37 rimmed rifling twist

[samari46]

I'm planning on rebarreling a British #4 action from 303 British to the 37 rimmed which is nothing more than the 303 case necked up to take 375 cast boolets. I have a copy of a line drawing given to me and it just shows a tiny shoulder. But since it will headspace off the rim no biggie. I have a older semi preturned 375 barrel blank which is marked 1x12 twist and slugs out at .377 so I'm thinking it was originally made for a 38-55. Heaviest cast bullet will be 300 grains. so this twist besides the other things may be too fast. Maybe 1x14 or even 1x16. Thanks in advance for your suggestions and comments. Frank

[Wayne Smith]

It is arguable that there is no practical too fast a twist, i.e. Overstabilizing a boolit. In theory this might be possible but in a practical applied sense I doubt it. Ideal twist maybe not, but twist stabilization is measured by boolit length, not weight, as well. Give us the length of the boolit and it can be put into some calculators - but I'd go with what I have.

[Chill Wills]

You are basically making a 38-50 Remington Hepburn at 0.376" groove diameter. It should be a fun rifle. I agree that you will have all the twist you will need for 300gr bullets. Should you want to, bullets as long as 1.350" or a little+ could work.

[Outpost75]

I have found that fast twist and heavy bullet makes for a pleasant "blooper" rifle with the lightest charge which reliably gets the bullet out of the barrel. I would recommend that you try about 8 grains of Unique with a soft 300-grain bullet for about 900 fps and see how much fun you can have.

[samari46]

I have the Lyman 375449 with gas check mold but haven't cast with it yet and still have some of the sample cast bullets that some of the members here were most kind and generous to send to me. 300 grains may be optimistic as may have to seat below the case neck. Good analogy regarding the 37 rimmed versus the 38-50 Hepburn. Then there is the problem of flat point bullet noses getting caught on the ring inside the receiver and maybe the barrel. Need to find a #4 MKII action with trashed barrel, I have a #5 action with just the receiver and bolt everything else I'm having to buy. the #5 action has a trashed front trigger guard screw hole so maybe having to drill out for 8mm trigger guard screw. Plans are having the barrel somewhat like the Remington varmint style but only 22". Thanks again, much for for thought. Frank

[marlinman93]

I'd argue that too fast a twist can be worked with, but might result in never being able to push a bullet very fast, and remain accurate. If the twist is too fast the velocity needs to be reduced to ensure the bullet doesn't try to "strip" lead as it's pushed down the bore's rifling. In order for a particular bullet to work it might need the charge reduced so much that in the end it's simply a plinker, and not a very accurate one.
There's a reason that certain twist rates work better for certain bullet weights and diameters. Never good to go too fast or too slow. A little bit either way can always be worked with; but there is such a thing as too fast a twist rate.

[EDG]

The GMDR site has loading data for the .375 Win with a 12" twist.

It is easy to see that the accuracy goes down the drain as the velocity goes up past 1000 fps.

http://www.gmdr.com/lever/lowveldata.htm

[samari46]

EDG, out of all the powders they tested it seems 4198 did seem to give velocities similar to the 38-55 as sort of a schutzen loading. Many of the ones were fast burning pistol powders. Think some schutzen shooters use a 1x16 or 1x18 twist in their rifles. I nother that in one of the paragraphs listing case capacities of water the 9.3x57 was mentioned and my pre war 1928 98 mauser in that caliber has a 1x14 twist. The gents on either accurate shooting and nitro express forums have amassed a huge amount of data regarding the 9.3x57 using the PPU 286 grain round nosed bullet. Which is usually loaded to about 2100 FPS. This is about a 40,000 psi loading. One gent was experimenting with some of the lighter .366 diameter bullets. Some shot well and others not so much. The 1903A3 Springfield has a 1x10 twist, I've shot Sierra' 125 grain spitzers with just a little less than 40.0 grains of IMR 4895 in standard military cases and got X-ring accuracy. I got the data years back when I wrote them requesting less than full power loads. In essence between 38 to 40 grains max 4895. Course I had a Smith Corona A3 with a cherry barrel and had a Lyman 448 rear and a Lyman 17XNB front sight. You take off the entire front sight.You save both the long square KEY and the pin. put the key in its slot on the barrel and slide then slide the sight over the barrel keeping the key aligned under the sight and center up the two holed in the sides to the notch in the key and then use the pin to go through one side,then through the notch in the key and out the other of te sight. Think of the sight as a figure 8 the lower part is what gets mounted on the barrel and the top is the sight.With the above loading 1" at 100yds was easy. Bit more difficult with 72 year old eyes. Thanks for the link' Frank