay down - it pops out of the magazine. Looking at the magazine box visually, I can tell it has been widened slightly. I've had a gunsmith look at this and he can't seem to resolve it and indicates to me that the rail is not wide enough to grab the wider shell. Interestingly, I can load 3 rounds of 375 H&H just fine without any of them popping out. I am wondering if I should try replacing the bottom metal with a post 64 long action super grade or perhaps an Obendorf style bottom metal? Will these accommodate a slightly larger diameter shell enough to relieve some of the pressure on the spring? I could get a drop bottom metal from Blackburn or Sunnyhill but that would also require a drop belly stock if I'm not mistaken. I'm also wondering if this could be a problem with the wrong follower? Is another follower worth a try?
I'm sure there are lots of folks here who've converted a Win M70 action to a 404J. I greatly appreciate any help you could provide.

 

[baxterb]

It’s not just a matter of trying a different bottom metal or follower, it’s the geometry of the box combined with the mating surfaces under the action and the rails as well. It’s likely the front of the box is too narrow and the rounds are being pinched too narrow together to stay under the rail.

I had an issue with a non-feeding 9.3 and literally had to start from the beginning to get it resolved. That started with the magazine box and went from there. We had to alter the box dimensions per Mausers rule, then matched those dimensions under the action, then slightly altered the rails, then worked on the feed ramp, pretty much in that order.

If you want to read the whole bloody affair, you can find it here:

Well, I guess they won’t let me post a link. Send me a PM and I’ll send it to you.

 

[Shootist43]

Several years ago Von Gruff posted an article on the proper layout of a Mauser style magazine. Look it up and then compare yours to what it should be. Here is the link to his post

Proper Magazine Layout

This is an artical I have C&P from another forum so the authorship is by Tileyman of Australia I originally wrote this article for our club magazine, pulled together from a few sources including Ludwig Olsen's Mauser Bolt Rifles and De Haas' Bolt Action Rifles... hope you find it useful! Many...

www.africahunting.com

 

[baxterb]

Yes this is a great resource, thanks for the link. You follow the rules and things generally work! ;-)

 

[TOBY458]

JD Jones of SSK once told me they wouldn't convert a 7mm Rem Mag M70 to 416 Ruger due to it's wider case body at the shoulder, with resulting feeding issues. I would imagine the 404 is more of the same. They said it was a huge amount of work to do, and results aren't guaranteed.

 

[Matthias5662]

Shootist43, thank you for the great information (from Von Gruff). I've checked the magazine box dimensions and it is not correct for the "Mauser" formula - its too narrow. It appears I may be in for the same alterations that baxterb mentioned. I'll keep folks posted.

 

[Shootist43]

Matthias5662, I made several copies of the article and gave them to local Gunsmiths. None had ever seen it before. Von Gruff is a veritable warehouse of information.

 

[baxterb]

This is THE takeaway from that post:

“A magazine box designed for one cartridge works for others ONLY with the same identical front and rear diameters and the same span between them. Triangles between cartridge centrelines get steep when the box is too narrow, and rounds tend to cross-stack.”

Just follow the rules…

 

[nztimb]

Something you could think about is to do some measurements of the outside of the front of the mag box and the inside of the rear and it may be that you could leave the last 1/2 inch of the sides at the rear of the box and cut the rest away so the wood of the stock retains the shoulders of the cartridge. This is a 1905 Jeffery and they have cut the whole of the box away except for the rear and relied soley on the stock wood to get the correct "mag" dimensions.

 

[nztimb]

Well, I guess they won’t let me post a link. Send me a PM and I’ll send it to you.

It is understandable that for the sponsers of the forum that links to other forums are not allowed, but
you can C&P the contents of the article without it being a link and that works as I have found. Copy and save any pics and insert them where necessary so any information that is worthy of this forum can be added in that way.

 

[Nhoro]

I also used Von Gruffs useful post to get flat nose solids to feed in my CZ 550 Win Mag/Lott. Something so elegantly simple should be old news to manufacturers and gunsmiths but it appears that 100 yr old design is forgotten in todays world. Magazine width is vital for correct feeding and most manufacturers cut corners because of the almighty dollar. The 458 is not the biggest diameter case in the world but a magnum CZ reciever is manufactured too narrow for it. Imagine then how undersize other actions must be !

