I have a 375H&H U/O double rifle and am considering taking it out to 375 Weatherby in order to reduce back thrust and pressure as the action, according to my gunsmith, is not quite up to the 300gn loads it is regulated with.

My questions:
- will hand reaming it out to 375 Weatherby give as good a result as doing it on a lathe (which is not possible)

- how long would it take to do each chamber

thanks in advance

mike

quote:

- will hand reaming it out to 375 Weatherby give as good a result as doing it on a lathe (which is not possible)

- how long would it take to do each chamber

NO it will not be a good. I once took a 7x57 to 280 by hand in my much younger days. While it worked the chamber was far from perfect. Doesn't take long less than an hour for sure.

I wouldn't do it again on a bolt rifle much less a double

You would be better off setting the barrels vertically on the edge of a milling machine table, swinging the head, and driving the reamer with the chuck, or, by hand with a center in the chuck. Like you would if you were tapping a hole using the mill.

Mike

Why do you say it is not possible to do it on a lathe? Take it or send it to a gunsmith with a large lathe or a Knee mill. Either can be used. Turn the barrels in a large lathe with a 4 jaw using a spider in the steady, or turn the reamer with the barrels vertical over the edge of the Knee mill table. There are several good ways of holding the barrels for this, it just takes patience and time to set up.

Reaming without a ridgid setup will not give an accurate chamber. You could use hand power but the reamer and barrel must be indicated on a center line, and ridgidly held. Double rifles are rechambered without separating the barrels frequently. (And forcing cones lengthened on shotguns).
Roger

Sorry, I missed Malm's response. Didn't mean to repeat. R

some of the top gunsmiths that do barrel work do it on the lathe, BUT they use a special collet that floats to hold the reamers...in other words they are not solid. It can be done just as well by hand if one is experienced at doing it. It's not like threading a hole. You want the reamer to follow the bore. Say your bore is not straight or off and you attach the reamer solidly in the collet and the barrel is solid in the chuck, it's not necessarily so that the reamer will follow the pilot.

I have re-chambered a bolt rifle barrel from .375 H&H to .375 Weatherby and it came out well. The problem I foresee with hand reaming is, although reamers tend to self center, is that the pilot will not touch the bore until you are well into the original chamber. Prior to the pilot entering the bore, you could ream the chamber a little egg shaped if you weren't careful. If you are having a reamer made, ask the manufacturer to put a two inch pilot on it. It would be somewhat costly but would help in the alignment of new reamer to original chamber.

quote:

Originally posted by AussieMike:
I have a 375H&H U/O double rifle and according to my gunsmith, is not quite up to the 300gn loads it is regulated with.


mike

I find this fascinating, and a bit perplexing.

If it is regulated, and isn't coming apart or destroying the brass on the first shot, why is it "Not up to the load it is regulated with"? And, how would your gunsmith know it isn't up to those loads?

If you change the chambering, all bets are off with the regulation.

Before you do a thing with such a valuable rifle, send it to Champlins in Enid, Oklahoma to have J.J. Pedreau (sp?) look it over. Do not touch it until you have discussed the topic in detail with a truly knowledgeable double rifle gunsmith. Yikes!!

LD

Thanks Guys,

The speed of response is amazing. he reason the gunsmith thinks it is not up to the pressure is that the top lever gets stiffer and stiffer the more shots that I fire with the 300gn projectile.

The gunsmith I use for rebarrelling/rechambering is not prepared to set it up in a lathe - he is a bench rest guy and the the guns I have done by him shoot 0.5 minute groups all day and I thought he may be being precious about hand reaming but you guys have convinced me that is not the case.

I'll learn to live witrh it.

hanks again,

mike

quote:

Originally posted by Alberta Canuck:

quote:

Originally posted by AussieMike:
I have a 375H&H U/O double rifle and according to my gunsmith, is not quite up to the 300gn loads it is regulated with.


mike

I find this fascinating, and a bit perplexing.

