Warning

 

Close

Confirm Action

Are you sure you wish to do this?

Confirm Cancel
BCM
User Panel

Posted: 10/9/2014 3:42:17 AM EDT
Is there any harm in cutting a 12 inch M203 Barrel down to 9 inches.

I should have gone with the 9 inch when I purchased, but i was talked into the 12 . Now I am looking at shortening the barrel.
Link Posted: 10/9/2014 3:48:09 AM EDT
[#1]
How do you recrown a 40mm bbl?
Link Posted: 10/9/2014 4:03:36 AM EDT
[#2]
Barrels aren't that expensive are they?
Link Posted: 10/9/2014 5:53:32 AM EDT
[#3]
As the barrel being on the thinner side relative to other barrels, i don't think it would be that hard to re-crown. Plus, there isn't really much of one to begin with.

I called LMT about a week ago and a new 9" barrel would cost me about $300.
Link Posted: 10/9/2014 6:10:10 AM EDT
[#4]
Do that and sell the barrel you have now used...
Link Posted: 10/30/2014 10:13:29 PM EDT
[#5]
I have a 12" barrel that was dinged pretty bad on the crown.
I chucked it up in my lathe and turned off about an inch and recrowned.

The barrel is 7075 or some similar type of hard aluminum.  It was probably beyond the limits of my little 9X20 Jet lathe but I got it done.
Test fired and no problems.

Unless you have a large spindle bore lathe that's about as much as you can cut it down with using a steady rest.
You could part it off at 9" with a huge live center but I have no idea how to crown it accurately after.

My plan is to cut it back to 9" but I'm going to have to use my buddy's much larger Webb for that.
I've got an extra 12" and really like the look of a 9".
Link Posted: 11/1/2014 11:49:46 PM EDT
[#6]
I cut mine down yesterday and it shot just fine.
Just FYI
Link Posted: 11/2/2014 2:54:22 AM EDT
[#7]
Did you re-crown the barrel?
Link Posted: 11/3/2014 12:05:43 AM EDT
[#8]
Yes, once it was cut off I just gave the inside a little bevel.
The barrel was already indicated in on the bore so it was very easy.
The hard part is having access to a big enough lathe.
I ran about 50 rounds through it today with no issues.
Link Posted: 11/3/2014 9:08:21 PM EDT
[#9]
I've done a few barrels, using nothing more than a mini-lathe. A big lathe is not needed, if you don't have one. Re-crowning is pretty simple with a rounded file. The barrels are aluminum, and not steel, so cutting and crowning goes fast. I removed the plastic handguard from the barrels when I did mine, but I think you could chuck them with the inside jaws and avoid this. GROG
Link Posted: 11/5/2014 10:47:46 AM EDT
[#10]
That's what I did for the initial 1" cut:  chuck on the ID with the inside jaws as my chuck isn't big enough to clamp the OD.
I had issues with the tool trying to push/flex the barrel off axis so I used my steady rest.
Since the top part of the barrel has that raised portion I was limited in how short I could go with that setup so I just went to a bigger lathe that could clamp the OD.

GROG, I don't think it's much but do you know the velocity loss with the shorter barrel?
Link Posted: 11/5/2014 10:14:53 PM EDT
[#11]
I've fired both the 12" barrel, and the 9", using the same ammo, at a range of 400 meters, and both barrels were hitting within the 10 meter radius, considered a hit at that range. At some point, I do want to get a chrono and test them, but funds are short right now. Kitchen remodeling is eating every dime I have right now... GROG
Link Posted: 11/5/2014 10:21:06 PM EDT
[#12]
GROG, I can set up the chronograph and do that.  I'll post here and on your website when I get the data.
How many shots with each do you think would give reasonably reliable info?
Link Posted: 11/6/2014 9:31:29 AM EDT
[#13]
When I test casings for reloading data, I normally mark each casing with a letter and number, then mark the projectiles (when zinc, you can stamp them with the same letter/number combo as the casing). I keep a log of the launcher I use with each, barrel length, or anything else that changes between rounds. 5 rounds fired from each barrel shoud give you a good result. You can then do a drawing of the target area, indicating point of impact of each round fired, and break down each to it's chrono reading. This will give you the best results for comparing barrel length, and should indicate whether 3" makes a great difference. With the high/low pressure system, I doubt you will notice any, as the main thrust is imparted at ignition, and not during barrel travel. With a rifle, and pistol, you are effecting range and speed with barrel length. With the 40mm LV, all the power is generated when fired, and goes downhill from there. Happy testing, GROG
Link Posted: 11/6/2014 5:14:02 PM EDT
[#14]
These will be factory fresh chalks from your group buy a while back.
Close Join Our Mail List to Stay Up To Date! Win a FREE Membership!

Sign up for the ARFCOM weekly newsletter and be entered to win a free ARFCOM membership. One new winner* is announced every week!

You will receive an email every Friday morning featuring the latest chatter from the hottest topics, breaking news surrounding legislation, as well as exclusive deals only available to ARFCOM email subscribers.


By signing up you agree to our User Agreement. *Must have a registered ARFCOM account to win.
Top Top