Gator gas check problem

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  • Last Post 26 January 2022
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Norskie posted this 22 January 2022

I have some gator gas checks that are supposed to be for the .348 Win. I have an accurate bullet mold for casting .348 gas check bullets. The gas checks fit the shank properly. The problem I am having is seating and sizing. I made my own lubrisizer die sizing to .348. The force required to seat the check compresses the bullet and shaves the sides. Band diameter of my bullet as cast is .349-.350. Diameter of the gas check is .356. Is this the proper size for the gas check or is it to big? Any ideas or suggestions would be greatly appreciated. I may possibly make another sizing die or two in larger sizes.

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admiral posted this 23 January 2022

My Hornady .348 GC's are .354" and my Ideal .348 checks are .351". Have you tried sizing base first with a flat punch? I size all my rifle bullets base first in my RCBS Lube-a-matic II. Seats the gas checks just fine and there's no bullet distortion. By the way I size all my .348 Win cast bullets .354" and they chamber in all 4 of my M71's, both original Winchesters and Browning repro's.

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Norskie posted this 23 January 2022

I have just started casting for the .348. The punch I have is the one I got with the accurate mold. I will make another sizing die or two. I have the lyman one. Sounds like .348 is to small. These will be shot out of a win 71. Thanks for the info.

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Ken Campbell Iowa posted this 23 January 2022

i recommend doing a chamber image ... soft lead slug upset or cerrosafe ... before starting any serious cast load development ... 

takes about an hour and can save many times that ..... and $$$ ... wandering in the wrong forest ....

i prefer to upset a lead slug in a sacrificial case ... that way i can refer to it many times and determine throat dimensions and also visualize seating depth changes.

you have an interesting project ... keep us informed on how it progresses.

ken 

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Norskie posted this 23 January 2022

I normally slug the barrel and size accordingly. Model 71 doesn't appear to be as easy as say a revolver! It definitely is better to have a plan than to be guessing. I'm new to the .348. With casting tools being obsolete for it becomes a trial and error guessing game. Thanks for your tip.

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Ken Campbell Iowa posted this 23 January 2022

you need to slug both the barrel for it's bore and groove diameters ... but even more importantly ... the front of the chamber ... the case neck area and especially the * throat * dimensions.

for 60 years i have been seeking some simple rules to get decent .. and repeatable ... cast accuracy ...  so far, only one is 90 per cent repeatable ... maybe 95 per cent ... RULE ONE ...

the bullet must be a good fit even before it is fired ... the nose should be a snug fit in the barrel proper, and the rear large part of the bullet should be a snug fit in the back of the throat ( the freebore) ... the reason to measure your exact  chamber is that there is a tolerance in manufacturing, and your gun may not be what the blueprints show.

once you keep this one rule in mind, you can get most hunting rifles down to 2 moa or so .. plenty good for most purposes ...  

once you get down to 2 moa .. then you look at the other 756 rules for cast bullets ...  none of which seem to get repeatable results in every gun every time.   the one thing that is consistent is the fun of trying to find that darned RULE TWO ...

just some thoughts 

ken

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admiral posted this 24 January 2022

I almost never bother slugging bores on any quality sporting firearm made after WW2 except if it's chambered in a 19th century cartridge (38-55, 44-40, etc.). Your M71 has either a .348" or .349" groove most likely. What I would do is fire a full power jacketed bullet load in your rifle then measure the ID of the fired case neck. It will probably be .352''  or more. I have measured at least a dozen M71 originals and repro's and I don't even bother with chamber casts or slugging. I would load an over size bullet of at least .352''  in a dummy round and see if it chambers. Most original M71's have a short lead that will allow a full diameter front band to chamber but the Browning repro's have rifling immediately in front of the chamber. 

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Norskie posted this 24 January 2022

I ran a slug down the bore today. .350. Is what I measured. I think my next step is to ream out my size die and hope the .002 makes a difference in seating the gas check without smashing the bullet.

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Norskie posted this 24 January 2022

It seems very apparent that my homemade size die is to small. Maybe it's just time to powder coat! Are there any commercially available sizing dies? Is my .350 as cast bullet undersized for a win 71?

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Paul Pollard posted this 24 January 2022

Is the entry to your sizing die tapered? It should be. If I don't taper mine, they feel small and shave the bullet.

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Norskie posted this 24 January 2022

No taper. Just beveled at the mouth.

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MP1886 posted this 25 January 2022

No taper. Just beveled at the mouth.
That is part of your problem, not all of it for sizing.   Just think the smallest part of the bevel has a sharp edge.  A gradual taper is better as it leaves no sharp edge at the bottom. I also radius the opening, or top, of that taper.  You want the bullet to start in gradual and gentle.  A correctly made sizer die should be able to size a bullet a fair amount of thousands of a inch oversise unless your bullet alloy is very hard.  This gets harder as the diameter of the bullet gets larger. You also should polish the interior of the sizer die as best you can. 

 

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Norskie posted this 25 January 2022

That makes perfect sense. My machinist skills are hobby at best. What method do you use to taper the die?

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MP1886 posted this 26 January 2022

You can taper it with a variety of tools.  You can do it with a boring bar, a tapered reamer, a tapered countersink, and as a last resort a Dremel with a long straight fine grinding wheel.  Whatever you do you have to polish it till it shines! Depends what you have around your shop. I assume you have a lathe if you made the die. 

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Norskie posted this 26 January 2022

I do have a lathe, and now another project. Thank you.

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Norskie posted this 26 January 2022

As suggested, I chucked my sizing die in the lathe and added a taper. I then polished the entire die a little bit more than I had done when I initially made it. SUCCESS! I am now able to properly seat a gas check without any deformity. Now it's time work a load up. Thank you to everyone that provided their thoughts. Greatly appreciated.

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