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mk II M77 .223 barrel cut

This is a discussion on mk II M77 .223 barrel cut within the Ruger Bolt Action forums, part of the Rifle & Shotgun Forum category; 1st post here. I have this rifle (780 series, manuf 1991) in stainless with 22" barrel. 1:12 twist. zytel (boat paddle) stock. I want to ...


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Old April 6th, 2013, 09:00 PM   #1
 
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mk II M77 .223 barrel cut

1st post here. I have this rifle (780 series, manuf 1991) in stainless with 22" barrel. 1:12 twist. zytel (boat paddle) stock. I want to cut barrel to 16.5" and add peep sight and banded front sight. I know I can probably only shoot 50 gr bullets with this twist (regardless of bbl length), but will shortening the barrel noticeably affect ballistics? I only plan on shooting/hunting a max of 125 yds. I know velocity will probably drop 50 fps per inch lost, but will that really affect accuracy? If not 16.5", what about 18"? All my rifles have short barrels.
thanks for all your thoughts...



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Old April 6th, 2013, 11:44 PM   #2
 
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Can't help you, but.....
Welcome from Australia mate.
Glad to have you on board, nice folk here and lots of good info.
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Old April 7th, 2013, 03:49 AM   #3
 
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Howdy and welcome from Texas.
There is a lot of super people on this forum.
The total knowledge and experiences is GREAT!
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Old April 7th, 2013, 05:08 AM   #4
 
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18" is a bit of a sweet spot for the .223 in terms of velocity versus barrel length and I'd recommend that over 16" barrel.

Accuracy wise, it depends on the barrel. I had a Contender with a 14" heavy barrel that would shoot 1/4 MOA groups with 52 grain match bullets - in that case a short and stiff barre; worked very well. I've also had 16" heavy barrels on ARs that were working hard to be 1/5 MOA accurate and 2-3" groups at 100 yards are the norm on 16" standard weight barreled ARs where most 20" ARs will do 1.5 MOA with an A1 or A2 profiled barrel.

What a cut down M77 barrel will do will depend on the barrel harmonics as well as the quality of the cutting and re-crowning of the barrel.

1 in 12 twist was standard in the 20" M16A1 barrel and it did just fine with bullets as long as 55 grain FMJs. You'll want to keep the velocity up, but it should work just fine in a 16" barrel as well.

Last edited by Model 52; April 7th, 2013 at 05:11 AM.
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Old April 7th, 2013, 07:34 AM   #5
 
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thanks. most of my rifles are 18" (Rem 600's)..but wanted this one to be a little shorter. I'll probably cut it to 17". Thanks again for your help.
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Old April 7th, 2013, 09:48 AM   #6
 
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I would rebarrel it with a 1:9 twist.....
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Old April 7th, 2013, 10:30 AM   #7
 
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Rebarrel in 1:9? Probably right. But I only plan on shooting light bullets. May regret it later, but that is the plan right now.
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Old April 7th, 2013, 06:52 PM   #8
 
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......people REALLY need to stop talking about bullet weight, and twist.... Weight is a side note at best, it is bullet length and construction along with RPM that matters to stability, PERIOD.

Velocity * 720 / TWIST = RPM

If shooting "on the cheap" is your game, remember that old(TNT, SX, dog towns) tech bullets have a rpm ceiling of around 240,000RPM. Push near that and your group open wide, shortly before you destroy the bullet.
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Old April 7th, 2013, 08:47 PM   #9
 
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This should make for a handy little rifle. Barrels just over 16 inches work well for .223's but expect some velocity loss that won't matter much for ranges under 300 yds. Many .223's have short barrels.

The 1-12 twist should handle 55 gr. bullets and some heavier just fine. Get onto the Berger web site to see the twist calulator for specific length bullets for your 1-12 twist. The Sierra Infinity program also has a twist calculator.

Most .224 bullets today are relatively tough enough to withstand high velocities even when shot from fast twist barrels. I shoot 53 gr VMax's from a 1-9 twist .22-250 with no problems at over 3700 fps getting .5 inch groups and as a bonus can shoot the 68 & 75 grain hpbt also. Both these bullets are shorter than the 75 gr AMax. Bullet manufacturers post velocity ranges.

