Gas Checks

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akerlin
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Gas Checks

Post by akerlin »

I went and shot my Rio Grande 45/70 for the first time today. I started with some 315 grain cast lead bullets over 14.7 grains of Trail boss. The accuracy seemed pretty good. I then shot the same bullet over 54.1 grains of Varget. I figure it is pushing the bullet somewhere around 1725fps. After the second shot, the shots were all over the place. If I let the barrel cool down, the shots would return to original POI. I am wondering at that velocity if I need a gas check. I was also using Midway vegetable fibre wads over the charge. I had a few I loaded that didn't have wads. Those were really all over the place.
Last edited by akerlin on 08 Jun 2013 22:17, edited 1 time in total.
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Re: Gas Checks

Post by Missionary »

Good morning
Several factors are involved.
Bullet diameter. This is the first mostt important factor. If your bullet is not at least .001 over groove diameter you need a fatter bullet. In 45-70 I always start .002 over bore. Load that bullet into an empty unprimed case and see if it will chamber. If it does chamber it may still be under throat diameter. Time ago I bought some Cerrosafe to make throat casts so I know how that is shaped. So with every rifearm always think THROAT first. Fill that with a round that will chamber.

Initial and sustained pressure on bullet base. A very slow burning powder like 4350 does not "wack" a bullet base like lets say Unique would . Varget is a reasonably moderate burning powder so that at least looks good... But maybe your load is too much for the next consideration.
The lead mix are you using for this bullet. If this bullet was made from lets say 50-50 (WW - pure) then you should be into pure WW and maybe have to consider water dropping. I do not shoot Varget so have no idea what pressure this is generating.. Did you work up to this load or just start at max or nrear that "?

Your lube may not be holding up to the pressure. Lube does break down with enough heat and pressure. What lube are you using ? If it is a well established high pressure lube this should be OK.

I always recommend casters and lead shooters to wander over to Castboolits/Reloads and start reading. Might as well become a member. We only have years of experience to offer.
Mike in Peru
Way down south in Arequipa, Peru till June 2020.
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Re: Gas Checks

Post by Ranch Dog »

akerlin wrote:I went and shot my Rio Grande 45/70 for the first time today. I started with some 315 grain cast lead bullets over 14.7 grains of Trail boss. The accuracy seemed pretty good. I then shot the same bullet over 54.1 grains of Varget. I figure it is pushing the bullet somewhere around 1725fps. After the second shot, the shots were all over the place. If I let the barrel cool down, the shots would return to original POI. I am wondering at that velocity if I need a gas check. I was also using Midway vegetable fibre wads over the charge. I had a few I loaded that didn't have wads. Those were really all over the place.
It is not about velocity but the pressure behind the bullet that matters. You need to be very careful with wads, especially with rifle powders, simply put, the pressures are unpredictable but higher that normal. I did some work pressure trace work with fillers and wads with straight walled cartridges from the 357 Mag through the 45-70 Govt and honestly it scared the "filler" out of me. I don't use them period, in anything. Too unpredictable.

The 54 grains of Varget should be sitting around a 95% case capacity, it doesn't need any type of filler or wad to compress it. I think your guess of velocity is correct and without the wad it is probably generating about 21.0K PSI. With the wad it is anybody's guess but my guess would be near 40.0K PSI! Shoot it without the wad and see how it does.

The Trail Boss load is generating about 17.0K PSI but is not capable of the velocity that the rifle powder will deliver.
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Re: Gas Checks

Post by Ranch Dog »

I responded to your identical topic in the "Reloading" forum and then saw this topic in "Bullet Casting". So, I merged the two deleting the double topic in "Reloading".
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Re: Gas Checks

Post by runfiverun »

either slow the load down or use a gas check mold.
long about 14-1500 fps is where I lose it with plain base boolits.
gas check boolits have a better protected base and exit the barrel with that square base intact.
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