Poor Accuracy, New Barrel

[RippinSVT]

I'm posting in here rather than the 1911 tech forum because I know it'll get more attention from the serious accuracy guys, and the gun in question will be used to shoot AP eventually.  I recently fit a couple of 9mm Nowlin barrels into some guns, one is my 6" Metallic gun that I built from scratch, and it shoots really good, around 1-1.5" at 50yds.  The other I fit into a 5" Kimber belonging to my father in law.  It started out promising, but after shooting a lot it's not brilliant.  I cannot figure it out.  The barrel has good upper lug engagement at .046", the bottom lugs were fitted with the utmost care and it locks up very tight with zero play and perfectly even lug contact.  The hood has little side play, and the rear of the hood is evenly fitted and polished to full contact the breach face.  Again, every facet of the barrel fit was meticulous and done the same or better than the 6" gun. My issue is this: the gun will often put 3-4 shots into one ragged hole at 25 yards, then toss a shot WAY out, like 2-3" up or down, usually a few of them.  Then the next group will be a pattern, then perhaps another decent group for a few shots. The bushing is fit tightly to the slide, and the barrel is snug into the bushing but still moves freely.  The issue seems prevalent when the gun is warm. The loads are my 115gr match loads off my 1050 Ammobot and extremely consistent, although the 5" gun shows an annoying preference for 124's.  The gun has been benched by myself and my father in law, both of us very experienced shooters who do a TON of bench testing, as well as from my Ransom.  It's absolutely the gun, and it's not something obvious.  Worthy of note is that the gun shot terrible before the new barrel, like 3-4" at 25yds, and this is a very high trim Kimber model (not a Kimber fan personally). Here's what I'm figuring on double checking:

 

-Bushing could be springing the barrel after it warms up

-Extractor tension may be inconsistent, causing fliers

-Barrel hood might need filed off the breach face, there's a few schools of thought on this. I was always taught even contact fit, but Kart and others like a .001-.003" clearance

-Slide recesses inconcentric, causing erratic lockup (from Jerry Keefer).  I know Kimber built this gun on a Friday afternoon because they cut the VIS way too far back in the frame

-Recoil spring guide binding on front of lower lugs

-Perhaps a bad barrel, although rare they do happen, and I know a few of our fellow Bianchi dudes have had issues with Nowlin

 

I'm losing my mind here trying to resolve this issue. I've never had a gun that could shoot 3-4 shots into 1/2" at 25yds, then toss a shot 3" up and another 2" down and over.  It doesn't make sense.  But then, it shouldn't have been a 3-4" gun from the factory at $1600. There is no conceivable movement in lockup anywhere. .

 

Thanks,

Kyle

[Toolguy]

Sounds like something about the barrel. I would check the crown and clean it well and power lap it. It may be building up fouling, then clearing out, then building up again. 

[RippinSVT]

Good idea. I was thinking crown. It did seem to have some buildup there as if it was a tight spot. I'll recrown it.

[ffl]

What type of bullet? jacketed, plated or lead?  is your automatic machine varying the criimp?

 

I would check those issues that would be affected by heat first after Warrens suggesting.  What heats up first is the barrel and bushing.  binding up would keep the barrel from locking up in the same position.  and at 25 yards just a few thousandths of and inch could make the flyer.  lube the barrel with a good quality oil that stays when hot. or a good EP grease (light coating) on barrel where it locks up with bushing.

 

David

 

[RippinSVT]

Thanks David, that's one of my prime candidates currently. I might try (if tolerances allow) throwing my Briley spherical bushing in there to discount any binding. 

[Griz]

How well does the brass group?    I once had similar issues and my brass and bullet would both have fliers at the same time.  

 

It turned out that the magazine was too low in the gun, which cause some rounds to hang up momentarily, which robbed the slide of momentum, which because of the tight fit caused inconsistent lockup.  

 

A raised mag catch solved the flyers as well as the rare (1 in 192 rounds ) jam

[Service Desk]

I think that David is on the money, barrel / bushing bind and hood length bind when hot are the prime suspects.

[RippinSVT]

Okay guys, much thanks.  After work today I'll check the following:

 

-ejection pattern consistency (magazine and extractor issues)

-bushing bind/springing (replace with Briley if it'll fit)

-Hood length check (in conjunction with bushing, could cause binding after it heats up)

-recrown barrel

 

 

It's gotta be something stupid.  Something unusual.  Not that I'm a pro gunsmith, but all "normal" parameters that yield good accuracy check out.

[RippinSVT]

Found a couple issues:

 

-the extractor tension in this gun way super erratic. Just tuning that shrunk the groups by half with the horribly fit factory barrel

 

- the bushing on the Nowlin has gained a ton of slop in just a couple hundred rounds. Is it normal to have a pronounced step 1.25" back from the muzzle on the barrel OD? My other barrels only have a slight one at the last 1/4". This seems to be hanging up on the tight bushing coming in and out of battery. It's a pronounced .006" step. I've got another bushing and I'm thinking about turning the barrel down and refitting the bushing. My 6" Nowlin has this step, but it's way back like 3" and isn't touched by the bushing coming in and out of lockup.

[ffl]

put that barrel i a chuck in a lathe and stone that step so it is gradual

 

[Ross Carter]

You might check the slide stop pin diameter and the hole in the frame, John Nowlin made bushings and would re-bore the frame on problem guns.

[RippinSVT]

Pin diameter is good, only a couple thou clearance. Lug contact is tight, consistent, and even.

