Cutting barrel to a shorter length?

[Marvin S]

13/16 straight 40cal GM bbl. years ago I seem to remember it was recommended that you cut the breech end instead of the muzzle end. I assume this practice is no longer valid with modern barrels or is it?

[smallpatch]

If it's a new barrel, so sights and underlugs are not a problem, cut from the muzzle.  Then you only have to re crown.  Much easier than rethreading the breech.

[little joe]

Douglass recommended cutting 2 inches off the muzzle to 42 in, however I have saw many 44 inch ones shoot very good.

[Marvin S]

Yes it will be a brand new barrel. Seem to remember the reason was possible bore run out, bore not parallel or centered through entire length.

[hudson]

Some barrels are choked GM are not as far as I know. Push an oversized ball through an oiled barrel and check for tight spots then go from there.

[Marvin S]

Some barrels are choked GM are not as far as I know. Push an oversized ball through an oiled barrel and check for tight spots then go from there.

I値l check that. GM says their barrels are air gauged so I figure they should be a straight bore. I値l try to contact them.

[Scota4570]

GM says their barrels are air gauged so I figure they should be a straight bore. I値l try to contact them."

Air gauge tells you noting about straightness.  IT measures the size of the bore. 

I often get a 42" GM and cut it back of the individual project.  Often the bore it better centered at the muzzle than , say, 8" back.  No big deal, put the thin side up.  Alos take into consideration the breech end eccentric.  The thick side is where the CM logo is stamped. 

Be careful not the put the thin side, on the side, because it will make you sights look goofie. 

[Marvin S]

Air gauge would tell if it was choked or not. Thanks for the tips on clocking the barrel, I will heed your advice.

[Elnathan]

"GM says their barrels are air gauged so I figure they should be a straight bore. I値l try to contact them."

Air gauge tells you noting about straightness.  IT measures the size of the bore. 

I often get a 42" GM and cut it back of the individual project.  Often the bore it better centered at the muzzle than , say, 8" back.  No big deal, put the thin side up.  Alos take into consideration the breech end eccentric.  The thick side is where the CM logo is stamped. 

Be careful not the put the thin side, on the side, because it will make you sights look goofie.
[/quote]

How much off center? I was thinking of getting one of their 15/16 barrels at some point and giving it a light swamp (About .10-.125 taper and then have it flare back very near to breech width.) If the bore isn't  parallel to the exterior that complicates things a bit.

Also, I thought that the logo was stamped on the thin side of the barrel, not the thick side, so it would shoot high with the logo down.

[rick/pa]

Douglas barrels drilled the bore after the outside was finished. Runout was at the breech and they stamped their logo on the thin side so you put the stamp down.  I thought Green Mountain drilled the bore first and finished the outside between centers so the bore was centered.

[Marvin S]

Douglas barrels drilled the bore after the outside was finished. Runout was at the breech and they stamped their logo on the thin side so you put the stamp down.  I thought Green Mountain drilled the bore first and finished the outside between centers so the bore was centered.

That is my understanding.

Edit: Got a reply from Green Mountain. Checked with engineering and they said you can cut from the muzzle end.

Doesn稚 really tell me much but that痴 what they said. I値l keep previous advise in mind. Thanks

[Scota4570]

Douglas barrels drilled the bore after the outside was finished. Runout was at the breech and they stamped their logo on the thin side so you put the stamp down.  I thought Green Mountain drilled the bore first and finished the outside between centers so the bore was centered.

That only centers it at the ends.  The bore may not be straight.  When you cut it,  the bore could then be off center.  I just measured a GM barrel cut off that I recently worked.  The original muzzle is within 0.002" of centered.  8" back the bore is off by 0.015"  Not a problem.  Just check it and time the breech plug so your sights  are not way off to the sides of the dovetail. 

[Marvin S]

Thanks, I値l be cutting about four inches off. So I値l do that first and re crown then time plug accordingly.

[Dphariss]

13/16 straight 40cal GM bbl. years ago I seem to remember it was recommended that you cut the breech end instead of the muzzle end. I assume this practice is no longer valid with modern barrels or is it?

Cut the  breech.

Dan

[Marvin S]

Barrel should be here in a couple weeks. Guess I値l try to measure it and go from there or flip coin.

[rick/pa]

You could check the bore for straightness the way the old timers did. Run a string through the bore and tie each end to a bow. Hold the barrel up to the light and look through the bore. If the bore isn't straight, the string will have a gap between the string and bore.  Take to it an anvil and whack it with a hammer to straighten.  The trick is to know where and how hard to whack the barrel.

[Marvin S]

Big long box from Pecatonica showed up today earlier than expected. Looks good so far, I like the narrow lands of the newer GM barrel better than the older wide ones.

[Daryl]

Narrow lands makes for easier loading with snug ball/patch combinations.  Saw a fairly new GM barrel at Rendezvous last week and thought I was looking
at a Goodoien barrel. That is a good change by Green Mountain. This is not to say that their older barrels won't shoot well - they do, and sometimes, quite
spectacularly.

[Marvin S]

Yes, I have high hopes for it.