If it is regulated, and isn't coming apart or destroying the brass on the first shot, why is it "Not up to the load it is regulated with"? And, how would your gunsmith know it isn't up to those loads?

Yes...precisely....before I stuck a reamer in this thing I'd want a second opinion. I have a gut feeling it don't need reaming at all.

Damn, if you think the top lever gets tight with the H&H loads, what do you think it will do with the Wby loads?

well my opinion is Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaagh

Jim,

I think his idea was to load the bigger case down to H&H levels to reduce pressure. That would reduce the back thrust (lower pressure x same size case head diameter).

Steve

He could also do the thing that reduces pressure (?) in a weatherby; make the throat longer. But, How about the next guy who shoots a weatherby in it?

quote:

Originally posted by AussieMike:
Thanks Guys,

The speed of response is amazing. he reason the gunsmith thinks it is not up to the pressure is that the top lever gets stiffer and stiffer the more shots that I fire with the 300gn projectile.


mike

Mike, so does my Valmet O/U,but it has nothing to do with the pressures being too much for the rifle. It is because the firing pin retractor(s) have failed (work intermittently) and the warmer the action gets, the poorer they function. So essentially, the top lever has a lot more work to do in getting the pins back far enough so that the action can open at all. ...At least that's what some Valmet folks tell me.

So, as others have suggested, I'd send the gun to a double rifle specialist for examination and/or repair WAY before I'd re-chamber it.

(And the Weatherby case is not of substantially larger capacity anyway, so I doubt you could get the same performance with substantially lower pressures...unless there happens to be a powder out there that is just exactly right for the Weatherby capacity and your preferred bullet weight, and no such powder for the standard .375.)

Thanks again. The gunsmith who has looked at it is very good on doubles, accredited by some English factories. In fact, if you bought a Westley Richards 425 or 318 in the late 90's or earlier this century it was probably made by Rolf in Australia.

I have read that the cartride case takes up a reasonable amount of backthrust and that this is much more so with strighter sided cartridges.

Regarding powders, we have troble reliably sourcing powders, apart from those made locally by Australian Defence Industries. hese are sold under the Hogdon brand in the US. We don't have anything between 4350 and 4831SC so I use AR2209 (H4350) 80gns (book max 81.5) with the 300gn projectile to regulate. It won't regulate with AR2213SC (H4831SC). A powder a bit slower than 2209 would likely give a bit more recoil and a bit longer barrel time and allow me to operate at lower pressures.

The rifle is not a high end gun, $US2,500 will easily buy you one at an Aussie gun show, often with a factory fitted East German Zeiss scope but it is really accurate and well regulated (2MOA composite) and I use it for plinking so it sees a bit of use. It's been back to the gunsmith twice with this problem.

Thanks again for all the information.

mike

quote:

Originally posted by AussieMike:
I have a 375H&H U/O double rifle and am considering taking it out to 375 Weatherby in order to reduce back thrust and pressure as the action, according to my gunsmith, is not quite up to the 300gn loads it is regulated with.

My questions:
- will hand reaming it out to 375 Weatherby give as good a result as doing it on a lathe (which is not possible)

- how long would it take to do each chamber

thanks in advance

mike

Hello Mike,
Here is a page that discusses the subject of case thrust in a different way. It is focused on the finish of the chamber but talks about the case head thrust also.
Finite element analysis of case head strain.

Another page of finish discussion and engineering analysis
Coefficient of Friction

Thanks for the link. From the article ireload2 refers to it seems that only lowering the pressure will decrease the back thrust. Interestingly, the Brno has a very rough chamber with maching grooves. I wondered why they left the chambers in this state when everything else was polished/jewelled - perhaps the Czech engineers hoped it would decrease the load on the action.

mike

Hello Mike,
I suspect you are right about the chamber finish. Did you notice the comments about improved case life with a smoother chamber?
You might ask the manufacturer about the force to open the top lever.
One thing I forgot to mention. Have you tried a variety of brass. Softer brass might adhere to the chamber better.