 

 

David, this give me an excuse to use the 42" Southbend that I don't know how to use. I'm gonna blend the bump out to a taper.

[DougCarden]

Did someone say Crown????

 

Try an EGW bushing and see if you get any better results?

 

DougC

 

 

[Toolguy]

Kyle-

If you're ever in the KC area, come over to the shop and I will show you anything you want to know on the lathe.

[RippinSVT]

9 hours ago, DougCarden said:

Did someone say Crown????

 

Try an EGW bushing and see if you get any better results?

 

DougC

 

 

I was mostly sober during the fitting of said barrel. No Crown on the crown Douglas.?

 

8 hours ago, Toolguy said:

Kyle-

If you're ever in the KC area, come over to the shop and I will show you anything you want to know on the lathe.

 Thanks Warren! I might take you up on that.

[RippinSVT]

Okay, we turned the barrel down in the lathe to leave a gentle increase in diameter at the muzzle without the ridiculous bump that the bushing was

hitting, and fit a new bushing and substituted a light grease for oil in that area.  Fit a new extractor to yield consistent tension as well. Also checked for inconsistent hood contact at the breach face, but it was good so we polished it and called it done.  I'm gonna Ransom the gun again today if the weather clears for a bit, but I think I'm on my way.  Sidenote: Kimber has positively shit dimensions on their 9mm guns...getting the timing right on these guns with good VIS contact is a nightmare.  Everything I touch from now on will be Caspian, JEM, or STI.  I don't wanna deal with all the extra BS with out-of-spec tolerances and geometry.

Edited March 27, 2017 by RippinSVT

[RippinSVT]

And thanks for all the help guys!

[goldfieldshooter]

How did ir go Kyle?

[RippinSVT]

5 hours ago, goldfieldshooter said:

How did ir go Kyle?

 

Good results thus far, with little time to shoot it and a lot of rain putting a damper on things.  After turning the barrel down and fitting a bushing, the only wild fliers I'm getting are first shot hand-chambered rounds, but they are predicatably going high-right by a 2.5" at 25yds.  I believe that's just tight extractor tension, which I will tune out.  I threw it haphazardly into the Ransom rest and had generally good results with the majority of the 20-30 shots going into under an inch at 25yds.  Still have some fliers, but not wild ones, and not so bad that I can't attribute it to my poor Ransom technique.  I'll keep chugging away, this gun has been a headache from the start with out of spec tolerances and geometry.

Edited March 30, 2017 by RippinSVT

[RippinSVT]

Quick follow up: I had Jess Clark look at the gun a few weeks ago and he said the fit was very good, but that bushing seemed to have some tight spots when he spun it on the barrel. I put the barrel back in the lathe and turned down roughly .0005-.001" off the muzzle bump with emery cloth and put the same bushing back on and they thing is shooting absolute BUGHOLES. I'm talking hand fired groups for 6-10 shots into under a nickel size at 25. 4-5-6 shots totally into the diameter of a dime. Thanks for all the help guys.

 

For fun we dropped it into a 38 Super Les Baer with the 1.5/50 guarantee and it fit very snugly (luck) and it outshot the Baer barrel by 30-50%. 

[gm iprod]

Looking good. I have had a few issues with Kimber lately and have stepped back from them. The only one I own now is a 1 of 1000 Target Match 45ACP that shoots 2.75" of fa sandbag at 50y with 200gr SWC or 185gr Zero JHP.

 

We recently fitted a .355 6" KKM to a new Taurus 1911, according to my Gunsmith it was a better fit that the job we had done for another customer late last year on a 1 year old Kimber Stainless Target in 9mm.

 

Excuse the low flyer caused by Operator error (me) rest of group is seated at 25M off a tool box covered with a blanket. 115gr Zero at 1130fps. Shoots better with 125gr once we worked the load out for the customer.

[RippinSVT]

29 minutes ago, gm iprod said:

Looking good. I have had a few issues with Kimber lately and have stepped back from them. The only one I own now is a 1 of 1000 Target Match 45ACP that shoots 2.75" of fa sandbag at 50y with 200gr SWC or 185gr Zero JHP.

 

We recently fitted a .355 6" KKM to a new Taurus 1911, according to my Gunsmith it was a better fit that the job we had done for another customer late last year on a 1 year old Kimber Stainless Target in 9mm.

 

Excuse the low flyer caused by Operator error (me) rest of group is seated at 25M off a tool box covered with a blanket. 115gr Zero at 1130fps. Shoots better with 125gr once we worked the load out for the customer.

 

Awesome! I'm done messing Kimber even if the gun is a good deal.  I've got a 45 that shoots pretty well with a Kart in it, but the 2 9mm's I've worked on have been geometry nightmares.  

[IFlynn]

On 3/25/2017 at 3:45 PM, DougCarden said:

Did someone say Crown????

 

Try an EGW bushing and see if you get any better results?

 

DougC

 

 

 I'm trying to EGW bushing myself for the first time. A part that is machines to such precise tolerances is intriguing. Hopefully it turns out as great as they look online. 

[Service Desk]

12 hours ago, IFlynn said:

 I'm trying to EGW bushing myself for the first time. A part that is machines to such precise tolerances is intriguing. Hopefully it turns out as great as they look online. 

They work great on my bushing barrelled 1911's. The drop-in version requires very little work to achieve solid barrel support and just a tad of polishing to fit an STI slide.