Cut & thread barrel kills accuracy?

I have a bull barrel 308 rifle that had a 21” barrel. I just had it cut to 17” and threaded. Prior to this it would shoot 1” or less groups all day long. Got it back and shooting it with a can on I can’t get better than 6” groups at 100 yards. Everything is tight. Could the cutting and threading have mattered this much or is something else wrong?

How did it shoot after cutting, without the can?

Pretty wild. Something is out of square.

May be bad crown job. Probably needs totally different load work up than before.

Didn’t try it. Was excited to try can and just went through about fifty rounds trying to figure out what the heck.

I was planning on taking it to go shoot a pig in the morning but am taking ol faithful instead.

It shot good with anything I put in it before. I was shooting 165gr game king from custom reloads of Dallas today.

Try it with a thread protector, or a brake. 3-4 rounds should tell you something.

Try without the can. could be the threading was done poorly, could be the suppressor causing the issue. only one way to tell between them

So, it was shooting a 21" barrel and no muzzle device inside 1" ? Correct?

Cut to 17", add suppressor, same ammo, and now it is shooting 6" groups. Is that right?

If the threads are out of center, you would have struck a baffle already. Have you looked down the suppressor yet?

Cutting threads on-a barrel definitely changes the last 1/2” of your barrel you can’t move metal on the outside without moving it on the inside. This is especially the case with small rimfire barrels.

Im thinking you had a baffle strike like fireman suggested, and whomever cut your threads failed to indicate that bore in before cutting the threads.

Correct. I have not looked down can yet. Busy loading trailer for trip to ranch tomorrow. I will be there all day tomorrow and report back tomorrow night.

Cut and thread was done by class three machining. Not saying a mistake is impossible it I think they are pretty highly rated for doing good work?

Cutting a barrel most certainly can affect accuracy, but not so much because the barrel was cut, but more so along the lines of barrel/ammo synergy. Clint Smith did an article about 20 years ago where they cut a .308 barrel down 1" at a time from 22 or 24" to 16" and shot for groups at 100 yards using the same ammo. They used the same gunsmith to cut and recrown the barrel each time. Interestingly, the group sizes varied in something of a sine wave based on the length on that particular rifle with that particular ammo. So the two best groups came from about 3" different in barrel length.

Later the found that tweaking the ammo load could produce excellent results at virtually all of the barrel lengths, something many reloaders know and love to do. So it came down to matching loads, lengths, and harmonics to find the ideal for each length.

I would suggest to Sewer Rat that he test the barrel without the can and see how it performs. Adding a muzzle device can also have a significant impact on how a given barrel performs with a given load, but his numbers do seem a bit extreme. I have see a 1" grouping barrel (with a particular load) go to 4" group size and be 7 inches off to the side by adding a can. Removing the can produced the original grouping again.

Hopefully, testing without the can will reveal the barrel is still sound, or maybe it will reveal that it was crowned improper. Maybe the threading is off as stated. Hopefully, it doesn't just hate the can.

Tuning applies to everything that carries harmonic waves, from radio antennas to musical instruments and speaker enclosures.

Was the next place I was going.

Thread job is probably fine. A suppressor is a significant weight hanging off the end of the barrel.

For everyone that drops off a rifle to me for load development, I have to shoot it with the exact muzzle device that the rifle will shoot with full time. This rifle in question, just might not like the original ammo anymore. Most specifically the powder charge. Chad makes really good ammo, and he has tested his for sale ammo in a variety of rifles. But none of us can test seating depths and charges in every possible combination and come up with a charge that shoots well in every combo.

I have. 300 Win Mag ammo out there with the same brass, primer, powder, and bullet. All have a different CBTO, and all have a different charge. Some very by a few tenths grain from one to the next, but the overall spread is literally 5 gr of powder. That is due to the large variety of barrel lengths, contours, free-bore and muzzle devices I have had combinations of, across the board on all the .300 Win Mags.

Very interesting. I have two different 30 cal cans I will try it without and then if it shoots good try it with both cans and see if one does better than the other.

I had to take the scope off to send it in for threading and I put it on the same the best I could and it was shooting 8” right of where it was before I disassembled and sent it in.

I didn’t get to mess with it anymore this evening. I was out past dark loading up all this.



It is a rake for my tracked skid steer and a weld on rake for my dozer. I have been grubbing brush at the ranch with the excavator and need to rake and stack it. Plan is to go shoot some pigs in the morning and then weld this rake on and work on some brush tomorrow.

Wait wait wait! Was the scope change at the same time as the barrel cut? If so you may be looking at the wrong demon. If not, carry on.

If the threading was cut out of round, it will degrade accuracy. I've seen this personally on my 308. Mine would shoot about 7" to 9" groups with the can on. I took the can off and it would shoot sub 1" with my standard 155 grain ELDM bulk ammo. I put the can back on, and big groups. I took it to my gunsmith, and he said the threading was so out of round, it pegged his gauges. He chopped 1/2" off, and rethreaded the barrel. It shoots great now. Who threaded it?

Everyone has posted great info.

Will add

1. every torque setting was changed when took it apart and reassembled. Scope, stock etc.
2. New load will likely need to be developed, if its 1/12 twist are even more sensitive to shortening
3. Make sure mount is torqued correctly and not a pile of peel washers were needed to time it. Guy on here thought his was messed up but had like .200 worth of peel washers on it. Once we reduced it to 2-3 his accuracy issues stopped.

Confirm that mount and can are in spec, see 10-15 a month that arent. All cans have runout, most in the .015-.020 range. Had an arfcom guy report weird accuracy after threading. He came over and we ran some test and found out can had .040 runout. He sent it back to them and all is good now.

