M71 browning gunsmith CHAMBER CAST

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thepitchedlink

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Any smiths' around who are known for working on 71s? I have a Browning repro, works fine, but gives me pressure signs with all but the lowest power loads...seems to be an issue with these Brownings...a very short throat. So I was thinking of looking at having the throat let out a bit...then thought about maybe going to the AI version....seems there is some benefit with brass life...anyway...who could I chat to about doing it???

thanks
Pitched
 
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You will be getting lots of velocity if the pressure is up... you are just getting that velocity with less powder. If you throat it longer the pressure and velocity will drop (and possibly some accuracy) ... then you will have to load more powder to get the pressure and velocity back up...
 
Hi Guntech....I get really flat primers with even med strength loads....I posted another thread about it here a whole ago....I don't know how to link it. I even get primer flowing back abut, leaving a dimple on the primer....I've tried several powders. I can't find anything that doesn't show high pressure without running the loads at the bottom of the speed scale
 
I wouldn't screw it up, if it were me. Leave it as is. Those 71s are becoming collectable, too.

I think it's normal to show pressure signs with this cartridge based on the design. The tapered case generates a lot of back pressure on the case head. I have the same issue with my. 33WCF which is pretty similar in shape to the. 348 WCF.
 
thepitchedlink said:
Hi Guntech....I get really flat primers with even med strength loads....I posted another thread about it here a whole ago....I don't know how to link it. I even get primer flowing back abut, leaving a dimple on the primer....I've tried several powders. I can't find anything that doesn't show high pressure without running the loads at the bottom of the speed scale
Click to expand...

The bottom of the speed scale may not be the bottom... Have you actually chronographed the load? Unless you know what the velocity actually is, you are only guessing...
 
So you have actually chronographed some loads? List the load - powder, primer, brass, bullet make and weight. What about factory ammo? How does it compare? A sharp accurate picture of the fired primer would be nice to see.
 
Guntech, have you heard of a predilection for 348 primer pockets to loosen off quickly? I have read that 348 brass typically lasts 5 reloads before primers pockets become loose and primers begin to push backwards giving untoward pressure signs. Admittedly this is not current info but I have noticed that primers seated in 2-3x fired brass go in very easily on a hand seater compared to multi-fired 3006 brass. Cheers!
 
Finger Toes said:
Guntech, have you heard of a predilection for 348 primer pockets to loosen off quickly? I have read that 348 brass typically lasts 5 reloads before primers pockets become loose and primers begin to push backwards giving untoward pressure signs. Admittedly this is not current info but I have noticed that primers seated in 2-3x fired brass go in very easily on a hand seater compared to multi-fired 3006 brass. Cheers!
Click to expand...

I have had two 348s and loaded for both with no primer pocket issues.
And that is with a real mixture of old and new Winchester brass not to mention some old long-discontinued Remington brass as well
Further to that I also use 348 brass in my 450-348 AI and even after loading the daylights out of the brass there has been no problems.
 
Hey Kevan, I think the Brownings are quite different chamber dimensions than the original Winchesters, I have 3 originals and have never had pressure indications with them. Just using loads from CotW, never bothered to chronograph them, not really interested in the velocity as much as accuracy out of my old lever guns. If they can hit a pop can every time at 100 mtrs that is all one can ask IMHO.............
 
So bit of an update here...maybe I'm on to something. I don't have any new photos, but if you look at my other thread " m71 Primer Strikes" you van see what I'm playing with. I fired some more loads, 200gr hornadys with RL 19, 17, imr 4064,3031,H414,H4350.....even my starting loads showed pressure signs at the primer....quite flat and the primer flowing back a bit. Speeds where all around 2200-2300, which seems kinda fast for starting loads....I actually started 1 gr below starting loads

Anyway, still showing flat primers...3031 showing the least, but still a good "dimple " in the primer. Tinkering tonight with the fired brass I noticed something.....I can't push a bullet into a fired case....even after trimming and smoothing out the case mouth, I cannot seat a bullet by hand...even pushing it on the bench top I can't get a bullet to go into a fired case.
So what have I found here? A really tight chamber/neck? Would that give me pressure signs b/c the neck can't release the bullet? Gimme some thoughts here folks, thanks

Just measured my inside neck diameter of the fired cases...all around .342-343.
 
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Just a thought but could the thickness of the case neck of the cartridge be a wee bit too thick and thus not be allowing the neck of the case itself to expand properly during firing ?
If you have a case neck turning tool try shaving the case neck ever so slightly and reload and fire, then check the fired brass and see if a bullet will slip in.
 
If you have a little excessive headspace you can get those flattened primers. On firing the initial pressure backs the primer out a bit and as the pressure increases the case comes back and you have a flattened primer. The situation you mention could also be the cause. A bullet should slip into a fired brass. If it was me I would take it to a gunsmith to have the headspace checked and the throat opened up a bit probably just a matter of running a reamer in. I had a custom built & RM like that and I had to neck turn the brass and I finally had the rifle rechambered with a longer throat also.

Neil
 
Kevan said:
Just a thought but could the thickness of the case neck of the cartridge be a wee bit too thick and thus not be allowing the neck of the case itself to expand properly during firing ?
If you have a case neck turning tool try shaving the case neck ever so slightly and reload and fire, then check the fired brass and see if a bullet will slip in.
Click to expand...

I don't have a neck turning tool....but I just measured the fired brass neck vs. a new case, from the same bag. the fired case wall is actually .002 thinner then the new case
 
Neilm said:
If you have a little excessive headspace you can get those flattened primers. On firing the initial pressure backs the primer out a bit and as the pressure increases the case comes back and you have a flattened primer. The situation you mention could also be the cause. A bullet should slip into a fired brass. If it was me I would take it to a gunsmith to have the headspace checked and the throat opened up a bit probably just a matter of running a reamer in. I had a custom built & RM like that and I had to neck turn the brass and I finally had the rifle rechambered with a longer throat also.

Could be Neil...but that's sorta what I'm hoping to find here....who is a gunsmith that works on 71's and will have the tools for the 348? I can't imagine many guys have reamers and gauges for the 348 Win
Click to expand...
 
SO, bit more here. a new case, resized has a I.D. of .342" A fired case has a I.D. of .345"....it then resizes down to .342" Pacific Tool and Gauge has a neck reamer that can be run in on a T-handle.....anyone out there got some Cerrosafe to make a chamber cast with???

The diagram that Pacific sent me shows the neck diameter of the chamber reamer to be .346"

Or I guess i can look at turning some necks....more tools to buy and try
 
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Your reamer outside neck diameter should be cutting somewhere around .378........not .346, even your throat should be cutting at .349.......can't see where any reamer for the 348 Win would be cutting at .346 for anything..........
 
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