Shortened and recrowned factory model 70 barrel with interesting results

Hey guys!
So I’ve got a new model 70 in 30-06 and the thing will NOT shoot. I reload, and after 200 rounds trying different bullets/powders etc (Barnes 150/165/168, swift aframe 165, nosler partition 165, hornady 178 eldx with h4350 and h4895 and some factory Barnes 180 grain loaded ammo) and best case we’re talking 1.25-1.5” and not consistent at all, 1 group might be 1” and the next 2”.
I’ll also add that I tried to add some up pressure by adding a shim between the friend and barrel, and while it did seem to tighten things up a little bit overall it was far from great. The gun has always been on the low side for velocity compared to published load data which I found odd. so I decided to cut the barrel down to 21.5 inches and recrown with a target crown. Prior to doing this I chronographed 5 shots with the 178 gr eldx to see how much velocity I would lose and had an average velocity of 2545. I cut the barrel and recrowned it and headed back to the range with 5 more of the exact same load. Took 5 more shots over the chrono with an average of 2595 fps! These shot strings were fired on the same day around 3 hours apart. I GAINED 50 fps after shortening my barrel 2.5”, and shot a 0.88” 5 shot group, then fired some of the store bought 180 grain that had previously grouped like 2.5-3” at best and shot a 1.3” group.
Clearly something was very wrong with the last couple inches of barrel/crown. Hopefully I can work up something repeatable now cause I was getting close to wrapping this gun around a pole lol. Just thought I’d share some
Unusual results, any ideas why this would happen?

ZaneV said:

any ideas why this would happen?

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I think youre probably correct in your assessment. Something wrong with the chunk of barrel that you cut off.

@ZaneV - Don’t ask questions about answers you already have.

Glad you worked it out. How about a picture of the (now) accurate rifle setup.

Is the barrel free floated?

Have you checked for stress on the action to see if it needs to be bedded?

First things that I check

BeeMaa said:

@ZaneV - Don’t ask questions about answers you already have.

Glad you worked it out. How about a picture of the (now) accurate rifle setup.

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I realize I corrected it, I’m more curious what could cause the reduction in velocity. I don’t have any way to measure anything that small, and am assuming a tight spot in the bore. I’ll grab some and post tomorrow.

Andrew NOLA said:

Is the barrel free floated?

Have you checked for stress on the action to see if it needs to be bedded?

First things that I check

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First thing I checked as well, I checked that stuff when I cleaned all the packing grease out of it. The barrel is free floated and the action is bedded at the rear tang and recoil lug from the factory, the action fits in the stock well with no movement.

Assuming you’re shooting a 30-06. What loads are you using to only get those velocities? I get over 2800 fps with 180gr bullets and several powders in my M70. I have another in 270 that gives an easy 3000 with 150gr bullets. Those are bellow book max.

You just say Winchester 70 ? Is it a Featherweight rifle ?
If its a Featherweight it could be the smaller diameter is causing the barrel to "whip" and larger groups. You shortened it and there less "whip" so smaller groups.
Also could be you got a bad barrel and you just so happen to cut out the bad section.

Gomer said:

Assuming you’re shooting a 30-06. What loads are you using to only get those velocities? I get over 2800 fps with 180gr bullets and several powders in my M70. I have another in 270 that gives an easy 3000 with 150gr bullets. Those are bellow book max.

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Middle of the road loads that are now matching published data much more closely. Before cutting the barrel they were like 150 fps lower than any published data.

I gained 50fps cutting off 2.5” of barrel, so assuming there obvious issue with the end of the barrel reducing velocity. Had it not had an issue and had the full 24” it would’ve been significantly higher than I was getting.

coyote wacker said:

You just say Winchester 70 ? Is it a Featherweight rifle ?
If its a Featherweight it could be the smaller diameter is causing the barrel to "whip" and larger groups. You shortened it and there less "whip" so smaller groups.
Also could be you got a bad barrel and you just so happen to cut out the bad section.

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It’s a model 70 supergrade and it does have a sporter barrel. I had assumed Barrel whip, and that was actually the reason i decided to Shorten it as a last ditch effort to get it to
Shoot. The fact I increase velocity with a 2.5” shorter barrel tells me it was more then barrel whip though. I’m assuming a tight spot or something in the last 2.5” of the barrel.
I did some rough load development yesterday and 4 out of 6 loads were at or under an inch, and consistent. So it’s definitely fixed!

ZaneV said:

Middle of the road loads that are now matching published data much more closely. Before cutting the barrel they were like 150 fps lower than any published data.

I gained 50fps cutting off 2.5” of barrel, so assuming there obvious issue with the end of the barrel reducing velocity. Had it not had an issue and had the full 24” it would’ve been significantly higher than I was getting.

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Wbat was the temp difference between when you shot first and second? If the ammos been in the sun you can increase fps.

There are custom builders that do that exact thing.

chop a little off and re-crown it then shoot and repeat. Keep cutting a little off to find the best accuracy out of that particular barrel

farmer_john said:

Wbat was the temp difference between when you shot first and second? If the ammos been in the sun you can increase fps.

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Mid to high 60s both times and nothing sat in the sun for any amount of time.

Altitude sickness said:

There are custom builders that do that exact thing.

chop a little off and re-crown it then shoot and repeat. Keep cutting a little off to find the best accuracy out of that particular barrel

Experiment: effects of barrel length on velocity and accuracy, by Addison Mohler

Palomino Valley Gun Club Member, Addison Mohler, conducted an experiment where he explored the effects of barrel length as it relates to bullet velocity and accuracy. The following is as writeup of…

palominogunclub.org

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I had read that as well, glad I cut it and tried it cause it shoots great now!

On the phantom velocity; you said these are loads you worked up. This is a long shot but if you are using a hot powder it may be that in the 24" barrel you are reaching complete burn way before the muzzle thereby pressure starts dropping affecting muzzle velocity. When you shortened the barrel complete burn would happen closer to the muzzle when using the exact same loads which would improve efficiency. Just a thought.