Few rare guns just hate being suppressed. Had a guy have issues with factory threaded one, had issues with another shop redoing it, I did it and it passed all of mine and his alignment tests and still didn't like a can on it.

They are all alignment checked prior to boxing them up.



Do these on a cnc mandrel between centers most of the time for many years now, takes virtually all human error out of it. Only error that can be introduced is tailstock, which would just be a slight taper but still concentric.

Having said that I stand behind my work and if it can't be fixed I will buy it, have it rebarreled etc,

Luckily in 13 years now 40,000 plus only had to buy 2.

Shoot me an email if can't sort it out and we will go from there.

2/40,000. That is impressive.

More than that, the response is impressive. You do great work Morgan, thank you for the extra mile you go as well

Thanks man, that means a lot

With this being said, it seems we only got 50% of the story as the optic was messed with as well.
I bet the optic, or mount has some issue that is not standing out and as Chris said he’s chasing the wrong demon.

Sounds like your process for threads is well proven and kudos to you for coming on this thread and explaining how you do your work.

Shoot it without the can first. That will at least narrow it to the can or threads/muzzle. If it shoots check for baffle strikes, it could be as minor as a glint on one baffle. If you don't see any, you might have to have a reputable smith throw it in a lathe and dual indicate it to see if the muzzle and threads are concentric & in line to the bore, not the exterior of the barrel. Even if it clears all the baffles, it could cause problems if it's getting close to one side and not traveling down the center of them. I've seen it multiple times. Same with brakes.

Morgan cut down &threaded a couple factory barrels for me and the rifles got more accurate. My factory barrel crowns must have been crap.

If I ever get back to the States, I know I've got a .308 bull barrel heading Morgan's way. Maybe even my .243 too.

After the first 3-5 shots went that far astray, my first thought would have been to remove the can and see how it shot. If it still shot poorly, I'd torque-check every screw on the action and the mounts/rings. 'Tight' isn't necessarily 'right'. Then I'd try a different ammo for 3-5 shots. At that point I'd swap the optic.

As soon as I saw who cut and threaded I mentally ruled that out as the problem.
Something loose somewhere. Let us know.

Sorry for no update. I was hoping to shoot and figure this out today but the weather had other plans. With this wind I might be shooting six foot groups.

I finally got a chance to shoot the rifle today. I removed the surpressor and installed and thread protector and shot three rounds from my bench rest at 100 yards. The target was 18” square. One shot hit the paper. I am thinking something other than the threading is wrong. Instead of wasting more ammo I packed it up and am going to dig into it.

The scope, base, and rings (Swarovski/warne) are the original that I just removed to send the barrel for threading and I simply reinstalled with proper torque using my fat max wrench. The action is bedded into a Boyd’s stock. I torqued it to 40 inch pounds. I am going to order some Talley all in one base rings and mount the scope again and try that. I am at a loss. I have mounted I think eight scopes in the last year and have never had an issue.

This was a five shot group from before I sent the rifle in. It was a shooter. Now I can’t get but one out of three on paper.

Try checking the crown by putting a q-tip just inside and seeing if it catches any burs coming out. Also is the barrel free floated? Check that as well to make sure something didn’t get in there. Cutting a barrel down will change the harmonics and one load might not shoot as good, but I’ve never seen one go completely to crap like that. Something else is up. Hopefully it’s something simple.

Depending on the model, something as simple as a loose barrel nut?

Everything I am reading about Boyds stocks the torque settings are 25-35 pounds. Seeing posts where anything over that the accuracy went to crap, screw even starts making contact with the bolt when over 35. There’s an order to follow on which to tighten first

Would check trigger since it was removed as well and isn't dragging on anything.

Then after got the new scope mounted would try a bunch of different loads. Velocity changed, harmonics changed, might of had a recessed crown, now has a target etc.
very unlikely it’ll love them same load after all that changed. How it shot before with a certain load and doesn’t matter unless it was only threaded and not significantly shortened.

A quick google also showed there is a definite art and procedure to mounting those warn rings, and lots of post of erratic groups from them if any of those steps are missed.

Do your Warne rings have the stainless recoil lug, that sometimes unknowingly falls quietly to the mat on your bench?

I use those rings almost exclusively and never had an issue with them. But, that recoil lug is sometimes hard to hold in place while keeping enough pressure on them to attach to your rail.

Did you get this mystery solved?

Then I NEVER need to own one of those stocks.

And those rings are terrible.

EGW pic rail, Night Force Ultralite rings and you never have to worry about either of those extremely crucial parts.

Certainly you can't be talking about Warne rings, those are designed by super ninja engineers and manufactured by super technical goblins.

As always great info man, you know this stuff inside and out. Once kids get year or so older I’m gonna definitely have to take a class from you. Been wanting to get into that stuff for a while now.

It would be my pleasure to have you come out.

Boyds stocks that are pillar bedded and free floated have no issues and can be torqued easily past 70 in pounds.

Its all relative to what stock you have, and if it has pillars which is optional but really are not difficult to install.

I have a Rem. VLS in 7-08, and the Factory stock on it may be a Boyds, who knows, but they are pretty much the same. I made and added pillars, bedded it, removed the pressure bump, and it shoots great torqued to 55 lb.in.

That was my next thought. Add pillars to a Boyd's stock and it might be alright.

Any updates?

Sorry but no updates yet. Life has been crazy. Son is graduating high school tomorrow and have not had time to go shoot it again.