Magazine tube backing out under heavy recoil

[Ranch Dog]

I've been running RD 265 G.C.'s around 1600 fps and that is about all the wilder I want to go with loads in this light little rifle with a metal butt...

Greetings James, welcome to the forum!

[pricedo]

The JMB 92 is an old design going back to black powder days when pressures and recoil (and people) were much more modest.
Then came smokeless powder and significant increases in pressure, shock and recoil.
Steels used to make guns were improved to handle the increased stress but legacy designs remained pretty well unchanged including the small magazine retention pin of the 92 rifle.
The increased pressures and shock of modern smokeless cartridges are causing the weak magazine retention pins to fail.
When you put new wine in old bottles problems happen unless adjustments are made.
As more of these pins fail I can see the much stronger double threaded tube magazine retention assembly pioneered in the newer Rossi 92/454s becoming the new standard design.

[Trailboss]

As more of these pins fail I can see the much stronger double threaded tube magazine retention assembly pioneered in the newer Rossi 92/454s becoming the new standard design.

That would be a welcome change.

[BigeyeBob]

Hi Everyone,
I removed the magazine tube from my rifle this morning to better assess the issue and can report the following information:

On rifle models with the octagonal barrels the magazine passes through two sleeves affixed to the underside of the barrel, one in the forearm nosecap and the other ~3.5" from the end of the barrel. On my rifle the fit of the magazine tube in these sleeves is quite sloppy with the ID of the sleeves being ~0.010" larger than the OD of the magazine tube. The sleeve towards the end of the barrel contains an 0.098" diameter cross pin but it should be noted that the slot filed into the magazine tube to accept this pin is extremely shallow. Based on my measurements and some quick geometric calculations I estimate the slot to be only 0.010"-0.015" deep at the center. Considering that the ID of the sleeves is already ~0.010" larger than the OD of the magazine tube I am skeptical of the ability of this cross pin to prevent the magazine tube from sliding out under even modest recoil.

The second method of retaining the magazine tube is the screw that secures the plug in the end of the tube. This screw has a long unthreaded portion that enters into a blind hole ~1/16" deep in the underside of the barrel. It should be noted that the fit between the unthreaded portion of the screw and this hole is also rather sloppy with the hole being ~0.010" larger in diameter than the screw. Based on a small scratch in the bluing between the blind hole and the muzzle as well as rub marks on the magazine tube it appears that the recoil from the first +P round fired caused the magazine tube to slide forward ~1/2" and that each subsequent +P round caused the tube to slide out an additional ~1/8". I cannot tell for sure whether the screw had loosened or whether the magazine tube flexed enough to allow the pin to pop out of the hole even when tight but I suspect the former.

My first attempt to rectify the issue will be to remove some of the play in the sleeves holding the magazine tube and to take measure to prevent the end plug screw from backing out. I intend to accomplish this lining the bottom of the sleeves with aluminum foil tape (the kind sold for use on heating ducts) and applying blue loctite to the threads on the end plug screw. The tape in the sleeves should hopefully make the cross pin more effective by limiting play and also minimize the deflection at the end of the magazine tube making the end plug pin less likely to pop out of the blind hole in the barrel. I am hopeful that this will work but if it does not the next step will be to either limit myself to using tamer loads or to install a larger diameter cross pin (perhaps increasing the pin diameter to 0.120" from 0.098").

Thoughts?

-Steve

DIY92

Ive had a similar problem with my Rossi 357 24" Octagonal barrelled rifle .
The magazine tube came out after I fired quite a few hot loads .
I was unable to work out what happened , the screw/pin at the muzzle end was still in the tube and end cap.
Just the magazine spring pushed the tube out of the rifle .
I applied some loctite to the screw at the muzzle when I got home from my bush range , but haven't had a chance to get out and shoot again to see if the problem is fixed .
This weekend I will take a closer look at the tube sleeves and see what clearances are like.

BigEye Bob

[pricedo]

I can see the inherent weakness of the design plus the above described manufacturing sloppiness is leading to problems in some cases that logically depend on how heavy the loads are and how much the gun is shot.
The guys that fire a few shots to sight in with factory ammo and several shots yearly during the hunt will have less probability of the problem manifesting itself than those who shoot lots of heavy hand loads downrange.

[BigeyeBob]

I can see the inherent weakness of the design plus the above described manufacturing sloppiness is leading to problems in some cases that logically depend on how heavy the loads are and how much the gun is shot.
The guys that fire a few shots to sight in with factory ammo and several shots yearly during the hunt will have less probability of the problem manifesting itself than those who shoot lots of heavy hand loads downrange.

I thought about the problem some more recently and last week end I machined up a new magazine plug and a longer screw . I set the rifle up in my milling machine vice upside down well supported and wooden inserts in the vice and I drilled the dimple a bit deeper by 1/16" .
Going over this post again I noticed that SteveG had already suggested this .
The problem I had was trying to find what the thread is on the retaining screw , its so fine none of my thread pitch gauges could tell me what it was ,it matches with nothing on any of my gauges .
In the new magazine plug I tapped it 4M x 0.7mm (Metric for you Americans) ,it makes the screw a bit larger in diameter . I screwed the new screw in so it just bottoms out and takes out the play in the sleeve between the mag tube and the sleeve but not so far as to actually push the mag tube away from the barrel and put stress on the tube.
If it still jumps out its easy enough to machine up a longer pin and drill the dimple a bit deeper , the octagon barrel is pretty thick so there is a lot of room for a deeper dimple .
Just have to get out and test fire it to see if the fix has worked .
Got some stainless sling swivels studs coming from your side of the pond ( got them off Ebay ) one has 10x something thread so I'm going to drill and tap the for end cap to fix the front stud to , the back one will be a standard wood type screw , a pair of Uncle mikes stainless QD's are also on the way , just need a nice 1" leather sling to finish it.

[akuser47]

Good work thanks for sharing

[BigeyeBob]

As it was Australia Day long weekend I took the Rossi out and put some hot loads through it , The modification seems to have worked ,I checked the magazine tube after a few shots , and it never moved from its correct position . I managed to get a magazine full of rounds through it before a big tropical storm made me run for cover back into my vehicle .
The load I was using is 158Gn JFNSP Hornady projectiles over 16.9Gns of W296 , this load I use for feral hogs.

[golfish]

Steve,

I too had the mag tube jump the groove in my 44 mag 92..

Good afternoon Gentleman, I saw this gun on GB last night and thought about this post.

Do you think its the camera angle. This looks like a nice gun but the mag tube seems to extend further then the barrel.
http://www.gunbroker.com/Auction/ViewIt ... =412236845



Sorry if this is silly. I've been spending too much time on the net.

fish

[akuser47]

It sure does look like it is not seated in the reciever may be the pic no way to know unless a pic across the crown is able to be seen.