 

[Matthias5662]

Follow up. I printed out the "Mauser Formula" post referenced above and gave it to my 'smith. He'd not seen it before either. That said he'd been diligently working over the magazine box and follower and spring. The box now measures out exactly what it should front and back. Low and behold, it holds three down easily without undue pressure on the rail or any rounds popping out. I'm very thankful for the great information! Folks converting a 375 to a 404 should keep this gem of knowledge in mind - their gunsmith may not know about it.

 

[baxterb]

Follow up. I printed out the "Mauser Formula" post referenced above and gave it to my 'smith. He'd not seen it before either. That said he'd been diligently working over the magazine box and follower and spring. The box now measures out exactly what it should front and back. Low and behold, it holds three down easily without undue pressure on the rail or any rounds popping out. I'm very thankful for the great information! Folks converting a 375 to a 404 should keep this gem of knowledge in mind - their gunsmith may not know about it.

Great to hear.

 

[Shootist43]

Matthias5662, it is times like this that makes me proud and happy to be an AH member. Helping each other out is what this site is all about. Now go load up some ammo using a 400 Gr. bullet Like a Woodleigh PP SN, or a Swift A Frame and 84 Gr. of H4350 and have yourself a ball. This load shoots extremely well in quite a few 404(s). I get 2300 FPS out of my rifles, and that is exactly what Von Gruff told me to expect. Accuracy was less than an inch at 100 yds. for three shots.

 

[baxterb]

@Matthias5662 I was chatting with D'Arcy Echols about the 404 conversions earlier today and he sent me some pics that really help illustrate why the 404 is a challenging cartridge and also why keeping to Mauser's rule is so important. Also why that original Jeffery had its magazine box cut away.


30-06 box on left 404 on right

30 06 follower on top 404 on bottom

Loaded 404 mag box third from left. Note how wide the front of the box is compared to the 458 Lott far left and 375 H&H second from left

One of the 404s D'Arcy has built, this on a LH Model 70. Holds 4 down and 1 up with no drop belly magazine. Has accounted for plenty of bison and cape Buffalo.

Good stuff

 

[One Day...]

Yes indeed!

This has been discussed a few times indeed, and it looks like Von Gruff and I share the same sources (the two "bibles" being Ludwig Olsen's Mauser Bolt Rifles and Frank De Haas' Bolt Action Rifles)

In this post:
https://www.africahunting.com/threads/planning-out-a-10-75x68-build.56937/page-2#post-660519

I had posted the drawings:

I had also included a screen capture of an old Mauser catalog that showed that no less than 20 (yes, twenty!) different Mauser actions were once offered for sale, and of course the proper dimensions of the magazine box, and the proper geometry of the feeding rails and ramp (in addition to the obvious bolt face proper diameter and extractor proper profile & tension) were the reasons for the various offerings

 

[baxterb]

right on @One Day... !

Here are the majority of those dims:

 

[baxterb]

@One Day...

Do you know what the original tension spec was on the extractor blade?

 

[One Day...]

No I do not, but the rule of thumb was that a cartridge carried by the claw extractor into the chamber (hence the "controlled round feeding") was held tightly enough that one could take the bolt out of the action, clip a loaded cartridge under the extractor, and shake the bolt vigorously without the cartridge falling.

Of course the tension comes from the spring action of the extractor steel, but most of the secure holding results from the extractor claw having the proper length to be under spring tension when a cartridge is placed under it on the bolt face. For example, I had to replace the extractor on my CZ 550 .416 Rigby with a .375 H&H extractor (CZ offered both chamberings in the 550, built on the same magnum-length bolt). The original .416 Rigby extractor claw had been shortened too much at the factory when they fitted it to the .416 bolt head, and the extractor did not exert any meaningful tension on the cartridge head extractor groove. The longer claw of the .375 H&H extractor provided barely enough tension with a .375 H&H cartridge but was perfect for the .416 Rigby.

I would "guestimate" that positive tension would be the extractor being lifted and tensioned by the cartridge under it, about 0.25 to 0.35 mm off the bolt head. That would be about .01 to .015", although things work as soon as the extractor is lifted from the bolt head and under tension. From that perspective, 0.1 mm (.004") would technically suffice but not leave a lot of safety margin... The closer the tolerance on the bolt face (which was not a CZ 550 quality) the closer the tolerance can be on the claw length.

 

[baxterb]

When D'Arcy and I were working on my 9.3, we set the tension to .005" deflection on my Lapua brass and it works great. Given how exact Mauser was, I was just curious what his spec would have been. As you mention, it's a key component of CRF so I'm sure he devised some method of measure.