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Post by Hombre on Oct 13, 2019 20:17:24 GMT -7
Coming up with a Providence Tool Company Peabody .43 Spanish military rifle that has had the forearm cut back halfway and the internal barrel/bore is said by the seller to be pitted. The barrel is the original full length 33". I'm obtaining this Peabody as a project and will make some changes. At first I thought of rebarreling it into a 20" carbine in .38-55. Then the lil' light in me head went on and said, "Why not have the barrel cut back to 20" and then reline it to .38-55?" That way should prove less costly than having a new barrel installed/contoured to the original shape. By relining will maintain the original contour. Why yes, winter is coming on and already there seems idle time for 'the good idea Fariy' to come n' visit me. I'm looking at having John Taylor Machine (Puyallup, Washington) do the work/lining. In general the barrel liners he uses have either 14" or 18" twist. Bore and groove sizes are optional www.trackofthewolf.com/pdfs/catalog/page_208.pdfBeing as this will become a 20" carbine, not concerned with having it shoot out to 400-600 yards as a target iron, implying not heavier than 300 gr cast bullets to be used. I'm leaning towards the 18" twist, 235 - 275 gr Bull Shop cast bullet use mostly. Not out to shoot velocities above 1600-1800 fps and most of the time would be using 1400-1500 fps velocities. Black powder and smokeless use. Liner to be .368” bore, .375” groove diameter. Gives me the option of using (pardon my language here) them copper clad factory Winchester .38-55 bullet loads. What be thoughts on the twist rate? |
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Post by Bullshop on Oct 14, 2019 8:32:14 GMT -7
Personally I would go with the 1/14" twist. The 1/18" twist will limit bullet length and will affect performance long before your 600 yard limit. The standard 250gn flat nose bullets are for lever actions with the 1/18" twist and work good in those within the range limits of a conventional iron sighted lever action.
A single shot will have no bullet length restraints so can utilize longer more efficient bullet shapes that will be more resistant to atmospheric conditions.
I have a roller in 38-55 with a 1/14" twist and it too has shown its limits for bullet length.
This rifle shoots well to 800 yards with a custom 320gn bullet but with the Lyman 330gn Postell bullet becomes unstable at roughly 300 yards. I am using bullet weight here as I do not off the top of my head know the lengths of these bullets but the 330gn is visibly slightly longer than the 320gn.
The 320gn has been proven by our own Jr. to be stable and shoot well to 800 + yards. Jr. used this rifle and bullet to place with top youth honors when he was about 9YO. at a long range gong shoot in Amadon ND.
This same rifle with the 330gn Postell shoots very good 100 yard groups and holds accuracy to about 300 yards then bullet stability is lost and so accuracy. There is even an audible buzz past 300 yards indication the bullet beginning to spin off its axis.
Absolutely you can shoot to your self imposed 600 yard limit with the conventional lighter weight flat nose bullets but also just as absolutely certain your impact dispersion will be greater due to increased lag time and the winds effect on same. Shooting long range is not nearly as satisfying when missing or grouping is poor.
If your going to shoot long and 600 yards is long with these type guns then you may as well properly equip yourself to do so and with the 1/14" twist you will be better equipped to do so.
Interesting that when Winchester brought out their high pressure 38-55 in the form of the 375 Win big bore they went with a 1/12" twist even though they only offered the cartridge in 220gn bullet weight. The reason for this is not in external ballistics but in terminal ballistics. With external ballistics a certain rotational velocity can keep a bullet stable in flight and in some cases like mine with the 320 and 330gn bullets just barely but when that just barely stable impacts or even touches something in flight like a tree limb it can then easily tumble. The additional rotational velocity helps the bullet remain on a straight course in its terminal penetration even as the bullet is becoming deformed in expansion, to a point.
What we are seeing in modern high power rifles is that it is better if the bullet is rotating at a higher velocity than the minimum required as it does not seem to affect accuracy, again TO A POINT !
At a time when all cartridges were loaded with black powder the absolute minimum rotational velocity for stability was targeted for the purpose of reducing black powder fouling. Since we now have the option of smokeless powder the bare minimum twist rate for stability may not be the best choice. Even if loading with black powder in long range target shooting all you need to do to prevent powder fouling from being a problem is wipe the bore between shots, no biggie!
Anyway that's my opinion and worth what you paid for it.
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