I made the mistake of buying a Sabatti in 500 NE. First of all the front sight had to be changed to a higher and smaller diameter tru-glo globe style sight."
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Numerous friends, and I, have no trouble at all with the height of the original factory sights. However, in my experience, a smaller percentage of guys do have to modify the height of the sights, apparently due to their having a fuller, heavier face, a different length neck, maybe a different upper body build, or a combination of these. Such "problems" can happen with any double, no matter who made it. One double seldom fit the build of all people.
"A decent Pachmayer decelerator pad fitted, mercury reducer and the cast off in the butt straightened a little as it walloped me in the jaw every time."
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The original factory recoil pad was never intended to be used, because the length of pull must first be achieved for the intended shooter, which will vary from one person to another, depending on body build, as most everyone knows, and a "good" recoil pad fitted after cutting stock to appropriate length for LOP. Numerous of my friends, and I, have no problem at all using original factory stock, which does not smack us in the jaw at all---again, different facial build, length of neck, upper body build, etc. all factors into the equation.
Yes, Sabatti does use one action size, type, and weight for all of its big bore double rifles, but so does most of the other makers of modern double rifles in the world. The action, and all internal parts are far from weak, and are plenty strong enough for any and all calibers so chambered for. However, the overall rifle weight is what factors into the equation, due to different barrel weights on different calibers, making for increased recoil in the heavier calibers, such as the .500. The original factory rifle weight is about perfect for the .450/.400, at around 10 pounds, borderline for the .450,at about same weight, a bit too light for the .470, and entirely too light for the .500; adding mercury recoil reducer to buttstock helps, but it is not the most appropriate solution to the problem. The problem is that the monoblock, and the barrels within the monoblock, begin their taper way too soon, which reduces weight way too much. The British had it right a good long time ago, when they made many .500 with full outside diameter barrels out to as much as a foot, before said taper begins, thus keeping badly needed barrel weight and action weight where it needs to be, between the two hands when in firing position. To deal with this problem, I cut the original barrels off my .500 Sabatti, bored and reamed the original monoblock, installed new barrels in monoblock, chambered barrels to .500/.416 Rigby. Further, I made a new monoblock from scratch, with no taper to it; installed new barrels into it, chambered to the .500 nitro, which maintaining full outside diameter out to around 12" before taper, giving a final overall weight of around 12 pounds, about perfect for a .500. This makes for a nice two barrel set, both regulated by me, using somewhat modified methods learned from W. Ellis Brown in gunsmithing school class he taught, prior to his writing his book about same subject, Converting Double Shotguns to Double Rifles.
" Front trigger was then ground a bit on the back edge as it kept slicing my trigger finger open when firing the left barrel."
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I never had this problem, but it is easily dealt with, probably simply by filing down sharp edges.
It too was supposed to be regulated with Hornady factory DGX ammo. The test target from factory has them impacting on the same level 1" apart at 50m. I have never been able to get anything even close to this with mine. I have tried Woodleigh and now just recently have been able to obtain Hornady 570gn DGX bullets and played with various powder and weights to get anything from 1800-2000 fps. I don't know if they Hornady are bumping up the balistics of their factory ammo but 2000fps is as fast as I dare go. That equates to 108gn of ADI2209. Extraction is a bit sticky and primers starting to flattern. Still it shoots alot further apart than the factory test target.
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Some Sabatti doubles don't seem to be as well regulated as others, certainly. With all doubles, it is always best to use the same bullet profile, and bullet weight, as rile was originally regulated with by maker, and the same velocity as was originally regulated with by maker. I have seen many Sabatti rifles regulated well; all of my three are (my fourth one, as detailed above, in two barrel set, .500/.416 Rigby and .500 were regulated by me).
The "nitro for black" load, straight out of Graeme's book (72gn of ADI2208 with 440gn Woodleigh) shoots that well at 50m you can get each barrel to cut holes together they land that close.
"I have now fired several hundred rounds out of it experimenting with different loads to try and regulate that now every time you fire the first barrel( doesn't matter which one but I fire the front trigger or right barrel first) the bloody safety catch engages. This is not something you want to happen in the bush!"
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I suggest you do what I did with all my Sabatti doubles, and numerous other double rifles in my collection, to cut the automatic safety link, converting it to non automatic safety; that will solve the problem. I cannot help but wonder if, during recoil, you are shoving the safety back on, without realizing it?
" I need to find someone in Australia who is knowledgeable in Double rifles and start re-regulate it and fix the safety. Instead of telling me to flog it off and buy a "real" double- which I can't afford.
Goes to show the old saying is true- buy cheap, buy twice...