A real good compromise is the 1-10 twist. I had one in a .22-.250 that would shoot the 40 VMax at over 4000 fps with great accuracy and would also shoot the 68 hpbt. I have not shot 40's out of my 1-9 .22-.250 yet but would not be surprised to see good groups with intact bullets at 300 yds.
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Old April 8th, 2013, 06:18 AM   #10
 
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"Weight, twist, bullet length, construction"....all these things are way beyond my pay grade! For gosh sakes, I'm only a lowly forum newbie PVT. I know these things are so, so, important to maximize the potential of any firearm, but are probably "lost" on me and what I plan to do with the rifle. All in all, I REALLY appreciate being educated on the subject. After the work is done I will post photos (if I can figure that out) and shooting reults.
Now, what about peep sight recomendations? NECG R-100-571? NECG N-100? Williams WGRS receiver sight?
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Old April 8th, 2013, 07:44 PM   #11
 
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The NECG sights that I have seen are all steel and clamp onto the existing receiver bridge (back of the receiver). The next step would be to select a suitable front sight. Installation would probably entail the services of a gun smith but I could be wrong as there could be a "non-gunsmith" self installed sight of some kind. The proper front height sight, considering elevation ranges of the rear sight, would be selected followed by installation of the banded front sight allowing for the diameter of the cut barrel, possibly when the barrel is cut & crowned. A good crown is very important.

I would get online and order a Brownell's catalog and look at the various types of sights and I think they have a chart to select front sights based on height.

This should make up into a real handy tough little weapon well suited for pickup trucks and other vehicles. It would pack real well on a motorcycle.

The 1-12 twist should handle all 60 grain lead core flat based bullets. The 53 gr VMax should work. Many years ago I used the Sierra 52 gr. hollow point boat tail match bullet and found it considerably tougher than their other bullets including their 50's and 55's when shot through a 1-14 .22-.250 for shooting bigger sized varmints. I would guess that you would get about 3,000 fps out of a 55 gr. bullet.

My favorite .223 powder is IMR 8208 but Re 10X works very well along with 10 or so others.

Possibly if I got a good deal on a used .223 MKII I might go for something like that.
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Old April 8th, 2013, 07:59 PM   #12
 
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My boat paddle loves 55 grain bullets. It also shoot the Speer 70 grain sp's very well. I would try some out, you might be surprised.
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Old April 8th, 2013, 08:11 PM   #13
 
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Quote:
Originally Posted by BassMan View Post

Most .224 bullets today are relatively tough enough to withstand high velocities even when shot from fast twist barrels. I shoot 53 gr VMax's from a 1-9 twist .22-250 with no problems at over 3700 fps getting
If that is the case, you have a very smooth barrel. That puts you a tick over 290,000RPM. Which is that bullets ceiling.

You don't need to buy any software to calculate RPM, here is the formula.
MV * 720 / TWIST = RPM
if you want to know rpm limits (barrel smoothness Dependant), I already made the phone call to the mfg's.
F.Y.I. Varmint Bullet RPM Limits - Shooters Forum
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Old April 9th, 2013, 01:55 AM   #14
 
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I re-read this post. Because the Zytel stocked guns seem to have a following, I'd NOT cut this one down, but maybe get a new Hawk-Eye compact with the 16 1/2 barrel in the same caliber.....

I'd like to have a .223 Boat Paddle to match mine in 7.62x39.......
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Old April 9th, 2013, 08:23 AM   #15
 
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Again, thanks to EVERYONE for the detailed info, especially on bullet size/powder.

cptpoly, appreciate your thoughts on not cutting. It does give me pause...while I have cut other rifles, none has been this nice and none has had the "following" of which you write. I have since researched this rifle a little and do find that there is a following of people who collect these in all calibers. Seems like the skeleton (zytel) 223 is popular.
It is amazing to me how much brain power is consumed on this "hobby"---but I love it too.
I'm researching the Hawkeye compact.
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