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I'm mulling over having the barrel cut down the pre-safety 1894 that I had converted from .44 mag to .45 Colt about 6 years ago. It was re-barreled with a 20" Microgroove 1:20 twist barrel that I got from Numrich. I've been trying to figure out what effect that will have on it's accuracy, particularly with heavy bullets. One of my favorites is the 270-SAA and they drop at around 285 grains from my mold using reclaimed range lead. They fly at about 960 FPS with 9 grains of unique under them.

I've read a bunch and have still not got my head around what happens if I lower the bullet's rotation from 1 (1:20 x 20") to .80 (1:20 x 16") before it exits the muzzle? I've read a bunch on twist rates and and even found some calculations for working out bullet rotation. RPM is calculated as 12 divided by twist rate, times velocity, times 60 so I've read. In my case 12 / 20= 0.60 x 960= 576 x 60 = 34,560 RPM. At 960 FPS it would take a bullet 0.31 seconds to travel 100 Yards. More math then, 0.31 x 34,560 = 10,714 / 60 = 179 revolutions before it hits the target.

I came away with 2 thoughts after all that 1) Barrel length doesn't factor into the equation 2) My head hurts..... My Rugers single actions have a 1:16 twist and 7-1/2" barrels, lets call that a half a rotation before leaving the muzzle and they are dead nuts accurate with the same loads at 25 yards.

I like the idea of a short quick handling "trapper" but not at the cost of unstable and tumbling bullets. Whats the impact then on accuracy and stability if any of a less that full twist before leaving the muzzle?

Someone care to help out a ballistics challenged forum member?

Thanks!
 

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I seriously doubt it matters. Plenty of people have chopped 44 magnums with the even slower 1:38 twist to 16" trappers and none have reported negative performance in the shorter barrel. The only thing is you may lose a little velocity so might need to tweak your loads to keep them at the speed you want.
 

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I can’t tell you about a 1894 or 45/44 or ballistic affects but I did cut a Marlin 30AS that I had rebore to 356 Win to 16.5”. After using it for 2 deer seasons the only difference I can see is that you must concentrate a little more on trigger control and holding steady while aiming and shooting. I think this has to do with less weight on the front end and a little different balance. This gun is scoped with a Leupold vx1 1-4x. All in all I love the conversion. Accuracy off the bench has not suffered at all.
 

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My idea on this is you can do the math using those equations all you want...
But the only accurate way to determine the effect of cutting a barrel down
is to use a chrono.
I wouldn't think going from 20 to 18 would make any significant difference
for the purpose of target shooting.
I have a 44Mag I cut down from 20 to 18 and it changed it so little I never
even bothered to chrono it.
But it did make it a dream to carry in spring while I scout for game trails.
 

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Shortening (or lenghthening it) the barrel will not change the rate of rotation. It will still rotate one turn every 20 inches. Whether the barrel is 10" long or 40". 100 yards =300 feet=3600 inches /20= 180 rotations before the bullet gets to the target. Shorter barrel may make for a slower bullet which will take longer to get there at a slower RPM, hence same amount of rotations. RPM may vary a lot, but RPD (rotations per distance) will not. Within reason. There will be some loss as the bullet loses both forward and rotational speed, but it will be very slight.

Luisyamaha
 

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I think the most critical issue of having a barrel cut down (as far as accuracy goes), is to MAKE SURE THAT IT IS DONE CORRECTLY!!! An improperly executed crown on the muzzle will do more to hurt your accuracy than the loss of 4" of barrel length. I read somewhere once that "accuracy is simple: it's good bullets, going through good barrels". Hard to argue with that.

As a side note, I have a Rossi 92 in 45 Colt, with a 16" barrel. It is no less accurate than a Marlin 1894 CB Limited in 45 Colt with a 20".

Since you've already changed it some, I'd say go ahead and do it.
 

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Shortening (or lenghthening it) the barrel will not change the rate of rotation. It will still rotate one turn every 20 inches. Whether the barrel is 10" long or 40". Luisyamaha
Absolutely.

What will change is the velocity of the bullet. As the time it takes a bullet to travel that 20" increases or decreases so does the rotational speed (RPM) of the bullet. Most .45 Colt pistols have a faster 1:16" twist. But any potential loss of RPM by using a 1:20" twist barrel is more than offset by the higher velocities in rifle barrels, even a 16" long barrel. So, bullet stabilization should be no problem if you make the cut.

However, the 16" barrel will produce substantially lower velocities than the 20" barrel. Ballistics By The Inch calculated .45 Colt velocities for different length barrels. Their computations showed little difference in velocities in rifle length barrels.

However, their actual measured velocities revealed big velocity losses. In real firearms, "real world weapons", you may see a 200-300 fps velocity loss by going from 20" to 16".

This is the Ballistics By The Inch "real world weapons" table for .45 Colt:
Ballistics-by-the-inch-real-45-colt-data.jpg
 

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Absolutely.

However, their actual measured velocities revealed big velocity losses. In real firearms, "real world weapons", you may see a 200-300 fps velocity loss by going from 20" to 16".
I really doubt the OP is going to see 200-300 fps difference in only 4" of barrel. I have a Carbine Classic .45 Colt with two barrels, one the factory 20" and the other that I cut to 16". At the most I see about a 30 fps difference between them.
 

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Longer barrels are not inherently more accurate than shorter ones. Actually, the case can be made that shorter barrels, all other things being equal, are stiffer barrels, which leads to more consistency between shots and hence better repeatability (accuracy). With iron sights longer barrels provide more distance between front and rear sight, which makes sighting more precise, allowing for more accurate shooting. There are rifles made with bloop(?) tubes which extend the sighting radius while keeping the barrel short. The longer barrel may also allow for steadier holding, with the mass of the barrel further away from the body of the shooter. But this is not barrel accuracy, but better conditions for the shooter.

Luisyamaha
 

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Agreed ! Especially in a handgun cartridge designed and loaded with powder for a short barrel weapon.


I really doubt the OP is going to see 200-300 fps difference in only 4" of barrel. I have a Carbine Classic .45 Colt with two barrels, one the factory 20" and the other that I cut to 16". At the most I see about a 30 fps difference between them.
 

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Barrel length has NOTHING to do with bullet rotation rate.

Bullet RPM = MV X 720/Twist Rate (in inches)
 

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Just be careful to not cut it too short so it can be classified as a SBR. BATF says the measurement of the barrel length includes the length of the chamber in the measurement---not from the joint between the barrel and the receiver.
 

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Discussion Starter #14
I was right. You guys are awesome. Makes sense now and I very much appreciate all your input. Makes a whole lot more sense now.

I'm going to do it! I think I'll also get a chrono too, it'll help me tweak loads after the cut. A friend let me use his when I originally did it but I've moved.

Thanks for the legality tip also Cowboy23* I'll make sure the smith that's doing work is aware also.

Actually going to have him do a 16-1/4" cut. Leave a little extra on the odd chance the crown might get damaged and need to be redone in the future.

Try to get it dropped off at the smith this week. I'll post pictures and updates after it's done.

Sent from my Moto G (5) Plus using Tapatalk
 

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You will not regret the transformation. I have three shorty .44's (one factory, 2 shortened) and could not be happier in the deer hammering performance paired with the fast handling portability. The change in velocity is virtually non-existant; the previous table reference from Ballistics by the inch" appears to be a typo- the upper table is the one to look at. It shows velocities as barrel length is decreased in one inch increments.

BBTI - Ballistics by the Inch :: .45 Colt Results
 

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I agree with Gearhounds. I have one 94 44 I'm chopping to 16 and a 336 in 35 Rem for the same to be a Marauder clone. I have read accuracy tests where they started with a 20"+ barrel & shot groups after each reduction ti they got it down to 12". They found no accuracy issues throughout the test.
 

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The faster 1 in 20 twist rate will stabilize the heavier slugs better than the 1 in 38. I cut a Rossi 44 Mag down from 20" to 16 1/4" just because I always wanted to see how hard it would be to do. easier than I thought, I just took my time. Even cutting the sight dovetail and such was fun. I used a Rossi because if I screwed it up I did not want to ruin a JM.
Rossi.jpg IMG_0940.JPG IMG_0930.JPG
 

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I have a Glenfield made in the sixties that has a 16 14 inch barrel and is parkerized with a set of Brockman peep sights that came on it and it shoots just fine, it hovers around a 1inch group at 100 yards with the 125 gr Sierra Gameking HP. I use a case full of RL-7 with WW primers. I took the rear sight off and left the front winged sight on and attached a 3x9 Burris Timberline compact and it is really a worthy woods companion. I like the shorter barrels and have never seen a decrease in accuracy. Back in my younger days me and my buddy cut the barrel on a Remington 03A3 in 30-06 from 24 inches to 22 inches with a pipe cutter, it swaged the barrel and took quite a bit of file work, the pipe cutter is not the way to go. lol. The rifle was very accurate with the cut off barrel and accounted for quite a few deer including a white spike buck, I wish I still had it.
 

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"Cut the barrel from 20" to 16?"

why?

to lose velocity, cut your sight radius by 25% - or you ride in the back of a stryker or bradley and need the room?

if it's just because short(er) carbines are waaay cool - cut away!!
 
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